SSUSI-Lite is an update of an existing sensor, SSUSI. The current generation of Defense Meteorological Satellite Program (DMSP) satellites (Block 5D3) includes a hyperspectral, cross-tracking imaging spectrograph known as the Special Sensor Ultraviolet Spectrographic Imager (SSUSI). SSUSI has been part of the DMSP program since 1990. SSUSI is designed to provide space weather information such as: auroral imagery, ionospheric electron density profiles, and neutral density composition changes. The sensors that are flying today (see http://ssusi.jhuapl.edu) were designed in 1990 - 1992. There have been some significant improvements in flight hardware since then. The SSUSI-Lite instrument is more capable than SSUSI yet consumes ½ the power and is ½ the mass. The total package count (and as a consequence, integration cost and difficulty) was reduced from 7 to 2. The scan mechanism was redesigned and tested and is a factor of 10 better. SSUSI-Lite can be flown as a hosted payload or a rideshare – it only needs about 10 watts and weighs under 10 kg. We will show results from tests of an interesting intensified position sensitive anode pulse counting detector system. We use this approach because the SSUSI sensor operates in the far ultraviolet – from about 110 to 180 nm or 0.11 to 0.18 microns.
SSUSI-Lite is a far-ultraviolet (115-180nm) hyperspectral imager for monitoring space weather. The SSUSI and GUVI sensors, its predecessors, have demonstrated their value as space weather monitors. SSUSI-Lite is a refresh of the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) design that has flown on the Defense Meteorological Satellite Program (DMSP) spacecraft F16 through F19. The refresh updates the 25-year-old design and insures that the next generation of SSUSI/GUVI sensors can be accommodated on any number of potential platforms. SSUSI-Lite maintains the same optical layout as SSUSI, includes updates to key functional elements, and reduces the sensor volume, mass, and power requirements. SSUSI-Lite contains an improved scanner design that results in precise mirror pointing and allows for variable scan profiles. The detector electronics have been redesigned to employ all digital pulse processing. The largest decrease in volume, mass, and power has been obtained by consolidating all control and power electronics into one data processing unit.
Global Assimilation of Information for Action (GAIA) is a new initiative at The Johns Hopkins University connecting
decision-makers with the research community. GAIA's focus is on the near- and long-term effects of weather, climate,
and climate disruption on society and national security. The GAIA initiative, http://gaia.jhuapl.edu, makes use of
collaborative tools to bring together decision makers to address focused problems in settings that range from symposia
and workshops to specific socio-political-economic "games" to explore how decisions can be made and risks assessed.
GAIA includes a suite of visualization tools, documentation, analyses, and social networking capabilities. Here, we will
discuss the GAIA collaboration and recent GAIA projects, in particular the development of climate change national
security gaming scenarios and studies in public health, and how the GAIA project can aide in assessing national security
and public health concerns.
The Canary instrument is a miniature electrostatic analyzer designed to detect positively charged ions in the energy range 0-1500 eV. The Canary concept began with the development of a Micro-Electro-Mechanical (MEMS) Flat Plasma Spectrometer (FlaPS), which, integrated with electronics onto FalconSAT-3, reduced the size and mass of an ion plasma spectrometer to about 10x10x10 cm3 and 250 g. The successor to FlaPS was the Wafer Integrated Spectrometer (WISPERS), expanding the same instrument to seven sensors all with uniquely optimized energy ranges and azimuth/elevation look angles. WISPERS is due to fly on the USAF Academy's FalconSAT-5 satellite scheduled for launch in Spring 2010. FlaPS and WISPERS created a paradigm shift in the use of such instruments in a highly capable but small, low power package. The third generation, Canary (named after the "canary in the coal mine"
- an earlier technology used to provide low-cost, effective warning of danger to operators), will be flown on the International Space
Station (ISS) and used to investigate the interaction of approaching spacecraft with the background plasma environment around the ISS.
