This PDF file contains the front matter associated with SPIE Proceedings Volume 11151, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists

Japan Aerospace Exploration Agency (JAXA), Japan Meteorological Agency (JMA) and Japan Space Systems (JSS) are operating major Earth Observation Satellites. Ibuki (GOSAT) carrying TANSO-CAI and -FTS, GOSAT-2 carrying TANSO-CAI2 / -FTS2, Shizuku (GCOM-W) carrying AMSR2, Daichi-2 (ALOS-2) carrying PALSAR-2, DPR on GPM-core satellite of NASA and Shikisai (GCOM-C) carrying SGLI, are being operated by JAXA under cooperation with some domestic agencies, such as Ministry of Environment (MoE), National Institute of Information and Communications Technology (NICT). JMA is operating weather satellite Himawari-8 and -9 on geostationary orbit. JSS are operating ASTER on EOS-Terra satellite of NASA. For coming satellites or instruments, JAXA is going to operate CPR on EarthCARE satellite of ESA, ALOS-3 carrying the “wide-swath and high-resolution optical imager” and ALOS-4 carrying PALSAR-3. JSS is going to have HISUI on ISS. JAXA proposed to Japanese government, its Earth Observation program along with new mid-term plan which started from April 2018 for seven years. In addition to follow-on mission studies, several new studies are underway for near future missions, such as Lidar missions, Super low orbit missions and new geostationary missions with large segmented telescope for land observation.

On 29th of October, 2018, GOSAT-2 was launched as the successor to GOSAT which is the first satellite dedicated to the greenhouse gases observation..
After the about 16 hours critical phase, GOSAT-2 moved to the commissioning phase and the functional and performant checkout of the bus system in November was followed by the one of the mission instruments in December.
The first light of the TANSO-CAI-2 was taken in the beginning of November along with the bus system checkout and the checkout of the TANSO-CAI-2 stared in the beginning of December.
The checkout of the TANSO-FTS-2 started in the middle of December. The first light of the FTS-2 was taken in the middle of December as part of the checkout of itself because the about three weeks of outgas to avoid the contamination had been needed. Though a few anomalies had been found in the checkout, it confirmed that FTS-2 and CAI-2 had worked well and all performances and functions met the requirements and the differences from the design were little except the temperature of the band 4 and 5 of FTS-2.
All data acquisition was completed at end of December except the system total operation test which is the test using all relevant systems including the ground system and this test was performed in the beginning of January of 2019.

It is reported that the sensitivities of the short wavelength infrared bands of Thermal And Near-infrared Sensor for carbon Observation (TANSO) - Fourier Transform Spectrometer (FTS) on Greenhouse gases Observing SATellite (GOSAT) have been degraded with the wavenumber dependencies¹. These degradations affect to the XCO₂ and XCH₄ retrievals, so they have to be correctly considered in the retrieval algorithm. In this work, we developed a new algorithm to evaluate these degradations from on-orbit solar calibration spectra using principal component analysis. The effectiveness of this algorithm is to be able to distinguish the time-dependent components of the spectral variability from the independent ones. This possibly enables us to evaluate the temporal change of sensitivity more precisely. The degradation models were constructed by decomposing spectra, fitting principal components scores using the appropriate functions, and reconstructing those functions. The first components of the decomposed eigenvectors have less spectral dependencies for each band, because they are due to the angular dependency of reflectance of the diffuser plate. On the other hand, the other components have significant spectral dependencies and their temporal variabilities do not correspond to that of the first component. This fact indicates that the components have to be separately considered to construct the degradation models of TANSO-FTS.

This paper describes the current status of Advanced Land Observing Satellite-4 (ALOS-4) which will carry L-band SAR system, namely Phased Array-type L-band Synthetic Aperture Radar-3 (PALSAR-3) and SPace based Automatic Identification System for ships Experiment (SPAISE3). In particular, its mission and characteristics of both instruments; PALSAR-3 and SPAISE3 are shown.

Accurate measurements of forest biomass are important to evaluate its contribution as a source of CO2 absorption. Forest biomass correlates with forest canopy height, and thus global measurements of canopy heights lead to a better understanding of the global carbon cycle. Space-borne lidar has the unique capability of measuring forest canopy height. A vegetation lidar named MOLI (Multi-footprint Observation Lidar and Imager) has been designed to observe canopy heights more accurately, and MOLI is currently being studied in the Japan Aerospace Exploration Agency (JAXA). This paper introduces an overview of MOLI and its current status.

The Second-generation global imager (SGLI) empowers surface and atmospheric measurements related to the carbon cycle and radiation budget, with two radiometers of Visible and Near Infrared Radiometer (VNR) and Infrared Scanning Radiometer (IRS) which perform a wide-band (380 nm - 12 μm) optical observation not only with as wide as 1150-1400 km FOV but also with as high as 250 - 500 m resolution. Also, polarization and along-track slant view observation are quite characteristic of SGLI. SGLI provides the earth observing data for more than 28 standard products and 23 research products including clouds, aerosols, ocean color, vegetation, snow and ice, and other applications. SGLI-VNR has several on-board calibration methods, such as solar, LED and lunar calibration. In this paper, methodologies and results of solar and LED calibration of SGLI-VNR Non-Polarization (NP) telescopes with a deployable diffuser to illuminate the uniformly scattered solar and LED light to telescope and photo diode stability monitor (PD) are provided, respectively. In addition, inter-comparison of the solar and the LED calibration is conducted with NP-Nadir telescope, PD2 and PD4. The calibration area of the telescope and the PDs are less affected by the UV degradation, so that the PD2 and the PD4, as an independent calibrator, can correct the solar diffuser reflectance degradation for the NP-Nadir telescope. As a result, each trend of the solar and the LED calibration of the NP-Nadir’s VN5, 10, and 11 bands agrees 1% or less. It concludes that the response change in the NIR spectral regions (VN10 and 11 with wavelength of 868.5 nm) is stable and that in the shorter wavelength band (VN5 with wavelength of 530 nm) is less than 2 % over a year. Lessons learned of on-board calibrations are also stated for the next generation's global imager.

NASA’s Earth Science Division (ESD) advances our scientific understanding of the Earth as a system and its response to natural and human-induced changes in order to improve our ability to predict climate, weather, and natural hazards, and to meet the challenges of environmental change. Our planet is changing on all spatial and temporal scales and studying the Earth as a complex system is essential to understanding the causes and consequences of global to local environmental changes. ESD addresses the issues and opportunities of environmental changes and climate risks by answering the following key science questions through its program elements: • How is the global Earth system changing? • What causes these changes in the Earth system? • How will the Earth system change in the future? • How can Earth system science provide societal benefit? One of the key elements ESD uses to address these science questions is the Flight Program. Its Flight Program consists of a coordinated series of satellite and airborne missions for long-term global observations of the land surface, biosphere, solid Earth, atmosphere, and oceans. The Flight Program also includes infrastructure for operating these missions, processing their scientific data, and distributing them on a free and open basis to researchers, operational users, and the public. The Flight Program currently has 25 operating Earth observing space missions. There are 16 more missions and instruments planned for launch over the next five years. These comprise missions recommended by the National Academies 2017 Earth Science Decadal Survey, missions and selected instruments to ensure availability of key climate data sets, operational missions to sustain land imaging provided by the Landsat system, and small-sized competitively selected orbital and instrument missions of opportunity belonging to the Earth Venture (EV) program. Recently launched missions include the ICESat-2 spacecraft and two International Space Station (ISS) hosted instruments, the Global Ecosystem Dynamics Investigation (GEDI) LIDAR and the Orbiting Carbon Observatory-3 (OCO-3) spectrometer. Projects in development include the Sentinel-6A/B dual satellite altimetry mission; Landsat 9; the Pre-Aerosol, Cloud, and ocean Ecosystem (PACE) mission; the NASA-ISRO Synthetic Aperture Radar (NISAR); the Surface Water and Ocean Topography (SWOT) mission; Tropospheric Emissions: Monitoring of Pollution (TEMPO); the Timed-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) CubeSat constellation mission; the Multi-angle Imager for Aerosols (MAIA) pollution monitoring instrument; the Geostationary Carbon Cycle Observatory (GeoCARB); the Earth surface Mineral dust source InvesTigation (EMIT) spectrometer hosted on ISS; and the Polar Radiant Energy in the Far InfraRed Experiment (PREFIRE) CubeSat constellation mission. The 2017 Earth Science Decadal Survey recommends four new Flight Program elements (Designated, Explorer, and Incubation Targeted Observables) in addition to the above activities that comprise the Program of Record (POR). Multi-Center architecture studies for the Designated Targeted Observables and plans to address the other Flight Program elements are underway. An overview of Flight Program plans and current status will be presented.

The Orbiting Carbon Observatory-3 (OCO-3) was launched on 04 May 2019 and provides a new perspective to the important task of studying atmospheric carbon dioxide (CO₂) as well as solar-induced chlorophyll fluorescence (SIF), a bonus product, from space. The flight spare three-channel grating spectrometer instrument built for OCO-2 has been adapted for use on the International Space Station (ISS) as OCO-3 by modifying the entrance optics, using a new calibrator assembly, incorporating a two-axis pointing mirror assembly (PMA), and adding two context cameras. The ISS’ recessing orbit allows measurements to be collected from dawn to dusk in the equatorial to northern & southern mid-latitude regions and the PMA enables a new snapshot area mapping mode where ~80 km x ~80 km areas can be examined in more detail. The OCO-3 payload underwent an extensive ground test and calibration program in a 3 m diameter thermal vacuum chamber. The chamber has a port/window that allowed optical ground support equipment, including a heliostat, to illuminate the instrument under operating environmental conditions. The payload’s performance in space during the in-orbit checkout (IOC) period compares favorably with ground test results. Initial and not-yet-fully-calibrated retrieved estimates of the column-averaged dry air mole fraction of CO₂ (X_CO2) are reasonable when compared to ground-based measurements. SIF estimates show clear contrast between areas of high and low vegetation. There is high confidence that the three-year prime mission will deliver the data needed for science/research, data applications, and informed decision-making.

The NASA/Smithsonian Tropospheric Emissions: Monitoring of Pollution (TEMPO; tempo.si.edu) satellite instrument will measure atmospheric pollution and much more over Greater North America at high temporal resolution (hourly or better in daylight, with selected observations at 10 minute or better sampling) and high spatial resolution (10 km² at the center of the field of regard). It will measure ozone (O₃) profiles (including boundary layer O₃), and columns of nitrogen dioxide (NO₂), nitrous acid (HNO₂), sulfur dioxide (SO₂), formaldehyde (H₂CO), glyoxal (C₂H₂O₂), water vapor (H₂O), bromine oxide (BrO), iodine oxide (IO), chlorine dioxide (OClO), as well as clouds and aerosols, foliage properties, and ultraviolet B (UVB) radiation. The instrument has been delivered and is awaiting spacecraft integration and launch in 2022. This talk describes a selection of TEMPO applications based on the TEMPO Green Paper living document (http://tempo.si.edu/publications.html).

