Use of satellite image enhancement procedures for global cloud identification

As a preliminary step in the study of long-term global cloud properties variations and their contribution to the Earth radiation budget, a classification procedure to identify various types of clouds is discussed. This classification scheme highlighting the spatial heterogeneity of cloud structural arrangements is used to characterize and differentiate nine cloud types. The study takes advantage of the capacity of edge gradient operators' techniques generally used to calculate the magnitude and direction changes in the intensity function of adjacent pixels of an image, to identify the various cloud types. The specific approach, based on variations of the edge gradient magnitude and orientation, is applied on daytime global cloud physical features (cloud top temperatures derived from the 11-μm brightness temperature imagery) obtained from the National Oceanic and Atmospheric Administration-Advanced Very-High-Resolution Radiometer (NOAA-AVHRR) satellite observations. The results obtained are compared with those of the International Satellite Cloud Climatology Project (ISCCP) cloud classification algorithm which uses cloud optical properties and pressure levels to distinguish cloud types. Results of these two procedures show good agreement but substantial differences are noticed at polar areas.