The color of the world's ocean is determined primarily by the abundance of phytoplankton and their associated photosynthetic pigments. As the concentration of phytoplankton pigments increases, ocean color shifts from blue to green. Ocean color may thus be used to derive estimates of plankton abundance and primary productivity.
Designed to detect these small changes in ocean color, NASA's Coastal Zone Color Scanner (CZCS) was flown on the Nimbus-7 satellite launched in October 1978. During its 7 1/2 year operational lifetime (November, 1978 - June, 1986), CZCS acquired nearly 68,000 ocean color images.
Table of Contents:
- What do the data look like?
- What can I do with these data?
- What are the dataset parameters?
- What are the temporal and spatial resolution and coverages?
- What makes this dataset unique?
- What kind of hardware and software do I need?
- What else should I know about these data?
- How can I get these data?
- Glossary of Terms and Acronyms
CZCS data can be very beautiful and useful, as evidenced by the examples in the figures below. These images and others were created by Dr. Gene Carl Feldman at Goddard Space Flight Center.
Figure 1. This composite image of the Global Biosphere was created from all 60,000 CZCS images plus three years of land vegetation data collected by the NOAA Advanced Very High Resolution Radiometer (AVHRR) instrument. It show, for the first time, the patterns of plant life both on land and in the oceans as observed from space. Since this image contains data spanning several years, seasonal variabilities are not evident but regional trends are discernable. It can be seen from this image, for example, that the open oceans themselves are fairly plankton-poor while inland and semi-enclosed seas, coastal areas and the arctic are highly productive. Global data such as these provide crucial input to many global change and carbon flux models.
Figure 2. This global composite of all available CZCS data for the Northern Hemisphere is a subset of the data displayed in Figure 1, shown in a polar projection. The next three figures illustrate how CZCS data can provide valuable information on regional and local conditions.
Figure 3. Zooming in on the North Atlantic, we find this image of the Gulf Stream in the database. This scene clearly shows the front at the north wall of the Gulf Stream and warm and cold rings of entrained water. The plankton-poor waters of the Gulf Stream itself are a deep blue and in sharp contrast to the red, yellow and green coastal areas. The highly productive George's Bank fishing grounds off Halifax are also evident. From this image it can be seen that the warm core ring is rotating clockwise and the cold core ring is rotating counter clockwise. Thus this high resolution ocean color image illustrates several physical and biological processes typical of western boundary currents around the world.
Figure 4. Looking at the same region on a different day, we find this interesting image of the East Coast of the United States. The shallow coastal areas near Cape Cod and Long Island show high levels of productivity while several meso-scale features are seen in the Atlantic Ocean south of Long Island.
Figure 5. Zooming in on the previous image, we are now at the 1 kilometer pixel limit of these data and we can map and track the ocean color anomaly associated with an undersea acid waste dump located off the New Jersey coast.
Figure 6. Important seasonal changes are evident in CZCS data. Here, monsoonal variations in the Indian Ocean give rise to seasonal changes in phytoplankton concentrations. Following a period of pre-monsoon calm (May-June, composite, left), strong summer southwesterly monsoon winds generate upwelling of nutrient-rich waters, leading to the development of bloom conditions (September-October composite, right).
CZCS data have been extensively analyzed since 1986. They are used to calculate plankton primary productivity on a global scale, tracking regional and seasonal variabilities. This information in turn is used as input in various carbon cycle and global change models.
Since plankton populations vary with water conditions such as temperature and pollution content, CZCS data are also being used around the world to track environmental change in various regions. For example, scientists in Florida and Maryland are using these data to determine the changes that occured in the Everglades and the Chesapeake Bay during the period of data collection. Figure 5 above shows how CZCS may be used for environmental pollution monitoring.
Thirdly, CZCS data may be used to study physical oceanographic features since fronts, eddies and upwellings can be clearly visible in these data. The plankton distributions visible in Figures 3 and 4 above are occurring in response to particular oceanographic conditions.
Finally, when future ocean color missions such as SeaWiFS and MODIS become operational, CZCS will help provide a continuous timeseries of baseline information on conditions in coastal areas around the world since 1978.