Applications to air quality and health will be summarized. Other applications presented include: biomass burning and O₃ production; aerosol products including synergy with GOES infrared measurements; lightning NO_x; soil NO_x and fertilizer application; crop and forest damage from O₃; chlorophyll and primary productivity; foliage studies; halogens in coastal and lake regions; ship tracks and drilling platform plumes; water vapor studies including atmospheric rivers, hurricanes, and corn sweat; volcanic emissions; air pollution and economic evolution; high-resolution pollution versus traffic patterns; tidal effects on estuarine circulation and outflow plumes; air quality response to power blackouts and other exceptional events.

The Ice, Cloud, and land Elevation Satellite – 2 (ICESat-2) satellite mission launched in September 2018 from Vandenberg Air Force Base in California USA. The sole instrument is the photon-counting lidar Advanced Topographic Laser Altimeter System (ATLAS). Optimized to measure elevation change over the polar ice sheets and sea ice freeboard, ATLAS collects data globally. ICESat-2 data was released to the public in May 2019, and initial science discoveries are beginning to appear in the scientific literature. We describe the main components of the ICESat-2 mission, the standard data products, and our initial assessment of the on-orbit performance of the ATLAS instrument.

The Sentinel-6 (S6) Mission will provide continuity of ocean topography measurements beyond TOPEX-Poseidon (launched in 1992), Jason-1 (2001), OSTM/Jason-2 (2008), and Jason-3 (2016) for determining ocean circulation, climate change and sea level rise. Unlike past Jason missions, S6 will also contribute atmospheric temperature and humidity profile measurement in near real time to support operational weather forecasting. The S6 mission consists of two satellites to be launched approximately 5 years apart to extend measurement continuity for at least another decade. This mission will serve both the operational user community and also enable the continuation of multi-decadal ocean topography measurements for ocean circulation and climate studies. The first S6 satellite is planned to launch by the end of 2020 with a suite of instruments similar to the prior Jason series missions. Sentinel-6 is a cooperative mission with contributions from NASA, NOAA, ESA, and EUMETSAT. The ocean altimetry science payload is similar to the prior Jason missions, including a nadir altimeter, water vapor radiometer and precision orbit determination system instruments. The nadir altimeter is contributed by ESA and EUMETSAT and comprises a new dual-frequency (C and Ku band) synthetic aperture radar (SAR) altimeter (Poseidon-4). The NASA-provided payload is managed and developed by the Jet Propulsion Laboratory (JPL). It consists of the Advanced Microwave Radiometer for Climate (AMR-C) instrument that includes a new on-board absolute Supplemental Calibration Subsystem (SCS). The SCS is a key evolution of the radiometer instrument that will enable a significant improvement in the sea surface height measurement stability. The AMR-C provides the water vapor path delay correction to the ocean height measurement from the Poseidon-4 Radar Altimeter. The AMR-C is further enhanced by an experimental High-Resolution Microwave Radiometer (HRMR) that will demonstrate the capability of high frequency (90, 130, 166 GHz) radiometer channels for extending the wet path delay measurements into the coastal zone with ~5x finer spatial resolution compared with the traditional low-frequency AMR channels. The NASA payload also contains a Laser Retroflector Array (LRA) that supports ground-based laser tracking for precise orbit determination validation. As a secondary mission objective, S6 will also characterize atmospheric temperature and humidity profiles by measuring bending angles of GNSS signals occulted by the Earth’s atmosphere. These measurement products will be ground-processed within three hours of acquisition on board the satellite and made available for ingestion into national weather service models to support weather forecasting capabilities. This measurement is provided by the NASA-provided Global Navigation Satellite System for Radio Occultation (GNSS-RO) instrument. We present a description of the overall mission and focus on the NASA payload architecture, development status and (pre and post) launch expected performances.

A new satellite mission called Surface Water and Ocean Topography (SWOT) is being developed jointly by the U.S. National Aeronautics and Space Administration and France’s Centre National d’Etudes Spatiales. Based on the success of conventional nadir-looking altimetry missions in the past, SWOT will utilize the technique of radar interferometry for making wide-swath altimetric measurements of the elevation of surface water on land and the ocean’s surface topography. The new measurements will provide information on the changing ocean currents that are key to the prediction of climate change, as well as the shifting fresh water resources resulting from the dynamic water cycle. The noise level of conventional radar altimeters limits the along-track spatial resolution to 50-100 km over the oceans. The large spacing between the satellite ground tracks limits the resolution of two-dimensional gridded data to 200 km. Yet most of the kinetic energy of ocean circulation takes place at the scales unresolved by conventional altimetry. SWOT observations will provide the critical new information at these scales for developing and testing ocean models that are designed for predicting future climate change. In contrast to ocean observations, land surface water measurements are limited mostly to in situ networks of gauges. While radar altimetry over surface waters has demonstrated the potential of this technique in land hydrology, a number of limitations exist. Raw radar altimetry echoes reflected from land surface are complex, with multiple peaks caused by multiple reflections from water, vegetation canopy and rough topography, resulting in much less valid data over land than over the ocean. Yet one of the most threatening consequences of a warming climate is the shifting water resources. Monitoring the global water on land is critical for assessing the storage and discharge of lakes and rivers. The technology of SWOT is based on the heritage of the Shuttle Radar Topography Mission (SRTM) that successfully mapped the elevation of global land topography from a 10-day space shuttle mission. A higher frequency at Ka band (~35 GHz) is chosen for the radar to achieve high precision with a much shorter inteferometry baseline of 10 m. Small near-nadir look angles (~ 4 degrees), required for minimizing elevation errors, limit the swath width to 120 km. An orbit with inclination of 78 degrees and 22 day repeat period was chosen for gapless coverage and good tidal aliasing properties. With this configuration, SWOT is expected to achieve 1 cm precision at 1 km x 1 km pixels over the ocean and 10 cm precision over 50 m x 50 m pixels over land waters. Other payloads of the mission include a conventional dual-frequency altimeter for calibration to large-scale ocean topography, a water-vapor radiometer for correcting range delay caused by water vapor over the ocean, and precision orbit determination package (GPS, DORIS, and laser retroreflector). SWOT is currently being developed for a planned launch in 2021. This presentation will describe the current SWOT mission status, including technical development challenges regarding the Payload Instrument, Spacecraft, ground data system and calibration/validation plans.

The Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission represents NASA’s next investment in satellite ocean color and the study of Earth’s ocean-atmosphere system, enabling new insights into oceanographic and atmospheric responses to Earth's changing climate. PACE objectives include extending systematic cloud, aerosol, ocean biological and biogeochemical data records, making essential ocean color measurements to further understand marine carbon cycles and ecosystem responses to a changing climate, as well as improving knowledge of how aerosols influence ocean ecosystems and, conversely, how ocean ecosystems and photochemical processes affect the atmosphere. PACE objectives also encompass management of fisheries, large freshwater bodies, and water quality and reducing uncertainties in climate and radiative forcing models of the Earth system. PACE observations will also provide information on radiative properties of land surfaces and characterization of the vegetation and soils that dominate their reflectance. The primary PACE instrument – the Ocean Color Instrument (OCI) – is a hyperspectral imaging radiometer that spans the ultraviolet to shortwave infrared, with a ground sample distance of 1-km at nadir. This includes continuous collection of spectra from 340 nm to 890 nm in 5 nm steps. The PACE payload is complemented by two multi-angle polarimeters with spectral ranges that span the visible to near-infrared region. Scheduled for launch in late 2022-to-early 2023, the PACE observatory will enable significant advances in the study of Earth’s biogeochemistry, carbon cycle, clouds, hydrosols, and aerosols in the ocean-atmosphere system. We present a brief overview of the PACE mission, followed by a discussion of the capabilities and design concept of OCI.

The advent of small satellites and miniaturized instrument technology enables a new paradigm for observation from Low Earth Orbit (LEO). Passive microwave radiometer systems, such as SSM/I, AMSR-E, AMSU, ATMS, WindSat and GMI, have been providing important Earth observations for over 30 years, including but not limited to surface wind vector, atmospheric and surface temperature, water vapor, clouds, precipitation, snow and sea ice. Over the past several years, there has been a push to develop small satellite solutions for these critical measurements. The lower deployment cost of small satellites allows us to consider new ways to use these systems for Earth observation. Specifically, we may consider homogenous or heterogeneous constellations with the sensor elements either distributed in several orbit planes to improve revisit time, or as closely spaced trains to resolved short time scale processes, such as developing convection. In this presentation, we will discuss three recently developed, complementary small satellite technology demonstration sensors that span the capability currently offered by the existing fleet of microwave environmental sensors. These systems are COWVR, a low-frequency fully-polarimetric conical imager, TEMPEST-D, a mm-wave cross-track imager/sounder and TWICE, a conical sub-mm wave imager/sounder. COWVR is a technology demonstration sensor for the US Air Force designed to be a small-satellite equivalent to sensors such as SSM/I, AMSR, WindSat and GMI. TEMPEST-D is a NASA Earth Ventures technology demonstration project and has equivalence with cross-track sounders such as AMSU, ATMS and MHS. TWICE, built under a NASA technology project, covers frequencies band not yet flown in space. Combined, these systems offer the potential to image the Earth from 6-800 GHz. When deployed in a constellation, they enable new observations of dynamic physical processes and coupling between land, ocean, atmosphere and cryosphere. In this presentation, we will highlight the sensor design and status of each of the three radiometer technology demonstration projects. TEMPEST-D has been continuously operating on-orbit since September 2018 and COWVR is due to launch no earlier than January 2021. We will describe unique observations enabled by these systems when used in constellations, including time resolved measurements of dynamic atmospheric processes (e.g. developing convection) simultaneously with surface and atmospheric fluxes. We will show measured performance comparisons between these new small-sat sensors to the equivalent operational sensor, giving examples of on-orbit comparisons for TEMPEST-D and pre-launch measured data from COWVR and TWICE. Finally, we will discuss new mission concepts enabled by constellation sensor trains and distributed constellations, particularly as it relates to the observation goals identified in the US NRC Decadal Survey. We will highlight the potential for multi-sensor small-satellite constellations, showing recently acquired passive microwave and precipitation radar data from TEMPEST-D and RainCube.

Surface air pressure is the most important atmospheric variable for atmospheric dynamics. It is regularly measured by in-situ meteorological sensors, and there are no operational capabilities that could remotely sense the pressure over the globe. The poor spatiotemporal coverage of this dynamically crucial variable is a significant observational gap in weather predictions. To improve forecasts of severe weather conditions, especially the intensity and track of tropical storms, large spatial coverage and frequent sampling of surface barometry are critically needed for numerical weather forecast models. Recent development in remote sensing techniques provides a great hope of atmospheric barometry in large spatiotemporal scales. Currently, NASA Langley Research Center tries to use the concept of Differential-absorption Barometric Radar (DiBAR) working at the 50-56 GHz O2 absorption bands to fill the observational gap. The numerical simulation shows that with this DiBAR remote sensing system, the uncertainty in instantaneous radar surface air pressure estimates can be as low as ~1 mb. Prototype instrumentation and its related laboratory, ground and airborne experiments indicate that satellite DiBAR remote sensing systems will obtain needed air pressure observations and meet or exceed the science requirements for surface air pressure fields. Observational system simulation experiments (OSSEs) for space DiBAR performance based on the existing DiBAR technology and capability show substantial improvements in tropical storm predictions, not only for the typhoon track and position but also for the typhoon intensity. Satellite DiBAR measurements will provide an unprecedented level of the prediction and knowledge on global extreme weather conditions. A space multi-frequency differential oxygen absorption radar system will fill the gap in the global observations of atmospheric air pressure, increase our knowledge in the dynamics, and significantly improve weather, especially severe weather such as typhoon and hurricane, predictions. Advanced tropical storm forecasts are expected with the studied capability. The development of the DiBAR system and associated OSSE results will be presented.

