INTEGRATING TOOLS FOR SURFACE WATER QUALITY MANAGEMENT - Integrating GIS, Remote Sensing, and Mathematical Modelling for Surface Water Quality Management - page 64

Figure (3-3): The relationship between reflectance and wavelength as affected by the concentration of suspended
sediment (Ritchei et al., 1976).
Since the mid 1980's remote sensing studies of suspended sediments have been made using data from
satellite platforms such as Landsat (Kritikos et al. 1974; Carpenter and Carpenter 1983; Khorram
1985; Ritchie et al. 1990; Harrington et al. 1992), SPOT (Lathrop and Lillesand 1989; Froidefond et
al. 1993), IRS (Chubey and Subramanian 1992), AVHRR (Strumpf and Pennock 1991; Froidefond et
al. 1993), and CZCS (Coastal Zone Color Scanner) (Amos and Toplis 1985; Mayo et al. 1993). These
studies have shown significant relationships between suspended sediments and radiance or reflectance
from spectral wave bands or combinations of wave bands on satellite and aircraft sensors.
Many studies have developed statistical relationships (algorithms) between concentration of
suspended sediments and the radiance or reflectance for a specific date and site. Few studies have
taken the next step and used these algorithms to estimate suspended sediments for another time or
space (Whitlock et al. 1982, Curran and Novo 1988; Ritchie and Cooper 1988, 1991). Once
developed, an algorithm should be applicable until some cathcment event changes the quality (size,
color, mineralogy, etc.) of suspended sediments delivered to lake.
CHL-aorophyll-a
Another application of remote sensing is the measurement of CHL-aorophyll-a. Lakes and other water
bodies depend upon their catchments for nutrients and other substances to sustain biological activities.
While these nutrients and substances are required for a healthy aquatic environment, an excess of these
inputs leads to nutrient enrichment and eutrophication of the lake as discussed earlier. The rate of
eutrophication depends on topography, soils, land use, and runoff on the contributing catchment.
Eutrophication of a water body can be quantified in terms of trophic level or concentration of the
CHL-aorophyll contained in the algae/phytoplankton cells. While aging of water bodies is a normal
process, better information on eutrophication (CHL-aorophyll content) in a lake will allow better
management plans to be developed to control the source in nutrient input from the catchment.
Monitoring the trophic level or concentration of CHL-aorophyll-a (algal/phytoplankton populations) is
the key to managing eutrophication in lakes. The algal population is a water quality parameter that if it
is too large can be a problem. Algal concentration can be monitored by collecting samples, extracting
CHL-aorophyll, and measuring concentrations in the extracts by photometric techniques in the
laboratory. Remote sensing has been also used to measure CHL-aorophyll concentrations and patterns.
Most remote sensing studies of CHL-aorophyll in water are based on empirical relationships between
radiance/reflectance in narrow bands or band ratios and CHL-aorophyll. Thus field data must be
collected to calibrate the statistical relationships or to validate the models developed.