Larry Paxton, Andrew Christensen, Daniel Morrison, Brian Wolven, Hyosub Kil, Yongliang Zhang, Bernard Ogorzalek, David Humm, John Goldsten, Robert DeMajistre, Ching-I. Meng
The Global Ultraviolet Imager (GUVI) is an imaging spectrometer on the NASA TIMED spacecraft which was launched on December 7, 2001. This instrument produces a far ultraviolet (FUV) data cube of spatial and spectral information at each step of a scan mirror - that scan mirror covers 140 deg in the cross track direction - a span that includes on limb. GUVI produces simultaneous monochromatic images at five "colors" (121.6 nm, 130.4 nm, 135.6 nm, and in broader bands at 140-150 nm and 165-180 nm) as its field of view is scanned from horizon to horizon. The instrument consists of a scan mirror feeding a parabolic telescope and Rowland circle spectrometer, with a wedge-and-strip detector at the focal plane. We describe the design, and give an overview of the environmental parameters that will be measured. GUVI is a modified version of the Special Sensor Ultraviolet Spectrographic Imager (SSUSI), which was launched on the DMSP Block 5D3 F16 satellite on October 18, 2003 and is slated to fly on DMSP satellites F17 through F20, as well. We present some results the science analysis of the GUVI data to demonstrate its relevance to the space weather community.
The SABER instrument on TIMED continuously measures certain infrared limb radiance profiles with unprecedented sensitivity. Among these are emissions of CO2 ν3 at 4.3 μm, routinely recorded to tangent heights of ~140-150 km, and NO at 5.3 μm, seen to above ~200 km and ~300 km, respectively. We use these infrared channels of SABER and coincident far ultraviolet (FUV) measurements from GUVI on TIMED, to study the geometric storm of April 2002. These all give a consistent measure of auroral energy input into the lower thermosphere at high latitudes. Emission in yet another SABER channel, near 2.0 μm, correlates well with enhanced electron energy deposition. We also have, in the 5.3-μm emissions from the long-lived population of aurorally produced NO, a tracer of how this energy is transported equator-ward and released over an extended period of time, a few days. In this paper, we discuss the global patterns of energy deposition into the expanded auroral oval, its transport to lower latitudes, and its loss as revealed by the NO 5.3-μm emissions.
Nicholas Paschalidis, Nick Stamatopoulos, Kosta Karadamoglou, George Kottaras, Vasilis Paschalidis, Emmanuel Sarris, Donald Mitchell, David Humm, Larry Paxton, Ralph McNutt
Many remote sensing instruments include the detection of photon/particle events, position decoding and time-of-hit measurement. Microchannel plates (MCPs) are widely used to detect photons and particles for position sensing and relative time of impact in imaging and time-of-flight (TOF) spectrometers. Two dimensional delay lines are used for fast and accurate readout of MCPs. Instruments that use these techniques are Neutral Atom Imagers and Particle Spectrometers to study planetary magnetospheres; photon counting detectors for spectrographic imaging in the far-UV and extreme-UV to study the earth's aurora and airglow; laser range finders. In all these there is a requirement of accurate and/or fast time interval measurement. An advance TOF system-on-a-chip has been developed that includes the complete signal processing electronics for MCP readout: two channels (start- stop) of amplifiers and constant fraction discriminators (CFDs), an 11-bit Time to Digital Converter (TDC), and control/readout logic. The TOF chip is capable for a time resolution of <50ps including time walk and time jitter, the dead time is as low as 0.5us; the power dissipation is a function of counting rate and time resolution-for resolution of ~100ps the power is <20mW at rates <100K/sec and <50mW at rates <1M/sec. The TOF chip flies on the NASA/IMAGE spacecraft launched in 2000 and is part of many other science instruments such as particles and fields, and laser altimeter on MESSENGER.