Earth’s ionosphere responds dynamically over a wide range of temporal and spatial scales to changes in the magnetosphere and solar wind from above, and to neutral atmospheric dynamics from below. Determining the dynamics and coupling of Earth's magnetosphere, ionosphere, and atmosphere by vector magnetic field measurements at all altitudes is essential, as the field plays a major role in controlling the distribution of ionospheric plasma. It is difficult to measure the magnetic B-field, either locally or globally, at the altitudes of the upper mesosphere and lower thermosphere (UMLT) where the transfer of energy and momentum between the plasma and neutral components of the system occur. The 118-GHz imaging magnetometer will measure all four Stokes parameters as a function of frequency about the Zeeman-split center of the 118-GHz molecular oxygen line. We are developing an array of fully-polarimetric millimeterwave radiometer/spectrometers operating near 118 GHz. These low cost, low power, low mass polarimetric 118 GHz millimeter-wave array receivers do not require cooling to meet the sensitivity requirements. With digital spectrometers we will be able to integrate the complete end-to-end system. This work will enable a second generation small satellite mission with an off-nadir viewing instrument comprised of 120 such receivers (arranged so that each spot on the Earth is observed simultaneously by four receivers each) that will globally map the magnetic field in the mesosphere at 42-76 km altitude at a horizontal resolution ~100 km with 1-sigma error of 40-120 nT, in typical mesospheric temperature conditions.

Copernicus Sentinel-2 mission provides continuity to services relying on multi-spectral high-resolution optical observations over global terrestrial surfaces. The key mission objectives for Sentinel-2 are: (1) To provide systematic global acquisitions of high-resolution multi-spectral imagery with a high revisit frequency, (2) to provide enhanced continuity of multi-spectral imagery provided by the SPOT series of satellites, and (3) to provide observations for the next generation of operational products such as land-cover maps, land change detection maps, and geophysical variables. The corresponding user requirements have driven the design towards a high spatial resolution, wide field of view and large spectral coverage instrument. The mission has already a constellation of 2 satellites (Sentinel-2A and Sentinel-2B) launched in 2015 and 2017, each having a 7.25-year lifetime with consumable sized for 12 years. To cover the 20-year overall mission duration, two additional satellites Sentinel-2C and Sentinel-2D were founded by the European Commission and are under development. Some modifications were implemented for the two new satellites: (1) on the technical side, modifications to improve further the instrument performance up to End of Life (thermal improvements to reduce the focal plane temperature, optimization of MTF at detector and instrument level) (2) added in orbit activities to improve interinstrument calibration with the Moon calibration. The first set of radiometric and geometric performances of the VNIR and SWIR channels from the test campaign performed in 2018 and early 2019 are compared with performances of the two in-flight instruments.

Sentinel-5 is an Earth atmospheric monitoring mission developed within the Copernicus program. The mission objective is to monitor the composition of the Earth’s atmosphere on a daily basis. TNO is developing the UV1 spectrometer subsystem as well as the two telescope subsystems. In this paper, the design of the UV1 spectrometer is described and its major design and verification challenges are discussed.

The UV1 optical design is based on a classical Offner-type spectrometer which has been adapted to employ freeform optics and an aspheric off-axis grating. It generates a magnification of 0.4. A structural, monolithic housing has been designed that is optimized for stability, accessibility and integration of optical components. To realize a thermo-mechanically stable construction, both housing and mirror bodies are built from aluminum. Four out of five mirrors have a dedicated black coating for absorbing out-of-band light. For further stray light suppression, a graded short-pass filter is employed on the last optical element just in front of the detector.

Performance verification of a standalone spectrometer without telescope, entrance slit, limiting aperture stop and flight detector is a major challenge. For this verification TNO developed dedicated ground support equipment that will be used under both ambient and vacuum conditions; a dedicated optical stimulus that mimics the illumination from the telescope in terms of pointing and NA, a Slit Assembly that mimics the homogenizer entrance slit and a Test Detector to determine the image plane and to measure the optical performance with high accuracy.

At the time of writing this article, the first (proto-flight) model has been aligned and performance verification is about to start.

EarthCARE is the sixth Earth Explorer mission of the European Space Agency's (ESA) Living Planet Program. It is being developed in collaboration with the Japan Aerospace Exploration Agency (JAXA). It has the fundamental objective of improving understanding of the processes involving clouds, aerosols and radiation in the Earth’s atmosphere. The payload of EarthCARE consists of two active and two passive instruments. ESA is developing three of the instruments, an ATmospheric LIDar (ATLID), a Multi-Spectral Imager (MSI) and a Broad-Band Radiometer (BBR). JAXA is developing the Cloud Profiling Radar (CPR). The four instruments will provide co-located data from a single platform, which may be processed individually and in a synergistic manner, to provide a range of products, such as the vertical structure of aerosols and clouds, the corresponding broad-band and narrow-band radiances at the top of the atmosphere, and complementary information for scene identification. ATLID is a backscatter LIDAR, operating at a wavelength of 355 nm, that will record atmospheric echoes from an altitude of 40 km to ground. It incorporates a high resolution spectral filter, which enables the relative separation of aerosol and molecular backscatter. It also measures cross and co-polar components of the Mie backscatter on separate channels. The BBR instrument will make separate measurements of reflected solar radiation and radiated thermal emission from the scene. The MSI instrument will make measurements in seven bands ranging from the visible spectrum, near infrared, short wave infrared, down to thermal infrared, across a 150 km swath. This will aid in scene identification and provide some aerosol information. This paper will provide an overview of the design and function of the instruments and a description of the current progress achieved in their integration and characterization.

The ALTIUS Mission (Atmospheric Limb Tracker for Investigation of the Upcoming Stratosphere) aims at the development of a limb sounder based on a small satellite concept (i.e. PROBA-Next small platform).

ALTIUS will monitor the distribution and evolution of stratospheric ozone at high vertical resolution in support of operational services and long term trend monitoring. It will provide detailed stratospheric profile information at high vertical resolution, which is a valuable addition to ozone total column for data assimilation systems based on nadir sounders used by operational centers. In addition, some secondary scientific mission objectives are targeted, including measurements of vertical concentration profiles of other atmospheric species.

The ALTIUS Mission was first proposed by the Belgian Institute for Space Aeronomy and, after several studies in different programmes within ESA, is now being developed as an element of ESA’s Earth Watch Programme currently with the participation of Belgium, Canada, Luxembourg and Romania.

The ALTIUS Mission concept consists of three spectral imagers flying at an altitude of approximately 700 km Sun- Synchronous Orbit on-board the next generation of PROBA platform. The ALTIUS Instrument shall allow observation of the Earth’s atmospheric bright limb in an extended spectral region from the Ultraviolet to the Short Wave Infrared (SWIR). In addition, the ALTIUS instrument shall perform solar and stellar occultation observations in the dark limb.

The ALTIUS Instrument three hyperspectral channels are based respectively on Acousto-Optic Tuneable Filters (AOTFs) in the Visible (440-800nm) and SWIR (900-1800nm) range, and a cascade of Fabry Perot Interferometers (FPI) in the UV (250-370nm). The use of tuneable active spectral filter shall allow the ALTIUS Instrument to perform observations with a spectral resolution ranging between 1nm and 10nm in an extremely versatile operational concept.

The use of the AOTFs and Fabry Perot technologies constitutes a novelty in the limb sounding missions and its development critical aspects as well as its performances have been proven in the frame of an extensive Instrument predevelopment phase.

In this phase the critical technologies necessary to ensure the performance and functionalities of the ALTIUS Instrument have been designed, developed and qualified. In particular the following pre-developments were undertaken to pave the way towards Instrument Preliminary Design Review:

Design, manufacturing and qualification of the VIS AOTF Assembly and RF control electronics;

Design, manufacturing and qualification of the UV FPI assembly stack and control electronics;

Development and qualification of UV filters and coatings.

Design and manufacturing of sensor electronics based on selected CMOS sensor for UV and VIS channels;

Design, manufacturing and partial qualification of the Instrument mechanism;

Bread-boarding of the full VIS channel for functionality and end-to-end performances verification.

This paper presents the status and main results of the above-mentioned ALTIUS Instrument pre-development activities. In particular: major outcomes during the development process, achieved performances and lessons learned for the continuation of the ALTIUS Instrument flight model design are being highlighted.

ESA actively participates in the development of numerous hyperspectral instruments. The degree of innovation, compactness, or overall technical performance constitute the starting constraint for each prospective instrument.

With the launch of the CHRIS instrument in 2001, ESA contributed to the demonstration and evaluation of new hyperspectral technologies. The objective was to achieve a better understanding of Earth’s spectral reflectance. As of today, a strong heritage for spaceborne hyperspectral instruments exists in Europe and more challenging instrument capabilities can be addressed. Hence, a study for a hyperspectral imaging mission in the context of the Copernicus Space Component Expansion programme has been initiated and targets the realization of an instrument covering the VNIR (visible and near-infrared) and SWIR (short-wave infrared) spectral range. The main goal of this mission is to deliver new services for food security, sustainable agriculture and raw materials detection. In another endeavor, ESA’s 8th Earth Explorer mission, the focus lies on the study of vegetation fluorescence and photosynthetic activity. A hyperspectral imager has effectively been built as an elegant breadboard and is planned to be ready for launch in 2022. Other hyperspectral instruments following the route towards compactness and lower cost have been also supported by ESA in recent years. For instance, HyperScout, a hyperspectral instrument, has been launched in February 2018. CHIMA, a Compact Hyperspectral Instrument for monitoring the atmosphere was tested on breadboard level. ELOIS is a higher-performing hyperspectral instrument for land application, for which the development of the Engineering Model has been completed. And CSIMBA is another compact hyperspectral instrument for land applications, of which flight units are currently being manufactured. Evolving technologies, such as complex blazed grating structures, hyperspectral image sensors and free-form optics manufacturing and metrology, enable the achievement of a better instrument performance and hence expand the scope of its use. This communication provides an overview of existing and planned hyperspectral instruments in which ESA participates. Different instrument characteristics and design concepts are described and categorized in view of the targeted applications. The current status of key instrument technology is elucidated and discussed in the perspective of future applications.

