The Visible/Infrared Imaging Radiometer Suite (VIIRS) is a key sensor on the Suomi National Polar-orbiting Partnership (NPP) satellite in orbit as well as for the upcoming Joint Polar Satellite System (JPSS). VIIRS collects Earth radiometry and imagery in 22 spectral from 0.4 to 12.5 μm. Radiometric calibration of the reflective bands in the 0.4 to 2.5 μm wavelength range is performed by measuring the sunlight reflectance from Solar Diffuser Assembly (diffuser is Spectralon®). Spectralon® is known to solarize due to sun UV exposure at the blue end of the spectrum (~0.4 – 0.6+ μm) as seen by laboratory tests as well as on orbit data from MODIS and NPP. VIIRS uses a Solar Diffuser Stability Monitor (SDSM) to monitor the change in the Solar Diffuser reflectance in the 0.4 – 0.94 μm wavelength range to correct the calibration constants. The SDSM measures the ratio of sun light reflecting from the Solar Diffuser to a direct view of the sun. As the intensity of the light reaching the SDSM in both Solar Diffuser view and sun view is a function of the sun’s angle of incidence (AOI), the SDSM response to sun AOI has to be characterized. This paper presents details of the test setup including an extended collimated source simulating the sun across all SDSM bands. The prelaunch characterization results for the JPSS-1 (J1) VIIRS SDSM are presented. Comparison with NPP on orbit yaw maneuver SDSM results shows similar behavior demonstrating that the J1 test successfully characterized the SDSM response to sun AOI.
The Visible/Infrared Imaging Radiometer Suite (VIIRS) is a key sensor on the Suomi National Polar-orbiting
Partnership (NPP) satellite launched on October 28, 2011 into a polar orbit of 824 km nominal altitude. VIIRS collects
radiometric and imagery data of the Earth’s atmosphere, oceans, and land surfaces in 22 spectral bands spanning the
visible and infrared spectrum from 0.4 to 12.5 μm. The radiometric response for VIIRS spectral bands in the 600 – 2300
nm wavelength range (I1, M5, M6, M7 / I2, M8, M9, M10 / I3, M11), which started with significant signal to noise ratio
margin at beginning of life, has shown some degradation on orbit. This degradation has been correlated with UV
exposure of the VIIRS optics. UV exposure of witness samples from the Rotating Telescope Assembly (RTA) mirrors
by Aerospace Corporation showed reflectance loss with the same spectral signature as the response degradation observed
for VIIRS. The investigation and root cause determination for the VIIRS response degradation are discussed in separate
A model of VIIRS throughput degradation has been developed from witness sample UV exposure test results made by
Aerospace. A direct relationship is assumed between UV dose (fluence) and the reflectance degradation of the RTA
mirrors. The UV dose on orbit for the primary mirror is proportional to the incident earthshine and its solid angle of
view. For subsequent mirrors the UV dose is weighted by solid angle and preceding mirror UV reflectance. UV dose is
converted to reflectance change based on witness sample exposure measurements. The change in VIIRS throughput is
calculated by multiplying the reflectance of the four RTA mirrors and agrees with the on-orbit measured response
changes as a function of UV exposure time. Model predictions of the radiometric sensitivity for the affected VIIRS
bands show positive margin at end of life for all affected bands.
Hyperspectral systems are increasingly being mated with on-board target detection algorithms. However the only way to test these algorithms is with field testing which are expensive and inherently unrepeatable. This paper will describe a Hyperspectral Scene Generator that can display hundreds of programmable high resolution spectra simultaneously. This allows a target to be inserted into a previously measured field for testing of a hyperspectral sensor and target detection algorithms in the lab. The design of the Hyperspectral Scene Generator is presently applied to the Visible and Near InfraRed (VNIR) and Short Wave InfraRed (SWIR) but may also be applied to the MidWave InfraRed (MWIR) and Long Wave InfraRed (LWIR) spectral region. Funding for this study is provided from Office of the Secretary of Defense and Director, Operational Test and Evaluation (DOT&E) to investigate the development of a hyperspectral scene generator that will have broad application to many hyperspectral systems.