CZCS was a multi-spectral line scanner developed expressly for the measurement of ocean color. Its sensitive optical detectors measured reflected solar energy in five spectral bands or channels: Channel 1,.433-.453 microns (blue) for chlorophyll absorption, Channel 2, .510-.530 microns (green) for chlorophyll correlation, Channel 3, .540-.560 microns (yellow) for yellow substance or "Gelbstoff" (used to indicate salinity), Channel 4, .660-.680 microns (red) for aerosol absorption, Channel 5 .700-.800 microns (far red) for land and cloud detection. An additional thermal detector measured emitted thermal radiance from the Earth's surface in the infrared, 10.5-12.5 micron range, (Channel 6) for surface temperature calculations.
CZCS data have 8 bit resolution. The scan width is 1556 km centered on nadir and the ground resolution for Level 1 products is 0.825 km at nadir, 1 km nominally.Approximately 66,000 2-minute individual scenes were collected. Level 1 and 1A data products contain at-spacecraft raw radiance counts with calibration and Earth location information appended, but not applied. Most of the Level 1 products were processed further into 4 km,reduced resolution Level 1a products which were in turn processed into Level 2 individual scene products and Level 3 composite products which contain six derived geophysical parameters for each CZCS scene:
- Phytoplankton Pigment Concentrations
- Diffuse Attenuation Coefficient
- Normalized Water-Leaving Radiance @ 440 nm
- Normalized Water-Leaving Radiance @ 520 nm
- Normalized Water-Leaving Radiance @ 550 nm
- Aerosol Radiance @ 670 nm
The products described above are all available in their original formats and resolution. Selected products are also available in heirarchical data format (HDF)The Level 1 products are 1968 x 972 (or fewer) pixels and average 13 MB uncompressed. The Level 1a and Level 2 products are 492 x 243 (or fewer) pixels and average 0.78 MB uncompressed, (1.4 MB for HDF formated versions).
Due to various instrument and power problems, CZCS data collection rates varied greatly over the life of the CZCS mission, as shown in Figure 7 below. The spatial distribution was also non-uniform and highly variable.
Figure 7. Plot of CZCS temporal coverage showing the number of CZCS data files collected per year
CZCS was the first instrument devoted to the measurement of ocean color and flown on a spacecraft. Although other instruments flown on other spacecraft had sensed ocean color, their spectral bands, spatial resolution and dynamic range were optimized for land or meteorological use and had limited sensitivity in this area, whereas in CZCS, every parameter was optimized for use over water to the exclusion of any other type of sensing.
Being satellite mounted, CZCS was able to provide measurements of ocean color over large geographic areas in short periods of time in a way that was not previously possible with other measurement techniques, such as from surface ships, buoys and aircraft. These measurements were used by oceanographers to infer the global distribution of the standing stock of phytoplankton for the first time.
Because of the size of the Level 1 data products (approximately 12 MB each), many users have difficulty storing and manipulating those products on machines with less than 250 MB of disc space.We recommend using the Level 1A , 2 or 3 products if you have limited disc space. However, if you want full resolution, 1 km data, you must use Level 1.
SeaDAS, an extension of the SEAPAK software package developed at Goddard Space Flight Center, is capable of processing CZCS data. It is available from the SeaDAS Web site
CZCS read software programs are available for all of the CZCS data formats. The DAAC also maintains libraries of HDF software and documentation and user-contributed tools. All of these software, data and documentation products are available from the Goddard DAAC. You will find all of them listed or available directly from our Ocean Color Data and Resources Web site.
