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Data Access
CZCS Data
[rule]
Readme Contents
Data Set Overview
Sponsor
Original Archive
Future Updates
The Data
Characteristics
Source
The Files
Format
Name and Directory Information
Companion Software
The Science
Theoretical Basis of Data
Processing Sequence and Algorithms
Scientific Potential of Data
Validation of Data
Contacts
Points of Contact
References
[rule]
Data Set Overview
This data set is a collection of monthly composites of ocean
chlorophyll concentration derived from the Coastal Zone Color
Scanner (CZCS) instrument flown aboard the Nimbus-7 satellite from
October 1978 through June 1986. This concentration provides a
direct measure of the abundance of phytoplankton and its
variability in space and time over most of the world's oceanic
regions. The CZCS data set represents the only source of
satellite-derived, global oceanic biomass productivity, and serves
as an important precursor to the next generation of advanced ocean
color instruments. These include the Sea-Viewing Wide
Field-of-View Sensor (SeaWiFS), launched on August 1, 1997, and
future missions conducted as part of NASA's Earth Science
enterprise.
Sponsor
The production and distribution of this data set are being funded
by NASA's Earth Science enterprise. The data are not copyrighted;
however, we request that when you publish data or results using
these data please acknowledge as follows:
The authors wish to thank the Distributed Active Archive
Center (Code 902.2) at the Goddard Space Flight Center,
Greenbelt, MD, 20771, for producing the data in its
present format and distributing them. The original data
products were produced by the Nimbus Project Office in
collaboration with the NASA Goddard Space Flight Center
Space Data and Computing Division, the NASA GSFC
Laboratory for Oceans, and the University of Miami
Rosenstiel School of Marine and Atmospheric Science.
Goddard's share in these activities was sponsored by
NASA's Earth Science enterprise.
Original Archive
The geophysical data from which this CZCS monthly composite data
set is derived were produced by the Nimbus Project Office in
collaboration with the NASA Goddard Space Flight Center (GSFC)
Space Data and Computing Division, the NASA GSFC Laboratory for
Oceans, and the University of Miami Rosenstiel School of Marine
and Atmospheric Science. This global processing effort was
initiated in 1985 and completed in early 1990. See Feldman et al.
(1989) for a complete description of the processing system used to
generate these products. The level 3 monthly composite data
product, with a spatial resolution of 20 km at the equator, was
used to generate these 1 degree x 1 degree averages. The complete
suite of CZCS-derived geophysical parameters is currently
available from the Distributed Active Archive Center (DAAC) at
NASA GSFC.
Future Updates
The CZCS data set is currently classified as a static data set,
and is unlikely to be reprocessed in the near term due to new data
sources, including the Ocean Color and Temperature Sensor (OCTS),
which operated from August 1996 to May 1997, and SeaWiFS.
The Data
Characteristics
* Parameters: Chlorophyll (pigment) concentration, defined as
the sum of the concentrations of chlorophyll-a and
phaeophytin- a
* Units: mg/m^3
* Typical Range (monthly average):
0.05 mg/m^3 (e.g., tropical non-coastal waters) to 30
mg/m^3 (e.g., coastal waters, North Pacific, North
Atlantic)
* Temporal Coverage: November 1978 - June 1986
* Temporal Resolution: monthly composites, monthly composites
over temporal coverage of data set,
and composites over temporal coverage of data set.
* Spatial Coverage: Global Ocean
* Spatial Resolution: 1 degree x 1 degree
Source
The data source for this data set was the Coastal Zone Color
Scanner (CZCS) flown on Nimbus-7.
Nimbus-7 was launched in October 1978 and was a research-and-
development satellite serving as a stabilized, Earth observing
platform for the testing of advanced systems for sensing and
collecting data in the pollution, oceanographic, and
meteorological disciplines. It provided an opportunity to assess
each instrument's operation in the space environment and to
collect a sizable body of data with the global and seasonal
coverage needed for support of each experiment. The mission also
extended and refined the sounding and atmospheric structure
measurement capabilities demonstrated by experiments on previous
Nimbus observatories.
Nominal orbit parameters for the Nimbus-7 spacecraft are
Launch date: 10/24/78
Orbit: Sun synchronous, near polar
Nominal altitude: 955 km
Inclination: 99.3 degrees
Nodal period: 104 minutes
Nodal Increment: 26.1 degrees
Equatorial crossing time: 11:50 AM (local time)
CZCS, one of eight instruments aboard Nimbus-7, had six spectral
bands (channels); four chiefly for ocean color, each of 20
nanometer (nm) band width and centered at 443, 520, 550, and 670
nanometers. These are referred to as channels 1 through 4,
respectively. Channel 5 sensed reflected solar radiance, but had a
100 nanometer bandwidth centered at 750 nanometers and a dynamic
range that was more suited to land. Channel 6 operated in the 10.5
to 12.5 micrometer region and sensed emitted thermal radiance for
derivation of equivalent black body temperature of the sea
surface. Channel 6 failed within the first year of the mission,
though, and so was not used in the global processing effort.
