AVHRR Pixel Level Clear-Sky Classification Using Dynamic Thresholds (CLAVR-3)

Abstract Clear-sky classifications from the Clouds from the Advanced Very High Resolution Radiometer (AVHRR)-Phase 1 (CLAVR-1) program are used to create an 8-day rotating clear-sky radiation dataset. This dataset is used to create satellite zenith angle dependent, dynamic, cloud/no-cloud albedo and temperature thresholds for ocean and six different vegetation index groups in 10° latitude intervals over the globe. Individual pixels from ambiguously classified 2 × 2 pixel arrays from CLAVR-1 (MIXED and RESTORED-CLEAR) are reexamined at the individual pixel level, using these dynamic thresholds, and reclassified as CLEAR, MIXED, or CLOUDY. This methodology is referred to as the CLAVR-3 algorithm. It is found that many of the MIXED (partially cloudy or mixed overcast) pixels from CLAVR-1 are cloud free after using the dynamic thresholds. A smaller number of RESTORED-CLEAR pixels are found to be CLEAR, while many are classified MIXED. Poleward of about 80°N and 60°S, the CLAVR-1 algorithm does not provide suf...

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