Remote Sensing of Turbidity Mapping from Digital Camera Imagery
Sultan AlSultan 1 , H. S. Lim 2 , M. Z. MatJafri 3 , K. Abdullah 3 and M. N. A. Bakar 4
1Dr., Al Sultan Environmental Research Center. Al Madina Rd., P.O.Box.
242 Riaydh Al Khabra, Al Qassim, Saudi Arabia.
Tel: +966504890977, Fax: +96663340366
Email: allssultan7@hotmail.com
2Student, 3 Assoc. Prof. Dr., 4 Dr., School of Physics,
University of Science Malaysia,
11800 Penang, Malaysia
Tel: +604-6533888, Fax: +604-6579150
Email: mjafri@usm.my,
khirudd@usm.my
ABSTRACT
A complete set of normal digital camera data and ground-based measurements are used to test an
algorithm for retrieval of turbidity distribution in the Prai Estuary, Penang, Malaysia. The main
objective was to test the algorithm developed for total suspended solids (TSS) to be used for
turbidity mapping. Empirical relationships are established between the raw digital number of the
digital camera imagery bands and turbidity values obtained from field measurements. The digital
imageries were captured from a light aircraft at a low altitude of 4400 feet. A bigger study area of
coverage was obtained by using a mosaic image from eight digital images. Water samples locations
were determined using a handheld GPS. The digital image was separated into three bands assigned
as red, green and blue bands for multispectral algorithm calibration. The digital numbers were
extracted corresponding to the ground-truth locations for each band and later used for the
calibration of the developed algorithm. The efficiency of the present proposed algorithm, in
comparison to other forms of algorithm, was also investigated. Based on the values of the
correlation coefficient (R) and root-mean-square deviation (RMS), the proposed algorithm is
considered superior. The calibrated TSS algorithm was used to generate the water quality map. The
water quality image was geometrically corrected and the image was filtered to remove random
noise. The generated map was colour-coded for visual interpretation. This preliminary result
indicated that the previously developed algorithm for TSS was suitable used for turbidity mapping
of the Prai Estuary, Penang, Malaysia.
1.0 INTRODUCTION
Water turbidity is an expression of the optical properties of water, which cause the light to be
scattered and absorbed rather than transmitted in straight lines. It is therefore commonly regarded as
the opposite of clarity. As water turbidity is mainly caused by the presence of suspended matter,
turbidity measurement has often been used to calculate fluvial suspended sediment concentrations
(Wass, et al., 1997).
Mostly, satellite data will be used for water quality monitoring, but the major disadvantage
of satellite data is that, they cannot see through the clouds. Airborne digital camera imageries were
selected in this present study because of several reasons. First was the airborne digital images
provide higher spatial resolution data for mapping a small study area. Second was the airborne
digital data acquisition can be carried out according to our planned surveys. The satellite
observation times are fixed for a particulate study area. Third was the digital imagery offers many
advantages over film-based cameras. There is a great saving of time because the data can be loaded
directly to a computer for processing, as there is no need for film processing and scanning (Wicks,
2003). Remote sensing techniques have been widely used for water quality studies in coastal
regions and in inland lakes (Ekstrand 1992, Ritchie et al.1990, Baban 1993, Dekker and Peters
1993, Dekker, et al., 2001, Forster et al. 1993, Allee and Johnson 1999, Koponen et al. 2002). In
this study, algorithm was used to determine the turbidity distribution in the surface of seawater. The
algorithm used in this study was developed based on the reflectance model for TSS. Various types
of algorithms were tested and their accuracies were noted. Finally, the optimum algorithm was
selected and used to generate a turbidity map over Prai Estuary, Penang, Malaysia.