The first diffraction gratings on curved substrates were manufactured by employing ruling engines by H. A. Rowland. Due to the ruling principle, these gratings are characterized by equidistant parallel lines if the line pattern is projected along the optical axis onto a tangential plane in the vertex of the grating substrate. The Offner spectrometer is based on such a classical grating on a convex spherical substrate. This spectrometer type shows very good field correction properties. Therefore, it is among the most promising spectrometer types to meet the demands of hyper-spectral imaging. A further improvement of the optical performance is based on the modification of the surface figure of the substrate to an aspherical shape while keeping the mentioned constant grating line distribution. There are many reasons to employ interference lithography/holography - and in particular the direct blazing approach - even for the generation of the specific Offner grating line distribution on the convex substrate. A main benefit of this method is the attainable nearly perfect angular orientation of the blaze facets for the whole grating aperture. Here the achievable well defined blaze structure leads to best diffraction efficiencies close to the theoretical optimum - independent from the local curvature of the substrate. To manage the more complex recording setups of direct blazed Offner gratings, reliable methods for testing the wave front quality are a necessary pre-condition. A corresponding test method based on holographic principles will be introduced in the following text. The aspherical Offner grating was designed for the application in the UV-1 spectrometer within the Sentinel 5 mission, which is part of the European Earth Observation Program Copernicus". The spectrometer is a passive grating imaging spectrometer with a swath width of 2.670km and a spatial resolution of 50x50km².

The objective of ESA’s Next Generation Gravity Mission is long-term monitoring of the temporal variations of Earth’s gravity at high time (3 days) and space (100 km) resolution. Such variations carry information about mass transport in the Earth system produced by the water cycle and the related mass exchange among atmosphere, oceans, cryosphere and land, and will complete our picture of Global Change with otherwise unavailable data. The basic datum is the distance variation between two satellites measured by a laser interferometer; as a necessary complement, accelerometers measure the non-gravitational accelerations, to be separated from the gravity signal in the data processing. The optimal satellite formation comprises two pairs of satellites, at 100 km mutual distance, on low (≈340 km) circular orbits with 89° and 70° inclination. The NGGM is a candidate Mission of Opportunity of ESA’s Earth Observation programme. Studies and technology development activities have advanced the maturity of the system concept and of the key subsystems (attitude and drag control, proportional thrusters, laser optics and electronics) for the mission to be proposed for adoption in 2022 and launch in the 2026-2028 time frame. The latest stand of the ESA studies is illustrated, concerning both the platform (featuring drag-free control, high-stability temperature control, drawing on the heritage of GOCE) and the laser interferometer instrument, for which two designs have been extensively studied, “Transponder” and “Retro-Reflector”, one of which will be selected for flight. A hybrid breadboard of the “off-axis” Retro-Reflector concept is being built and tested.

This paper presents the Arctic and Nordic Imager as a concept investigated by the European Space Agency (ESA) and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). The concept addresses a recognized gap in the near-real-time coverage at high latitudes (above 55 degrees) from geostationary satellites, due to viewing geometry over polar areas. The paper recalls the context, summarises the requirements customized for it, describes the main trades, features and sizing parameters of the mission and sensor, and illustrates potential implementations. The requirements are similar to those of geostationary systems. They call for near-real-time multispectral optical observations in the Visible, Near Infrared, Short Wave Infrared, Water Vapour, and Thermal Infrared bands, at moderate spatial resolution. The mission profile proposed uses Highly Elliptical Orbits (HEO). The sensor concept is largely derived from GEO imagers in operation or in development, due to very similar requirements. In the current instrument concepts, the area of interest is covered using a scanning mirror in two directions. A telescope and complementing optics then redirect the optical beam to focal plane assemblies and optical detectors. The instrument also includes calibration subsystems and all necessary equipment i.e. cryocoolers for infrared detectors and electronics for data handling. The major trades are to do with meeting the very demanding optical performance, and to a lesser degree with the radiometric one. These include aperture sizing, definition of scanning law and principle, telescope concept, cryostat design, and image registration. The resulting concepts yield state-of-the-art large space optical instruments.

We present RAAD (Rapid Acquisition Atmospheric Detector), a detector designed to study Terrestrial Gamma ray Flashes (TGFs) and other fast hard X-ray and soft gamma-ray phenomena. TGFs are bursts of radiation from thunderstorms which occur on sub-microsecond timescales. Most detectors used to study TGFs have been limited by deadtime and timing precision, and sometimes poor calibration at lower energies. We will present calibration and space qualification tests of a detector aimed at the 20 keV - 2500 keV range with ~ 100 ns time response and good spectral resolution. This uses 2 X 2 arrays of two different scintillation crystals, Cerium Bromide and Lanthanum BromoChloride, both of which have very fast decay times. We couple them to both standard photomultiplier tubes (PMTs) and silicon photomultipliers (SiPMs) along with custom electronics designed to provide very fast sampling with very low power consumption per channel. Each crystal array fits into < 1U of a cubesat, and provides ~20 cm² of effective area to photons < 200 keV and ~10 cm² at 600 keV. The RAAD concept is the winner of the Mini-satellite competition held by the UAE Space Agency in 2018, largely developed with undergraduates at NYUAD, and is expected to be fully developed and launched by 2020. Two detectors, one with PMTs and one with SiPMs will be deployed on a 3U CubeSat, providing head to head performance tests for both crystal types and light sensor types. This will serve as a proof of concept showing how such detectors could be deployed in a network of CubeSats to study TGFs and other phenomena.

Long-wavelength infrared (LWIR) focal plane arrays (FPAs) needed for Earth Science imaging, spectral imaging, and sounding applications have always been among the most challenging in infrared photodetector technology due to the rigorous material growth, device design and fabrication demands. Future small satellite missions will present even more challenges for infrared FPAs, as operating temperature must be increased so that cooler (and radiator) volume, mass, and power can be reduced. To address this critical need, we are working on following three technologies. 1) Type-II superlattice (T2SL) nBn type barrier infrared detector, which combines the high operability, spatial uniformity, temporal stability, scalability, producibility, and affordability advantages of III-V detectors. 2) The resonator pixel technology, which uses metasurface light trapping techniques to achieve strong absorption in a small detector absorber volume, thereby enabling enhanced QE and/or reduced dark current. 3) High dynamic range 3D Readout IC (3D-ROIC), which integrates a digital reset counter with a conventional analog ROIC to provide a much higher effective well capacity than previously achievable. The resulting longer integration times are especially beneficial for high flux/dark current LWIR applications as they can improve signal-to-noise ratio and/or increase the operating temperature. By combining these three technologies, this project seeks to demonstrate a cost-effective, high performance LWIR FPA technology with significantly higher operating temperature and sensitivity than previously attainable, and with the flexibility to meet a variety of Earth Science TIR measurement needs, particularly the special requirements of small satellite missions.

In this paper, results from the development of InAs/GaSb superlattice focal plane arrays (FPAs) at IRnova will be presented. A versatile and robust detector design is used that allows for adjustment of the detection cut-off wavelength from 2.5 μm up to 14.5 μm with only minor changes in the detector design. Performance of the fabricated detectors has been reviewed in terms of external quantum efficiency (EQE), dark current and noise for three designs with cut-off wavelengths of 4, 5.5 and 11 μm at 80 K (referred to as DEEP BLUE, RED HOT and VLWIR, respectively). Measurements on the 15 μm sized photodiodes demonstrated 70% EQE for the MWIR designs, and almost 40% - for VLWIR. At the same time, the dark current stayed close to the Rule07 benchmark for all studied samples. Noise mechanisms have been discussed and their relation to the passivation was examined. Mature in-house processing and passivation technique of resulted in very high spatial uniformity of VGA focal plane arrays (FPAs), i.e. low relative deviations of EQE (< 6%) and of dark current density (< 12%) and narrow noise distributions for both RED HOT and DEEP BLUE FPAs. We show also that <99.5% of these arrays operate close to the fundamental noise limit.

Ultraviolet (UV) and infrared (IR) detector and array technologies have proven to be at the heart of many remote sensing instruments for various NASA missions. These exciting AlGaN ultraviolet avalanche photodiode (UV-APD) and HgCdTe-graphene photodetector and focal plane array (FPA) technologies are being developed for high performance UV and IR sensing to support and further advance a variety of NASA Earth Science applications. This paper will present our recent results on GaN/AlGaN UV-APDs grown by metal-organic chemical vapor deposition (MOCVD) on GaN substrates with avalanche gains greater than 5×106, and high responsivities. We are also developing room temperature operating graphene-enhanced HgCdTe mid-wave infrared (MWIR) detectors and focal plane arrays (FPAs). These compact and low-cost MWIR sensors can benefit various NASA remote sensing applications. For MWIR detection it is very desirable to develop IR detector technologies that operate at or near room temperature to minimize cooling requirements. The 2-5 μm MWIR spectral band is useful for measuring sea surface temperatures, cloud properties, volcanic activities, and forest fires, among other applications. Using low size, weight, power, and cost MWIR sensors on smaller platforms in low orbit can enable improved measurements of thermal dynamics with high spatial resolution. We will discuss modelling and experimental results for these devices.

Since the first paper published by Sakaki and Esaki in 1978, it is well known that InAs and GaSb constitute a nearly lattice-matched material system offering great flexibility in the design of IR optoelectronic devices. After four decades, the III-V type-II superlattice (T2SL) detector technology is under strong development as a possible alternative to HgCdTe. The novel ideas coming in design of detectors have enhanced the position of T2SLs in IR materials detector technology. It appears that T2SLs are especially helpful in the design of unipolar barriers.

In this paper fundamental physical properties of two material systems, HgCdTe and T2SLs, are compared together with their influence on detector performance: dark current density, RA product, quantum efficiency, and noise equivalent different temperature. In comparison with HgCdTe, fundamental properties of T2SLs are inferior. On the other hand, T2SL and barrier detectors have several advantages to include lower tunnelling and surface leakage currents, and suppressed Auger recombination mechanism. Up to date, the promise of superior performance of these detectors has not been realized yet. In the paper we present that the performance of T2SL detectors (dark current, current responsivity, and noise equivalent difference temperature) is lower than bulk HgCdTe photodiodes.

Due to stronger, less ionic chemical bonding of III-V semiconductors, these materials are attractive due to manufacturability and stability. It is also predicted that the interband T2SL quantum cascade devices will outperform the performance of the high operating temperature HgCdTe detectors.

