Cloud detection with MODIS: Capabilities and limitations

Clouds are important in both weather and climate. Models, particularly General Circulation Models (GCMs), make extensive comparison with satellite derived cloud amount as part of model assessment. Total cloud amount from different satellite algorithms can vary significantly even among accepted standards, as shown in a comparison of annual zonal mean cloud fraction from CLAVR, ISCCP and UW-HIRS. Global distributions demonstrate expected patterns but can differ in magnitude by more then 10%. This is far from the stated 1% requirement of Ohring et al (2002). This presentation investigates how spectral testing, field-of-view size and cloud optical depth impact cloud detection algorithm of MODIS on the Aqua and Terra EOS satellites.