The incentive to acquire ocean-color imag- 
ery from a Satellite platform developed in the 
1960s when aircraft and shipboard studies dem- 
onstrated it would be possible to use satellite- 
acquired data to measure the spectra of sunlight 
reflected from ocean waters. The radiance re- 
flected from the ocean in the visible wavelength 
region (400-700 nm) is related to the concentra- 
tion of chlorophyll and other plant pigments 
present, since chlorophyll is a green pigment and 
the color of the water changes from blue to 
green as the concentration of chlorophyll in- 
creases. lf the concentration of chlorophyll is 
known, the amount of phytoplankton in ocean 
waters can be calculated. Thus, satellite- 
acquired ocean-color data constitute a powerful 
tool for determining the abundance of ocean bio- 
ta on a global scale. As discussed in the follow- 
ing sections, many applications have been devel- 
oped that take advantage of this simple concept 
relating the color of the ocean to the amount of 
phytoplankton it contains. 
The CZCS measured the radiance reflected 
from the sea's surface in the visible and near- 
infrared (VNIR) region and in the thermal-infrared 
(TIR) region. The information from the visible 
wavelengths was used to calculate chlorophyll 
concentration, whereas sea-surface tempera- 
ture was calculated from the information ac- 
quired from the TIR band. Data from the near- 
infrared band (750 nm) was used to correct the 
data acquired in the visible bands for the effects 
of the atmosphere. 
The amount of radiance reflected from the 
ocean is very small compared to the atmospheric 
radiance arriving at the sensor due to Raleigh 
scattering. Since the atmospheric radiance con- 
stitutes as much as 90% of the apparent ocean- 
color signal, it is necessary to correct radiance 
measured by the satellite for the effects of the 
atmosphere. Successful development of accu- 
rate atmospheric-correction algorithms was a 
crucial step in making CZCS data useful in quan- 
titative oceanographic studies, and one of the im- 
portant conclusions drawn from the CZCS experi- 
ence was that the utility of atmospheric-correction 
algorithms is a key consideration in the design of 
any ocean-color sensor. 
From a scientific perspective, acquisition of 
ocean-color data from space in the early 1990s is 
a high-priority goal that has been recognized in 
reports of the National Research Council of the 
National Academy of Sciences. For example, 
satellite-acquired ocean-color measurements are 
key to the success of the Global Ocean Flux Study 
(GOFS), a major component of the National 
Science Foundation's Geosciences Initiative. In 
addition to the U.S. scientific community, scientists 
from Europe, Japan, and from many other coun- 
tries are also interested in participating in GOFS, 
and an international Joint GOFS program for the 
1990s will soon be formalized under the auspices 
of the International Council of Scientific Unions. 
The scientific uses of ocean-color data will be en- 
hanced if the next mission is concurrent with 
NASA and European Space Agency (ESA) altime- 
ter (TOPEX, ERS-1) and scatterometer (NSCAT, 
ERS-1) missions, scheduled for the early 1990s.° 
These satellite-borne instruments will measure glo- 
bal ocean winds and currents, and this information 
will help explain global patterns in the distribution 
of phytoplankton determined from satellite- 
acquired ocean-color measurements. 
Commercial and operational users of ocean- 
color data also are intensely interested in a follow- 
on mission to the CZCS. During the period when 
CZCS data was available, a focused effort was 
mounted by NASA (JPL) and NOAA to develop 
? TOPEX is the Topography Experiment satellite, ERS-1 is the 
ESA's first Earth Remote Sensing satellite, which will carry an 
Active Microwave Instrument (AMI) and an Along-Track 
Scanning Radiometer (ATSR), and NSCAT is the scatterome- 
ter scheduled to fly on the Naval Research Oceanographic 
Satellite System (NROSS) 