The Stellar Absorption and Refraction Sensor (STARS) is a compact, large-aperture instrument that combines a UV-IR imaging spectrograph with a co-aligned visible-light imager to make simultaneous absorptive and refractive stellar occultation measurements. The absorption measurements provided by the spectrograph allow the determination of vertical profiles of atmospheric constituents. The coincident refraction observations made by the image yield high-precision measurements of atmospheric density, pressure, and temperature and provide independent knowledge of both the refracted light path and Rayleigh extinction, which are critical in reducing the uncertainty in the retrieved constituent profiles in the lower atmosphere. STARS employs a two-axis gimbaled telescope to acquire and track the star and a two-axis, high-precision, fast-steering mirror to correct for spacecraft jitter and maintain the star within the spectrograph field of view. The relative star position measured by the imager provides position feedback to the active tracking loop of the fast-steering mirror. With funding from NASA's Instrument Incubator Program, a laboratory facility has been developed to demonstrate the overall instrument performance and, in particular, its capability to acquire and track a setting, refracting, and scintillating star, to compensate for various degrees of platform jitter, and to provide the pointing knowledge required for accurate determination of the atmospheric quantities. The combination of built-in image tracking and motion compensation capabilities, small size, and limited spacecraft resource requirements makes STARS and its tracking mechanism suitable for deployment on existing and future commercial spacecraft platforms for applications that require high-precision pointing. In this paper, we present details of the instrument design and its expected performance based on our laboratory tests.
Operational sensors are designed and intended to reliably produce the measurements needed to develop high-value key environmental parameters. The Special Sensor Ultraviolet Spectrographic Imager (SSUSI) is slated to fly on the next five Defense Meteorological Satellite Program launches (beginning with the launch of F16 in Fall 2001). SSUSI will routinely produce maps of ionospheric and upper atmospheric composition and image the aurora. In this paper we describe these products and our validation plans and the process through which we can assure our sponsors and data products users of the reliability and accuracy of these products.
The Special Sensor Ultraviolet Spectrographic Imager (SSUSI) is currently slated for launch on the Defense Meteorological Satellite Program (DMSP) F-16 in November 2001. This instrument consists of a scanning imaging spectrograph (SIS) whose field-of-view is scanned from horizon-to-horizon and a nadir-looking photometer system (NPS). It will provide operational information about the state of the atmosphere above 100 km. The unique problems incurred by the observational requirements (e.g. that we be able to make daytime and nighttime observations) and the design trade-offs needed to meet those requirements were strong drivers on calibration requirements. Those design trade-offs and the expectation that the instrument calibration will change appreciably in-flight have led to the requirement to perform a large instrument characterization in-flight using only natural sources. We focus, in this paper, on the flight characterization of the SSUSI instrument. This includes discussions of the stellar calibration approach for radiometric calibration, measurements of internally scattered light, sensitivity to the South Atlantic Anomaly, measurements of changing pulse height distributions, and measuring changing reflectivity of a nadir viewing scan mirror. In addition, the calibration of the NPS system using natural sources is addressed.
This paper describes the design and performance of the detectors and electronics developed for the Global UV Imager (GUVI) aboard the NASA TIMED spacecraft, to be launched in May 2000. GUVI employs two alternate design detectors that are compact sealed units with MgF windows, CsI photocathodes, and wedge-and-strip anodes. The focal plane is 15.6 mm X 16.5 mm with images quantized to 176 spectral by 14 spatial pixels, although access to image data over the entire 25-mm dia active area is provided. Moderate detector resolution is achieved at a relatively low gain. Science emphasis is on high throughput, good image stability, and high radiometric accuracy. Significant detector aging is anticipated over an extended mission with sustained high counting rates. Custom hybrid front-end electronics were developed to enable direct coupling to the wedge-and-strip anodes. This eliminates inter-electrode potentials and the associated image distortion and shift with counting rate. A parallel fast channel provides pulse pile-up rejection. XY position, binning, and compression algorithms are performed in software by a fast, radiation- hardened RISC processor. A full-custom ASIC counts input and output rates for each detector.