The future of spaceborne systems for Earth Observation is moving towards formations of multiple lightweight spacecrafts, either to enhance the surface temporal coverage or to augment the system performance by increasing the number of simultaneous observation modes. In the case of Synthetic Aperture Radars (SAR), the latter option is of particular relevance and is mainly brought forward by bistatic and multistatic SAR system concepts. In this context, The ESA Earth Explorer 10 Candidate STEREOID (Stereo Thermo-Optically Enhanced Radar for Earth, Ocean, Ice, and land Dynamics) is promoting the launch of 2 sub-500 Kg satellites spacecraft carrying a receive-only radar instrument as main payload, and flying in a re-configurable formation with Sentinel-1 C or D, which will be used as illuminator. From the radar standpoint, the main novelty will be brought by the large orbital (along-track) separation of the 2 companions from the transmitter, with baseline values that exceed 200 km. Such unprecedented line-of-sight diversity, in angular terms, is in fact deemed to significantly boost the sensitivity to 3D motion and deformation of over land, ice and sea surfaces. The system will be designed to operate in two main formation configurations: 1) A ‘stereo’ configuration, where one satellite will fly ahead of Sentinel-1 whereas the other will follow behind, at approximately the same distance; 2) a ‘XTI/ATI’ configuration, where the two satellites fly close to each other, and hence on the same side with respect to Sentinel-1. In the first configuration the system captures the widest angular diversity, in the second configuration the system gains single-pass interferometric capabilities that allow to perform either topography or coherent target velocity retrieval. As the mission acronym suggests, the system carries an additional medium resolution multispectral payload with a VNIR and a TIR component, that shall not be considered less relevant than the microwave one. Although the orbit configuration and the viewing geometry is generally not ideal for an optical payload in isolation, the assimilation of such simultaneous optical and radar observations are indeed considered fundamental for the achievement of several mission goals, such as for the enhanced retrieval and interpretation of the sea surface currents. Several technical and scientific challenges shall be dealt with in the next few years, i.e. during the study phase of the mission. This work will provide an overview of these challenges, focusing in particular on to the coherent and incoherent signal properties of the STEREOID bistatic measurements, on their benefits as well as their negative implications on retrieval performances, and on the possible assimilation strategies for their integration with the optical measurements.

The value of operational satellite systems for decadal climate trending can be greatly enhanced by implementing on-orbit transfer standards for testing and improving calibration accuracy. This concept is an important part of the Climate Absolute Radiance and Reflectivity Observatory (CLARREO) mission recommended as a Tier 1 mission in the 2007 Decadal Survey.

The Absolute Radiance Interferometer (ARI) was designed to measure absolute spectrally resolved infrared radiance (200 – 2700 cm^-1 at 0.5 cm^-1) with ultra-high accuracy (<0.1 K, k = 3 brightness temperature). A key feature of the ARI instrument is the On-orbit Verification and Test System (OVTS), which provides end-to-end calibration verification of the ARI measurements with direct on-orbit traceability to international standards (SI). The ARI instrument has demonstrated the required radiometric accuracy for CLARREO and has achieved NASA Technology Readiness Level 6.

The International Space Station (ISS) would provide an affordable opportunity to demonstrate this new capability. The ISS orbit gives good time of day coverage for latitudes below 52 degrees, and the natural precession of the ISS offers many orbit crossings for radiance intercomparisons with operational satellites in sun-synchronous orbits. Thus, the ARI could serve as an on-orbit reference calibration standard for the operational infrared sounders, and these sounders could in turn be used to create climate benchmark products at all latitudes. In this approach, an ARI mission on the ISS would leverage operational instruments to provide a demonstration of the new climate decadal trending capability offered by spectrally resolved radiances with high accuracy proven on-orbit.

The Meteosat Third Generation (MTG) programme is intended to provide meteorological data from the geostationary orbit as a continuation of the Meteosat Second Generation (MSG) services at least until the mid-2040s. The programme consists of a twin satellite concept, based on three-axis stabilised platforms: four imaging satellites (MTG-I) and two sounding satellites (MTG-S). The first MTG satellite is currently scheduled for a launch around the fourth quarter of 2021. Images from the Flexible Combined Imager (FCI) instrument on board the MTG-I satellites will be used to derive Atmospheric Motion Vectors (AMVs) in a wide range of frequencies, from visible to infrared, ensuring the continuity of the Full Earth Scan service currently provided by Meteosat-11. AMVs are derived from satellites by tracking clouds or water-vapour features in consecutive satellite images. They are an important meteorological product because they are assimilated in Numerical Weather Prediction (NWP) models and contribute to the improvement of forecast scores. The MTG-FCI AMV extraction algorithm is largely based on that of MSG, with a few important differences (three images instead of four, no intermediate product averaging, etc.). This MTG-FCI AMV algorithm strategy is expected to provide more instantaneous information on the wind vectors, which is more suitable for the smaller-scale evolution of NWP models. In this paper, the current status of the MTG-FCI AMV prototype is presented, together with a detailed comparison of the MSG and MTG-FCI AMV algorithm performances using one month of MSG data. The impact of the new MTG-FCI strategy on the AMV product and its performance against forecast are also analysed.

Ground penetrating radars (GPR) are widely used for detection of underground buried objects. Synthetic aperture radars (SAR) are common instruments for land remote sensing. GPRs with synthetic aperture radar technique (GPR-SAR) are popular instruments to obtain image of the buried objects. To know about dielectric contents, position and shape of the buried target objects, ordinary GPR-SAR is insufficient, because angle between transmit and receive antenna is fixed. Therefore, information is lacked, mainly about microwave propagation velocity of soil which affects measurement accuracy of position of various buried objects. Multi-angle GPR-SAR, a new method, is proposed and can change angle between transmit and receive antennas. In the multi-angle GPR-SAR, a lot of angle points between the antennas can be set, and much more detailed information can be obtained related to buried objects and surrounding soil. A new indoor experiment instrument of full-polarimetric, multi-angle and bi-static GPR-SAR have been developed, which enables us to evaluate possibility of imaging various already-known buried objects. Outline of the instrument is introduced, and polarimetric calibration and imaging capability are verified.

2019 is the new era for space programs in Taiwan. The 3rd phase of the “National Space Technology Long-Term Development Program” in Taiwan (3rd phase space program) has been started since 2019 and plans to be completed in 2028. Serving as a follow-on mission of Formosat-5, Formosat-8 program plans to develop six remote sensing satellites, constructing a constellation, for global coverage and multiple local revisits over Taiwan every day. According to the mission planning of the 3rd phase space program, the remote sensing satellites are designed to meet most of the requirements from the end users. Besides, NSPO will also promote the local space industry under the authorization of the government. The satellite development approach for Formosat-8 satellite program is initiated differently from the past. Local industry and research institutes will cooperate with NSPO to develop most of the key components and core technologies. How to qualify newly developed key components and core technologies will be very critical in this program. The first satellite of Formosat-8 will be treated as a flight demonstration platform for the follow-on five satellites. There are more than fifteen key components and core technologies will be developed and verified in the Formosat-8 program. The development strategy and current status will be demonstrated in this paper.

The Environmental Mapping and Analysis Program (EnMAP) is a German space borne science mission that aims to characterize the Earth’s environment on a global scale. The single payload of the satellite is the Hyperspectral Imager (HSI). It is capable of measuring the solar irradiance reflected from the Earth’s surface as a continuous spectrum in the spectral range of 420nm to 2450nm, with an average spectral sampling of 6.5nm (VNIR) and 10nm (SWIR). The EnMAP swath of 30km is sampled with 30m in along and across track direction.

In these proceedings, we first give a brief overview the instrument design. We then explain the calibration strategy, which is a combination of on-ground and in-flight calibration measures. The on-ground calibration is presented in more detail. It aims to create a complete baseline calibration of the EnMAP instrument comprising a radiometric, spectral, geometric, polarimetric and straylight characterization. In orbit, a diffuser is used for absolute radiometric calibration via sun viewing. On-board calibration light sources ensure radiometric stability in between sun-viewings and spectral stability over the mission lifetime.

Finally, we share first characterization data which are prototypical of the final instrument calibration.

The Plankton, Aerosol, Cloud ocean Ecosystem (PACE) mission Ocean Color Instrument (OCI) is the next generation ocean color sensor following on from the SeaWiFS and VIIRS designs, to be launched into low Earth orbit in 2022. Like those heritage sensors, OCI has cross track scanning fore-optics, the reflectivity of which (referred to here as the response versus scan angle or RVS) must be characterized prior to launch. The expected test setup, component reflectivity measurements, instrument model, and heritage sensor testing were used to generate simulated RVS data. This simulated data set was then used to verify the functionality of the analysis software in preparation for the upcoming ground test campaign. The analysis software is designed to characterize the RVS for all OCI bands over the full range of scan angles to be measured on orbit as well as verify compliance with the sensor design requirements in near real-time.

Space-based astrophysical and remote sensing observations often require the detection and measurement of light originating from distant and relatively faint objects. These observations are highly susceptible to scattered light which may introduce imaging artifacts, obscure object details, and increase measurement noise. This paper describes the initial work of characterizing representative black materials used in coronagraph instruments and other spaceborne instruments. Measurements of “blackness” and the achieved reflectance of black silicon are provided in the spectral range from 400nm to 2500nm using 8o directional hemispherical measurements. The bidirectional reflectance of black silicon was also measured at discrete wavelengths, 633nm, and 1064nm, using the optical scatterometer located at NASA Goddard Space Flight Center’s Diffuser Calibration Laboratory (DCL). A 100mm diameter black silicon sample was fabricated and optically characterized. The BRDF of other well-known black materials such as Z306 and Fractal Black are also presented and discussed.

Landsat 9 is planned for launch in December 2020 to continue the mission of observing changes on the Earth’s surface that began in 1972 with the launch of Landsat 1. Like Landsat 8, Landsat 9 will carry two imaging instruments: Operational Land Imager 2 (OLI-2), designed and built by Ball Aerospace**, and Thermal Infrared Sensor 2 (TIRS-2), manufactured by NASA Goddard Space Flight Center (GSFC). As of this writing, both sensors have completed the instrument-level ground testing and are ready for integration into the spacecraft. Data collected during the pre-launch performance testing are analyzed to assess the usability of responses of the video reference pixels (VRPs) located on the focal planes of OLI-2 and Landsat 8 OLI for more accurate detector bias estimates, develop a methodology to correct for nonlinearities in the OLI-2 response and compare it to the OLI correction approach, and determine the spatial performance of TIRS-2.

For the VIIRS (Visible Infrared Imaging Radiometer Suite) onboard the JPSS (Joint Polar Satellite System) missions, extensive ground testing is performed to characterize some aspects of the sensor that cannot be mea- sured once the instruments are on-orbit. Two such parameters are the response versus scan angle (RVS) and polarization sensitivity. The pre-launch tests that characterize these parameters share a number of similarities. This paper will show that the polarization test data can be used to generate RVS results that are comparable to the results produced from the RVS test itself. The polarization test data also provides additional information about how the RVS changes with both scan angle and polarization state.

The Suomi National Polar-orbiting Partnership (SNPP) Visible Infrared Imaging Radiometer Suite (VIIRS) has been on-orbit for more than seven years. VIIRS has 22 spectral bands, among which fourteen are reflective solar bands (RSB) covering a spectral range from 0.410 to 2.25 μm. The SNPP VIIRS RSB have performed very well since launch. The radiometric calibration for the RSB has also reached a mature stage after almost seven years since its launch. Numerous improvements have been made in the standard RSB calibration methodology. Additionally, a hybrid calibration method, which takes the advantages of both solar diffuser calibration and lunar calibration and avoids the drawbacks of the two methods, successfully finalizes the highly accurate calibration for VIIRS RSB. The successfully calibrated RSB data record significantly improves ocean color products, whose stringent requirements are especially sensitive to the calibration accuracy, and helps the ocean color products to reach maturity and high quality. It has also greatly improved the accuracy and quality of other environmental data records (EDR) and high level science products. Nevertheless, there are still many challenging issues to be investigated for further improvements of the VIIRS sensor data records (SDR). In this presentation, the robust results of the RSB calibrations and instrument performance are presented and updated. Challenging issues and further improvements in the RSB calibration will also be addressed.

