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DMSP SSM/I Pathfinder Daily EASE-Grid Brightness Temperatures

Summary

The NOAA/NASA Pathfinder Program Special Sensor Microwave/Imager (SSM/I) Level 3 Equal-Area Scalable Earth-Grid (EASE-Grid) Brightness Temperatures consist of gridded data in one of three projections, Northern Hemisphere, Southern Hemisphere and full global. The data gridding technique maximizes the radiometric integrity of the original brightness temperature values, maintains high spatial and temporal precision, and involves no averaging of original swath data.

Coverage is global and begins 9 July 1987; processing is ongoing. Resolution is 25 km for all channels; 85 GHz channels are also provided at 12.5 km resolution. There are 18 brightness temperature files per day for a given projection, and two corresponding time files. Data are contained in flat binary files, either one grid per file consisting of 2-byte integer arrays of brightness temperatures in tenths of kelvin, or in the case of time files, 1-byte integer arrays consisting of Coordinated Universal Time (UTC) in tenths of hours.

Data are available via FTP as processing is completed. Users can order temporal or spatial subsets of data with the Graphical Interface for Subsetting, Mapping, and Ordering (GISMO) Web-based tool. Users can also request the complete data set or a long time series of data. Users may also order historical data on CD-ROM, while supplies last.

For more information about related projects, please see NOAA/NASA Polar Pathfinder Data. For more information on the NSIDC EASE-Grid, geolocation tools for working in EASE-Grid, and other products available in EASE-Grid, please see All About EASE-Grid.

ERROR ALERT, PLEASE READ

Citation

To broaden awareness of our services, NSIDC requests that you acknowledge the use of data sets distributed by NSIDC. Please refer to the citation below for the suggested form, or contact NSIDC User Services for further information. We also request that you send us one reprint of any publication that cites the use of data received from our Center. This helps us to determine the level of use of the data we distribute. Thank you.

The following example shows how to cite the use of this data set in a publication. List the principal investigators, year of data set release, data set title, dates of data you used (for example, June to September 2001), publishers (NSIDC), and digital media.

Armstrong, R. L., K. W. Knowles, M. J. Brodzik and M. A. Hardman. 1994, updated current year. DMSP SSM/I Pathfinder daily EASE-Grid brightness temperatures, [list dates of data used]. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.

Overview Table

Table of Contents

1. Data Set Overview
2. Applications
3. Theory of Measurements
4. Acquisition Materials and Methods
5. Preparation and Description
6. Notes and Plans
7. Products and Access
8. References
9. Document Information

1. Data Set Overview

Data Set Introduction

NOAA/NASA Pathfinder SSM/I Level 3 EASE-Grid Brightness Temperature data were generated by the Special Sensor Microwave/Imager (SSM/I) mounted on the Defense Meteorological Satellite Program (DMSP) F8, F11, and F13 platforms. Coverage is global and extends from 9 July 1987; processing is ongoing. Resolution is 25 km for all channels; 85 GHz channels are also provided at 12.5 km resolution.

Gridded data for a series of three projections, the EASE-Grid Northern Hemisphere, Southern Hemisphere and Cylindrical (global) have been produced.

Binary data arrays contain spatially interpolated data. The data gridding technique maximizes the radiometric integrity of the original brightness temperature values, maintains high spatial and temporal precision, and involves no averaging of original swath data. Backus-Gilbert optimal interpolation is used to artificially increase (16 times) the density of brightness temperature measurements in the satellite swath reference frame (sample interval of 25 km for 19, 22 and 37 GHz, and 12.5 km for 85 GHz). This process uses actual antenna patterns to create the oversampled array, and the net effect is as if the additional samples had been made by the satellite radiometer itself, i.e., the beam patterns and spatial resolutions of the interpolated data approximate those of the original samples. This method is based on the earlier work of Galantowicz and England (1991) and Poe (1990). The brightness temperature for a given EASE-Grid cell is obtained from the oversampled array by the nearest neighbor method. No averaging of original swath data is employed (e.g., no "drop-in-the-bucket").

The Backus-Gilbert technique also allows resolution enhancement, but with a noise penalty. To avoid the noise penalty, the brightness temperatures for all channels in the 25 km grids were interpolated to the effective field of view (EFOV) at -3 db of the 19 GHz V-polarized channel. Brightness temperatures for 85 GHz channels in the 12.5 km grids were interpolated to the EFOV of the 85 GHz V-polarized channel. Please see Derivation Techniques/Algorithms for further detail.

