substances (Klemas and Polis, 1977; Gordon and Morel, 1983; Alberts and Filip, 1994;
Bukata et al., 1995). Although Case 1 conditions normally prevail offshore, they may
also occur: 1) in coastal and near shore areas in arid regions, where shelf geology is
limited and deep water occurs just off the coastline; 2) during droughts resulting in
highly reduced or no runoff; or 3) other instances where currents introduce offshore
water in localized areas lacking significant terrestrial runoff. Obviously, Case 2
conditions intergrade spatially with Case 1 conditions in relation to distance from
coastlines and river plumes. Physical dynamics and seasonality can result in state
changes for a given location. The chlorophyll prediction algorithms for Case 1 and Case
2 waters are often different, and both sets may be required in coastal zones. Note that
certain in situ water column processes (ex. phytoplankton blooms or amplified
scattering by carbonates from coccolithophores or whiting events) can shift the optics
of offshore waters away from true Case 1 conditions.
Most approaches for remote estimation of phytoplankton biomass are based on the
absorption of sunlight by algal pigments in the presence of light scattering by algal cells
and non-algal particles. This interplay of pigment-specific absorption and particle
scattering produces graded responses in the emergent reflectance signals detectable by
radiometer instruments. This chapter will examine the nature of these graded responses
and their utilization in various quantitative and qualitative assessment schemes for
spatial and temporal patterns of phytoplankton abundance.
Coastal, estuarine, and inland water habitats present serious challenges to the
interpretation of diagnostic light signals because of the diversity of optically active
constituents, which partially mask fundamental phytoplankton absorption and scattering
relationships (Carder et al., 1989; Gallegos et al., 1990; Ritchie et al., 1994; Schalles
et al., 1998a). Field spectroscopy measurements in turbid inland and coastal Case II
waters have increased substantially in the past decade (Wang et al, 1996; Kahru and
Mitchell, 1998; Dekker et al., 1997; Schalles et al., 1998a, 1998b; Gitelson et al., 2000;
Cunningham et al., 2001; Lahet et al., 2001; Gons et al., 2002; Brando and Dekker, 2003;
Dall 'Olmo et al.,2003). These and similar studies have led to the production of new
chlorophyll prediction algorithms for Case 2 waters. Several Case 2 algorithms are
operational for sensors on aircraft (Kallio et al., 2003) and satellites (Ruddick, 2004).
The chlorophyll algorithms for Case I waters (Gordon and Morel, 1983; O'Reilly
et al., 1998) are universally based on a simple interaction of phytoplankton density with
water - as cell densities increase, chlorophyll and carotenoid absorptions increasingly
dominate at blue wavelengths and generally cause decreased reflectance, whereas cell
scattering increasingly dominates at mid-green wavelengths and causes increased
reflectance (see detailed explanations below). A simple blue to green ratio has a robust
and sensitive relationship to chlorophyll a concentrations in Case I waters. The
relationship becomes less sensitive at higher chlorophyll levels (above ~ 30 µg/l chl a).
The relationship is also sensitive to changes in the ratios of chlorophyll a (hereafter, chl
a) to total algal pigment and total carotenoids (Aiken et al., 1995). Furthermore, this
simple relationship can be highly compromised by the effects of CDOM and/or tripton
particles in turbid, Case II estuarine and near shore waters and even waters well
offshore in regions of large river plumes. For example, the influence of the Orinico
plume can extend across the entire central Caribbean (Muller-Karger et al., 1989).
CDOM material in the Orinoco plume caused significant overestimation of chlorophyll
using Coastal Zone Color Scanner (CZCS) data. In many estuaries, CDOM and tripton
dominate the optical processes of water column components (Bowers et al., 2003). Cole
and Cloern (1987) estimated that phytoplankton accounted for only 5% of light
attenuation in South San Francisco Bay. Biogenous calcite can substantially increase
28
Schalles
Bukata et al., 1995). Although Case 1 conditions normally prevail offshore, they may
also occur: 1) in coastal and near shore areas in arid regions, where shelf geology is
limited and deep water occurs just off the coastline; 2) during droughts resulting in
highly reduced or no runoff; or 3) other instances where currents introduce offshore
water in localized areas lacking significant terrestrial runoff. Obviously, Case 2
conditions intergrade spatially with Case 1 conditions in relation to distance from
coastlines and river plumes. Physical dynamics and seasonality can result in state
changes for a given location. The chlorophyll prediction algorithms for Case 1 and Case
2 waters are often different, and both sets may be required in coastal zones. Note that
certain in situ water column processes (ex. phytoplankton blooms or amplified
scattering by carbonates from coccolithophores or whiting events) can shift the optics
of offshore waters away from true Case 1 conditions.
Most approaches for remote estimation of phytoplankton biomass are based on the
absorption of sunlight by algal pigments in the presence of light scattering by algal cells
and non-algal particles. This interplay of pigment-specific absorption and particle
scattering produces graded responses in the emergent reflectance signals detectable by
radiometer instruments. This chapter will examine the nature of these graded responses
and their utilization in various quantitative and qualitative assessment schemes for
spatial and temporal patterns of phytoplankton abundance.
Coastal, estuarine, and inland water habitats present serious challenges to the
interpretation of diagnostic light signals because of the diversity of optically active
constituents, which partially mask fundamental phytoplankton absorption and scattering
relationships (Carder et al., 1989; Gallegos et al., 1990; Ritchie et al., 1994; Schalles
et al., 1998a). Field spectroscopy measurements in turbid inland and coastal Case II
waters have increased substantially in the past decade (Wang et al, 1996; Kahru and
Mitchell, 1998; Dekker et al., 1997; Schalles et al., 1998a, 1998b; Gitelson et al., 2000;
Cunningham et al., 2001; Lahet et al., 2001; Gons et al., 2002; Brando and Dekker, 2003;
Dall 'Olmo et al.,2003). These and similar studies have led to the production of new
chlorophyll prediction algorithms for Case 2 waters. Several Case 2 algorithms are
operational for sensors on aircraft (Kallio et al., 2003) and satellites (Ruddick, 2004).
The chlorophyll algorithms for Case I waters (Gordon and Morel, 1983; O'Reilly
et al., 1998) are universally based on a simple interaction of phytoplankton density with
water - as cell densities increase, chlorophyll and carotenoid absorptions increasingly
dominate at blue wavelengths and generally cause decreased reflectance, whereas cell
scattering increasingly dominates at mid-green wavelengths and causes increased
reflectance (see detailed explanations below). A simple blue to green ratio has a robust
and sensitive relationship to chlorophyll a concentrations in Case I waters. The
relationship becomes less sensitive at higher chlorophyll levels (above ~ 30 µg/l chl a).
The relationship is also sensitive to changes in the ratios of chlorophyll a (hereafter, chl
a) to total algal pigment and total carotenoids (Aiken et al., 1995). Furthermore, this
simple relationship can be highly compromised by the effects of CDOM and/or tripton
particles in turbid, Case II estuarine and near shore waters and even waters well
offshore in regions of large river plumes. For example, the influence of the Orinico
plume can extend across the entire central Caribbean (Muller-Karger et al., 1989).
CDOM material in the Orinoco plume caused significant overestimation of chlorophyll
using Coastal Zone Color Scanner (CZCS) data. In many estuaries, CDOM and tripton
dominate the optical processes of water column components (Bowers et al., 2003). Cole
and Cloern (1987) estimated that phytoplankton accounted for only 5% of light
attenuation in South San Francisco Bay. Biogenous calcite can substantially increase
28
Schalles