The CZCS infrared temperature sensor (channel 6,10.5-12.5 microns) failed within the first year of the mission. Sometime in 1981 it was determined that the sensitivity of the other CZCS sensors was degrading with time, in particular channel 4.Sensitivity degradation was persistent and increased during the rest of the mission. In mid 1984 NIMBUS-7 Mission personnel experienced turn-on problems with the CZCS system which were related to power supply problems and the annual lower power summer season of NIMBUS-7. Also spontaneous shut down of the CZCS system began occurring. These also persisted for the rest of the mission. From March 9, 1986 to June, 1986 the CZCS system was given highest priority for the collection of a contemporaneous data set of ocean color. It was turned off in June at the start of the low power season with the intention of turning it back on in December when power conditions would be more favorable. Attempts to reactivate the CZCS system in December 1986 met with failure. The CZCS sensor was officialy declared non-operational on 18 December 1986. (ESRIN, 1995)
A "proof-of-concept" experiment, CZCS showed that satellite ocean color measurements could be reliably used to derive products such as chloroplyll and sediment concentrations and provided justification for the future ocean color missions SeaWiFS and MODIS. The algorithms developed to analyze CZCS data were a considerable step forward from those available earlier, and included corrections for atmospheric backscatter, limb brightness and Gelbstoff. Ground truth campaigns led to empirical correlation of ocean color and biomass. CZCS also showed the need for good radiometric calibration and stability and the necessity of sufficient ground truth data to verify sensor and algorithm performance over time.
The entire CZCS datset has been archived at the Goddard Space Flight Center Distributed Active Archive Center. You may browse and order CZCS data using our CZCS Web-based Browser. If you do not have access to the web, the Ocean Color Dataset Support Team can perform customized searches for you. Simply send us your search criteria at firstname.lastname@example.org or 301-614-5268 (fax). We will contact you to determine the method of shipment you prefer, whether electronic or media.
"CZCS Sensor Guide Document", prepared by the Distributed Active Archive Center, NASA Goddard Space Flight Center, Greenbelt, Maryland, 1995.
"Ocean Color From Space", HTML version prepared by the Distributed Active Archive Center, NASA Goddard Space Flight Center, Greenbelt, Maryland, 1995.
"The Living Ocean: Observing Ocean Color From Space", NASA Publication PAM-554, Goddard Space Flight Center, Greenbelt, Maryland, 1993.
"Coastal zone color scanner 'system calibration': A retrospective examination." R.H. Evans & H.R. Gordon, Journal of Geophysical Research, Vol.99. No. C4, pages 7293-7307, April 15, 1994.
The April 15, 1994 issue of the Journal of Geophysical Research (Volume 99, Number C4) contains a Special Section entitled "Ocean Color From Space: A Coastal Zone Color Scanner Retrospective." Additional CZCS and ocean color references are listed on the GES DISC Ocean Color Website.
AVHRR: Advanced Very High Resolution Radiometer
Calibration: the adjustment or systematic standardization of the output of a quantitative measuring instrument or sensor.
Chlorophyll: any of a group of related green pigments found in photosynthetic organisims.
Contemporaneous: originating, existing or happening during the same period of time.
CZCS: Coastal Zone Color Scanner
Dynamic Range: the range between the maximum and minimum amount of input radiant energy that an instrument can measure.
ESRIN: European Space Research Institute
Gelbstoffe: particulate matter, usually outflow sediment from rivers, which, when suspended in water, gives it a yellowish color. (from German: "yellow stuff").
Infrared Light: electromagnetic radiation having wavelengths longer than red light (7700 angstroms) but less than radio waves (~.1 meter).
MODIS: Moderate Resolution Imaging Spectrometer
Nadir: the point on the Earth directly below an orbiting satellite.
Nimbus: NASA Meteorological Satellites (1 through 7)
NOAA: National Oceanic and Atmospheric Administration.
Photosynthesis: the process by which chlorophyll-containing cells in green plants convert incident light to chemical energy and synthesize organic compounds from inorganic compounds, especially carbohydrates from carbon dioxide and water, with the simultaneous release of oxygen.
Phytoplankton: drifting, often microscopic oceanic plants which conduct the process of photosynthesis.
Primary productivity: the rate at which photosynthesis proceeds.
Radiometer: a device that detects and measures electromagnetic radiation.
SeaWiFS: Sea-viewing Wide Field-of-view Sensor
Spatial Resolution: the size of the smallest object recognizable using the detector.
Spectral Band: a narrow range of the electromagnetic spectrum.
Spectral Response: the relative amplitude of the response of a detector vs. the frequency of incident electromagnetic radiation.
Visible Light: electromagnetic radiation with wavelength in the 3900 to 7700 angstrom range.