absorption by water with increasing wavelength (Figure 6) and blue dominated,
wavelength specific scattering efficiencies (Smith and Baker, 1981). Modest increases
in phytoplankton density, accompanied by increased pigment absorption (Figure 8),
result in strongly decreased blue reflectance (tropical lagoon example in Figure 7 and
point A 1 in Figure 8), while scattering outcompetes absorption in the green peak region
and results in increasing reflectance (points B 1 and B 2 in Figure 8). The ratio of 443 to
555 nm (Figure 10) is strongly and inversely correlated and has been used to estimate
chl a. The relationship, however, is nonlinear and becomes increasingly less sensitive
with increasing pigment (especially above 10 µg/l).
Figure 10. Comparison of two common chlorophyll algorithms: (1) ratio of 453/555 nm for Case
1 waters and (2) ratio of 700/670 nm for turbid and/or eutrophic Case 2 waters. Data are from the
mesocosm dilution and enrichment experiment in Figures 8 and 9.
Algorithms based on Q band, red absorption and the NIR reflectance peak feature
are favored in situations with high chl a and/or Case 2 optical conditions (Dekker et al.,
1996; Gower et al., 1999; Ammenberg, 2000; Gitelson et al., 2000; Gons et al., 2002).
A band ratio using the NIR peak near 700 nm and the red Q band may largely isolate
the chl a signal from other pigment and CDOM absorption activity. The NIR feature
builds much more rapidly than the Q band region with increasing cell densities (Figures
8 and 9), producing an exploitable response. A ratio of 700 nm to 670 nm (Gitelson
et al., 2000), applied to our tank mesocosm data, produced a strong relationship to chl
a, with good sensitivity above 10 µg/l (Figure 10).
Different phytoplankton taxa often have differentiable colors, i.e. are members of
the “green algae”, golden brown algae”, etc., with these variations clearly related to
spectral differences in absorption by accessory pigments (Sathyendranath et al., 1987;
Rowan, 1989; Richardson, 1996). Thus ecologically different oceanic provinces, with
differing proportions of dominant phytoplankton groups, may have differing absorption
44
Schalles
wavelength specific scattering efficiencies (Smith and Baker, 1981). Modest increases
in phytoplankton density, accompanied by increased pigment absorption (Figure 8),
result in strongly decreased blue reflectance (tropical lagoon example in Figure 7 and
point A 1 in Figure 8), while scattering outcompetes absorption in the green peak region
and results in increasing reflectance (points B 1 and B 2 in Figure 8). The ratio of 443 to
555 nm (Figure 10) is strongly and inversely correlated and has been used to estimate
chl a. The relationship, however, is nonlinear and becomes increasingly less sensitive
with increasing pigment (especially above 10 µg/l).
Figure 10. Comparison of two common chlorophyll algorithms: (1) ratio of 453/555 nm for Case
1 waters and (2) ratio of 700/670 nm for turbid and/or eutrophic Case 2 waters. Data are from the
mesocosm dilution and enrichment experiment in Figures 8 and 9.
Algorithms based on Q band, red absorption and the NIR reflectance peak feature
are favored in situations with high chl a and/or Case 2 optical conditions (Dekker et al.,
1996; Gower et al., 1999; Ammenberg, 2000; Gitelson et al., 2000; Gons et al., 2002).
A band ratio using the NIR peak near 700 nm and the red Q band may largely isolate
the chl a signal from other pigment and CDOM absorption activity. The NIR feature
builds much more rapidly than the Q band region with increasing cell densities (Figures
8 and 9), producing an exploitable response. A ratio of 700 nm to 670 nm (Gitelson
et al., 2000), applied to our tank mesocosm data, produced a strong relationship to chl
a, with good sensitivity above 10 µg/l (Figure 10).
Different phytoplankton taxa often have differentiable colors, i.e. are members of
the “green algae”, golden brown algae”, etc., with these variations clearly related to
spectral differences in absorption by accessory pigments (Sathyendranath et al., 1987;
Rowan, 1989; Richardson, 1996). Thus ecologically different oceanic provinces, with
differing proportions of dominant phytoplankton groups, may have differing absorption
44
Schalles