Larry Paxton, Andrew Christensen, David Humm, Bernard Ogorzalek, C. Pardoe, Daniel Morrison, Michele Weiss, W. Crain, Patricia Lew, Dan Mabry, John Goldsten, Stephen Gary, David Persons, Mark Harold, E. Brian Alvarez, Carl Ercol, Douglas Strickland, Ching-I. Meng
The Global Ultraviolet Imager (GUVI) on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) mission will determine the variability in thermospheric composition, and its response to auroral inputs as well as measuring those inputs. GUVI is the result of twenty years of work in designing large field of regard far ultraviolet (110 - 180 nm) imagers for spaceflight. These systems are based on the concept of a horizon-to-horizon 'monochromatic' imager. The field of view of a spectrograph is swept from horizon to horizon using a scan mirror. The spectrograph uses a grating to spectrally disperse the light. A two-dimensional detector is used to record spatial and spectral information simultaneously. Images are obtained at discrete wavelengths without the use of filters; this reduces if not eliminates much of the concern about instrumental bandpasses, out-of-band rejection, and characterization of filter responses. Onboard processing is used to bin the spectral information into 'colors' thereby reducing the overall data rate required. The spectral bandpass is chosen to lie in the far ultraviolet so that the sunlit and dark aurora can be imaged. We review the instrument's as delivered performance and the TIMED science requirements. TIMED will be launched May 18, 2000 and will inaugurate the Solar-Terrestrial Connections program at NASA.
The Global Ultraviolet Imager of the NASA Thermosphere, Ionosphere, and Mesosphere Energetics and Dynamics mission has been calibrated at the Optical Calibration Facility of the Applied Physics Laboratory. This spectrographic imager has a 0.74 degree(s) X 11.6 degree(s) field-of-view, a 140 degree(s) X 11.6 degree(s) field-of-regard and collects data in 176 wavelength bins in the spectral range from 120 - 180 nm. The calibration of this far ultraviolet instrument requires continuously variable wavelengths and angles within a high- vacuum system from the light source to the instrument. An optical calibration facility has been developed providing a bright, uniform, wavelength-selectable, collimated light beam, which is mapped in situ to correct for intensity drifts in the lamp. The facility design and the calibration procedure are discussed.
David Humm, Larry Paxton, Andrew Christensen, Bernard Ogorzalek, C. Pardoe, Ching-I. Meng, Daniel Morrison, Douglas Strickland, J. Evans, Michele Weiss, W. Crain, Patricia Lew, Dan Mabry, John Goldsten, Stephen Gary, Keith Peacock, David Persons, Mark Harold, E. Brian Alvarez, Carl Ercol
The Global UV imager (GUVI) is an imaging spectrometer on the NASA TIMED spacecraft. GUVI produces simultaneous monochromatic images at five 'colors' as its field of view is scanned from horizon to horizon. The instrument consists of a scan mirror feeding a parabolic telescope and Rowland circle spectrometer, with a wedge-and-strip detector at the focal plane. We describe the design, and give an overview of the environmental parameters that will be measured. GUVI is a modified version of the Special Sensor UV Spectrographic Imager (SSUSI), which will fly on the DMSP Block 5D3 satellites S-16 through S-20, We present some results from the optical calibration of the five SSUSI units.
KEYWORDS: Data modeling, Atmospheric modeling, Device simulation, Imaging systems, Rayleigh scattering, Data conversion, Data acquisition, Space operations, Airglow, Aerospace engineering
Numerous instruments for UV-visible optical measurements of terrestrial backgrounds have recently flown or are scheduled for launch in the near future. In order to maximize the scientific return from such flight opportunities, simulations of data acquired by imaging and spectrographic imaging instruments spanning wide wavelength ranges are required to support experiment planning and post-launch data analysis/fusion activities. We are currently developing comprehensive capabilities for modeling these types of remote sensing data suitable for a number of mission-support applications, with specific focus on data acquired by the UVISI instruments on the Midcourse Space Experiment satellite. These capabilities are described in this presentation. The core modeling capabilities reside in a suite of well-tested first principles and empirical modeling codes for atmospheric radiances arising from a variety of physical processes (e.g., photoelectron impact excitation, Rayleigh and aerosol scattering, solar resonance and resonant fluorescence scattering, chemistry). Image generation and LOS spectral radiance evaluation techniques permitting continual change in observer location and viewing geometry without incurring large computational burdens have been set up to ingest the radiance modeling results to create high fidelity synthetic satellite data. Illustrative examples are presented.
