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The Visible Infrared Imaging Radiometer Suite (VIIRS) is a key sensor carried on the
NPOESS (National Polar-orbiting Operational Environmental Satellite System) Preparatory
Project (NPP) mission [1] (http://jointmission.gsfc.nasa.gov/viirs.html), and is
scheduled to launch in October 2011. VIIRS sensor design draws on heritage instruments
including AVHRR, OLS, MODIS, and SeaWiFS. It has on-board calibration components
including a solar diffuser (SD) and a solar diffuser stability monitor (SDSM) for the
reflective solar bands (RSB), a V-groove blackbody for the thermal emissive bands (TEB),
and a space view (SV) port for background subtraction. These on-board calibrators are
located at fixed scan angles. The VIIRS response versus scan angle (RVS) was
characterized prelaunch in lab ambient conditions and will be used on-orbit to
characterize the response for all scan angles relative to the calibrator scan angle (SD
for RSB and blackbody for TEB). Since the RVS is vitally important to the quality of
calibrated radiance products, several independent studies were performed and their
results were compared and validated. This document provides RVS results from three
groups: the NPP Instrument Calibration Support Team (NICST), Raytheon, and the Aerospace
Corporation. A comparison of the RVS results obtained using a 2nd order polynomial fit to
measurement data is conducted for each band, detector, and half angle mirror (HAM) side.
The associated RVS fitting residuals are examined and compared with the relative
differences in RVS found between independent studies. Results show that the agreement is
within 0.1% and comparable with fitting residuals for all bands except for RSB band M9,
where a difference of 0.2% was observed. Band M9 is highly sensitive to the atmospheric
water vapor variations during the sensor ambient testing at Raytheon, and its correction might be a contributor to the observed RVS uncertainty differences. In general, NICST
results have shown slightly larger RSB RVS uncertainties but still well within the 0.3%
total uncertainty allowed for the RVS characterization defined in the Performance
Verification Plan.
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