As the first step in the processing of Pathfinder data, a common Benchmark Period (April 1987 to November 1988) was chosen to facilitate the analysis and comparison of individual Pathfinder data products. Note that the SSM/I Benchmark Period is somewhat shorter (August 1987 to November 1988) than the Pathfinder Benchmark Period because the data record started with the launch of the DMSP-F8 satellite in July 1987.

Objective/Purpose

The NOAA/NASA Pathfinder Program is designed to provide scientists with time-series of global-scale remote sensing data ahead of the EOS satellite launches. The Pathfinder concept involves careful reprocessing of existing data sets and then making them readily available as high quality products for global change research. Since the polar regions hold special significance for global change research, the Polar Pathfinders have established a cooperation to maximize the scientific potential of polar data. Polar Pathfinders data sets use a common multi-resolution grid structure based on the NSIDC Equal-Area Scalable Earth (EASE-) Grid as a standard reference system for comparative data analysis.

Summary of Parameters

The NOAA/NASA Pathfinder SSM/I Level 3 EASE-Grid Brightness Temperatures data set contains the following parameters:

• Brightness Temperature data files
• Corresponding time files
• Geolocation files containing latitude and longitude coordinates for each projection and grid resolution used.

Discussion

The goal of the SSM/I Pathfinder product team is to produce a consistent time series of continuous gridded SSM/I data using the Backus-Gilbert interpolation. For more information about the Pathfinder Project, please review the NOAA/NASA Pathfinders.

Related Data Sets

TOVS Pathfinder Path-P Daily and Monthly Arctic Atmospheric Grids
AVHRR Polar 1 km Level 1b Data Set
DMSP SSM/I Daily Polar Gridded Brightness Temperatures
Global Monthly EASE-Grid Snow Water Equivalent Climatology
Nimbus-7 SMMR Pathfinder Daily EASE-Grid Brightness Temperatures
Northern Hemisphere EASE-Grid Weekly Snow Cover and Sea Ice Extent
For Level 2 SSM/I brightness temperatures, please visit Remote Sensing Systems' data pages

Investigator Name And Title

Richard L. Armstrong
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
(303) 492-6199

Title of Investigation

NOAA/NASA Pathfinder SSM/I Level 3 EASE-Grid Brightness Temperatures

2. Applications

Brightness temperatures are used to derive land surface, ocean, and atmospheric characteristics.

3. Theory of Measurements

Please see the Data Acquisition Methods section below.

4. Acquisition Materials and Methods

Sensor/Instrument Description

Please see the SSM/I sensor/instrument description.

Acquisition Methods

The source for the raw antenna temperature and brightness temperature data for this data set is Remote Sensing Systems, Santa Rosa, California (Wentz 1991).

For a detailed discussion of the theory behind the processing methods used here, please refer to:

Poe, G.A. 1990. Optimum Interpolation of Imaging Microwave Radiometer Data. IEEE Transactions on Geoscience and Remote Sensing 28(5):800-810.

Galantowicz, J.F. and A.W. England. 1991. The Michigan Earth Grid: Description, Registration Method for SSM/I Data and Derivative Map Projections. Technical Report 027396-2-T. Radiation Laboratory Dept. of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor.

Data Notes

• Please see the Summary of EASE Grid Map Projection Parameters.
• Please see Frequently Asked Questions.
• Please see All About EASE-Grid.

5. Preparation and Description

Spatial Characteristics

Spatial Coverage

Spatial coverage is global.

Southernmost Latitude:    90.0° S
Northernmost Latitude:     90.0° N
Westernmost Longitude: 180.0° W
Easternmost Longitude:  180.0° E

There are two EASE-Grid projections, as illustrated below.

Northern and Southern Hemispheres (Lambert's equal-area, azimuthal). Data are in separate files for the separate hemispheres.
Global (cylindrical, equal-area).

Spatial Resolution

Spatial resolution is 25 km for all channels; 85 GHz channels are also provided at a spatial resolution of 12.5 km.

The latitude/longitude precision of gridded values is 0.00001 degrees.

Projection

The data are presented in Northern and Southern Hemisphere and global views. Please review the Summary of EASE-Grid Map Projection Parameters for details on the EASE-Grid projection.

