Hooray! The ESA EnVision mission is adopted.
Onboard the spacecraft, there will be a suite of three spectrometers, VenSpec. One of these is called VenSpec-H where the H stands for high spectral resolution. Its scientific objectives consist in measuring variations of minor species’ abundances in the atmosphere of Venus. H2O, SO2, CO and OCS will be measured to characterize the potentially ongoing volcanic activity. These observations will allow us to understand both the importance of volatiles in volcanic activity on Venus and their effect on cloud maintenance and dynamics. VenSpec-H will measure these molecules in nadir viewing geometry, in infrared transparency windows of Venus’ nightside to probe the troposphere and in infrared spectral ranges on the dayside to measure the mesosphere. In this paper, the scientific requirements enabling our scientific objectives will be demonstrated. An intercomparison exercise was first led to reproduce modelled and observational reference spectra. The molecular vertical profiles, the aerosols’ model and the CO2 continuum contribution were validated for the different spectral windows. This enabled us to determine the spectral bands, their bandwidth and the resolving power necessary for our purposes. Along the way, we identified possible improvements and science avenues. Some of them impact the instrument design, such as the need for polarimetric measurements. Others are related to remaining uncertainties in the model and laboratory measurements that will complement the investigation.
EnVision is ESA’s upcoming mission to Venus with a launch scheduled in 2031. One of the payloads on board is the VenSpec suite,1 containing three spectrometer channels, one of which is VenSpec-H. VenSpec-H (Venus Spectrometer with High resolution) performs absorption measurements in the atmosphere of Venus in four near-infrared spectral bands. VenSpec-H is developed under Belgian management and builds on heritage from instruments on Venus-Express and TGO. Techniques used in these precursor instruments are improved and complemented with new technologies to comply with the scientific goals of the EnVision mission. The operating wavelength range (1.15 - 2.5 μm) imposes stringent temperature requirements on the instrument to make nightside measurements below the Venus clouds possible. Most importantly, the spectrometer’s optical components are held in a separate cold section inside the instrument, cooled down to −45°C, to remove thermal background from the signal. To avoid heat dissipation close to the spectrometer optics, the electronic boards are kept in a separate box. Besides that, some mechanisms, placed in the warmer part of the instrument at the entrance or exit of the cold section, had to be developed: a turn window unit to protect the interior of the instrument during the aerobraking phase of the mission, a filter wheel mechanism to select the spectral bands of interest, and an integrated detector-cooler-assembly to register the spectra. Some passive optical elements in the spectrometer had low technological readiness at the start of the project. One of them is a freeform corrector plate, used to compensate for aberrations introduced in the system by a parabolic mirror. This device is developed by the Brussels Photonics lab of VUB (Brussels) using a supply chain with shape adaptive corrective polishing and dedicated metrology. Another is the echelle grating, used to disperse the incoming light into its spectral components, which is built by AMOS. Both devices are highlighted in this article.
When developing new astronomical instruments, there is a need to perform the characterization of their individual components, especially the detectors, to ensure that their performances comply with the scientific objectives of the instrument. A visible-near infrared (VIS-NIR) facility was developed for the absolute and relative radiometric characterization of space-based detectors at the Royal Belgian Institute for Space Aeronomy (BIRA-IASB). The facility operates from 0.4 to 2.65 μm in an ISO-5 environment. It offers a tunable monochromatic flux with a high level of straylight rejection (10 − 8) and 2% uniformity, over a four-decade range of intensity with adjustable bandwidth. Latency measurements are also possible. Thermalization is offered within a precision of 7 mK between 50 K and 382 K. The ultimate vacuum level of the detector chamber is below 10 − 6 mbar. A robust security system avoids both reaching temperatures outside the operational range of the detector and its electronics, and contamination due to vacuum loss. The facility was already used to characterize the VIS-NIR detectors of the Moons And Jupiter Imaging Spectrometer (MAJIS), one of the instruments on board the Jupiter ICy Moons Explorer (JUICE). The versatility provided by the VIS-NIR facility allows its use for the characterization of other astronomical detectors.
