Valerie G. Duval

MISR: A multiangle imaging spectroradiometer for geophysical and climatological research from Eos

The scientific objectives, instrument concept, and data plan for the multiangle imaging spectroradiometer (MISR), an experiment proposed for the Eos (Earth Observing System) mission, are described. MISR is a pushbroom imaging system designed to obtain continuous imagery of the sunlit Earth at four different view angles (25.8 degrees , 45.6 degrees , 60.0 degrees , and 72.5 degrees relative to the vertical at the Earths surface), in both the forward and aftward directions relative to nadir, using eight separate cameras. Observations will be acquired in four spectral bands, centered at 440, 550, 670, and 860 nm. Data analysis algorithms will be applied to MISR imagery to retrieve the optical, geometric, and radiative properties of complex, three-dimensional scenes, such as aerosol-laden atmospheres above a heterogeneously reflecting surface, nonstratified cloud systems, and vegetation canopies. The MISR investigation will address a number of scientific questions concerning the climatic and ecological consequences of many natural and anthropogenic processes, and will furnish the aerosol information necessary. >

MISR prelaunch instrument calibration and characterization results

Each of the nine cameras that compose the Multi-angle Imaging SpectroRadiometer (MISR) has been rigorously tested, characterized, and calibrated. Requirements on these tests include a 3% (1/spl sigma/) radiometric calibration requirement, spectral response function determination of both the in- and out-of-band regions, and distortion mapping. The latter test determines the relative look-angle to the ground corresponding to each focal plane detector element. This is established to within one-tenth of the instantaneous field-of-view. Most of the performance testing was done on the cameras as they completed assembly. This was done to take advantage of the serial delivery of the hardware, minimize the required size of the thermal-vacuum facilities, and allow testing to occur early in the schedule allocated for the hardware build. This proved to be an effective strategy, as each of the test objectives was met. Additional testing as an integrated instrument included verification of the data packetization, camera pointing, and clearances of the fields-of-view. Results of these studies have shown that the MISR cameras are of high quality and will meet the needs of the MISR science community. Highly accurate calibration data are on-hand and available for conversion of camera output to radiances.

Development of the Wide-field Infrared Survey Explorer (WISE) mission

WISE is a NASA MIDEX mission to survey the entire sky in four bands from 3 to 25 microns with sensitivity about 500 times greater than the IRAS survey. WISE will find the most luminous galaxies in the universe, find the closest stars to the Sun, and detect most of the main belt asteroids larger than 3 km. WISE launch is scheduled in November, 2009 on a Delta 7320-10 to a 525 km Sun-synchronous polar orbit. This paper gives an overview of WISE including development status and management approach. WISE flight system design is single string with selected redundancy and graceful degradation. Wherever possible, design heritage from prior missions is pursued and properly reviewed to reduce development time and cost. Further risk reduction is achieved since the WISE spacecraft has no deployable mechanisms and no propulsion. Nonetheless, a complex space mission with a sophisticated cryogenic IR telescope such as WISE demands a partnership of multiple organizations in government research, academia, and industry. With a cost cap and relatively short development schedule, it is essential for all WISE partners to work seamlessly together. This is accomplished by a single management team representing all key partners and disciplines in science, systems engineering, mission assurance, project and contract management. WISE uses a variety of management tools including frequent team interaction, schedule, milestone and critical path analysis, risk analysis, reliability analysis, earned value analysis, configuration management, and management of schedule and budget reserves. After a successful mission critical design review in June, 2007, WISE has completed building most of the flight hardware, and started integration and test within payload and spacecraft.

The MISR Calibration Program

Abstract The Multiangle Imaging SpectroRadiometer (MISR) is currently under development for NASAs Earth Observing System. The instrument consists of nine pushbroom cameras, each with four spectral bands in the visible and near-infrared. The cameras point in different view directions to provide measurements from nadir to highly oblique view angles in the along-track plant. Multiple view-angle observations provide a unique resource for studies of clouds, aerosols, and the surface. MISR is built to challenging radiometric and geometric performance specifications. Radiometric accuracy, for example, must be within ±3%/1σ, and polarization insensitivity must be better than ±1%. An onboard calibrator (OBC) provides monthly updates to the instrument gain coefficients. Spectralon diffuse panels we used within the OBC to provide a uniform target for the cameras to view. The absolute radiometric scale is established both preflight and in orbit through the use of detector standards. During the mission, ground data p...

Evaluation of high-quantum-efficiency silicon photodiodes for calibration in the 400-nm to 900-nm spectral region

The reflectance and internal quantum efficiency (QE) of three single-element photodiodes are determined using two different light-trapping devices. The QED-200 light trapping device which is based on inversion layer photodiodes exhibits the best performance within the short wavelengths of the visible spectrum (VIS), while the A-O device based on p-n photodiodes, performs best in the long wave VIS up to 950 nm. The combination of the two light-traps provides nearly 100 percent external QE coverage from 400 to 950 nm. The reflectances and internal QE were determined within this spectral range for three photodiodes: UV100, an inversion layer photodiode; X-UV100, a shallow diffused n-p photodiode; and 10DPI/SB, a blue-enhanced p-n photodiode.

