20 August 2008 Removal of contaminated pixels from the desert target for AVHRR vicarious calibration
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Abstract
Desert-based vicarious calibration plays an important role in generating long-term reliable satellite radiances for the visible and near-infrared channels of Advanced Very High Resolution Radiometer (AVHRR). Lacking an onboard calibration device, the AVHRR relies on reflected radiances from a target site, e.g., a large desert, to calibrate its solar reflective channels. While the radiometric characteristics of the desert may be assumed stable, the reflected radiances from the target can occasionally be affected by the presence of clouds, sand-storms, vegetation, and wet surface. These contaminated pixels must be properly identified and removed to ensure calibration performance. This paper describes an algorithm to remove the contaminated pixels from AVHRR measurements taken over the Libyan Desert based on the characteristics of consistent Normalized Difference Vegetation Index (NDVI) land-cover stratification. We first apply a NDVI histogram-determined threshold to screen pixels contaminated with vegetation in each individual AVHRR observation. Our analyses show that the vegetation growth inside the desert target has negligibly small impact on the AVHRR operational calibration results. Two criteria based on the maximum NDVI compositing technique are then employed to remove pixels contaminated with clouds, severe sand-storms or wet sand surface. Compared to other cloud screening methods, this algorithm is capable of not only identifying high reflectance clouds, but also removing low reflectance of wet surface and nearly indifferent reflectance of severe dust storms. The use of clear pixels appears to improve AVHRR calibration accuracy in the first three-four years after satellite launch.
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Fangfang Yu, Xiangqian Wu, "Removal of contaminated pixels from the desert target for AVHRR vicarious calibration", Proc. SPIE 7081, Earth Observing Systems XIII, 70810H (20 August 2008); doi: 10.1117/12.792559; https://doi.org/10.1117/12.792559
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