The NOAA-20 Visible Infrared Imager Radiometer Suite (VIIRS) has been in orbit for more than one and a half years. VIIRS has 22 bands, among which 14 are reflective solar bands (RSBs) covering a spectral range from 0.410 to 2.250 μm. The RSBs are calibrated on-orbit using an onboard solar diffuser (SD), whose on-orbit degradation is tracked by an onboard SD stability monitor (SDSM). NOAA-20 VIIRS is also scheduled to view the Moon approximately monthly and the lunar observations are used to track the RSB on-orbit changes as well. Both SD and lunar calibration results for the RSBs are shown and it is demonstrated that the two sets of the calibration coefficients diverge with time, especially for short wavelength bands. The divergence is due to the nonuniformity of the SD degradation, a phenomenon observed in SNPP VIIRS and the two MODIS instruments. Because of this divergence, a hybrid method, which properly combines the SD and lunar calibration results, need to be applied to generate the RSB calibration coefficients look-up tables (LUTs) as has been done for SNPP VIIR RSBs. The challenging issues of the RSB calibration using the SD/SDSM and the Moon are also addressed and discussed.

The Visible Infrared Imaging Radiometer Suite (VIIRS) aboard Suomi National Polar-orbiting Partnership satellite performs radiometric calibrations of its reflective solar bands through an onboard sunlit solar diffuser (SD). On orbit, the bidirectional reflectance distribution function of the SD changes over time. The change factor, known as the H-factor, is determined by an onboard solar diffuser stability monitor (SDSM) using the signal strength ratio determined by observing the Sun through an attenuation screen and the sunlit SD. The sunlight goes through another attenuation screen before striking the SD. The screen relative transmittances can be accurately characterized with on-orbit data, except for the regions where the solar azimuth angles are at or close to the extremes. It is unfortunate that over the initial orbits (< orbit 154) of the SNPP, the solar azimuth angle is at one of the extreme regions. Since there are no SDSM data over the initial orbits, the measured H-factors from late orbits are extrapolated to orbit zero to find a scale factor that yields, at orbit zero, the final H-factor of a value of one. The accuracy of the extrapolation depends on the quality of the transmittances of the screens. Due to inaccuracy of the transmittances over the initial orbits, the scale factor may not be accurate. Here, we use our previously developed technique to determine the H-factor without using the screen transmittances and thus are able to examine the accuracy of the scale factor and obtain the H-factor time change rate at early satellite orbits.

Once on orbit, the bidirectional reflectance distribution function (BRDF) of the solar diffuser (SD) of the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the NOAA-20 satellite changes over time. The change factor is determined by an onboard solar diffuser stability monitor (SDSM). However, the design band central wavelengths (412 to 926 nm) of the SDSM detectors do not cover the VIIRS short wave infrared (SWIR) bands which have band central wavelengths from 1.238 to 2.257 μm. Although it is known that the SD BRDF changes at a much slower rate in time over longer wavelengths, the change over some of the SWIR bands’ central wavelengths may still be large enough to be ignored. To determine the NOAA-20 VIIRS SD BRDF change factor over the SWIR band wavelength region, we use the solar photon wavelength power law approach that has been applied to the VIIRS instrument onboard the Suomi National Polar-orbiting Partnership satellite. In this work, we show the results for the NOAA-20 VIIRS.

The VIIRS instruments aboard the SNPP and NOAA-20 (N20) satellites have 14 reflective solar bands (RSB) covering a spectral range from 412 nm to 2250 nm. The radiance of each VIIRS RSB is calculated from a quadratic function of the background-subtracted digital count, 𝑑𝑛, with the quadratic coefficients determined during pre-launch testing. On orbit, calibration is maintained using observations of a sunlit solar diffuser (SD), which views the Sun every orbit through a fixed attenuation screen. The SD observations, which are at nearly the same radiance level every orbit, provide a timevarying overall calibration adjustment factor, the F-factor. But there is no designed on-orbit mechanism for calibration at multiple radiance levels, so the relative strengths of the quadratic coefficients continue to be fixed at the pre-launch values. On a few rare occasions, the VIIRS instruments have passed through a partial solar eclipse during the part of the satellite orbit when the SD is illuminated by the Sun (near the South Pole). As of August 2019, the SNPP and N20 VIIRS SDs have observed five and three partial solar eclipses, respectively. While these events are rare, they offer a unique opportunity to test the RSB calibration using the SD at different radiance levels. In this paper, we compare the reduction in the measured SD signals during an eclipse to the predicted radiance reduction based on the Sun-Moon geometry and a solar radiance model. We find good agreement between the data and model for all events, indicating that the VIIRS RSB gain linearity has remained fairly stable on-orbit. The most significant deviation is for the N20 short-wave infrared bands, which had non-linearity concerns during pre-launch testing. We also investigate the SNPP results using different versions of the prelaunch quadratic gain coefficients.

This optical remote sensing satellite has a high-resolution PMS camera, which has a panchromatic band (PAN) and four multispectral bands (MS). The PMS camera do not contain onboard calibration subsystem. So, the satellite is designed to allow a three-axis attitude control system pointing the camera to the lunar. Through the lunar imaging, the cameras’ long-term stability of the radiances is hope to be evaluated. The lunar is known as an excellent radiometric reference because of the stable reflectance of its surface in the visible and near-infrared spectral regions. It is the nearest planet to the earth. In orbit lunar imaging does not rely on ground calibration site and weather. Although earth-orbit satellite lunar observation is efficient to monitoring camera’s radiation performance or achieving absolute radiation calibration, attitude control and imaging parameters matching problem should be solved. Some key points of lunar imaging were proposed to solve the mismatch of integration time and push-broom velocity. In addition, this paper summarizes the improved scheme for lunar imaging, obtains clear images at different lunar phase angles, and shows the preliminary results of the geometric parameters and irradiance of the lunar observation. It has accumulated experience in the follow-up satellite lunar observation.

Scientific studies require radiation fluxes over the Earth to be accurate within 1% for shortwave fluxes and 0.5% for outgoing longwave fluxes. The validation of in-orbit instrument performance requires both stability in calibration source and also calibration corrections to compensate for instrument changes. The Moon offers an external source whose signal variance is predictable and non-degrading. CERES detectors register the signal output from the entire face of the Moon. Lunar observations performed by CERES Flight Models (FM) 1 through 4 have been successful in assisting validation of radiances to the required accuracy. CERES Flight Model 5 (FM-5) is on Suomi/NPP spacecraft, orbiting since October 2011. This paper uses lunar measurements to validate detector output of FM-5. These measurements are adjusted to remove orbital effects due to variations in distance between Moon and Sun, distance between the satellite and the Moon and lunar phase angle. These effects create a total variation in lunar irradiance of 20% in the total channel and 8% in the shortwave channel. The change in orientation of the Moon as seen by the detector is called libration and causes variations of about 1% of the irradiance. A consistent dataset spanning at least 2 years in length is required to remove variations due to libration. The major uncertainties remaining in the measurements are assumed to be due to changes of the spectral responses of the channels due to degradation of optical surfaces in orbit. The results demonstrate that lunar observations can be used to validate FM-5 measurements.

SNPP and NOAA-20 VIIRS have been on orbit for more than 7.5 and 1.5 years, respectively. Since their nadir doors opened on 21 November 2011 and 13 December 2017, respectively, the two VIIRS instruments have been making observations of the moon on a near-monthly basis as a monitor of their reflective solar bands (RSBs) on-orbit gain changes. The VIIRS RSB are primarily calibrated by an onboard Solar Diffuser (SD) panel and an accompanying Solar Diffuser Stability Monitor (SDSM). However, due to a non-ideal behavior in the SD degradation, discovered recently, the SD/SDSM calibration contains non-negligible errors, especially for the short wavelength bands, that can significantly impact the accuracy of the sensor data and eventually the science products. On the other hand, the lunar surface is very stable and can be used to provide more reliable characterization of on-orbit gain changes of the RSB, especially for the long-term trend. The RSB calibration coefficients derived from the lunar calibration are generally consistent with those derived from the SD/SDSM calibration, but clear differences in trend are seen due to aforementioned SD calibration errors, especially for the short wavelength bands. Thus, the lunar calibration plays a key role in both SNPP and NOAA-20 VIIRS RSB calibration and critical for obtaining high accuracy and quality of the sensor data records (SDR) as well as the environmental data records (EDR), especially the ocean color EDR. In this paper, we comprehensively review the VIIRS lunar calibration methodology and the improvements we have made to refine the lunar calibration results, especially the removal of the seasonal oscillations in the derived calibration coefficients due to imperfection of the lunar view geometric effect correction. The lunar calibration results for the two instruments are shown and discussed.

Two VIIRS instruments are currently operated in space; one on-board the S-NPP satellite launched in October, 2011 and another on-board the NOAA-20 satellite launched in November, 2017. The VIIRS design has included a unique day/night band (DNB), which can make both daytime and nighttime observations in the reflective solar spectral region. It has a broad spectral response, covering wavelengths from 500 to 900 nm, and an extremely large dynamic range. The DNB collects data in three gain stages: LGS, MGS, and HGS for low, mid, and high gain stage, respectively. Its HGS has excellent low-light sensitivity and is capable of detecting bright stars through the instrument space view port. Similar to other reflective solar bands (RSB), the DNB LGS and MGS responses to the Moon can be used to monitor their on-orbit calibration stability. This paper describes various strategies that we have developed to use the moon and stars for the DNB on-orbit calibration and calibration inter-comparisons and presents the results for the S-NPP and NOAA-20 VIIRS. Key technical issues, such as identifying the stars and processing data collected at different gain stages and aggregation modes, are also discussed, along with the efforts planned for future improvements.

In the frame of the monitoring of Sentinel 2 MSI sensors in orbit, a method for inter-band calibration validation, using Antarctic site, has been developed and tested. The method relies on the directional hemispheric reflectance found in ASTER data base. In order to consider that the spectral shape of the directional directional reflectance is the same as the directional hemispheric one, wavelengths have to be limited to the spectral range below 0.9 μm. Thus this method cannot perform the inter-band calibration for the whole set of spectral bands of MSI but only from B1 to B8A. Results for B9 seem also correct although the central wavelength is a little bit beyond 0.9 μm.

