Total Suspended Solids (TSS) Mapping Using ALOS Imagery over Penang Island, Malaysia

Abstract

Remote sensing technique is very effective method for water quality mapping through analysis of satellite images over a large coverage of study area. The objective of this study was to test the feasibility of using the ALOS digital image for total suspended solids (TSS) mapping over Penang Island, Malaysia. A new algorithm was developed for detecting and mapping water pollution from the ALOS satellite image. The algorithm used was based on the reflectance model, which is a function of the inherent optical properties of water, and these in turn can be related to the concentration of the pollutants. Water samples were collected using a small boat simultaneously with the acquisition of the satellite image and later analyzed in the laboratory to determine the real concentration of the TSS level. Water sample's locations were determined by using a handheld GPS. A simple atmospheric correction, namely darkest pixel technique was performed in this study. This is a very simple correction, based on 2 assumption: The first assumption is that in the darkest water pixel of the image there is total light absorption and the radiation light recorded by this pixel comes from the atmospheric path radiance and secondly it is assumed that the atmospheric path radiance is uniform all over the image. The radiation of the darkest water pixel (assumed to represent the atmosphere) is subtracted from the whole image. The darkest pixel is found by searching for the lowest values over water for all wavelengths. The digital numbers for each band corresponding to the sea-truth locations were extracted and then converted into radiance values and reflectance values. The reflectance values were used for calibration of the water quality algorithm. The calibrated TSS algorithm was then used to generate the water quality maps of the study areas. The newly developed algorithm can estimate TSS concentration with linear correlation coefficient square (R) of 0.92. The result obtained indicated that reliable estimates of TSS values for the Penang Island, Malaysia, could be retrieved using this technique.