Andrew Christensen, Richard Walterscheid, Martin Ross, Ching-I. Meng, Larry Paxton, Donald Anderson, Geoffrey Crowley, Susan Avery, John Craven, Robert Meier, Douglas Strickland
The global ultraviolet imager (GUVI) investigation is designed to provide quantitative observations and interpretation of the Earth's airglow and auroral emissions in support of the NASA thermosphere, ionosphere, mesosphere, energy and dynamics (TIMED) mission. It addresses TIMED objectives dealing with energetics, dynamics, and the specification of state variables. The instrument provides multiple-wavelength, simultaneous `monochromatic' images of the far-ultraviolet emission (115 to 180 nm) using a scan mirror to sweep the instantaneous field of view of a spectrographic imager through an arc of up to 140 degree(s) aligned perpendicular to the orbit plane of the spacecraft. The instantaneous field of view is 11.8 degree(s) by 0.37 degree(s) (adjustable) along the slit and perpendicular to the slit, respectively. The field of view is mapped to a two-dimensional image plane with up to 64 spatial pixels by 160 spectral pixels of spectral width 0.4 nm per pixel. Binning of pixels can be performed along both the spatial and spectral axes of the array to reduce the demands on the downlink telemetry. The f/3 Rowland circle scanning spectrographic imager is outfitted with a toroidal grating ruled at 1200 grooves per millimeter. The fore-optics consists of a plane scanning mirror and an off-axis parabolic telescope. The detector is a photon-counting microchannel plate with a wedge and strip anode mounted in a sealed tube.
This paper details recent advances in modeling and imaging capabilities since the work of Cox et. al. and Strickland et. al. The emphasis of current work is on simulating imaging data to be obtained by instruments such as SSUSI (spectral sensor ultraviolet spectrographic imager) on DMSP (Defense Meteorological Satellite Program), UVISI (ultraviolet and visible imaging and spectrographic imagers) on MSX (Midcourse Space Experiment) and GUVI (global ultraviolet imager), an instrument selected for NASA's TIMED mission. Some of the modeling capability to be discussed is presently being used to analyze dynamics explorer far ultraviolet images. Modeling improvements include the ability to efficiently calculate radiances as a function of solar azimuth in addition to zenith viewing angle, to calculate radiances for non-spherical density distributions of absorbing species, to input new model atmospheres, ionospheres, and auroral oval precipitation parameters, and finally, to access our radiance models through a much improved user-interface within a windows environment. Key improvements to our imaging software allow for limb and disk emission in global displays, easier mapping of information onto any one of several projections, and displaying simulated dayglow, nightglow, and aurora in full orbit `strip' images (distance along the orbit versus cross-track look angle or distance) as will be obtained by SSUSI. The above improvements are discussed with the aid of figures which show important solar azimuth effects, simulated global DE-1 130.4 nm data, geometrical projections that allow one to visualize the portion of the globe viewed by a low Earth polar orbiting sensor like SSUSI, and full orbit images of simulated SSUSI disk and limb data.
The Midcourse Space Experiment Satellite (MSX) has a suite of ultraviolet and visible imaging spectrographs and imagers that cover the wavelength range from 110 to 900 nm. The versatile pointing capability of the satellite allows observations in the earth limb and below the horizon with observations during the day and night. The wavelength resolution (1 - 3 nm) for the spectrographs and high spatial resolution in the filtered imagers allows experiments covering a multitude of background phenomenology issues. Experiments are designed to look at ultraviolet through the visible clutter issues for many different scene conditions in the earth limb and below the horizon. Hyperspectral images of terrain and ocean features for specific locations are in the planning stages specially at specific ground truth locations. Atmospheric emission sources during the day and night in different global locations. Atmospheric emission sources during the day and night in different global locations from the poles to the equator will be observed for both assessment of radiance and clutter issues as well as for input into atmospheric radiance models.
While visible and UV range sensors are frequently designed to see the ground, the short-wavelength region known as 'solar-blind' (below 320 nm wavelength) includes emissions originating at altitudes above 30-140 km. The solar-blind range is being investigated for remote sensing of the composition, dynamics, and energetics of the Earth atmosphere, as well as for use in passive sensor acquisition and tracking systems. An examination is presently conducted of the PSD of mid-UV images from a recently launched satellite.