Grid Description

The SSM/I EASE-Grids are a set of three equal-area projections, two azimuthal equal-area projections, for either Northern or Southern Hemisphere, and a global cylindrical equal-area projection, with grid resolutions of 25 km x 25 km and 12.5 x 12.5 km. Please see the Summary of EASE Grid Map Projection Parameters for more information, or All About EASE-Grid for more information on related products and tools.

Temporal Characteristics

Temporal Coverage

The goal of the SSM/I Pathfinder product team is to produce a continuous time series of SSM/I data using a single consistent processing and interpolation scheme. Data become available on the FTP site as processing is completed. All data are available via FTP, and historical data through 2004 are also available on CD-ROM. For a list of missing dates, see SSM/I Data Availability.

There are usually 18 brightness temperature files per day for a given projection, except from 1 February 1989 through 31 December 1991. For this period no data exist for the 85 GHz channels due to degradation of 85 GHz channels after heating cycles during Northern Hemisphere winters as a result of increased solar illumination on the SSM/I (Wentz 1992). Only 10 brightness temperature files are available per day during these dates, and all files are in the low (25 km) resolution grid.

In the interests of providing users with reliable 85 GHz data from SSM/I sensors on subsequent platforms (DMSP-F11 and others) as quickly as possible, DMSP-F8 85 GHz data for the questionable period of 1 February 1989 to 31 December 1991 have not been processed.

Temporal Resolution

The data are daily, separated by ascending and descending passes.

Data Characteristics

Sample Data Record

Using the Unix command "od -d" (the -d tells the computer to interpret each 16-bits as unsigned integers) on the Northern Hemisphere, 19 GHz, Horizontal polarization, ascending data for 1 August 1987, a sample data record looks like:

0000000 00000 00000 00000 00000 00000 00000 00000 00000
*
0267520 00000 00000 00000 01492 00000 00000 00000 00000
0267540 00000 00000 00000 00000 00000 00000 00000 00000
*
0272360 00000 00000 01490 01487 01490 01498 00000 00000
0272400 00000 00000 00000 00000 00000 00000 00000 00000
*
0275220 00000 00000 00000 01498 01491 01494 01499 01495
0275240 01496 00000 00000 00000 00000 00000 00000 00000
0275260 00000 00000 00000 00000 00000 00000 00000 00000
*

The asterisks indicate that all the missing data are zeroes.

Also, please review the SSM/I Pathfinder images featured in NSIDC's EASE-Grid Image Gallery.

Data Granularity

Each T_B file represents gridded data for a single sensor channel and polarization, derived from either ascending or descending orbits (e.g., 37 GHz, horizontal, ascending) for one day. Each time file represents the corresponding time of the swath sample used for the interpolation of the given grid cell, for either ascending or descending orbits for that day.

Data Format

Data are flat binary array data, stored as 2-byte unsigned integers, compressed, little-endian byte-order. Subsetted data ordered through GISMO prior to July 2005 are big-endian. GISMO subsets ordered after July 2005 are little-endian.

Data represent temperatures in tenths of kelvin. There are 18 brightness temperature files per day for each projection. There are two files (arrays) for each day (ascending and descneding orbits) for each projection and for each sensor channel (frequency and polarization).

File Naming Convention

The file naming convention differs as a function of distribution media (CD-ROM or FTP).

The naming convention for T_B files on CD-ROM is as follows:

yyyy/proj/Dddd_ddd/rdddpccc.GZ

where:

The T_B files obtained from NSIDC's FTP site follow the naming convention:

EASE-Fxx-zzyyyydddp.ccc

where:

There are two time files per day (ascending and descending passes) for a given projection, both at 25 km resolution. Data are 1-byte unsigned integers, representing UTC in tenths of hours. The CD naming convention includes the path name:

yyyy/proj/Dddd_ddd/LdddpTIM.GZ

where:

Time files from NSIDC's FTP site follow the convention:

EASE-Fxx-zzyyyydddp.tim

where:

Data for each projection are distributed with geolocation data files. Each file contains 4-byte signed integer arrays representing latitude and longitude at the center of each cell for the respective grids in hundred thousandths of degrees (i.e., five decimal places). The data are compressed as both little-endian (also known as PC- or VAX-byte order) and big-endian (also known as Unix-byte order). In these files, .LSB indicates "least-significant byte," (i.e., PC byte-order), and .MSB stands for "most-significant byte" (Unix-byte order).

The CD naming is:

ggpppooo.GZ

where:

Geolocation files can be obtained online from NSIDC at http://nsidc.org/data/ease/tools.html.

