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
papers.
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.
Laser bulk damage thresholds were measured for both single-crystal YAG and for diffusion-bonded YAG structures
using 600 picosecond pulses at 1064 nm. The tested samples included 3-layer sandwich structures with doped cores
of various thicknesses. An undoped-YAG end cap was diffusion-bonded on one end of each of the sandwiches. The
1064 nm laser source was focused to a 13 micron diameter spot at the boundary region between the core and the
undoped endcap. Measurements included the evaluation of single- and multiple-pulse damage thresholds at single
sites, as well as thresholds for continuous 90%-overlap scans. The single-site thresholds at the diffusion-bonded
boundary were close to that of single-crystal YAG. However, the continuous scans revealed isolated microscopic
sites where the damage threshold was as much as 4 times lower than that of single-crystal YAG.
Northrop Grumman Space Technology (NGST) has developed and tested a Long-wave Hyperspectral Imaging Spectrometer (LWHIS) that operates in the 8 to 12.5 micron band. An overview of the system design has been described elsewhere. This paper describes the system characterization and radiometric calibration of this instrument using NGST’s Long-wave Hyperspectral Test Facility which uses a 1375K globar source assembly, a monochromator, a collimator and a fine pointing mirror to provide image quality and FPA alignment data. Image quality characterization results presented here include measurement of the instrument’s Modulation Transfer Function (MTF), spatial co-registration of spectral channels (spectral smile), cross-track spectral error (spatial smile), and spectral calibration. Radiometric calibration results for laboratory targets are also presented.
Northrop Grumman Space Technology (NGST), using internal funding, has designed, built and is testing a Long Wave Hyperspectral Imaging Spectrometer (LWHIS) that operates in the 8 to 12.5 micron band. This instrument was designed to be compatible with aircraft platforms so that flight data in this wavelength band can be used for phenomenological analysis. The instrument provides up to 256 contiguous spectral channels with 17 nm of dispersion per pixel (pixels are binned in normal operation to provide 128 spectral channels). The entrance aperture is 3.5 cm and feeds a F2/5 reflective triplet front end. The focal plane is a 256 x 256 array of 40 micron pixels which can be binned to form an 80 micron superpixel. With a fixed frame rate of 60 Hz, the instrument provides a ground sample distance of 1m at 1.1km altitude. This paper describes the physical characteristics of the design and presents the predicted performance based on NGST internal models. Design trades and test data will be presented. A more detailed look at the characterization and calibration of this instrument will be presented in a companion paper "Long Wave Hyperspectral Imaging Spectrometer -- System Characterization and Calibration."
The end-to-end calibration plan for the Hyperion EO-1 hyperspectral payload is presented. The ground calibration is traceable to a set of three high quantum efficiency p-n silicon photodiode trap detectors the responsivities of which are traceable absolutely to solid state silicon diode physical laws. An independent crosscheck of the radiance of the Calibration Panel Assembly used to flood the Hyperion instrument in field and aperture was made with a transfer radiometer developed at TRW. On-orbit measurements of the sun's irradiance as it illuminates a painted panel inside the instrument cover are compared to the radiance scale developed during pre-flight calibration. In addition, an on-orbit calibration lamp source is observed to trace the pre-flight calibration constants determined on the ground to the solar calibration determination.
This paper describes the calibration transfer path from primary standards representing fundamental physical quantities through the calibration radiance source used in Hyperion instrument level absolute calibration. The calibration transfer path and hardware design of the primary and secondary standards and their validation for end-to-end calibration of the sensor are presented. The primary standards reside at the TRW Radiometric Scale Facility and include two high quantum efficiency Silicon photodiode trap detectors; an electrically self-calibrated pyroelectric detector serves as a secondary standard for crosscheck. The end-to-end sensor calibration is accomplished with a Calibration Panel Assembly (CPA) source, which is illuminated by a NIST traceable FEL 1000 transfer standard lamp. An independent crosscheck of the Spectralon reflectance properties is made with a transfer radiometer. An error analysis of the transfer path is presented. The basic strategy of the Hyperion end-to-end calibration is to reduce the size of the sensor responsivity error tree and to provide control of systematic errors as much as possible through cross-calibration.
Larry Yujiri, Hiroshi Agravante, Steven Fornaca, Bruce Hauss, Ronald Johnson, Roger Kuroda, Bill Quon, Arlen Rowe, Thomas Samec, Merit Shoucri, Karen Yokoyama
A passive millimeter-wave (PMMW) camera capable of generating a real time display of the imaged scene, similar to video cameras, has been developed at TRW and is undergoing field testing. The camera operates at 89 GHz, acquiring images at a frame rate of 17 Hz. This work reports on the video imaging generated by the camera. This research is carried out under the Passive Millimeter-Wave Camera Consortium, a cost-shared program between the Defense Advanced Research Programs Agency and an industrial consortium that includes Honeywell, McDonnell Douglas and TRW. It is managed for the Department of Defense by NASA-LaRC.
Larry Yujiri, Hiroshi Agravante, Mike Biedenbender, G. Samuel Dow, Martin Flannery, Steven Fornaca, Bruce Hauss, Ronald Johnson, Roger Kuroda, Karen Jordan, Paul Lee, Dennis Lo, Bill Quon, Arlen Rowe, Thomas Samec, Merit Shoucri, Karen Yokoyama, John Yun
A passive millimeter-wave camera capable of generating real time displays of the imaged scene, similar to video cameras, has been under development at TRW over the past two years. The camera operates at 89 GHz, has a 15 degree(s) X 10 degree(s) field-of-view, an aperture of 18' diameter, and displays the acquired image at a frame rate of 17 Hz. A major enabling technology is the focal plane array of direct detection MMIC receivers which guarantees reliable and low cost manufacturing of this camera, in addition to providing it with unique operational features. This work reports on progress achieved to date in the development and manufacturing of this new sensor technology.
TRW is developing High Temperature Superconducting (HTS) electronics to dramatically improve the performance of space- based communications systems. These systems demand high speed analog-to-digital converters, high speed digital multiplexers, and quadriphase modulation of rf carrier signals. TRW has demonstrated an HTS high-speed multiplexer and a digital phase modulator that operates at microwave frequencies. The latter is the fundamental building block of a Quadriphase Modulator Exciter (QME). TRW has also developed an HTS cryogenic packaging subsystem which uses a commercially available palm-sized cryocooler. This package represents the first demonstration of an HTS self-supporting system. Package verification tests revealed that the package is capable of supporting high speed I/O and demonstrates reliable connectivity through multiple interfaces. The successful operation of a digital phase modulator has been demonstrated with this package.
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