Detecting Cirrus-Overlapping-Water Clouds and Retrieving their Optical Properties Using MODIS Data

Different methods have been proposed to detect multilayer clouds using passive remote sensing data. Baum et al. (1995) used the CO2-slicing technique applied to the High Resolution Infrared Radiation Sounder (HIRS) data to determine cirrus cloud heights. The spatial coherence technique (Coakley and Bretherton 1982) was applied to the advanced very high resolution radiometer (AVHRR) data to determine low cloud heights. Ou et al. (1996) presented a threshold test scheme to distinguish AVHRR pixels that contain overlapped clouds and non-overlapped low and high clouds. Baum and Spinhirne (2000) used a bispectral method on moderate-resolution imaging spectroradiometer (MODIS) airborne simulator (MAS) 1.6-μm and 11-μm data to identify areas containing overlapped clouds. All of these methods were focused on detecting overlapped clouds but not on the retrieval of cloud optical depth. Also, no methods have been applied over extensive areas or long time periods. Other algorithms used a combination of microwave, visible, and infrared measurements (Sheu et al. 1997; Lin et al. 1998; Ho et al. 2003) but were restricted to high thick clouds only over the ocean.