MAJIS (Moons And Jupiter Imaging Spectrometer) is the visible and infrared imaging spectrometer of the ESA L-Class mission JUICE (JUpiter Icy moons Explorer). MAJIS plays a major role for achieving the JUICE main scientific objectives, which include the compositional study of the Galilean moons, their past and present activity, and its relation with observed surface features. It will also study the composition, structure, chemistry and dynamics of the Jovian atmosphere. MAJIS is composed of two spectral channels: the VIS-NIR (0.5µm-2.35µm), and the IR (2.25µm-5.54µm). Both channels are equipped with a Focal Plane Unit (FPU) mainly including a Teledyne H1RG Focal Plan Array (FPA), one Focal Plane electronics (FPE) and one filter. A dedicated facility was developed at the Royal Belgian Institute for Space Aeronomy (BIRA-IASB) for the characterization of the Flight (FM) and Spare (SM) models of the MAJIS VIS-NIR FPU. The radiometric capabilities of the facility include: (1) the tuning of the monochromatic flux provided to the detector over a four-decade range of intensity, (2) optical configurations for dark conditions, uniform light beam or convergent light beam with the same focal ratio as MAJIS, and (3) relative and absolute radiometric scales at the FPA plane. This work describes the radiometric characterization campaign of the MAJIS VIS-NIR SM FPU and the respective data analysis methods used to derive some of the detector key parameters such as the gain, the dark current, the linearity, the full-well capacity and the operability. A comparison with the performances of the FM VIS-NIR FPU is also provided.
The JUICE (JUpiter ICy moons Explorer) mission by ESA aims to explore the emergence of habitable worlds around gas giants and the Jupiter system as an archetype of gas giants. MAJIS (Moons and Jupiter Imaging Spectrometer) is the visible to near-infrared imaging spectrometer onboard JUICE which will characterize the surfaces and exospheres of the icy moons and perform monitoring of the Jupiter atmosphere. The launch is scheduled for 2023 with the first MAJIS observations inside the Jovian system occurring more than 8 years later. The MAJIS optical head is equipped with two Teledyne H1RG detectors, one for each of the two spectrometer channels (VIS-NIR and IR). This paper describes the characterization of the VIS-NIR Focal Plane Unit. These detectors will be operated in a non-standard way, allowing near/full-frame retrieval over short integration times (<< 1 sec) while maintaining good noise performance. After a quick description of the characterization strategy that was designed to evaluate the performances of the VIS-NIR detector according to the MAJIS operational specifications, the paper will address the data analyses and the main results of the characterization campaign. The major performance parameters such as dark current, linearity, noise, quantum efficiency, and operability will be presented and compared with the requirements.
We present measurement protocols of performances, test and calibrations of new compact solid-state photodetectors based on β-Ga2O3 oxides, and optimized for the UVC. They present reduced dark currents, permitting room temperature operation suppressing need for a cooling system (mass and power savings) and avoiding cold surfaces that traps environmental contamination. Detectors' response peak around 215-220 nm with a bandpass of 30 nm, allowing to observe the UVC wavelength band responsible of ozone creation in the stratosphere (Herzberg continuum, 200-242 nm) and to achieve solar-blindness for wavelengths above 250 nm. Other key assets of β-Ga2O3 detectors are their radiation hard properties (longer lifetime), and possible sensitivity (several hundreds mA/W at -5 V) that allows operation at lower voltages (reduced power), a key asset for Space applications. These detectors, evaluated, tested and calibrated, will be integrated on the INSPIRE-7 nanosatellite to be launched in 2023.
KEYWORDS: Sensors, Frequency modulation, Fermium, Jupiter, Radiometry, Radio optics, Quantum efficiency, Data modeling, Temperature metrology, Spectroscopy
MAJIS is part of the science payload of the ESA L-Class mission JUICE to be launched in 2022 with an arrival at Jupiter in 2030. MAJIS will perform imaging spectroscopy through two channels: VIS-NIR (0.50 µm - 2.35 µm) and IR (2.25 µm - 5.54 µm). The Royal Belgian Institute for Space Aeronomy (BIRA-IASB) and the Royal Observatory of Belgium (ROB) contribute to MAJIS with the characterization and calibration of the VIS-NIR Flight Model (FM) and Spare Model (SM) detectors, including the design, development, and validation of the setup, as well as the data processing pipeline. The FM and SM detectors are characterized under different illumination conditions (along four decades of dynamical range), temperature (125 K - 144 K), beam uniformities, exposure times, and/or data acquisition rates. In this paper, we describe the optical performances of the facility, which can be configurable for dark conditions, uniform light beam, and convergent beam with same focal ratio as MAJIS convergence optics. We provide a relative radiometry scale for the typical characterization measurements, as well as a fully characterized flux that will allow us to perform characterization measurements in an absolute radiometry scale, such as quantum efficiency (QE). In addition, we describe the thermal performances provided by the bench reaching different temperature scenarios, including the expected operating temperature of the detector at 132 K. The characterization facility was completed and subjected to validation tests in early 2020. The MAJIS VIS-NIR FM detector was delivered for its complete characterization in June 2020.