The following lists the primary purpose of each CZCS channel.
433-453 nm (blue) -- chlorophyll absorption
510-530 nm (green) -- chlorophyll concentration
540-560 nm (yellow) -- Gelbstoffe concentration
660-680 nm (red) -- aerosol absorption
700-800 nm (far red) -- land and cloud detection
CZCS was a cross-track scanning system. The Instrument Field of
View (IFOV) of each detector was .865 mrad, yielding a resolution
of 825 m at the satellite subpoint. The swath covered 1566 km in
width from a maximum scan angle of approximately 40 degrees. Data
were then transmitted to a receiving station at a rate of 800
kbps.
Due to the power demands of the various onboard experiments, the
CZCS sensor was operated on an intermittent schedule. In 1981 it
was determined that the sensitivity of the other CZCS channels 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. Spontaneous shut down of the CZCS system began
occurring as well and 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 1986.
A detailed description of the CZCS instrument and the Nimbus-7
satellite is available on the Goddard Space Flight Center
Worldwide Web site.
The Files
Format
* File Size: 259200 bytes, 64800 data values
* Data Format: IEEE floating point notation
* Headers, trailers and delimiters: none
* Land, water, or ice mask: land and ice (-999.9)
* Fill value: -99.
* Image orientation: North to South
Start position: (179.5W, 89.5N)
End position: (179.5E, 89.5S)
Name and Directory Information
Naming Convention:
The file naming convention for the CZCS data files is
czcs.chlrcn.1nmego.[yymm].ddd (monthly composite)
czcs.chlrcn.1ncego.[mm].ddd (monthly climate)
czcs.chlrcn.1nxego.ddd (data set climate)
where:
czcs = data product designator (CZCS)
chlrcn = parameter name (chlorophyll concentration)
1 = number of levels
n = vertical coordinate, n = not applicable
m or c = temporal period, m = monthly c = climatology
e = horizontal grid resolution, e = 1 x 1 degree
go = spatial coverage, g0 = global ocean
yy = year
mm = month
ddd = file type designation (bin=binary, ctl=GrADS control
file)
Directory Path
/data/inter_disc/biosphere/czcs_color/yyyy
/data/inter_disc/biosphere/czcs_color/climate
where yyyy is the year.
Companion Software
Several software packages have been made available on the CIDC
CD-ROM set. The Grid Analysis and Display System (GrADS) is an
interactive desktop tool that is currently in use worldwide for
the analysis and display of earth science data. GrADS meta-data
files (.ctl) have been supplied for each of the data sets. A GrADS
gui interface has been created for use with the CIDC data. See the
GrADS document for information on how to use the gui interface.
Decompression software for PC and Macintosh platforms have been
supplied for datasets which are compressed on the CIDC CD-ROM set.
For additional information on the decompression software see the
aareadme file in the directory:
software/decompression/
Sample programs in FORTRAN, C and IDL languages have also been
made available to read these data. You may also acquire this
software by accessing the software/read_cidc_sftwr directory on
each of the CIDC CD-ROMs
The Science
Theoretical Basis of Data
The theory of measurement behind remote sensing of oceanic
chlorophyll is based on the fact that the content of water, be it
organic or inorganic particulate matter or dissolved substances,
affects its color. Ocean water, containing very little particulate
matter, scatters light as a Rayleigh scatterer with the well known
deep purple or bluish color of the ocean. As particulate matter is
added to the water, the scattering characteristics are changed and
the color is changed. Photosynthetic pigments as found in
phytoplankton (e.g., chlorophyll-a) preferentially absorb higher
energy blue light but reflect green light through scattering
processes similar to those that result in the "greenness" of land
vegetation. Thus, as the concentration of phytoplankton increases,
ocean color shifts from blue to green. However, some
phytoplankton, such as the various red tide organisms, can change
the water to colors such as red, yellow, blue-green, or mahogany.
Inorganic particulate matter in water, such as that originating
from river discharge, has a different color from organic material,
typically brownish in color but sometimes varying with red. By
sensing the color with very high signal-to-noise ratios, the CZCS
measurements provide a mechanism for analyzing that color for the
content of the water.
