Water Quality Mapping Using Landsat TM imagery over Penang Island, Malaysia

This study uses an empirical model, based on actual water quality of total suspended solids (TSS) measurements from the Penang Strait, Malaysia to predict TSS based on optical properties of satellite digital imagery. The study area is Penang Island, Malaysia which is situated within latitudes 5 12’ N to 5 30’ N and longitudes 100 09’ E to 100 26’ E. The proposed algorithm is based on the reflectance model that is a function of the inherent optical properties of water, which can be related to its constituent’s concentrations. Concentrations of total suspended sediment (TSS) can be estimated by establishing an optical model that correlates the TSS with the radiance. Seawater reflectance in particular is dependent on the coefficient of absorption and backscattering of their inherent optical properties. 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 efficiency of the proposed algorithm was investigated based on the observations of correlation coefficient (R) and root-mean-square deviations (RMS) with the sea-truth data. The proposed algorithm is considered superior to other tested algorithms based on the values of the correlation coefficient, R=0.93 and root-meansquare error, RMS=9 mg/l. This algorithm was then used to map the TSS concentration over Penang, Malaysia. The TSS map was color-coded and geometrically corrected for visual interpretation. Introduction Water pollution problem becomes increasingly critical in this present-day, whether in the developed or developing countries. Water management is one of the important issues in this 21st century. Remote sensing is a useful and advanced technique for mapping water quality. Determination of water quality parameters using regression algorithm technique has been adopted by in many workers [Dekker, et al., (2002), Tassan, (1993) and Doxaran, et al., (2002)]. The objective of this study is to evaluate the feasibility of using spatial digital satellite images for TSS mapping over Penang by using a newly developed algorithm. Map Asia 2008 Kuala Lumpur, Malaysia ©GIS Development Water quality parameter used in this study is the Total Suspended Solids (TSS). We used high spatial digital camera image, with a pixel size of 1.1 m, for the purpose. Water samples were collected simultaneously with the image taken from an aircraft at an altitude of 8000ft.; the water samples were used in the training analysis. STUDY AREA The study area is Penang Island, Malaysia which is situated within latitudes 5 12’ N to 5 30’ N and longitudes 100 09’ E to 100 26’ E (Figure 1). The corresponding TSS measurements were collected at several selected locations. Laboratory analysis for the determination of TSS follows the procedure as suggested by Strickland and Parsons 1972. Figure 1: The location of the study area OPTICAL MODEL OF WATER A physical model relating radiance from the water column and the concentrations of the water constituents provides the most effective way of analyzing remotely sensed data for water quality studies. Reflectance is particularly dependent on inherent optical properties: the absorption coefficient and the backscattering coefficient. Remote sensing reflectance given by Doxaran et al. (2002) as Q R r n R Rrs ) 1 ( ) 1 )( 1 (