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CD-ROM Documentation for DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures

Though NSIDC no longer distributes the DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperature data on CD-ROM, this documentation is retained for users who have previously acquired the data via CD-ROM. The following sections provide more information regarding these data on CD-ROM:

For full documentation on this data set, refer to the DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures user guide document.

File and Directory Structure

The directory structure of the CD-ROM is described in the next section of this document, File Naming Convention.

File Naming Convention

Brightness temperature files on the CD-ROM are named according to the following convention and as described in Table 1. Note: The file naming convention includes the directory path.

yyyy/proj/Dddd_ddd/rdddpccc.GZ

where:

Table 1. Naming Convention for Brightness Temperature Files on CD-ROM
Variable Description
yyyy 4-digit year
proj Projection
  NORTH: Northern Hemisphere, azimuthal
  SOUTH: Southern Hemisphere, azimuthal
  GLOBL: full global, cylindrical
Dddd_ddd Enclosing 5-day pentad directory where ddd is the 3-digit day of year
r Resolution
  L: 25 km resolution
  H: 12.5 km resolution, for 85 GHz only
ddd 3-digit day of year
p Direction of pass (A: ascending, D: descending)
ccc Channel and polarization (19H, 19V, 22V, 37H, 37V, 85H, or 85V)
GZ Identifies this as a gzipped file

Time files on CD-ROM are named according to the following convention and as described in Table 2. Note: The file naming convention includes the directory path.

yyyy/proj/Dddd_ddd/LdddpTIM.GZ

where:

Table 2. Naming Convention for Time Files on CD-ROM
Variable Description
yyyy 4-digit year
proj Projection
  NORTH: Northern Hemisphere, azimuthal
  SOUTH: Southern Hemisphere, azimuthal
  GLOBL: full global, cylindrical
Dddd_ddd Enclosing 5-day pentad directory where ddd is the 3-digit day of year
L 25 km resolution
ddd 3-digit day of year
p Direction of pass (A: ascending, D: descending)
TIM Indicates the contents are time data
GZ Identifies this as a gzipped file

 

Error Sources

Error in CD-ROMs Produced Before 09 August 1995

  1. A typographical error occurs in the README files contained on the EASE-Grid DMSP-F8 SSM/I Level 3 Brightness Temperature CD-ROMs produced before 09 August 1995. This affects the Full Global F8 Volumes 1.0 through 9.0 and Northern Hemisphere F8 Volumes 1.0 through 7.0. In the projection information for the "M" grids (also referred to as "global"), the following two equations are incorrect:

    r = R/C * lambda * cos(30) + r0 s = R/C * sin(phi) / cos(30) + s0

    The correct equations are:

    r = r0 + R/C * lambda * cos(30) s = s0 - R/C * sin(phi) / cos(30)


    Please note that this is only a typographical error in the documentation; the data are correct on all the CD-ROM volumes. In the documentation files on all CDs produced after 09 August 1995, the equations have been corrected. We apologize for any inconvenience this may have caused.

  2. Data users should be aware that an error occurred when writing the file "/1987/GLOBL/D223_227/L223DTIM.GZ" on the EASE-Grid Global Volume 1.0 CD-ROM that resulted in a zero file length. Download the replacement file, EASE-F08-ML1987223D.TIM.gz, available via FTP.

  3. Data users should also be aware that an error occurred when writing the file "/1988/GLOBL/D186_190/L189A19H.GZ" on the EASE-Grid Global Volume 11.0 CD-ROM. Download the replacement file, EASE-F08-ML1988189A.19H.gz, available via FTP.

Data Access

Full time series of the data are available via FTP as processing is completed. See the SSM/I-SSMIS Data Availability Web page for specific dates by platform. After January 2005, data are no longer distributed via CD-ROM. Instead, data are made available on our public FTP site as the data are produced.

Software and Tools

A TOOLS directory accompanies the data on CD-ROM that includes gzip utilities, routines for IDL users to display and manipulate images, and C and FORTRAN routines for use in converting grid row/column coordinates to latitude and longitude. The TOOLS directory contains three subdirectories: GZIP, IDL, and SOURCE. A description of each subdirectory follows.

Note: Due to the file naming convention, some file names will exist on at least three separate CD-ROMs, one for each projection and more for separate years (for example: L213A37H.GZ). If you plan to use data for the same dates from more than one projection, reproduce the year and the NORTH-SOUTH-GLOBL directory structure on your machine; or change your local file names so that they are unique.

