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 172

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Figure (8-13a) Figure (8-13b)

Figure (8-13c) Figure (8-13d)
Figure (8-13 a,b,c,d): qualitative comparison of temporal images and model trends at different measuring
locations inside the lake

Discussion on Results

The qualitative analysis using the preliminary comparison of images and modeled profiles can give a
good indication of the general model trends and can be used as a first tool for judging the model
performance. Also, comparing temporal trends using time series (pixel to pixel comparison) developed
from the set of the model maps and images at different locations shows acceptable similar trends at
some locations. The associated uncertainties with the atmospheric corrections and the presence of
floating and submerged vegetation are seen as the main reasons for the variations at certain time steps
between the image and the model pixel values. From the performed analysis we can conclude that
qualitative calibration using MODIS could be used as an initial step before the detailed analysis of the
images and before applying any algorithms to develop concentration maps.

8.5. SPATIAL AND TEMPORAL QUANTITATIVE CALIBRATION OF WATER QUALITY MODEL

At this level of calibration the images are used for quantitative analysis to extract water quality
concentration maps for both TSM and CHL-a. The methodology is generally based on the application
of an empirical or statistical approach for remote sensing data analysis. The maps are used to extract
concentrations of TSM and CHL-a at both temporal and spatial levels to be used for model calibration.
In this method of calibration the set of MODIS images is used to develop a time series data set for
both TSM and CHL-a concentration maps that is then used as input data for calibrating the model at
the main locations (namely, the exits of main drains into the lake water body).