The MODIS reflective solar bands (RSB) include both the low-gain and high-gain spectral bands depending on their
specific applications. MODIS RSBs are calibrated on-orbit by an on-board solar diffuser. In order to avoid detector
response saturation when calibrating the high-gain bands, an optional attenuation screen, made of a metal plate with
pinhole arrays, is placed in front of the SD panel. Since no pre-launch system-level characterization was made for the SD
screen (SDS) vignetting function (VF), a series of spacecraft (Terra and Aqua) yaw maneuvers were carried out to
perform on-orbit characterization of the VF. Assuming that the low-gain bands and the high-gain bands have the same
VF, the current VF was derived from yaw observations using the MODIS low-gain bands through taking the ratio of
their SD responses with and without the SDS in place. In this study, we attempt to characterize the SDS VF directly
using detector responses of individual high-gain bands with the SDS in place only. The corresponding SD responses
without the SDS, not available from measurements due to saturation, are calculated using detector gains, the SD bi-directional
reflectance factor (BRF), and the view geometry that matches the yaw observations with the SDS in place.
Results and discussions are focused on the band dependent and detector dependent features of the SDS VF, and their
potential impact on the RSB calibration.
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