KEYWORDS: Sensors, Frequency modulation, Fermium, Jupiter, Telecommunications, Data modeling, Control systems, Temperature metrology, Staring arrays, Spectroscopy
MAJIS is part of the science payload of the JUICE mission to be launched in 2022. BIRA-IASB and ROB contribute to MAJIS with the characterization of the VIS-NIR Flight Model (FM) and Spare Model (SM) detectors, including the design, development, and validation of the setup, as well as the data processing pipeline. The VIS-NIR detectors are thermalized within a temperature range from 125 K to 150 K during their characterization campaigns. Moreover, the temperature of their electronic units must always remain above 120 K to avoid any irreparable damage, and below 160 K for operative conditions. Likewise, to avoid any risk of contamination, the detector should preferably be operated below 10-5 mbar of vacuum. To fulfill these requirements, a complete security system was developed; it includes redundant thermal control loops, alarms from every pressure and temperature monitoring devices in use, and a robust semi-automatic control system for the pumping and cryocooling equipment. Moreover, the security system is complemented by the Temperature Ground Support Equipment (TGSE), which provides a LabVIEW user-friendly interface to communicate the status of the detector and the vacuum chamber in real-time. This subsystem was successfully validated in May 2020, before the delivery of the FM detector in June 2020. In this paper, we summarize the design, implementation and validation tests of the security system as well as the thermal and vacuum performances of the facility. We also show the thermal behavior of the detector during acquisitions representative of typical MAJIS observations.
MAJIS (Moons And Jupiter Imaging Spectrometer) is one of the science instruments of the ESA L-Class mission JUICE (Jupiter ICy Moons Explorer) to be launched in 2022 with an arrival at Jupiter in 2030. MAJIS will perform imaging spectroscopy through two channels: VIS-NIR (0.50 um - 2.35 um) and IR (2.25 μm - 5.54 μm). The Royal Belgian Institute for Space Aeronomy (BIRA-IASB) and the Royal Observatory of Belgium (ROB) contribute to MAJIS with the characterization of the VIS-NIR Flight Model (FM) and Spare Model (SM) detectors, including the design, development and validation of the setup, and the data processing pipeline. Typical detector characterization measurements were performed during the campaigns but also calibrated measurements such as Quantum Efficiency (QE). Since some of the characterization measurements require different illumination conditions, temperature, beam uniformity, exposure time, and/or data acquisition procedure, the characterization setup is configurable for dark conditions, uniform light beam, and convergent beam with same focal ratio as MAJIS convergence optics. The thermal-vacuum characterization facility was completed at BIRA-IASB premises and was subjected to validation tests on late 2019 and early 2020. MAJIS VIS-NIR FM detector was delivered for its complete characterization in June 2020; SM characterization shall be performed after time of meeting. In this paper, we summarize the optical and thermal performances of the facility, the detector's mechanical integration method and its optical alignment into the setup, the security system implemented, the general operation of the setup during the characterization campaign, and FM preliminary result analyses.
Acousto-optical tunable filters (AOTFs) are still little known to the Earth atmosphere remote sensing community. The bulk of passive atmospheric remote sensing instruments remains divided into two families: those relying on interferometric techniques (mostly for the long-wave absorbing species), and those based on diffraction gratings (better suited for UV-VIS absorbing species). Still, AOTFs have some unique features which should deserve more attention, in particular their angular acceptance, and their polarization sensitivity. The first one because it allows to work in an imaging setup, the second because many atmospheric processes have a polarizing effect. In this paper, we will present different AOTF-based instrument concepts (or even prototypes) which take advantage of these features in order to improve the sate-of-the-art of measurement techniques in several fields of atmospheric science. We will first present the improved NO2 camera: its new capabilites, the subsystems which have been changed, and some preliminary results. Then, we will discuss two other potential applications: the study of the solar spectral irradiance variability in the UV, and the detection of auroral polarized emissions. For each concept, we will discuss the current challenges faced by the existing instruments, and analyze how the use of AOTFs could overcome them. A suggestion for the AOTF selection will be made, and the expected instrument performance will be estimated.
