Bhatt, R; Doelling, DR; Angal, A; Xiong, XX; Haney, C; Scarino, BR; Wu, AS; Gopalan, A (2020). Response Versus Scan-Angle Assessment of MODIS Reflective Solar Bands in Collection 6.1 Calibration. IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, 58(4), 2276-2289.

The Moderate Resolution Imaging Spectroradiometer (MODIS) instruments onboard the Aqua and Terra satellites have been operated for nearly two decades, producing high-quality earth observation data sets suitable for a broad range of scientific studies regarding the earth & x2019;s land, ocean, and atmospheric processes. The high radiometric accuracy of MODIS reflective solar band (RSB) calibration has also served as benchmark measurements for on-orbit cross-calibration studies. As the two MODIS instruments have operated well beyond their design lifespan of six years, the measurements from the onboard calibrators alone become inadequate to characterize the sensor & x2019;s response at all scan angles, as evinced by long-term drifts observed at certain scan positions of the Aqua-MODIS 0.64- and 0.86- bands in Collection 6 (C6) data set. The latest MODIS Level 1B C6.1 data set incorporates earth-view response trending from invariant desert sites as supplemental inputs to characterize the scan-angle calibration dependencies for all RSB. This article presents a deep convective cloud (DCC)-based calibration approach for an independent evaluation of the MODIS RSB response versus scan-angle (RVS) performance in C6.1. The long-term calibration stability and RVS differences in C6.1 have been significantly improved for Aqua-MODIS RSB. The observed RVS differences of more than 2 & x0025; in Aqua-MODIS C6 bands 1 and 2 have been reduced to within 1 & x0025; in C6.1. Some RSBs of Terra-MODIS have suffered temporal drifts up to & x007E;2 & x0025; and calibration shifts up to 3 & x0025;, particularly around 2016 when the Terra satellite entered into safe mode. The DCC approach has been found very effective in tracking the on-orbit RVS changes over time.