The relationship between chlorophyll content of the ocean and the
measured CZCS radiances in the blue and green portion of the
visible electromagnetic spectrum is described further in Ocean
Color from Space
Processing Sequence and Algorithms
The algorithm used for estimating the chlorophyll content of the
ocean from CZCS measurements involves the use of radiance ratios
as described in Gordon et al. (1980) and Gordon et al. (1983).
The general form of the equation is
log(C) = a + b*log[Lw(1)/Lw(2)]
where
C is the chlorophyll concentration (mg/m^3)
a,b are regression coefficients
Lw(1),Lw(2) are the atmospherically corrected radiances for a
pair of CZCS channels
For CZCS chlorophyll processing, these channel pairs are taken to
be
(443, 550 nm), for C < 1.5 mg/m^3
(520, 550 nm), for C > 1.5 mg/m^3
The regression coefficients are different for the two wavelength
pairs. They are also somewhat dependent on the type of
phytoplankton present as well as the amount of suspended
particulates (Viollier and Sturm 1984).
The atmospherically corrected radiances represent the energy
exiting at the ocean-atmosphere interface after penetrating the
surface and being reflected back by inorganic and organic matter
in subsurface layers. These so-called "water-leaving radiances"
are the radiances the satellite would have observed in the absence
of an overlying atmosphere.
Thus, the fundamental quantity of interest, Lw, which contains
information on the chlorophyll content of the ocean, can be
expressed as
Lw(i)=L(i)-La(i)=L(i)-Lr(i)-Lp(i)
where
L(i) is the satellite-measured backscattered radiance at
wavelength i
La(i) is the atmospheric contribution to the radiance at
wavelength i
Lr(i) is the molecular (Rayleigh) scattering contribution to
the radiance at wavelength i
Lp(i) is the atmospheric aerosol scattering contribution to
the radiance at wavelength i
The molecular and aerosol scattering contributions also
incorporate the effect of ozone on the radiances, since the CZCS
channels are located in that part of the visible spectrum
containing the weak Chappuis ozone absorption band. Ozone data
derived from the Total Ozone Mapping Spectrometer (TOMS) aboard
the same satellite is used for this purpose. The atmospheric
contribution to the satellite- observed radiances is on the order
of 80% to 90% of the signal. Thus an accurate means of determining
this contribution is required to extract meaningful information on
ocean composition from the observed radiances. The procedure for
performing the atmospheric correction of CZCS radiances can be
found in more detail in Williams et al. (1985).
Once the chlorophyll estimates have been derived from individual
CZCS measurements, the resultant data are then binned to a fixed,
linear latitude-longitude array of dimension 1024 lines by 2048
pixels, corresponding to a spatial resolution of about 18 km at
the equator. All of the individual chlorophyll values falling
within each pixel area are averaged together over four time
scales: daily, 5-day, monthly, and annually. As part of the
averaging process, the input values are first screened for cloud
and land contamination, the presence of Sun glint, abnormal values
of water-leaving radiances, and low solar angle, among others.
After averaging, the composite chlorophyll concentrations are
converted to 8-bit values using appropriate scale and offset
coefficients. Because of the poor and highly variable temporal and
spatial sampling the level 3 CZCS averages are generally referred
here to as composites instead of averages. The resulting Level 3
Composite data product is one of the official CZCS archive
products located in the Goddard DAAC, and is the data set from
which the monthly 1 degree x 1 degree chlorophyll product is
derived.
A more detailed description of the CZCS data processing system is
described in the appropriate sections of Satellite Ocean Color
background document.
The following steps were performed by the Goddard DAAC on the
original Level 3 Monthly Composite data to create this data set.
For each month and each 1 degree x 1 degree latitude-longitude
grid box
1. All scaled (8-bit) chlorophyll values in the 2048 x 1024
input array located within a circular area circumscribing the
given grid box were arithmetically averaged together to
produce the composite value of scaled chlorophyll for that
grid box.
2. All resulting composite values in the 360 x 180 monthly array
were then converted from their byte values (1 to 245) to the
corresponding floating point chlorophyll values using the
following transformation equation:
Log(chlorophyll) = .012*(byte value) - 1.4
3. Pixel values of 0 (no data) were set to -99.
4. Pixel values of 246-251 were not used in the original file.
5. Pixel values of 253 (land), 254 (ice), and 255 (continental
outline) were all set to -999.9.
6. The resulting remapped chlorophyll data (with embedded
land/ice mask) were output to a flat IEEE binary file.
7. Twelve monthly climatology (each month is a composite of the
entire temporal for that month) files were derived from the
monthly composite chlorophyll data.
8. One composite climatology file (over temporal coverage of
data set) was produced from the twelve monthly climatology
files.