Vertical perspective, mercator, and tilted perspective projection images are presented which contain calculated dayglow, nightglow, and aurora. These images are discussed in terms of their structure's sources, which encompass composition variations, solar zenith angle changes, and changes in the path length experienced on going from disk-viewing to limb-viewing. Both a global thermospheric model (MSIS-86) and a global ionospheric model (the International Reference Ionosphere) are used to respectively specify neutral composition and the profiles of OI and OII.
The Special Sensor Ultraviolet Spectrographic Imager (SSUSI) sensors that will be carried by USAF Defense Meteorological Satelite Program Block 5D3 satellites can measure FUV emission in five bands across the disk and onto the limb. An account is presently given of the environmental data records that are to be derived from SSUSI's dayglow disk data, as well as to projections of the disk viewing capabilities of the SSUSI system for any sum of Lyman-Birge-Hopfield bands excluding the regions around 130.4, 135.6, and 149.3 nm. The findings obtained are independent of any assumed model atmosphere.
A model is presented which calculates intensities of Rayleigh-scattered sunlight to large solar zenith angles (SZAs). The intensity integrand contains appropriate transmission functions and a volume emission rate profile with SZA varying along the line-of-sight. The calculation is performed for a spherically-symmetric model atmosphere and allows for limb and nonlimb viewing. We compare O I 6300 A nightglow and N2(+) 4278 A auroral signals to their Rayleigh-scattered counterparts at various SZAs beyond the terminator, addressing the major problems encountered by operational sensors when a rapid change in scattered sunlight intensity occurs at the terminator. To illustrate the effects of baffling systems, we examine three simple baffle designs being considered for a nadir-viewing photometer system to be flown on Defense Meteorological Satellite Program (DMSP) Block 5D3 satellites. The results show how far these photometers must be beyond the terminator to make good airglow and auroral measurements.
The UVISI instruments, comprising five spectrographic imagers and four imagers, will fly on a DoD mission in the early 1990s. We analyze, in a preliminary way, the applicability of these instruments to resolution of outstanding problems in the nature of the celestial cosmic diffuse ultraviolet background radiation.
Larry Paxton, Ching-I. Meng, Glen Fountain, Bernard Ogorzalek, Edward Darlington, Stephen Gary, John Goldsten, David Kusnierkiewicz, Susan Lee, Lloyd Linstrom, Jeffrey Maynard, Keith Peacock, David Persons, Brian Smith, Douglas Strickland, R. Daniell
We review some of the features of the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) and describe the environmental parameters that will be produced on an operational basis from this instrument's data. The associated algorithms are summarized. SSUSI consists of a scanning imaging spectrograph (SIS) whose field-of-view is scanned from horizon to horizon and a nadir-looking photometer system (NPS). The SIS produces simultaneous monochromatic images at five 'colors' in the spectral range 115nm to 180nm. The NPS consists of three photometers with filters designed to monitor the airglow at 427.8nm and 630nm and the terrestrial albedo near 630nm. SSUSI will fly on the DMSP Block 5D3 satellites S-16 through S-19. In a companion paper we provide more details on the Special Sensor Ultraviolet Spectrographic Imager (SSUSI).
Larry Paxton, Ching-I. Meng, Glen Fountain, Bernard Ogorzalek, Edward Darlington, Stephen Gary, John Goldsten, David Kusnierkiewicz, Susan Lee, Lloyd Linstrom, Jeffrey Maynard, Keith Peacock, David Persons, Brian Smith
We describe the Special Sensor Ultraviolet Spectrographic Imager (SSUSI). This instrument consists of a scanning imaging spectrograph (SIS) whose field-of-view is scanned from horizon to horizon and a nadir-looking photometer system (NPS). The SIS produces simultaneous multispectral images over the spectral range 1 150 to 1800A. The NPS consists of three photometers with filters designed to monitor the airglow at 4278A and 6300A and the terrestrial albedo near 6300A. SSUSI will fly on the DMSP Block 5D3 satellites S-16 thru S-19. The instruments will be calibrated at the Applied Physics Laboratory's Optical Calibration Facility.
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