Recent Improvements in the MODIS Cloud Mask

摘要

Significant improvements have been made to the MODIS cloud mask (MOD35) in preparation for Collection 5 reprocessing and forward stream data production. Most of the modifications are realized for nighttime scenes where polar and oceanic regions will see marked improvement. For polar night scenes, two new spectral tests using the 7.2 μm water vapor absorption band have been added as well as updates to the 3.9-12 μm and 11-12 μm cloud tests. More non-MODIS ancillary data has been added for nighttime processing. Land and sea surface temperature maps provide crucial information for middle and low-level cloud detection and lessen dependence on ocean variability tests. Sun-glint areas are also improved by use of sea surface temperatures to aid in resolving observations with conflicting cloud vs. clear-sky signals, where visible and NIR reflectances are high, but infrared brightness temperatures are relatively warm. Details and examples of new and modified cloud tests are shown and various methods employed to evaluate the new cloud mask results. Day vs. night sea surface temperatures derived from MODIS radiances and using only the MODIS cloud mask for cloud screening are contrasted. Frequencies of cloud from sun-glint regions will be shown as a function of sun-glint angle to gain a sense of cloud mask quality in those regions.