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Coastal Zone Color Scanner (CZCS) Data Set Readme
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Access for
Coastal Zone Color Scanner (CZCS) Data
Level 1a
Level 2
Level 3
Software
Contents of the
Coastal Zone Color Scanner (CZCS) Data Set
Readme
- Data Set Information
Satellite and Instrument Information
Data Set Organization
Data Access Information
- Getting Data
Reading Tapes
Reading the CZCS Data Files
Processing/Analysis Software Packages
- References
Points of Contact
Data Set Updates
Appendix: Differences between CRTT Tape and CRTT
Archive Formats
README for the Nimbus-7 Coastal Zone Color Scanner (CZCS) Data
Set
Production and distribution of this ocean color data set
are funded by NASA's Mission To Planet Earth (MTPE) Program. The data
are not copyrighted; however, we request that when you publish data or
research results utilizing these data, please acknowledge as follows:
The authors would like to thank the Coastal Zone
Color Scanner (CZCS)(Project (Code 970) and the Distributed Active
Archive Center (Code 610.2) at the Goddard Space Flight Center, Greenbelt,
MD 20771 for the production and distribution of these data,
respectively. These activities are sponsored by NASA's Mission to
Planet Earth Program.
The CZCS data set is a global ocean color data set derived
from satellite observations. In most oceanic regions, the color of the
ocean is primarily determined by the abundance of phytoplankton and
their associated photosynthetic pigments. As phytoplankton pigment
concentration increases, ocean color gradually shifts from blue to
green. NASA developed the CZCS to utilize this characteristic of ocean
color for the observation of pigment distribution in the oceans. The
CZCS was launched on the Nimbus-7 satellite in October 1978. During the
91 months of its operation (October 1978 - June 1986), CZCS acquired
nearly 68,000 images, each covering up to 2 million square kilometers of
ocean surface.
Nominal orbit parameters for the Nimbus-7 spacecraft
are:
| Launch
date | 10/24/78 | | Orbit | Sun-synchronous, near polar | | Nominal Altitude | 955
km | | Inclination | 104.9
° | | Nodal
Period | 104 minutes |
| Equator Crossing Time | 12:00 noon (ascending) | | Nodal Increment | 26.1
° |
CZCS, one of eight instruments aboard Nimbus-7, had six spectral
bands (or channels); four used primarily for ocean color (backscattered
solar radiation), each channel of 20 nanometer bandwidth, centered at
443, 520, 550, and 670 nm. These are referred to as channels 1 through
4, respectively. Channel 5 sensed reflected solar radiance, but had a
100 nm bandwidth centered at 750 nm and a dynamic range 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. (Channel 6 failed within the first year of the mission, and
so was not used in the global processing effort.) Channels 1-4 were
preset to view water only and saturated when the IFOV was over most
types of land surfaces, or clouds.
Due to the power demands of the various on-board experiments, the
CZCS sensor was operated on an intermittent schedule. In 1981, it was
determined that the sensitivities of the CZCS channels were degrading
with time, channel 4 in particular. Sensitivity degradation was
persistent and increased during the rest of the mission. In mid-1984,
Nimbus-7 mission personnel experienced turn-on anomalies with the CZCS
system, which were related to power supply problems. Spontaneous
shutdown 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. Later attempts to turn the system back on were unsuccessful.
The five CZCS data products archived at the Goddard Space
Flight Center Distributed Active Archive Center (Goddard DAAC) include:
Level 1, Level 1a, Level 2, Level 3 PST (Postage Stamp) images, and
Level 3 Composite images. Level 1 and 1a data contain calibrated
radiances and earth location information for each CZCS scene (a maximum
of 2 minutes of data). Level 1 data are at full Local Area Coverage
(LAC) resolution (1 km) and level 1a data are subsampled (every 4th
pixel, every 4th line) providing 4 km Global Area Coverage (GAC)
resolution. Level 2 data were derived from the level 1a data, and
contain six derived geophysical parameters for each CZCS scene. The
level 3 PSTs are earth-gridded (binned) composites of the derived
geophysical parameters, along with compositing statistics, at various
temporal resolutions (daily, 5-day weekly, and monthly). They contain
the sums of the values, the sums of the squares of the values, and the
number of valid samples in each composite bin. The level 3 data are
binned to a fixed, linear latitude-longitude (equal angle) grid of
dimension 1024 (latitude) x 2048 (longitude) with ~18.5 km resolution at
the equator. The level 3 Composites are the means of the level 3 PST
products represented as 8-bit raster images.
