17 Some Reflections on Thirty-Five Years of Ocean Color Remote Sensing
295
L w (443/L w (550), with my atmospheric correction ideas to try to estimate the accuracy with which C could be estimated. This work led to three important conclusions,
if the assumptions underlying the correction algorithm were correct. First, knowledge of the value of the parameter α is much more important than the actual aerosol
concentration, i.e., given knowledge of α the error in C is only a weak function of
the aerosol optical thickness. Second, for low values of C, e.g., ≤ 0.2 mg/m
3 , accurate values can be retrieved as long as α is not overestimated. Third, as C increases,
the accuracy with which α must be known also increases; however, accuracies in
C considerably better than ±(1/4) log 10 (C), for C ≤ 1.0 mg/m
3 are possible with
only a coarse estimate of α. This work was reported at the IUCRM Colloquium on
“Passive Radiometry of the Ocean” at the Institute of Ocean Sciences, Patricia Bay
near Victoria, BC, Canada from June 14 to 21, 1978 (Gordon and Clark, 1980).
The IUCRM Colloquium was the precursor to “Oceanography from Space”
Venice 1980. More important, it also provided one of the first opportunities for those
interested in water color to exchange ideas. Most at the meeting understood that the
CZCS was not optimally designed for ocean color. At the “Working Group on Water
Color” session at the end of the meeting, several proposals were made concerning
the specifications of a dedicated ocean color instrument (a CZCS follow-on sensor)
with due respect for the requirements of atmospheric correction and of the absorption and scattering properties of water constituents. These are summarized in Table
II in Morel and Gordon (1980).
With the exception of the “low priority” bands at 610 and 640 nm and the absence
of a band near 670 nm, the specifications closely resemble the final configurations
of SeaWIFS and MODIS. In addition, the Working Group also recommended that a
program be established to assess the “spatial and temporal variation of the phytoplankton pigment concentration on a global scale. This Global Assessment of
Phytoplankton Pigments (GAPP) would consist of utilizing the CZCS to prepare
monthly or bi-monthly worldwide maps of the pigment concentration and hence
provide an estimate of the total phytoplanktonic biomass of the world oceans as
well as the spatial and temporal variation of the primary productivity” (Morel and
Gordon, 1980). Thus, even before launch, when many considered CZCS to be a
boondoggle being carried out by lunatics, those knowledgeable in oceanic optics
could see important improvements that could be made in the system, and important
applications of the ocean color data.
17.4 CZCS Launch, Initial Imagery and Validation Cruises
CZCS was launched in October 1978, and the first image I saw was from Orbit
116 (November 1, 1978). Because there was a history of space-borne instruments
failing soon after launch, every effort was made to try to validate the CZCS data
and the algorithms as soon after launch as possible. Thus, the NET organized two
cruises in the Gulf of Mexico to commence as soon as imagery was available. R.
Austin and C. Yentsch organized a cruise aboard the NOAA Vessel Researcher, with
Team members R. Austin, C. Yentsch and S. El-Sayed participating. Dennis Clark
295
L w (443/L w (550), with my atmospheric correction ideas to try to estimate the accuracy with which C could be estimated. This work led to three important conclusions,
if the assumptions underlying the correction algorithm were correct. First, knowledge of the value of the parameter α is much more important than the actual aerosol
concentration, i.e., given knowledge of α the error in C is only a weak function of
the aerosol optical thickness. Second, for low values of C, e.g., ≤ 0.2 mg/m
3 , accurate values can be retrieved as long as α is not overestimated. Third, as C increases,
the accuracy with which α must be known also increases; however, accuracies in
C considerably better than ±(1/4) log 10 (C), for C ≤ 1.0 mg/m
3 are possible with
only a coarse estimate of α. This work was reported at the IUCRM Colloquium on
“Passive Radiometry of the Ocean” at the Institute of Ocean Sciences, Patricia Bay
near Victoria, BC, Canada from June 14 to 21, 1978 (Gordon and Clark, 1980).
The IUCRM Colloquium was the precursor to “Oceanography from Space”
Venice 1980. More important, it also provided one of the first opportunities for those
interested in water color to exchange ideas. Most at the meeting understood that the
CZCS was not optimally designed for ocean color. At the “Working Group on Water
Color” session at the end of the meeting, several proposals were made concerning
the specifications of a dedicated ocean color instrument (a CZCS follow-on sensor)
with due respect for the requirements of atmospheric correction and of the absorption and scattering properties of water constituents. These are summarized in Table
II in Morel and Gordon (1980).
With the exception of the “low priority” bands at 610 and 640 nm and the absence
of a band near 670 nm, the specifications closely resemble the final configurations
of SeaWIFS and MODIS. In addition, the Working Group also recommended that a
program be established to assess the “spatial and temporal variation of the phytoplankton pigment concentration on a global scale. This Global Assessment of
Phytoplankton Pigments (GAPP) would consist of utilizing the CZCS to prepare
monthly or bi-monthly worldwide maps of the pigment concentration and hence
provide an estimate of the total phytoplanktonic biomass of the world oceans as
well as the spatial and temporal variation of the primary productivity” (Morel and
Gordon, 1980). Thus, even before launch, when many considered CZCS to be a
boondoggle being carried out by lunatics, those knowledgeable in oceanic optics
could see important improvements that could be made in the system, and important
applications of the ocean color data.
17.4 CZCS Launch, Initial Imagery and Validation Cruises
CZCS was launched in October 1978, and the first image I saw was from Orbit
116 (November 1, 1978). Because there was a history of space-borne instruments
failing soon after launch, every effort was made to try to validate the CZCS data
and the algorithms as soon after launch as possible. Thus, the NET organized two
cruises in the Gulf of Mexico to commence as soon as imagery was available. R.
Austin and C. Yentsch organized a cruise aboard the NOAA Vessel Researcher, with
Team members R. Austin, C. Yentsch and S. El-Sayed participating. Dennis Clark