GZIP Directory

The /TOOLS/GZIP/ directory contains four subdirectories: MSDOS, SGI, SOURCE, and SUN. The SUN and SGI directories contain copies of the latest available GZIP Unix source code, one for Sun platforms and one for SGI platforms. The MSDOS directory contains a self-extracting archive file for DOS (PC) systems. The copyright and distribution information are in the file /TOOLS/GZIP/README.GNU.

Note: You may also obtain GZIP directly over the internet from GNU's GZIP Web site.

Sun/SGI platforms GZIP Installation

Note: For help on using gzip, enter the following at the command prompt:

gzip -h

PC platforms GZIP Installation

If you do not already have GZIP, copy and execute the file /TOOLS/GZIP/MSDOS/GZIP*.EXE on your machine. It will create a set of files and documentation for you to use for installation on your platform.

Other Unix platforms GZIP Installation

If you do not already have gzip, follow these steps to install it:

  1. Copy the tar file /TOOLS/GZIP/SOURCE/GZIP.TAR to your machine.

     
  2. Enter the following at the command prompt:

    tar xvf GZIP.TAR

    This will expand the file and it contents into the directory gzip-x.x.x.
     
  3. Follow the instructions in the INSTALL file.
Using GZIP (Users with IDL)

Once gzip/gunzip are installed, users with IDL need only set the environment variable EASE_GZIP to the location of the executable on the local file system. The IDL EASE Tools will do the rest.

Using GZIP (Users without IDL)

Once you have obtained a copy of gzip (which includes gunzip after installation), follow these steps to begin uncompressing the .GZ files:

  1. Copy the files you want from the CD-ROM to a directory on your own system.
     
  2. Uncompress any single file or multiple files with the .GZ extension by entering the following at the command prompt:

    gunzip -v /your_path/DATAFILE.GZ

    where your_path is the directory path to the .GZ files saved on your local machine, and DATAFILE.GZ is the file you want to uncompress. The -v option stands for verbose output.

    Note: To uncompress multiple files, use shell wildcards for pattern matching. Be sure to calculate the necessary disk space for the files you are uncompressing.

IDL Directory

Users who currently have IDL should read the file /TOOLS/IDL/README.IDL, in addition to reading the information in this file. Unix users with IDL can now read data directly into IDL from the CD-ROM, performing gunzipping and byte-swapping on the fly, using the latest version of the ssmi_read procedure (included in ssmi.pro beginning with revision 3.1 of that file), included in the IDL EASE tools.

The IDL directory contains routines for IDL users to display and manipulate images in IDL. These routines contain several updates to the Prototype Version 1.0 tools, including the new grid definitions. Prototype versions of the tools should be replaced with these new ones.

Note to IDL users: the IDL tools included on the CD-ROMs will uncompress gzipped files on the fly on Unix platforms. If you plan to use IDL to read and manipulate these data, consider using this capability to bypass the need to copy and uncompress data to your hard drive via GET_EASE_DATA.CSH. See the SOURCE Directory section below for more information about GET_EASE_DATA.CSH.

SOURCE Directory

The SOURCE directory contains C and FORTRAN subroutines for the family of EASE-Grids to convert between grid row/column coordinates and latitude/longitude coordinates. The SOURCE directory also contains a file called GET_EASE_DATA.CSH, that is an example of a C Shell script that may be used and/or tailored to the user's system to gunzip and byte swap a number of data files at one time.

The /TOOLS/SOURCE/GET_EASE_DATA.CSH script takes two input arguments:

Each uncompressed data filename will consist of the filename base from the CD-ROM, with no extension. For example, entering the following command at the command prompt:

get_ease_data.csh '/CDROM/1979/NORTH/D001_005/L002/37H*' ./

will uncompress to the files:

./L002A37H
./L002D37H

which will be write-protected in the destination directory. This script may need some adjustment on different platforms, but may prove to be a useful tool during the tedious process of extracting compressed data from the CD-ROM. The user should verify, before running GET_EASE_DATA.CSH, that enough local disk space exists for the uncompressed versions of data being extracted.

 

Technical Contact

For more information or technial assistance, please contact us at:

NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449  USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org


Document URL

http://nsidc.org/data/docs/daac/nsidc0032_ssmi_ease_tbs/nsidc0032_ssmi_ease_tbs_cdrom_doc.html