Modeling SNPP VIIRS reflective solar bands optical throughput degradation and its impacts on the relative spectral response

摘要

Right after the opening of the NADIR door of the Visible/Infrared Imager/Radiometer Suite (VIIRS) aboard the Suomi National Polar-orbiting Partnership (SNPP) satellite, it has been observed that the detector gains of the near infrared (NIR) bands have decreased much faster than expected. This large decrease is attributed to the optical reflectance degradation of the Rotating Telescope Assembly (RTA) mirrors. We have established a physical model to describe the degradation. In this Proceeding, we use the model to fit the up-to-date observed data to update the model parameters' values and the degradation projections. We have adjusted our original model slightly to address the additional optical throughput degradation for the short wave infrared (SWIR) bands, occurred right after the spacecraft Sun Point mode anomaly (orbits 2101-2133; March 24-26, 2012). The RTA optical throughput degradation over the reflective solar bands (RSB) and the additional throughput degradation over the SWIR bands after the Sun Point mode anomaly are not constant across the optical wavelength and therefore impact on a detector's relative spectral response (RSR). Using the models, we establish the degradation versus wavelength curve at any orbit and use the curve to compute the associated impact on the RSR. We further use this degradation modulated RSR to compute the impact on sensor calibration and the Earth View reflectance at Sensor Data Record (SDR) level.