The following table summarizes information about the CZCS data
products:
| Level |
Parameters | Units | Resolution | File Ext. |
|---|
| 1 | Calibrated
radiances | mW/(cm2.sr.µm) | 1km x 1km | .ni7 |
| 1a | Calibrated
radiances | mW/(cm2.sr.µm) | 4km x 4km | .ni7-4 |
| 2 | Pigment Concentration | mg/m3 | 4km x 4km | .fm4 | | Diffuse Attenuation
Coefficient | none | 4km x 4km | Normalized
water-leaving radiance
@ 443 nm | mW/(cm2.sr.µm) | 4km x 4km | Normalized
water-leaving radiance
@ 520 nm | mW/(cm2.sr.µm) | 4km x 4km | Normalized
water-leaving radiance
@ 550 nm | mW/(cm2.sr.µm) | 4km x 4km | | Aerosol
radiance @ 670 nm | mW/(cm2.sr.µm) | 4km x 4km |
| 3 | Same as for level 2,
plus the
standard deviation of each,
the number of valid level 2
pixels,
and the number of days | ~18.5 km
@ equator | .dailypst |
| .weeklypst |
| .monthlypst |
| .monthlycomp |
Normalized water-leaving radiance is the radiance emanating from the
water surface with no atmospheric attenuation and the sun located at
zenith. These radiances are calculated at 443 nm, 520 nm, and 550 nm.
Aerosol radiance is the radiance due to aerosols alone, and has been
calculated for the 670 nm wavelength for use in atmospheric correction.
Pigment concentration is the sum of the chlorophyll a and
phaeophytin concentrations. The diffuse attenuation coefficient defines
the exponential reduction of radiation for either upwelling or
downwelling radiance or irradiance.
Getting Data
Level 1a GAC, level 2 GAC, and level 3 monthly composite data (in
Hierarchical Data Format (HDF), described below) are
available by anonymous ftp from:
ftp://disc.gsfc.nasa.gov/data/czcs/
Level 1a data, categorized annually, is found in the directory
http://disc.sci.gsfc.nasa.gov/data/czcs/level_1a/gac_data. CZCS Level 2 data, also categorized
annually, is found in either http://disc.sci.gsfc.nasa.gov/data/czcs/level_2/gac_data or
http://disc.sci.gsfc.nasa.gov/data/czcs/level_2/brs_data. The The gac_data files comprise all of the
level 2 derived geophysical products, while the brs_data files are
raster images of pigment concentration. This data access method does
not provide any geographical information by which CZCS scenes for
particular regions of interest may be located. It is, however, the
fastest way to obtain data files if the CZCS filename is known.
In order to find CZCS level 1, level 1a, and level 2 data for a
specified region, the tool to use is the CZCS data browser, accessible
through the World Wide Web. To initiate a browse session, go the
following URL:
http://disc.sci.gsfc.nasa.gov/BRS_SRVR/czcsbrs_main.html
The CZCS Browser allows a user to specify location and time criteria,
which the browser uses to select CZCS scenes meeting the given
specifications. Location criteria may be entered as latitude/longitude
coordinates, or a search area can be designated using an interactive
map. Time criteria are specified using the browser interface. The
browser returns all scenes with the proper time criteria and some
portion contained in the search region. Browse images (pigment
concentration) can be viewed for possible selection, and the user then
specifies data type, data format, and transmission method for DAAC order
processing. (Note: browse images, which are generated as on-the-fly
GIF images, can also be saved directly during a browser session.)
The following describes another method for obtaining CZCS and other
types of data from the DAAC. [In general, the methods described above
are now the preferred ways of obtaining CZCS data.]