SOLAR/SOLSPEC, a spectroradiometer measuring solar spectral irradiance is an instruments of the SOLAR payload mounted on the zenith external platform of the European Columbus module of the International Space Station. Solar flux is received by the SOLAR instruments thanks to the Coarse Pointing Device (CPD). A complementary Sun position tracking module, the Position Sensitive Device (PSD), is integrated in SOLAR/SOLSPEC. The PSD module has been a useful tool to monitor for misalignments between the CPD and the SOLAR payload. It is used in SOLAR/SOLSPEC’s operations to follow the quality of the Sun tracking. The PSD module is also valuable to monitor for SOLAR/SOLSPEC’s three spectrometers (ultraviolet, visible, infrared) angular response in orbit. We first give a detailed description of the PSD’s functionalities. We then present the results of the PSD data analysis. We will show that the PSD module has, despite working in a severe space environment, preserved its full potential from 2008 up to 2017 thanks to its design and appropriate selection of components. We conclude that its robustness makes of the PSD module a simple, yet reliable, instrument useful for future long term space-based missions.
The space environment is considered hazardous to spacecraft, resulting in materials degradation. Understanding the degradation of space-based instruments is crucial in order to achieve the scientific objectives, which are derived from these instruments. This paper discusses the on-orbit performance degradation of recent spacebased solar instruments. We will focus on the instruments of three space-based missions such as the Project for On-Board Autonomy 2 (PROBA2) spacecraft, the Solar Monitoring Observatory (SOLAR) payload onboard the Columbus science Laboratory of the International Space Station (ISS) and the PICARD spacecraft. Finally, this paper intends to understand the degradation processes of these space-based solar instruments.
Multiband filter radiometers (MBFRs) are extensively used in national networks for UV climate monitoring and information to the public about the potential risk of solar UV exposure. In order to provide an international, uniform expression of the Global UV index measurements, a harmonized calibration scale is needed. In this paper we present the results of the first international intercomparison of MBFRs held in Oslo in 2005. The purposes are to evaluate the UV-index scale of different radiometers and to provide a harmonized UV-index scale based on the radiometers individual directional and absolute spectral response functions. In total 43 MBFR radiometers and 4 high resolution spectroradiometers were assembled, representing UV-monitoring networks operated by institutions in US, Spain, Greece, Poland, Belgium, UK, Austria, Norway, Sweden and Finland. The radiometers are operating worldwide, with stations in the Antarctica and Arctic, North- and South-America, Africa, Europe, Middle-East and Nepal. All sky conditions were realized during the campaign period. The agreement between the users' own processed UVI and the reference is generally very good; within ±5% for 22 out of 26 data sets (75%) and ±10% for 23 out of 26 (88%). Solar zenith dependent discrepancies and drift in the users' UVI scales is seen, but the performance of most radiometers is generally very good. All the objectives planned for the intercomparison were fulfilled and the campaign considered a success.
Since our major concern on the stratospheric ozone depletion is possible adverse effects on the biosphere, it is important to establish the way to determine biologically effective doses of solar UV radiation. The spore dosimetry system measuring the lethality of dry bacterial spores on membrane filters has been developed to meet this purpose. The methodology to evaluate experimental correlation with spectral measurements based on the effectiveness calculation has been applied in several field comparisons carried out at Nea Michaniona (Greece), Brussels (Belgium), and Sao Martinho (Brazil). When plotted against UVB irradiance (total energy below 320 nm), the calculated values of MED (minimal erythema dose), SID (spore inactivation dose) and DND (DNA damage dose) exhibited increasing exponents in power regressions, while the exponents from spore dosimetry exceeded those of the calculated values. The results of calculated versus observed values of SID indicate a general convergence at low to modest dose rates, but at high dose rates the calculated ones tended to yield lower values than those obtained from direct biological measurements.
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