Determination of effective reflectance of sub sea objects in landsat TM images: A case study of the Coral reefs of Khark and Kharkoo islands (NW of Persian Gulf)



The difference between effective reflectance from sub sea objects and water suspended materials is a function of attenuation coefficient (k) of light intensity in bodies of water. The amount of C-Cmin (here C is digital number) identifies the effective reflectance and it is possible to differentiate the effective reflectance from sub sea objects and water suspended loads using a specific display image of band ratios. In a ratio display image of Landsat TM band pairs, this difference is a function of (1- e ki)/(1 – ekj). This value for Khark and Kharkoo sub sea objects (Coral reefs and sandy beds) in the Landsat TM image of 1998 is always positive and less than one. Thus a RGB false color of the atmospherically corrected ratio image of effective reflectance (C-Cmin) display image as
(C – Cmin)b2/(C – Cmin)b1 ; (C – Cmin)b3/(C – Cmin)b2 ; (C – Cmin)b4/(C – Cmin)b3 : (RGB)
shows the best separation of the sub sea objects. The proposed model has been used for detecting coral reefs and sandy beds around two Iranian islands in the Persian Gulf, Khark and Kharkoo. The results have been checked by field studies and draft maps, which show a good correlation with a high overall accuracy of about 90%.