GSFC DAAC online Information Management System (IMS) provides online
search and order capabilities for several Earth science data sets. The
system is open to the public, but access to certain restricted products
requires special authorization. Follow the instructions below to
connect to the GSFC DAAC computer via TCP/IP protocol (Internet).
1) Type the following command from your computer connected to the
Internet:
telnet disc.gsfc.nasa.gov
If the message HOST UNKNOWN appears, use the direct TCP/IP address
192.107.190.139. You should receive the message "Connected to
disc.gsfc.nasa.gov".
2) After you have connected to the Goddard DAAC system, you will be
prompted to log onto the system. Enter the following user name and
password
Username: daacims Password: gsfcdaac A
series of informational messages will be displayed, followed by a user
registration screen and the actual data system menu screens. For more
information on the Goddard DAAC system capabilities and supported data
sets, contact our User Services Office at:
User Services Office
Goddard Distributed Active Archive Center
NASA Goddard Space Flight Center, Code 610.2
Greenbelt, MD 20771
phone: 301-614-5224
fax: 301-614-5268
email: daacuso@disc.gsfc.nasa.gov
Reading Tapes
If you obtained the data
by FTP, please go to the section Reading the CZCS Data
Files.
Data are available on 4 mm (DAT), high or low density 8 mm (Exabyte),
and 6250 ~ bpi 9-track tapes. Tapes are created with UNIX utilities
"dd" and "tar" on a Silicon Graphics 440 system. The no-swap device and
a block size of 63.5 KB are used, which translates to a blocking factor
of 127. Tapes may be requested in "dd" or "tar" file format. By default
the data are archived and distributed in compressed format; however,
they are available in uncompressed format by special request. Each tape
distributed by the Goddard DAAC contains printed paper labels with the
names of the files it contains in the order they were written. Files
are compressed using the standard UNIX "compress" command, indicated by
a ".Z" appended to the data file name.
The same utility that was used to create the tape, "dd" or "tar,"
must be used to access the data. If compressed files are requested, the
data are compressed before the "dd" or "tar" utility is executed.
Therefore, compressed data should be uncompressed after copying it from
tape to local disk.
To read a "tar" format tape on a computer with a UNIX operating
system, use the command:
tar -xvbf <filename> 127
where xvbf are tar command key arguments as follows:
x indicates that the data are to be read from tape
v requests
verbose output; i.e., processed file names will be listed
b states
that a blocking factor is specified
f states that an archive name
is specified.
The fields in < > are system specific and may
specify a device, such as a tape drive, or a file directory. The
specific parameters depend on your local workstation configuration
(e.g., this will be "/dev/8mm1nr" if you read the tape off the 8mm1 tape
drive on the DAAC computer with the "no rewind" option).
127 is the
blocking factor.
To read a tar format tape on a VAX computer with a VMS operating
system, you will need vmstar public domain software. Use the command
mount /FOREIGN/RECORD=512/BLOCK=65024 <tape drive>
vmstar xvf <tape drive>
To get vmstar, log into the Western Kentucky University anonymous FTP
server:
ftp://ftp.wku.edu/vms/fileserv/VMSTAR.ZIP
The file is compressed inthe zip format. Follow the instructions for
installation and unpacking in the README files.
To read a "dd" format tape on a computer with a UNIX operating
system, use the command
dd if=<dev> of=<filename> bs=65024
where if=<dev> specifies the tape drive with "no rewind"
option (e.g., if=/dev/8mm1nr for the DAAC computer.)
of=<filename> specifies the desired output file name
bs=65024
indicates the block size in bytes
To read "dd" format tapes on a VAX computer with a VMS operating
system, simply use the "copy" command. Public domain software, lzw, is
available to read the UNIX compressed data format on VAX VMS. To read
compressed data files, you must first use "vmstar" or the "copy" command
to unload the data from tape. Then issue the "lzw" command.
