22 August 2005 Analysis of MODIS solar diffuser screen vignetting function
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Abstract
Twenty of the 36 MODIS spectral bands are reflective solar bands (RSB). They are calibrated on-orbit by an onboard solar diffuser (SD). For the high-gain ocean color bands (8-16), an attenuating solar diffuser screen (SDS) is used in front of the SD panel to avoid detector saturation caused by direct solar illumination of the SD. The use of the SDS, a metal plate with uniformly distributed pinholes, introduces an additional factor to the radiometric calibration uncertainty. Since a system level characterization of the SDS transmission versus SD viewing geometry was not performed pre-launch, the vignetting function (VF) for both Terra and Aqua MODIS had to be characterized on-orbit. The VF can be derived either from SD observations made with and without the SDS in place during specially planned spacecraft yaw maneuvers or by using routine SD calibration pairs (with and without the SDS) accumulated over a long period in order to cover all possible viewing geometries. In this paper we present details of the methods used to characterize the MODIS SDS VFs and examine the results derived from both spacecraft yaw maneuvers and long-term SD calibration pairs. The VF results obtained for Terra and Aqua MODIS are discussed and compared. In addition, an estimate of the calibration uncertainties introduced by the SDS is provided.
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X. Xie, X. Xie, X. Xiong, X. Xiong, D. Moyer, D. Moyer, J. Sun, J. Sun, X. Liu, X. Liu, W. Barnes, W. Barnes, } "Analysis of MODIS solar diffuser screen vignetting function", Proc. SPIE 5882, Earth Observing Systems X, 58820T (22 August 2005); doi: 10.1117/12.615394; https://doi.org/10.1117/12.615394
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