17 Some Reflections on Thirty-Five Years of Ocean Color Remote Sensing
291
These issues were addressed by Warren Hovis, the NET leader (Sensor Scientist).
The second was the development of an atmospheric correction algorithm (removal
of the “air light” described by Clarke et al., 1970). The group charged with this
consisted of Austin, Gordon, J.L. Mueller, Sturm, and W.H. Wilson. The third was
the development of in-water algorithms. This group consisted of Anderson, Austin,
Baker, Clark, El-Sayed, R.C. Smith, Wrigley, and Yentsch. Mueller, Smith, and
Wilson were not NET members, but nevertheless directly participated in NET activities and made important contributions to the NET’s algorithm development effort.
It should be emphasized again that, at the time of the NET’s formation, there were
no algorithms available for processing the incoming data.
17.2.1 Bio-Optical Algorithms
The main thrust of the in-water algorithm group was to try to acquire as much data
as possible, in a large variety of waters, relating the water-leaving spectral radiance, L w (λ), or the upwelling spectral radiance (propagating toward the zenith) just
beneath the water surface, L u (λ), to the concentration of chlorophyll a, the total
mass of suspended material, or Total Suspended Matter (TSM), the concentration of
some detrital materials (e.g., phaeophytin a), etc. The NET’s data collection began
after its formation and continued through 1979.
The first time I ever saw anything resembling a bio-optical algorithm was at
a NET meeting in Miami in December 1977. At that time Ray Smith presented
preliminary data that convinced me that one might be able to discern perhaps
5–6 levels of chlorophyll a based on measurement of L w (λ). Prior to that, I
had felt that the CZCS would be more useful in estimating sediment concentrations in coastal areas than in estimating chlorophyll a. From then on, I was a
believer.
As part of the NET’s efforts, there were two significant cruises prior to launch
and three post-launch cruises. The data from both pre- and post-launch cruises were
pooled for the final algorithm. Figure 17.1 provides the station locations of the NET
cruises organized by Dennis Clark as chief scientist. Clearly the focus of algorithm
development by the NET was the waters off the coast of the United States.
Most of these sites would be considered to be Case 1 waters (Morel and Prieur,
1977; Gordon and Morel, 1983); however, some Case 2 waters were observed (off
the Mississippi Delta and off the Chesapeake Bay). The oligotrophic waters of the
Sargasso Sea were included in the data set as well. The principal measurements
on the pre- and post-launch cruises were the spectral water-leaving radiance (made
with an in-water spectral radiometer designed at the SIO Visibility Laboratory) and
the concentrations of chlorophyll a and phaeophytin a measured fluorometrically
(Clark, 1981).
Figure 17.2 provides examples of the spectra obtained and the final “blue-green”
algorithm for estimation of the pigment concentration (C, the sum of the concentrations of chlorophyll a and phaeophytin a). In the final analysis, the data from
Clark’s cruises suggested that, in Case 1 waters, given measurements of L w (λ), it
291
These issues were addressed by Warren Hovis, the NET leader (Sensor Scientist).
The second was the development of an atmospheric correction algorithm (removal
of the “air light” described by Clarke et al., 1970). The group charged with this
consisted of Austin, Gordon, J.L. Mueller, Sturm, and W.H. Wilson. The third was
the development of in-water algorithms. This group consisted of Anderson, Austin,
Baker, Clark, El-Sayed, R.C. Smith, Wrigley, and Yentsch. Mueller, Smith, and
Wilson were not NET members, but nevertheless directly participated in NET activities and made important contributions to the NET’s algorithm development effort.
It should be emphasized again that, at the time of the NET’s formation, there were
no algorithms available for processing the incoming data.
17.2.1 Bio-Optical Algorithms
The main thrust of the in-water algorithm group was to try to acquire as much data
as possible, in a large variety of waters, relating the water-leaving spectral radiance, L w (λ), or the upwelling spectral radiance (propagating toward the zenith) just
beneath the water surface, L u (λ), to the concentration of chlorophyll a, the total
mass of suspended material, or Total Suspended Matter (TSM), the concentration of
some detrital materials (e.g., phaeophytin a), etc. The NET’s data collection began
after its formation and continued through 1979.
The first time I ever saw anything resembling a bio-optical algorithm was at
a NET meeting in Miami in December 1977. At that time Ray Smith presented
preliminary data that convinced me that one might be able to discern perhaps
5–6 levels of chlorophyll a based on measurement of L w (λ). Prior to that, I
had felt that the CZCS would be more useful in estimating sediment concentrations in coastal areas than in estimating chlorophyll a. From then on, I was a
believer.
As part of the NET’s efforts, there were two significant cruises prior to launch
and three post-launch cruises. The data from both pre- and post-launch cruises were
pooled for the final algorithm. Figure 17.1 provides the station locations of the NET
cruises organized by Dennis Clark as chief scientist. Clearly the focus of algorithm
development by the NET was the waters off the coast of the United States.
Most of these sites would be considered to be Case 1 waters (Morel and Prieur,
1977; Gordon and Morel, 1983); however, some Case 2 waters were observed (off
the Mississippi Delta and off the Chesapeake Bay). The oligotrophic waters of the
Sargasso Sea were included in the data set as well. The principal measurements
on the pre- and post-launch cruises were the spectral water-leaving radiance (made
with an in-water spectral radiometer designed at the SIO Visibility Laboratory) and
the concentrations of chlorophyll a and phaeophytin a measured fluorometrically
(Clark, 1981).
Figure 17.2 provides examples of the spectra obtained and the final “blue-green”
algorithm for estimation of the pigment concentration (C, the sum of the concentrations of chlorophyll a and phaeophytin a). In the final analysis, the data from
Clark’s cruises suggested that, in Case 1 waters, given measurements of L w (λ), it