Reading the CZCS Data Files
The
following table lists the format and available processing software for
the CZCS data products:
| Data |
Format | Software Package |
|---|
| Level 1 | CRTT Archive | SEAPAK/DSP | | Level 1a
| HDF/DSP | SeaDAS/SEAPAK/DSP | | Level
2 | HDF/DSP |
SeaDAS/SEAPAK/DSP | | Level 3 PST | DSP |
SEAPAK/DSP | | Level 3 Composites* | DSP |
SEAPAK/DSP |
* Many of these images are also available as flat data files (i.e.
without the DSP header, metadata and compositing statistics). In
addition, there are several seasonal, climatological and regional
composites available as flat data files. See Section 4.3.3 below for
more information on this file set.
The formats of each of the data products are briefly summarized
below.
CRTT Format:
The original level 1 CZCS data was produced and stored
on 9-track magnetic volumes in CRTT Tape format. See the Nimbus-7
Coastal Zone Color Scanner Level 1 Data Product User's Guide for a
complete description of the CRTT Tape format. This Guide may be ordered
from the Goddard DAAC User Support Office (see section 6). The CRTT Tape
format has been slightly modified to produce the so-called CRTT Archive
format. The CZCS level 1 data that the Goddard DAAC archives and
distributes is in the CRTT Archive format. See the Appendix at the end
of this README for a complete description of the differences between the
CRTT Tape and Archive formats.
For processing information see the Processing/Analysis
Software Packages section.
DSP Format:
Level 1a, level 2, level 3 PST, and level 3 composite
images are available in DSP format. DSP is a user-interactive satellite
data analysis package that was developed at the Rosenstiel School of
Marine and Atmospheric Sciences (RSMAS) at the University of Miami.
DSP operates on either DEC-VAX or Unix Workstation computers. The
primary application of this package is for the processing and
interpretation of CZCS and Advanced Very High Resolution Radiometer
(AVHRR) data. DSP images can be converted to the SEAPAK format using the
SEAPAK package (see description below). Data from DAAC DSP files can be
extracted and read using publically available software packages from the
DAAC.
For more information on the DSP format, please contact the RSMAS at the University of
Miami (Dr. Robert Evans.)
Flat Binary File Format:
Several additional time/space composites (climatological,
seasonal, annual, regional) also exist as single parameter images. These
are available as flat files, without any headers, metadata or
compositing statistics. These include full resolution global 2048
(longitude) x 1024 (latitude) pixel images as well as reduced resolution
global 512 x 512 pixel images subsampled from the full resolution global
images with a 4 x 2 reduction factor. The regional images are 512 x 512
pixel images at full resolution of the global product. They are simply a
sector of the full global 2048 x 1024 composite grid. They are composed
of 512 records, each record 512 eight bit bytes and each pixel value
given by a count ranging between 0 and 255. The region, temporal
coverage and parameter are clearly indicated by the naming convention.
More information on these flat image files may be found in the file
CURRENT_IMAGE_INFO.TXT which is located with the files at the anonymous
ftp site or available from the Goddard DAAC.
These files are available via anonymous ftp at:
ftp://savaii.gsfc.nasa.gov/data/
World Wide Web access to these data, along with ASCII data and browse
images, is available from the SeaWiFS Project. SeaWiFS is the acronym
for the Sea-viewing Wide Field-of-view Sensor, NASA's next generation
ocean color instrument.
HDF:
HDF is the standard data format of the entire Goddard
EOSDIS Version 0 (V0) and the SeaWiFS Project. HDF was developed by the
National Center for Supercomputing Applications (NCSA) Software
Development Group. Additional explanation of HDF can be found at the
HDF Web site. HDF provides several different "data models" which can be
used to store data products. The data models currently provided by HDF
included Scientific Data Sets (SDS), Raster Image Sets (RIS), Vdatas,
and Vgroups. Level 2 HDF browse files may be viewed and ordered using
the online Web browser (http://disc.sci.gsfc.nasa.gov/data/dataset/CZCS/),
and level 1a and level 2 data may be obtained via anonymous ftp from:
ftp://disc.gsfc.nasa.gov/data/czcs/
Level 1a data, categorized annually, is found in the directory
http://disc.sci.gsfc.nasa.gov/data/czcs/level_1a/gac_data. CZCS Level 2 data, also categorized
annually, is found in either http://disc.sci.gsfc.nasa.gov/data/czcs/level_2/gac_data or
http://disc.sci.gsfc.nasa.gov/data/czcs/level_2/brs_data. The gac_data is for all of the Level 2
derived products, while the brs_data files are raster images of pigment
concentration.
