Establishing a global algorithm for water quality mapping from multi-dates images  H. S. Lim, M. Z. MatJafri, K. Abdullah and M. N. A. Bakar School of Physics Universiti Sains Malaysia, 11800 Penang Abstract The problem of difficulty in obtaining cloud-free scene at the Equatorial region from satellite platforms can be overcome by using airborne imagery. Digital camera was used as a sensor in this study. This technique was cheaper and economical compared with other airborne studies. Digital images were captured at three locations, which were Prai river, Muda river and Merbok river estuaries from a low altitude flying aircraft. Six sets of digital data were captured on five different days. Water samples were collected simultaneously with the airborne image acquisition. The station locations of the water samples were detemined using a hand held GPS. Atmospheric correction for multidate images was performed by selecting average digital number of grass as a reference. The digital colour images of the study areas were separated into three bands (red, green and blue) for multi-spectral analysis. The digital numbers were extracted corresponding to the ground-truth location for each band and later used for calibration of the water quality algorithm. The algorithm was developed based on the reflectance model, which is a function of the inherent optical properties of water and this in turn can be related to the concentration of its constituents. Finally, TSS maps were generated using the proposed calibrated algorithm to the study areas. The data produced a high degree of accuracy. The TSS maps were geometrically corrected and colour-coded for visual interpretation. The result showed that the established global algorithm can be used to generate a TSS map after simple atmospheric correction. |