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Coastal Zone Color Scanner (CZCS) Data Set Readme

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.

Data Set Information

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.

Satellite and Instrument Information

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.

Data Set Organization

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.

Data Access Information

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 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, MD20771
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 publicly 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.

 

References

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).

Points of Contact

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, MD20771
phone: 301-614-5224
fax: 301-614-5268
email: daacuso@disc.gsfc.nasa.gov

Data Set Updates

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.

Appendix: Differences Between CZCS Level 1 CRTT Tape and CRTT Archive Formats

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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