The appropriate software for the processing of CZCS HDF files is
SeaDAS, which was developed for the analysis of SeaWiFS HDF data.
Processing/Analysis Software Packages
CZCS data levels 1, 2, and 3 can be analyzed with either SEAPAK or
DSP, while level 1a can be analyzed and processed with DSP. Level 1 can
be processed to level 2 with either SEAPAK or DSP, while level 2 can
only be processed to level 3 with DSP. SeaDAS can be used to examine
(but not process) Level 1a and Level 2 CZCS HDF files.
SEAPAK Software System:
SEAPAK is an interactive satellite data analysis package
that was developed at the NASA/Goddard Space Flight Center for the
processing and interpretation of CZCS and AVHRR data. Both UNIX and
PC-AT class platforms are supported, although the SEAPAK UNIX package is
a subset of the PC version. The UNIX version works only on Silicon
Graphics machines, although there are plans to port to SUN platforms
next. The entire UNIX SEAPAK package (the 23 files named
seapak_alpha.tar.Zaa through seapak_alpha.tar.Zaw) and a file named
README.SEAPAK.PLEASE with installation instructions are in the current
remote directory. Individual pieces of the package (documentation,
executables, data, etc.) are in the seapak directory. The ANNOUNCEMENT
file has further instructions and more detailed information on the
contents of the software package. The README.doc should also be
consulted for setup and usage instructions. The PC version is in the
pcseapak/version4 directory. See the README.doc file for installation
instructions.
The UNIX and PC versions of SEAPAK are available via anonymous ftp:
UNIX: ftp://shark.gsfc.nasa.gov/seapak/
MS-DOS: ftp://shark.gsfc.nasa.gov/pcseapak/
There are a few stand-alone VAX executables available which perform a
limited number of functions, primarily reformatting files into SEAPAK
image format. These are available via anonymous ftp from:
ftp://manono.gsfc.nasa.gov/programs/seapak/
Details concerning the stand-alone DSP routines may be found in the
file czcs_products.text
and in help files accompanying the routines which are indicated by their
.hlp extensions.
DSP Software System:
DSP is a software system supporting oceanographic
satellite data and image processing developed by the Rosenstiel School
of Marine and Atmospheric Sciences (RSMAS) at the University of Miami.
It operates on either DEC-VAX or UNIX Workstation computers. Some
stand-alone routines for DEC-VAX machines (VAX executables) for the
analysis and manipulation of CZCS images are available via anonymous ftp
from:
ftp://manono.gsfc.nasa.gov/programs/miami/
Details concerning the stand-alone DSP routines may be found in the
file czcs_products.text
and in help files accompanying the routines which are indicated by their
.hlp extensions.
SeaDAS Software System:
SeaDAS is a comprehensive image analysis package for
processing, displaying, analyzing, and quality control of all SeaWiFS
(Sea-viewing Wide Field-of vew Sensor) data products (L0, L1A, L2, L3
Binned, L3 SMI, L1A-, L2-, L3-Browse) and ancillary data (Wind,
Pressure, Humidity and Ozone) from NMC (National Meteorological Center
and TOVS (TIROS Operational Vertical Sounder). All SeaDAS source code is
freely available for download via FTP. Note that the use of SeaDAS
requires an IDL license.
SeaDAS may be operated on either an SGI Indigo2 or SUN Sparc 10, or
larger systems. Recommended minimum system requirements are:
Memory: 96 MB
Disk: 3 GB
Tape Drive: 4MM(DAT) or 8mm Exabyte
Display: 19" Console or X-terminal, 1280x1024 resolution, 8-bit, 256
colors.
