MISR empirical stray light corrections in high-contrast scenes

[摘要] We diagnose the potential causes for the Multi-angle ImagingSpectroRadiometer's (MISR) persistent high aerosol optical depth (AOD) biasat low AOD with the aid of coincident MODerate-resolution ImagingSpectroradiometer (MODIS) imagery from NASA's Terra satellite. Stray lightin the MISR instrument is responsible for a large portion of the high AODbias in high-contrast scenes, such as broken-cloud scenes that are quitecommon over ocean. Discrepancies among MODIS and MISR nadir-viewing blue,green, red, and near-infrared images are used to optimize seven parametersindividually for each wavelength, along with a background reflectancemodulation term that is modeled separately, to represent the observedfeatures. Independent surface-based AOD measurements from the AErosolRObotic NETwork (AERONET) and the Marine Aerosol Network (MAN) are comparedwith MISR research aerosol retrieval algorithm (RA) AOD retrievals for 1118 coincidences tovalidate the corrections when applied to the nadir and off-nadir cameras.With these corrections, plus the baseline RA corrections and enhanced cloudscreening applied, the median AOD bias for all data in the mid-visible(green, 558 nm) band decreases from 0.006 (0.020 for the MISR standardalgorithm (SA)) to 0.000, and the RMSE decreases by 5 % (27 % comparedto the SA). For AOD_{558 nm} < 0.10, which includes about halfthe validation data, 68th percentile absolute AOD_{558 nm} errors forthe RA have dropped from 0.022 (0.034 for the SA) to < 0.02(~ 0.018).

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