Given a clear day acquisition on DomeC site, a first set of computations of Top Of Atmosphere (TOA) reflectances for MSI spectral bands is performed using the three ASTER reflectances corresponding respectively to small, medium and coarse grain size for snow. The spectral reflectances are normalized by the B2 value. The comparison of the three normalized TOA reflectances to the actual one given by MSI enables to select the right snow grain size. Then the second step is the atmospheric parameters adjustment. Water content is assessed thanks to B9 band centered at 0.945 μm and ozone is assessed thanks to mainly B3 band centered at 0.56 μm. For a clear day, the aerosol optical thickness is weak and thus the TOA reflectance is not very sensitive to the more or less low abundance of continental aerosols. The ratio of normalized reflectance given by MSI to the normalized reflectance given by the computation is assessed for each spectral band between B1 and B9 and is compared to the inter-band calibration validations performed with other methods.

The Clouds and the Earth's Radiant Energy System (CERES) project provides observed flux and cloud products for the climate community. To accomplish this goal, the CERES project must merge six CERES instruments, along with two MODIS sensors, two VIIRS sensors, and twenty GEO imagers in order to produce a climate-quality dataset. The input satellite sensors must be properly calibrated and known sensor anomalies must be removed before operational processing. The GEO imager radiances are radiometrically scaled to the Aqua-MODIS C6.1 calibration reference using all-sky tropical ocean ray-matched (ATO-RM) coincident radiance pairs. However, monthly-ATO-RM calibration analysis is inadequate for detecting sensor L1B radiance anomalies, which may span only a few days. The CERES monthly-ATO-RM calibration method was modified to increase the number of ray-matched pairs in order to apply the ATO-RM calibration method on a daily basis. The goal of the daily-ATO-RM calibration method is to detect slight L1B radiance anomalies by limiting the daily gain noise over the record. To test the daily-ATO-RM calibration method, the GOES-16 record, with known L1B radiance anomalies, was evaluated. The GOES-16 channel 2 (0.65 µm) daily-ATORM gain standard error is 1% and thereby allows for confident identification of days with calibration anomalies greater 3%, or three standard deviations (σ). The daily-ATO-RM calibration method detected the three known L1B calibration anomalies, however, there were two daily gains that exceeded three σ that were not associated L1B anomalies. Similarly, the daily-ATO-RM was able to identify the calibration discontinuity of NOAA20-VIIRS in the Land SIPS L1B V001 processing

The primary objective of the CLARREO Pathfinder (CPF) mission is to demonstrate essential measurement technologies to enable highly accurate decadal change observations traceable on-orbit to SI standards. Another important objective of the CPF is to demonstrate inter-calibration with the VIIRS sensor and to show that such high-accuracy reference inter-calibration is achievable. To satisfy this requirement, it is important to understand and quantify uncertainties in VIIRS sensor measurements. Based on prelaunch test results, the reflective solar bands of both SNPP and NOAA-20 VIIRS have exhibited polarization sensitivities in the shortest wavelength bands, with an unexpectedly larger sensitivity observed for NOAA-20 VIIRS, particularly in bands M1 to M4. In this study, we use VIIRS Level-1B reflectance data collected over the Pseudo-Invariant Calibration Sites over North African desert region to examine the polarization associated uncertainty for these four bands. Impact due to BRDF on the reflectance data is considered by comparing baseline results obtained from the same viewing and solar zenith angles under relatively low polarization sensitivity. Impact due to detector relative difference in polarization sensitivity is examined by normalizing reflectances by the value of the middle detector. Results of this study provide useful information on VIIRS uncertainty contribution due to polarization when conducting CPF and VIIRS inter-calibration.

The Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission will launch no earlier than summer 2022. The primary payload is the Ocean Color Instrument (OCI). OCI is a hyperspectral imaging radiometer that will measure top-ofatmosphere radiances from 340nm to 2260nm at approximately 1km spatial resolution. The spectral resolution will be 5nm from 340nm to 890nm to enable the production of innovative ocean color products on a global scale (OCI will provide global coverage every 2 days). There are 7 different multispectral bands in the shortwave infrared to support atmospheric correction for ocean color and aerosol and cloud studies. Ocean color applications require state of the art radiometric accuracy (approximately 0.5%, excluding the absolute calibration uncertainty). Considerable effort has been invested in the planning of the prelaunch calibration campaign and the on-orbit calibration capabilities. This paper describes the current plans for the prelaunch calibration and characterization campaign of the OCI Engineering Test Unit (ETU), which is scheduled to begin towards the end of 2019. The prelaunch calibration campaign will characterize all sensor characteristics that are expected to influence radiometric sensitivity: absolute calibration (i.e. radiometric gains), signal to noise ratio, nonlinearity, response versus scan angle, dynamic range, signal to noise ratio, and sensitivities to polarization and temperature. In addition to these one-time characterization tests, two types of tests have been developed that monitor the evolution of several OCI radiometric characteristics: a Limited Performance Test (LPT, expected duration about 8 hours), and a Comprehensive Performance Test (CPT, expected duration about 2 days).

For over 40 years ESA’s Earthnet Programme has played a significant role as part of ESA’s mandatory activities, being a major contributor to the Global Earth Observation System of Systems (GEOSS). This role involved providing the framework for integrating non-ESA missions, i.e. Third Party Missions (TPM), into the overall ESA Earth Observation (EO) strategy. Complementary to ESA-owned EO missions, the programme allows European users access to a large portfolio of TPM and is particularly important for promoting the international use of EO data.

In line with the Earthnet Programme objectives first established in 1977, ESA aims to foster cooperation and collaboration with not only other national space agencies, but also commercial mission providers. In recent years the availability of low cost small satellites and the innovation of constellations resulted in an increased number of commercial companies who have established business models to provide information services fed by their own satellite systems. These New Space players are now portraying an important role in the EO international strategy. Some of these new missions are potential candidates for Earthnet TPMs, and ESA have therefore set up a project to assess the quality and the suitability of these missions and also to establish dialogues with the various mission providers in order to improve the overall coherence of the EO system. This project is known as the Earthnet Data Assessment Pilot (EDAP).

The EDAP consortium, headed by Telespazio VEGA UK is aimed at the provision of various clusters of expertise to perform an early data quality assessment of existing or future EO missions from national or commercial providers, which may potentially become TPMs within ESA’s Earthnet Programme. Complementary to this support is a focus on the generation of methodologies and guidelines for training and capacity building with each mission provider in regards to performing efficient data quality assessments in preparation for future missions.

This work presents how the EDAP activities are organized and executed, and will also provide details of the various missions included within each of the instrument-specific domains covering Optical Sensors, Synthetic Aperture Radar (SAR) and Atmospheric missions. Important multi-mission aspects will also be presented for studies that will require inputs from several missions, possibly spanning multiple instrument domains; such studies contribute to interoperability across existing and future missions and help foster synergies between these missions.

The fusion of multispectral (MS) and hyperspectral (HS) data has been limited by the availability of space systems that have the capacity to host both imagers simultaneously. High-performing single instrumentation across a large wavelength range is both difficult from an engineering perspective as well as expensive. However, in recent years, external payload platforms on the International Space Station (ISS), such as Bartolomeo and Multi-User System for Earth Sensing (MUSES), have surfaced and created more possibilities for MS/HS data fusion to produce high resolution in both spectral and spatial domains.

We present a proof-of-concept and breadboard for a low-cost MS imager that optimally complements a HS imager. Design characteristics of the MS imager prototype include the ability to produce high-spatial resolution images (~2.5m Ground Sample Distance), robust communications allowing seamless integration into the ISS downlink system, data fusion algorithms and methods, on-board computational processing, and ground mission control. A cost-benefit-risk analysis of the MS imager design will provide insight into ideal MS/HS joint operation.

As demonstrated by K. Perlmutter et al., a low-cost MS imager adds value to a hyperspectral data stream, thereby increasing the relevance of Earth Observation applications for public policy-makers and humanitarian organizations, a central goal of the John Glenn Humanitarian Observatory program in The Ohio State University Battelle Center for Science, Engineering, and Public Policy.

This paper presents a conceptual system design by which the requirements of the Landsat mission, or Sentinel-2, or potential commercial missions may be accomplished and extended. For simplicity, I will just refer to Landsat or Smart Landsat (SL). These new methods enable the Landsat system to significantly increase the quality of the information acquired while meeting all of the requirements of the Landsat Mission. The key difference between the old and new Landsat system designs is in the data acquisition strategy. The traditional Landsat acquires images of all the Earth’s surface it passes over. This means that the vast majority of the data is redundant as most of the surface had not changed since the previous data acquisition. The Smart Landsat (SL) employs active data acquisition rather than passive. This means that it only acquires data from areas that are changing. In other words, it acquires Information.

Optical choppers are common components utilized in a wide variety of systems, for the modulation of light, including for generating controlled laser impulses, of as high as possible frequencies and with certain (required) profiles. Classical choppers have rotational disks, but such configurations are limited in terms of chop frequencies to 10 kHz, although issues already appear from around 3 kHz. Solutions to overcome this drawback include the development of Micro-Electro-Mechanical Systems (MEMS) or of macro-choppers with rotational shafts. To our knowledge, we have introduced the latter solution (patent pending). Our previous studies on choppers with cylindrical and spherical shafts are briefly pointed out in this work, while we approach a third possible solution, of choppers with conical shafts. Optomechanical aspects are discussed, performing the Finite Element Analysis (FEA) of the rotational shafts, for a certain range of constructive parameters, and for rotational speeds of up to 60 krpm. The possible limits of the rotational speed at which choppers with such conical shafts are obtained–from the point of view of their structural integrity and level of deformations.

EnMAP is a German hyperspectral satellite mission. The Remote Sensing Technology Institute of the German Aerospace Center is responsible for the stray light characterisation of the satellite’s spectrometers. This paper describes the light source developed for that purpose and how it will be employed to characterise the in-band, in-field stray light. This type of stray light can be characterised by measuring the point spread function (PSF) at multiple locations on the detector. Because of the cumulative effect of stray light, it is necessary to characterise the PSF in the near- and far-field. The PSF can span a range of more than 6 orders of magnitude from the peak to the wings at the edges of the detector, exceeding the intrinsic dynamic range of the instrument. Therefore a high dynamic range (HDR) PSF measurement is required: A spectrally and angularly narrow spot of light is guided onto the instrument then measurement frames of multiple signal levels are acquired. The signal level is controlled by changing the instrument’s integration time or changing the neutral density filter of the light source. The overexposed pixels in the higher signal level frames are excluded, then the multiple image frames are combined into one HDR frame which can then be used in the stray light correction algorithm. This HDR ’bracketing’ technique is demonstrated here with DLR’s HySpex VNIR-1600 airborne imaging spectrometer.

On-orbit characterization of the response versus scan-angle (RVS) is one of the most challenging aspects of the reflective solar band (RSB) calibration for the MODIS instruments onboard the Terra and Aqua spacecraft. The degradation of the solar diffuser, together with the lack of onboard calibrators (OBCs) to cover additional scan angles, other than the one for the lunar observations, has resulted in the use of Earth view responses from the pseudo-invariant desert sites to track the on-orbit RVS changes. This approach has been implemented in Collection 6 (C6) and C6.1 for bands 1-4, 8 and 9 of both instruments and also band 10 of Terra MODIS. As the missions continue to operate over a decade beyond their designed life and the instrument optics continue to degrade, it is expected that the OBC based RVS currently applied to other bands, specifically the high-gain ocean bands, will be inadequate to maintain the long-term calibration stability. An interband calibration approach is formulated and implemented in this paper. The proposed approach relies on the use of a spectrally matching stable reference band to evaluate the long-term calibration stability of the high-gain ocean bands that typically saturate while viewing the selected calibration deserts. Results from this approach indicate a noticeable drift for Terra MODIS bands 11 and 12 whereas the Aqua bands continue to show excellent temporal stability. These results are consistent with the corrections derived by the NASA Ocean Biology Processing Group (OBPG) and are expected to have minimum impacts on the downstream science products.