The SeaDAS software requirements consist of:
Operating System:
IRIX 5.3 (SGI) or Solaris 2.4 (SUN)
Languages: C (SGI V3.19, SUN V
3.0.1), FORTRAN(SGI V 4.0.2, SUN V 3.0.1), IDL 4.0.1
Software
Libraries: HDF 3.3r4p4 (included in SeaDAS).
SeaDAS is available for download via anonymous FTP from:
ftp://shark.gsfc.nasa.gov/seadas/
June 1997 update: The new version of SeaDAS (SeaDAS 3.0) is now
available via FTP and offers expanded image analysis capabilities.
You may request the following files and documents about
CZCS and the Goddard DAAC from the User Services Office (USO):
Documentation Available Online
CZCS
Starter Kit
Level
1 Guide
Level
1a/Level 2 Guide
Level
3 Guide
CZCS HDF Product Specification
CZCS
Sensor Guide
Documentation Available as Hardcopies
Level 1 Data Product User's Guide
This is a Technical Memorandum
produced by NASA which describes the scientific and technical objectives
of the CZCS experiment, the instrument itself, the level 1 processing
algorithms, data calibration, and tape formats.
PC-Seapak User'S Guide (Version 4.0)
This is a User's Manual
produced by NASA for PC-SEAPAK, an image processing/analysis software
package. It includes a description of the system and the individual
programs.
Seapak User'S Guide (VAX) (Version 2.0)
This is a User's Manual
for SEAPAK for the VAX. Volume I is a description of the system and
Volume II includes descriptions of the individual programs.
Nimbus-7 User'S Guide
This is a 1978 document produced by the
Nimbus Project at NASA GSFC (1978) describing the Nimubus 7 mission
objectives, the spacecraft itself, and the multiple payloads onboard,
including CZCS.
These files and documents are available from Goddard DAAC User
Services (see contact info below).
Data Producer Information:
Dr. Gene Feldman
Earth Science Data Operations Facility, Code 610.2
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
phone:
301-286-9428
fax: 301-286-1775
email: gene@seawifs.gsfc.nasa.gov
DSP information:
Dr. Robert Evans
RSMAS/MPO
University of Miami
Miami, FL
33149
email: bob@miami.rsmas.miami.edu
SEAPAK information:
Dr. Charles McClain
Laboratory for Hydrospheric Processes, Code
971
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
email: mcclain@calval.gsfc.nasa.gov
User Services Office
Goddard Distributed Active Archive Center
NASA Goddard Space Flight Center, Code 610.2
Greenbelt, MD 20771
phone: 301-614-5224
fax: 301-614-5268
email: daacuso@disc.gsfc.nasa.gov
As of 10/08/96, the CZCS level 1a and level 2 data
inventory (both data and browse files) were available and orderable
through the Goddard DAAC Information Management Service (IMS). The
remaining level 1a data, as well as the level 2 and level 3 PST and
composite data, will be inventoried and archived in the Goddard DAAC by
January 1997. As stated earlier, CZCS level 2 browse files may be viewed
using the CZCS
online Web browser, and level 1, la, 2, and level 3 data can be
ordered using the browser interface.
The original Level 1 CZCS data was produced and stored on
9-track magnetic volumes in CRTT Tape Format. In this original format,
two files were created per scene: an EBCDIC header describing the data,
and a data file containing the instrument scans. When the data were
transferred onto a digital optical disk, the format was slightly
modified to a CRTT Archive Format. A major change was the combining of
the separate files into one file and adding a format header block.
The CRTT Tape format has been retained for the most part. See the
Nimbus-7 Coastal Zone Color Scanner Level 1 Data Product User's Guide
for a complete description of the CRTT Tape format. This Guide may be
ordered from the DAAC User Support Office.
