294
I.e. Ritchie and F.R. Schiebe
remote sensing technology to study suspended sediments is given in reviews by
Curran and Novo (1988) and Dekker et al. (1995).
13.4.2 Chlorophyll
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 or "aging" of the lake. 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 chlorophyll contained in the algal/plankton cells. While aging of water
bodies is a normal process, better infonnation on eutrophication (chlorophyll content)
in a lake will allow better management plans to be developed to control the source in
nutrient input from the catchment and thus control the rate of "aging" in lakes.
Monitoring the trophic level or concentration of the chlorophyll (algal/phytoplankton populations) is key to managing eutrophication in lakes. The algal
population is a water quality parameter that if excessive can be a problem. Algal
concentrations can be monitored by collecting samples, extracting chlorophyll, and
measuring concentrations in the extracts by photometric techniques in the laboratory.
Remote sensing has also been used to measure chlorophyll concentrations and
patterns. As with suspended sediment measurements, most remote sensing studies of
chlorophyll in water are based on empirical relationships between radiance/reflectance in narrow bands Qr band ratios and chlorophyll. Thus field data must
be collected to calibrate the statistical relationship or to validate models developed.
Measurements (Fig. 13.3) have been made in situ (Quibell 1992; Han et al. 1994;
Rundquist et al. 1996) and from aircraft (Dekker et al. 1992; Gitelson et al. 1994;
Harding et al. 1995), Landsat and SPOT (Carpenter and Carpenter 1983; Lathrop and
Lillesand 1989; Strumpfand Tyler 1988; Dekker and Peters 1993) and CZCS (Hovis
1981; Gordon et al. 1983). These studies have used a variety of algorithms and
wavelengths to successfully map chlorophyll concentrations of the oceans, estuaries
and fresh waters. For example, Harding et al. (1995) used the following algorithm
based on aircraft measurements to determine seasonal chlorophyll-a content in the
Chesapeake Bay.
Log lO [Chlorophyll] = a + b (- Log 10 G)
Where a and b are empirical constants derived from in situ measurements and G is
[(R2l/(R1*R3)]. R] is radiance at 460 nm, R2 is radiance at 490 nm and R3 is radiance
at 520 nm. Using this algorithm Harding et al. (1995) mapped total chlorophyll
content in the Chesapeake Bay (see Colour Plate B.C).
While measuring chlorophyll by remote sensing technique is possible, studies have
also shown that the broad wavelength spectral data available on current satellites do
not permit discrimination between chlorophyll and suspended sediments (Dekker and
Peters 1993; Ritchie et al. 1994) due to the dominance of the spectral signal from
suspended sediment. Some recent research has concentrated on the relationship
I.e. Ritchie and F.R. Schiebe
remote sensing technology to study suspended sediments is given in reviews by
Curran and Novo (1988) and Dekker et al. (1995).
13.4.2 Chlorophyll
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 or "aging" of the lake. 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 chlorophyll contained in the algal/plankton cells. While aging of water
bodies is a normal process, better infonnation on eutrophication (chlorophyll content)
in a lake will allow better management plans to be developed to control the source in
nutrient input from the catchment and thus control the rate of "aging" in lakes.
Monitoring the trophic level or concentration of the chlorophyll (algal/phytoplankton populations) is key to managing eutrophication in lakes. The algal
population is a water quality parameter that if excessive can be a problem. Algal
concentrations can be monitored by collecting samples, extracting chlorophyll, and
measuring concentrations in the extracts by photometric techniques in the laboratory.
Remote sensing has also been used to measure chlorophyll concentrations and
patterns. As with suspended sediment measurements, most remote sensing studies of
chlorophyll in water are based on empirical relationships between radiance/reflectance in narrow bands Qr band ratios and chlorophyll. Thus field data must
be collected to calibrate the statistical relationship or to validate models developed.
Measurements (Fig. 13.3) have been made in situ (Quibell 1992; Han et al. 1994;
Rundquist et al. 1996) and from aircraft (Dekker et al. 1992; Gitelson et al. 1994;
Harding et al. 1995), Landsat and SPOT (Carpenter and Carpenter 1983; Lathrop and
Lillesand 1989; Strumpfand Tyler 1988; Dekker and Peters 1993) and CZCS (Hovis
1981; Gordon et al. 1983). These studies have used a variety of algorithms and
wavelengths to successfully map chlorophyll concentrations of the oceans, estuaries
and fresh waters. For example, Harding et al. (1995) used the following algorithm
based on aircraft measurements to determine seasonal chlorophyll-a content in the
Chesapeake Bay.
Log lO [Chlorophyll] = a + b (- Log 10 G)
Where a and b are empirical constants derived from in situ measurements and G is
[(R2l/(R1*R3)]. R] is radiance at 460 nm, R2 is radiance at 490 nm and R3 is radiance
at 520 nm. Using this algorithm Harding et al. (1995) mapped total chlorophyll
content in the Chesapeake Bay (see Colour Plate B.C).
While measuring chlorophyll by remote sensing technique is possible, studies have
also shown that the broad wavelength spectral data available on current satellites do
not permit discrimination between chlorophyll and suspended sediments (Dekker and
Peters 1993; Ritchie et al. 1994) due to the dominance of the spectral signal from
suspended sediment. Some recent research has concentrated on the relationship