Coastal zone color scanner
First satellite ocean color sensor, operational 1978–1986.
The coastal zone color scanner (CZCS) was a multi-channel scanning radiometer aboard the Nimbus 7 satellite, launched on 24 October 1978 and operational from 2 November 1978. Designed as a one-year proof-of-concept for water remote sensing, it remained in service until 22 June 1986, operating on alternate days due to shared power with another instrument. Its measurements of reflected solar energy in six channels at 800-meter resolution laid the groundwork for subsequent satellite ocean color sensors and international carbon cycle studies.
Quick Facts
- Launched
- 24 October 1978
- Operational start
- 2 November 1978
- End of service
- 22 June 1986
- Resolution
- 800 meters
- Number of channels
- 6
- Manufacturer
- Ball Aerospace & Technologies Corp.
- Bit rate
- 800 kbit/s
Facts from the source article.
Ocean color
The primary product of the CZCS was ocean color imagery, where the color derives from substances in the water such as phytoplankton and inorganic particulates. As phytoplankton concentration increases, ocean color shifts from blue to green; most CZCS images are false colored, with high phytoplankton levels appearing red or orange. These data allow calculation of material concentrations and biological activity in surface waters, providing a global picture of life in the oceans since phytoplankton forms the base of most marine food chains. Over years of recording, scientists observed changes in phytoplankton biomass, including red tide blooms. Phytoplankton also removes carbon dioxide during photosynthesis, linking ocean color to the global carbon cycle. Raw data transmitted at an average bit rate of 800 kbit/s were saved on magnetic tape at the ground station, then sent to the Image Processing Division at Goddard Space Flight Center. Processed data were archived at Goddard and made available worldwide, originally on 38,000 nine-track magnetic tapes and later migrated to optical disc. This archive was among the first to provide a visual preview (browse) of images for ordering data, serving as a model for the Earth Observing System's Distributed Active Archive Centers. After CZCS ceased observing in 1986, a 10-year gap followed until Japan's Ocean Color Temperature Scanner (OCTS) in 1996 and the United States' Sea-viewing Wide Field-of-view Sensor (SeaWiFS) in 1997. Current ocean color instruments include Aqua-MODIS, Copernicus Sentinel 3 Ocean and Land Colour Instrument (OLCI), and NOAA's Visible Infrared Imaging Radiometer Suite (VIIRS) on the Joint Polar Satellite System (JPSS) satellites.
Technical details
The CZCS instrument, built by Ball Aerospace & Technologies Corp., measured reflected solar energy in six channels to sense color from chlorophyll, sediments, and colored dissolved organic matter in coastal waters. It used a rotating plane mirror at 45 degrees to the optic axis of a Cassegrain telescope, scanning 360 degrees but collecting only the 80 degrees centered on nadir for ocean color measurements; the remainder viewed deep space and calibration sources. Incoming radiation was split by a dichroic beam splitter: one stream entered a polychromator, separating five wavelengths onto five silicon detectors, while the other stream went to a cooled mercury cadmium telluride detector for the thermal region (10.5–12.5 micrometers), cooled by a radiative cooler. To avoid sun glint, the scanner mirror could be tilted up to 20 degrees from nadir in 2-degree increments. Spectral bands at 0.443 and 0.670 micrometers centered on chlorophyll absorption bands, while 0.550 micrometers centered on the hinge point of minimum absorption; ratios of these channels closely paralleled surface chlorophyll concentrations. Data were processed with algorithms from field experiments to produce chlorophyll absorption maps. Coastal water and ocean current temperatures were measured at 11.5 micrometers. Additional bands at 0.520 micrometers aided chlorophyll correlation, and 0.750 micrometers sensed surface vegetation. Scan width was 1556 km centered on nadir, with ground resolution of 0.825 km at nadir.
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