Scientific Potential of Data
CZCS data provide the only source of global measurements related
to ocean biological productivity and its regional and temporal
variability over both short- and long-time scales. It is an
important source of information for a wide range of studies
pertinent not only to ocean biology but also to physical
oceanography and atmosphere and ocean interactions. Some
applications of the data include
* studies of phytoplankton dynamics (e.g., phytoplankton
blooms) as a function of nutrient availability and the
seasonal variation of solar energy required for
photosynthesis (Brock et al. 1992, Wroblewski et al. 1988)
* correlation studies relating the enhancement or suppression
of primary production to localized, transient phenomena such
as coastal upwelling or large-scale cyclic phenomena such as
El Niño (McClain et al. 1984, Feldman et al. 1984)
* use of the imagery to locate fronts, eddies coastal currents,
and other circulation features (Deuser et al. 1988)
* understanding of the role of marine biomass in the global
carbon cycle and how it may relate to environmental change
and influence global climate (Moore and Bolin 1986, Sundquist
and Broecker (eds) 1985)
In addition, the phytoplankton population as measured by
corresponding oceanic chlorophyll content can act as a natural
tracer for the presence of pollutants that suppress plant growth,
or for subtle changes in the environment (e.g., sea surface
temperature or salinity) that may affect phytoplankton growth.
Validation of Data
Not available at this revision.
Contacts
Points of Contact
For information about or assistance in using any DAAC data,
contact
EOS Distributed Active Archive Center (DAAC)
Code 902.2
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771
Internet: daacuso@daac.gsfc.nasa.gov
301-614-5224 (voice)
301-614-5268 (fax)
References
Brock, J.C., and C.R. McClain. 1992. Interannual variability in
phytoplankton blooms observed in the northwestern Arabian Sea
during the southwest Monsoon. J. Geophys. Res., 97(C1):733- 750.
Deuser, W.G., F.E. Muller-Karger, and C. Hemleben. 1988. Temporal
variations of particle fluxes in the deep subtropical and tropical
North Atlantic: Eulerian versus LaGrangian effects. J. Geophys.
Res., 93(C6):6857-6862.
Feldman, G., D. Clark, and D. Halpern. 1984. Satellite color
observations of the phytoplankton distribution in the eastern
equatorial Pacific during the 1982-1983 El Niño . Science,
226(4678):1069-1071.
Gordon, H.R., D.K. Clark, J.L. Muller, and W.A. Hovis. 1980.
Phytoplankton pigments from the Nimbus-7 coastal zone color
scanner: Comparisons with surface measurements. Science,
210:63-66.
Gordon, H.R., D.K. Clark, J.W. Brown, O.B. Brown, R.H. Evans, and
W.W. Broenkow. 1983. Phytoplankton pigment concentrations in the
Middle Atlantic Bight: Comparison of ship determinations and CZCS
estimates. Appl. Opt., 22(1):20-36.
McClain, C.R., L.J. Pietrafesa, J.A. Yoder. 1984. Observations of
Gulf stream-induced and wind-driven upwelling in the Georgia Bight
using ocean color and infra-red imagery. J. Geophys. Res.,
89:3705-3723.
Moore, B., and B. Bolin. 1986. The oceans, carbon dioxide, and
global climate change. Oceanus, 29(4):9-15.
Sundquist, E.T., and W.S. Broecker (eds). 1985. The Carbon Cycle
and Atmospheric CO2 Natural Variations Archean to Present,
American Geophysical Union, Washington, DC, 627 pp.
Viollier, M., and B. Sturm. 1984. CZCS data analysis in turbid
coastal water. J. Geophys. Res., 89:4977-4985.
Williams, S.P., E.F. Szajna, and W.A. Hovis. 1985. Nimbus-7
Coastal Zone Color Scanner (CZCS) Level 2 Data Product User's
Guide, NASA Tech. Mem. 86202, Washington, DC.
Wroblewski, J.S., J.L. Sarmiento, and G.R. Flierl. 1988. An ocean
basin scale model of plankton dynamics in the North Atlantic 1.
Solutions for the climatological oceanographic conditions in May.
Global Biogeochem. Cycles, 2(3):199-218.
------------------------------------------------------------------------
[NASA] [GSFC] [Goddard DAAC] [cidc site]
NASA Goddard GDAAC CIDC
Last update:Fri Aug 22 18:12:39 EDT 1997
Page Author: Page Author: George Serafino -- serafino@daac.gsfc.nasa.gov
Web Curator: Daniel Ziskin -- ziskin@daac.gsfc.nasa.gov
NASA official: Paul Chan, DAAC Manager -- chan@daac.gsfc.nasa.gov