MISR instrument development and test status

MISR will provide global data sets from Earth orbit using nine discrete cameras, each viewing at unique view directions. The design of this instrument is complete and has been refined following assembly and testing of an engineering model. The engineering model has been invaluable in identifying correctable design flaws, in resolving subsystem interface issues early in the program, and in providing the science team with as-built performance data to be used in the algorithm development. MISR will fly with an on-board calibrator consisting of Spectralon diffuse panels and photodiode detector standards. Both the use of Spectralon and flight detector standards have been developed by the MISR team. Currently the engineering team is assembling and testing the flight cameras, and the data teams are preparing for the post-launch geometric and radiometric calibration of the instrument, as well as developing algorithms to provide the science products. With a 3.3 Mb orbital average data rate, and global coverage each nine days, processing will be automated and standardized. Deliverables include calibrated, registered data sets, as well as aerosol/land surface, and cloud parameters.

Imaging spectrometry: concepts and system trade-offs

The concept of imaging spectrometry is finding broad application in scientific instrumentation for Earth-based, airborne, and space applications. An imaging spectrometer is characterized by the combination of imaging with complete sampling in the spectral domain. In so doing, material identification can be accomplished and displayed in conjunction with the conventional recognizable image. An imaging spectrometer incorporates a wide variety of technologies, including focal plane arrays, imaging and spectrometer optics, and spectral dispersing devices. The design of a successful system involves a complex set of trade-offs incorporating the properties and limitations of the various technologies. For applications in the infrared, additional technologies such as focal plane cooling are required, and the other technologies present more limitations and constraints. This paper describes the system design process for a typical application, and discusses the system performance parameters and trade-offs, including choice of system architecture, signal to noise ratio, system resolution, spectral performance, calibration, and the effect of artifacts such as detector non-uniformity.

Lessions learned in WISE image quality

The Wide-Field Infrared Survey Explorer (WISE) mission launched in December of 2009 is a true success story. The mission is performing beyond expectations on-orbit and maintained cost and schedule throughout. How does such a thing happen? A team constantly focused on mission success is a key factor. Mission success is more than a program meeting its ultimate science goals; it is also meeting schedule and cost goals to avoid cancellation. The WISE program can attribute some of its success in achieving the image quality needed to meet science goals to lessons learned along the way. A requirement was missed in early decomposition, the absence of which would have adversely affected end-to-end system image quality. Fortunately, the ability of the cross-organizational team to focus on fixing the problem without pointing fingers or waiting for paperwork was crucial in achieving a timely solution. Asking layman questions early in the program could have revealed requirement flowdown misunderstandings between spacecraft control stability and image processing needs. Such is the lesson learned with the WISE spacecraft Attitude Determination & Control Subsystem (ADCS) jitter control and the image data reductions needs. Spacecraft motion can affect image quality in numerous ways. Something as seemingly benign as different terminology being used by teammates in separate groups working on data reduction, spacecraft ADCS, the instrument, mission operations, and the science proved to be a risk to system image quality. While the spacecraft was meeting the allocated jitter requirement , the drift rate variation need was not being met. This missing need was noticed about a year before launch and with a dedicated team effort, an adjustment was made to the spacecraft ADCS control. WISE is meeting all image quality requirements on-orbit thanks to a diligent team noticing something was missing before it was too late and applying their best effort to find a solution.

The WISE science payload: management lessons learned

The Wide Field Infrared Survey Explorer is a NASA Medium Class Explorer mission which launched in December, 2009 to perform an all-sky survey in four infrared wavelength bands. The science payload is a cryogenically cooled infrared telescope with four 1024x1024 infrared focal plane arrays covering the wavelength range from 2.6 to 26 μm. The survey has been highly successful, with millions of images collected, and nearly daily discoveries of previously unknown astronomical objects. The WISE science payload was designed, built, and characterized by the Space Dynamics Laboratory at Utah State University. This paper provides a brief overview of the WISE science payload and its on-orbit performance and describes lessons learned from managing the design, fabrication, testing, and operation of a state-of-the-art electro-optical payload.

A payload-centric integration and test approach on the Wide-field Infrared Survey Explorer Mission

NASAs Wide-field Infrared Survey Explorer (WISE) mission was successfully launched on December 14, 2009. All spacecraft subsystems and the single instrument consisting of four imaging bands from 3.4 to 22 microns, a 40 cm afocal telescope, reimaging optics, and a two-stage solid hydrogen cryostat have performed nominally on orbit, enabling the trouble-free survey of the entire infrared sky. Among the many factors that contributed to the WISE post-launch success is the thorough pre-launch system integration and test (I&T) approach tailored to the cryogenic payload. The simple and straightforward interfaces between the spacecraft and the payload allowed the payload to be fully tested prior to integration with the spacecraft. A payload high-fidelity thermal, mass and dynamic simulator allowed the spacecraft I&T to proceed independently through the system-level thermal vacuum test and random vibration test. A payload electrical simulator, a high-rate data processor and a science data ingest processor enabled very early end-to-end data flow and radio-frequency testing using engineering model payload electronics and spacecraft avionics, which allowed engineers to identify and fix developmental issues prior to building flight electronics. This paper describes in detail the WISE I&T approach, its benefits, challenges encountered and lessons learned.