The newly launched polar-orbiting NOAA-20 satellite is the follow-on mission to the SNPP (Suomi National Polar-orbiting Partnership) satellite. Both satellites are in an afternoon orbit with a close equatorial cross time. The Visible Infrared Imaging Radiometer Suite (VIIRS) is a key sensor onboard NOAA-20 and SNPP. The two VIIRS sensors are within the same engineering design with nearly identical spectral ranges. Its on-board calibration components include a solar diffuser and a solar diffuser stability monitor for the reflective solar bands (RSB), a V-groove blackbody for the thermal emissive bands (TEB), and a space view as background reference. This study evaluates calibration performance of the NOAA-20 VIIRS RSB using the first internally released L1B data product by NASA Land SIPS, which has consistent calibration coefficient look up tables (LUT) throughout the entire mission. Several independent vicarious approaches are used to examine the stability and consistence of reflectance. The first approach is based on a double difference method by comparison with SNPP VIIRS using observations from simultaneous nadir overpasses (SNO) with Aqua MODIS. The second is based on the reflectance trends from 16-day repeatable orbits obtained over the widely used Liby-4 desert site so each data point has the nearly same viewing angles relative to the site. The third approach is to use the frequent overpasses over the Dome C snow site. Results of this study provide NOAA-20 VIIRS post-launch calibration stability performance and radiometric agreement with SNPP for the first 18 months of mission.

Hyperspectral imager can obtain both spatial information and spectral information at the same time, which is widely used in agriculture, biomedicine, environment monitoring. At present, hyperspectral imager is developing in the direction of lightweight, miniaturization and low power consumption. The miniaturization of hyperspectral imager includes the miniaturization of optical system and the miniaturization of detector system. In this paper, a miniaturization hyperspectral imager based on CMOS detector is proposed. The working range of is 400-1000nm, which contains 512 spectral bands. The field angle of hyperspectral imager is ±4 degree and the focal length is 99mm. The optical system consists of the telescope, the slit and the spectrometer. Considering the miniaturization of optical system, the spectrometer uses prism-grating spectroscopy. The CMOS sensor GSENSE400BSI is used in the detector system, whose pixel size is 11 micron*11 micron and pixel number is 2048*2048.The detector system consists of an imaging core board and an interface board, and the image output is Cameralink interface. Because of the high integration of CMOS sensor, the design of peripheral circuit can be greatly simplified. The total weight of the hyperspectral imager is not more than 2.5kg and the total power consumption is not more than 5W.The spectral imaging system has the advantages of lightweight, miniaturization and low power consumption. After testing, the spectrometer has good imaging quality.

The most significant shortage of the Dyson spectrometer is that the small clearance among the slit, image plane and the hemisphere lens makes the spectrometer difficult to assembly. To solve this problem, several approaches have been proposed. Such as inserting additional aspherical lenses in the optical path to enlarge the image distance, or using a fused silica lens and incorporates a built-in fold mirror to allow the detector sufficient clearance from the slit. In this paper, a Dyson imaging spectrometer with freeform surface has been designed. The freeform surface is used to enlarge clearance distance and compensate the large residual aberration without additional lenses. The design starts from a sphere Dyson system, and then the freeform surfaces are applied to optimize the initial configuration by the use of optical software. The design results show that the Dyson imaging spectrometer with freeform surfaces have great optical performance and easy to mounting which is crucial for development in the fields of aeronautics and astronautics remote sensing.

The VIIRS instruments on board the SNPP and NOAA-20 (N20) satellites have 14 reflective solar bands covering a spectral range from 412 nm to 2250 nm. Three of these are imaging bands (I bands) with a nadir spatial resolution of 375 m and 11 are moderate resolution bands (M bands) with a resolution of 750 m. The higher resolution in the I bands is achieved by a combination of more detectors, with the I bands having twice as many detectors of half the size for every M band detector, and a higher data rate, with the I bands having two sub-samples for every sample of M band data. To ensure calibration accuracy, any systematic difference in the response of the two sub-samples needs to be monitored and corrected in the calibrated products. In this paper, we use the solar diffuser calibrations to monitor the gain differences between the two sub-samples of the I bands both as a function of time and signal level. We find gain differences of about 0.1% for I1, 0.3% for I2, and <0.1% for I3 that are mostly constant over the range of signal values available in the SD calibration. These values are mostly consistent throughout the mission for both instruments. The results are remarkably similar for the two VIIRS instruments, including a slightly out-of-family behavior seen in a few detectors. We discuss possible causes for the difference and the impact on the aggregated Earth view images.

The geo-referencing information of the satellite imagery is obtained by the use of either attitudes and velocity/position provided by the satellite instrumentation , nevertheless the positioning using this approach depend directly on the quality of the ephemeris data. The image-to-image registration aims to find a geometric transformation relating two or more images in order to locate them in the same geographic reference. As the first Algerian high-resolution satellite ALSAT- 2A, has a nominal positional accuracy of around 300m, this last approach can be used to estimate and improve the raw image positional quality where these images are registered to orthoimages that are more accurate. Therefore, the resulting image have an enhanced geolocation quality than the one calculated using the estimation of the line of sight model. The purpose of this work is to provide a framework to automatically estimate the positional quality of Alsat2A image for cataloguing purpose, also to improve the geolocation accuracy of the level 1-A (geometrically raw) images by using other imagery that is already geo-localized with better accuracy. Landsat 8 orthoimagery coverage represents a data source that is worldwide available and its accuracy is sufficient for our work. Therefore, it is used as reference images to estimate and enhance the quality of raw ALSAT-2A images. This work is based on the use of open-source software such python, OpenCv and PostgreSQL and the open-data e.g. geo-referenced quick looks of landsat8 provided by EarthExplorer. Many experimentations has been conducted to decide on which algorithm is better to enhance the contrast and which spectral channel to use, also many methods for the homologue points extraction and description have been evaluated. Then, points of interest extracted from the reference orthoimagery are fed into a geographic database, allowing the use of these points as known ground points to estimate and enhance the quality of Alsat-2A imagery.

Next generation air quality sensors are currently planned to launch in the 2020-2021 timeframe. The Tropospheric Emissions: Monitoring of Pollution (TEMPO-United States) and Geostationary Environment Monitoring Sensor (GEMSKorea) are two such missions that will probe the boundary layer and lower troposphere at unprecedented spatial and temporal scales. These missions are designed to provide constraints on chemical forecast models and specifically to answer the question: “What are the temporal and spatial variations of emissions of gases and aerosols important for air quality and climate?” In preparation for these missions a number of airborne air quality field missions have been performed to collect data at similar spatial and temporal scales, and during relevant seasonal air quality episodes. This data is being used to improve the trace gas retrieval algorithms and explore the unique spatial scales and diurnal patterns that will be encountered when the Geostationary experiments are operational. This overview will present details of two of the instruments used during these campaigns, the GEO-CAPE Airborne Simulator (GCAS) and the Geostationary Trace Gas and Aerosol Sensor Optimization (GeoTASO) instruments. The instruments' performance will be compared to predicted on-orbit values for the TEMPO and GEMS sensors in the retrieval of high spatial resolution nitrogen dioxide and formaldehyde. Examples of vertical column retrievals will be presented under various source/weather conditions as well as some of the uncertainties that result from radiative transfer assumptions.

Baffles are connected in front of the space cameras and star sensors to prevent the stray lights entering to the electrooptical system. Star sensors are mounted in various places of a spacecraft and imposed to different mechanical and thermal loads. In this research a star sensor baffle with a specified dimension is considered to simulate and analyze the deflections in various conditions. Vibration force from the launcher and gravity force considered as the mechanical load. Launcher vibrant force considered as QSL force and heat load is only considered from the solar radiation and have been modeled for both cold and hot cases. Deflection of the baffle is obtained using finite element method. Heat and mechanical loads are considered both at the launch time and in the orbit. Different materials such as aluminum, titanium, and CFRP composite are selected to do comparison among them. Composite materials are considered in many layer orientation configurations. Monte Carlo method is used to do ray tracing and obtain the efficiencies of the baffle to prevent the stray light entering to the entrance pupil diameter of the camera. Results show that baffles in launch time suffer from some deflections that affect the performance. In the orbit condition, baffles have negligible deformation although the thermal part is dominant. In launch condition, deflection mainly caused from the mechanical load. In orbit condition, deflection mainly caused from the heat load.

For a long time, various types of satellites, especially remote sensing satellites, can be used to meet not only the needs of earth observation, such as the observation of land and ocean resources, atmosphere and environment, etc., but also the needs of human exploration from outer space. Facing with the frequent occurrence of the global natural disasters and man-made accidents, human beings needs urgently a new satellite system with the rapidly responsive and sensing capacity. In this paper, the satellite application mechanism of the software defined radio (SDR) technology is studied, and a new concept of multifunctional satellite system with the rapid event response is proposed. A single satellite integrates three or more functions such as remote sensing, communication and data transmission, etc. The switching time between functions in one satellite is better than 300 s. Satellites can be adapted to different orbits of GEO, MEO and LEO. According to different application requirements, several satellites which have the same or different functions can form a satellite system. This new multifunctional satellite system can meet not only the need of rapid response of natural disasters such as earthquake and meteorological disasters, but also requirements of remote sensing, communication and data transmission for the man-made disasters such as the search and rescue of missing aircrafts, conflagrations, etc.

The Arctic region and the Antarctic region, as the two-polar regions of the earth, are sensitive to the global change to be the research focus. However, the existing earth observing system satellite data in the two-polar regions of the earth is not enough. The Moon is the unique natural satellite of the earth, which has advantages of global-scale coverage and long observation time. Therefore, the moon-based platform turns out to be a potential platform to comprehensively and continuously observe the Earth on a global scale, especially for the contrastive study of the Earth two-polar regions. Moreover, comparing to the limited life of the current satellites, the longevity of the moon is helpful to collect long-term time series data, which makes it possible to research long-term earth science phenomena in the two-polar regions. This paper comparatively analyzes the angular coverage performance of the two-polar regions of the earth observed from the moon-based platform. The observation angles of long-period 40 years through the geometry model of the moon-based platform from different sensor locations on the moon are calculated. The sensors are set on four potential sites on the moon--- the North Pole, the South Pole, the Sinus Iridum area and the Mare Nectaris area. When the two-polar regions of the earth are observed from four different locations on the moon, the different observation angular characteristics are obtained. This is helpful for the site selection of the moon-based platform.