APPLICATION OF REMOTE SENSING FOR ADJUSTMENT AND CALIBRATION OF WATER QUALITY MODEL - Integrating GIS, Remote Sensing, and Mathematical Modelling for Surface Water Quality Management - page 173

8.5.1. Application of TSM Algorithms for development TSM Concentration maps

In literature several MODIS algorithms are developed for TSM extraction. These algorithms are site
specific, and depend on the characteristics and the inherent optical properties (IOP's) of the water
body. Previous work by Miller and McKee (2004) using the visible and NIR bands with the highest
spatial resolution (250 m) provided useful results for total suspended matter (TSM) in the coastal
waters off the northern Gulf of Mexico. The established linear relation was tested on the MODIS
image of Lake Edko as shown in Equation (8-4) :

1140.25*(MODIS Band 1) - 1.91 (8-4)

The extracted TSM concentrations applying this algorithm were very high compared to in situ measurements.
The main reason for this difference is the different environments in the areas under analysis. Figure (8-14)
shows the same previous selected pixel locations, the model predicted values, the image extracted
values applying the Miller and McKee algorithm and the corresponding field measured TSM
concentrations on 28 th June. The comparison shows a difference between the measured values and the
MODIS extracted values, with a RMSE of 33.27 mg/l. This shows that the developed algorithm is
likely to be site specific and it is affected by the IOP's of the lake water.

Figure (8-14): model predicted values, image extracted values and the corresponding field measured TSM
concentrations on 28 th June applying the algorithm developed by Miller and McKee, 2004

Applying the empirical approach to the analysis of remote sensing images as mentioned above is
based on the calculation of a statistical relation between the water constituent concentrations and
reflectance (or radiance). This approach needs extensive in situ data measurements of water quality
parameter concentrations. To relate the number of measurements within the water body to the 250 m
MODIS images in the case study under investigation, a limited number of measurements are available.
Therefore a local regression analysis was done using the set of points that were measured on 28 th of
June 2006 when a MODIS image is available; for the rest of data set that were measured on 27 th and
29 th of June the corresponding images were with high cloud coverage and were excluded from the
analysis. Since a similar case was developed for the turbid coastal waters of Mahakam Delta,
Indonesia, (Budhiman, 2004), where it was proved that there is an exponential relation between the
TSM concentration and MODIS band 1 (665 nm), the result of an exponential relation in the case of
Edko Lake is considered to be accepted with a value of R 2 = 0.85 under the existing conditions. Figure
(8-15) shows the regression analysis and the relationship between the measured TSM concentration
and the surface reflectance at band 1 (665nm).