The added format header block is the first 512 byte block in the
file. This block was written on a VAX prior to being written on the
platters. The files were then archived into the GSFC DAAC directly off
of the optical platters. The header block contains 16-bit (2 byte)
integers which only the first 16 are useful. Because the VAX writes to
memory in Little Endian order, if you are on a machine which uses Big
Endian order, you will have to swap the order of the bytes of the
integers. Little Endian byte order puts the byte at the least
significant positions in the word (the little end). Big Endian byte
order puts the byte at the most significant position in the word (the
big end). The DEC PDP-11/VAX and Intel 80x86 follow the Little Endian
model, while the IBM 360/370 and Motorola 680x0, and others follow the
Big Endian model. The byte swapping only applies to these first 16
integers of the header block. These bytes contain information on the
format of the file. In the following description, each HEADER refers to
a two byte integer.
HEADER( 1) 'magic' to signal archive header record HEADER(
2) 'magic' to signal archive header record HEADER( 3) Length
of data record (bytes) HEADER( 4) Number of documentation records
(2 normally) HEADER( 5) First data record offset (blocks) HEADER(
6) Type code (101=CZCS) HEADER( 7) Number of data records
(1-970) HEADER( 8) Orbit number HEADER( 9) Year of pass
HEADER(10) Header record offset (blocks) HEADER(11) Header
record length (bytes) HEADER(12) Documentation record length
(bytes) HEADER(13) -- HEADER(14) -- HEADER(15) --
HEADER(16) Scanner tilt (*100)
An example of the first 512 byte block from a CZCS level 1 file is
(this was done on an SGI IRIX with the Unix octal dump command:
od
-x 79005164931.ni7 .):
0000000 aaaa aaaa ec31 0200 1000 6500 d802 f703 0000016 bb07 0200
7602 d014 0000 0000 0000 5802 0000032 0000 0000 0000 0000 0000 0000 0000
0000 * 0001000
The variables translate to:
swapped hex bytes decimal comments ---
----- ------- -------- HEADER( 1) = aaaa aaaa 43690 magic
number HEADER( 2) = aaaa aaaa 43690 magic number HEADER( 3) =
ec31 31ec 12780 Length of record (bytes) HEADER( 4) = 0200 0002
2 Number of documentation records HEADER( 5) = 1000 0010
16 First data record offset (blocks) HEADER( 6) = 6500 0065
101 type code (101=czcs) HEADER( 7) = d802 02d8 728 number of
records HEADER( 8) = f703 03f7 1015 orbit number HEADER( 9) =
bb07 07bb 1979 year HEADER(10) = 0200 0002 2 header
record offset (blocks) HEADER(11) = 7602 0276 630 header record
length (bytes) HEADER(12) = d014 14d0 5328 documentation record
length (bytes) HEADER(13) = 0000 0000 0 --- HEADER(14) = 0000
0000 0 --- HEADER(15) = 0000 0000 0 --- HEADER(16)
= 5802 0258 600 scanner tilt (*100)
From this example the layout of the file is:
bytes
comment ----- ------- 0-31 File description. 1024-1654
Header information. Start at HEADER(10) and is HEADER(11) length. This
information is EBCDIC. 2048-7376 Documentation record. Start at next
block and is HEADER(12) length. 8192-20972 First record. Start at
HEADER(5) and is HEADER(3) length. 20992-33772 Next record. Start at
next 512 byte block and HEADER(3) length. ... Continue for a
total of HEADER(7) records. 9326592-9332224 The trailing documentation
record. The last 304 bytes are null characters. This file is padded out
to be an even multiple of 512 to keep integrity of the 512 byte blocks.
A description of the documentation records and the data records can
be obtained from the NIMBUS 7 Coastal Zone Color Scanner (CZCS) Level 1
Data Product User's Guide (NASA Technical Memorandum 86203). This Guide
may be ordered from the Goddard DAAC User Support Office.
The files have been tested on a VAX/VMS and a SGI/IRIX. The files
were retrieved from the GSFC DAAC archive and written to 8mm tape. The
files were then read from tape onto the appropriate machine being
tested. The files were then preprocessed with the ingest program that is
part of the DSP package from the University of Miami. DSP is a software
package that was written for analyzing CZCS data. The preprocess step
will change the format of each two-minute scene from CRTT to DSP. The
resultant file from the preprocess step was then used in analysis with
the DSP package.
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Atmos Composition