Data Manipulations

Derivation Techniques/Algorithms

The input orbital brightness temperature data for this product was ingested via the Remote Sensing Systems (RSS) software programs DECODE and QUAL1 (Wentz 1993). Switches were used to include the following options:

1. Along-scan bias corrections were turned on.
2. Sensor inter-calibrations (adjusting non-F8 SSM/I antenna temperatures to correspond to F8 SSM/I antenna temperatures) were turned off.
3. Data values during times that RSS has determined to be "periods of erroneous data," and identified in RSS files BADLOC.D08, BADLOC.D11, BADLOC.D13, were discarded prior to gridding and interpolation.
4. Groups of scans that RSS identified as corrupted by calibration error problems between 9 October 1990 and 29 August 1992 and identified in RSS files BADCAL.D08 and BADCAL.D11, were discarded prior to gridding and interpolation.
5. After 29 August 1992 calibration errors detected in RSS's DECODE processing were discarded prior to gridding and interpolation.

Over the course of a day, points at mid-to-high latitudes will be observed from multiple orbits. For a given grid cell location, only observations from a single orbit were used in the Backus-Gilbert interpolation. In order to ensure the most consistent local observation time at each location, we chose the sample from the orbit whose local time was closest to the equatorial crossing times shown in the following table. Actual equatorial crossing times do change slowly over the life of sun-synchronous satellites such as the DMSPs. The choice of these particular times was based on nominal crossing times at launch.

The antenna pattern coefficients used in the Backus-Gilbert interpolation were provided to NSIDC by John Galantowicz (Galantowicz 1995, Appendix C). The interpolated brightness temperatures represent optimally filtered data, that is, they represent what the sensor would have measured had it been directed at the center of the fixed grid cell. Depending on one's purposes, the Backus-Gilbert method can be tuned to enhance resolution, or reduce noise, but both cannot be achieved simultaneously. Galantowicz chose to generate coefficients that would minimize noise (i.e., that produced a pattern with lowest relative side-lobes):

"The 19 GHz pattern has the largest footprint of the four SSM/I frequencies, and the interpolated patterns of the other channels are able to fit it without high side-lobes. If the 19 GHz pattern were interpolated to a significantly smaller desired pattern--that is, either the 37 GHz or 85 GHz pattern--then the best achievable interpolated pattern would be distorted and have high side-lobe levels." (Galantowicz 1995, p. 211)

An example frequency response of Backus-Gilbert interpolation, as 3-D shaded relief (left) and the profile at y=0 (right). The side-lobes are the bumps outside the intervals x = ± 1/2 and y = ± 1/2. The decision to "tune" the EASE-Grid SSM/I brightness temperatures minimizes the side-lobes in the interpolation. Figures courtesy of K. Knowles, NSIDC.

The resulting EASE-Grid brightness temperatures for all channels in the 25 km grids represent the effective field of view (EFOV) at -3 db of the 19 GHz V-polarized channel, and the EASE-Grid brightness temperatures for 85 GHz channels in the 12.5 km grids represent the EFOV of the 85 GHz V-polarized channel. Users of the SSM/I EASE-Grid data can make inter-channel comparisons and develop geophysical algorithms based on the assumption that the gridded data represent brightnesses of the same geographical area. For further details, refer to Galantowicz (1995), Galantowicz and England (1991) and Poe (1990).

Data Processing Sequence

Processing Changes

Processing of the data has progressed over the course of several years. The goal of the product team has been to produce a consistent time series of continuous, gridded SSM/I data. However, over the course of the operational processing we have chosen at certain times to change some parts of the processing code. We have only made such changes after careful consideration of the consequences to the time-series, and then only when the changes will result in an overall better quality time series. The following changes have been made:

1. We determined through visual inspections of processed data that some data for 28 June 1989 were mislocated. As a result, we added the following line to our BADLOC.D08 file in order to eliminate the erroneous orbital data:
   1989 179  8.0 1989 179  8.2
2. Due to an error in the processing code, time data files for the F8 data (August 1987 through December 1991) contain times that were inadvertently truncated to tenths of hours, instead of rounded to the nearest tenth of an hour. This problem was corrected beginning with data for January 1992
3. The treatment of 'out of bounds' input data changed between the F8 and F11 data. For F8 data, input brightness temperatures that were out of bounds (defined to be less than 55.0 K or greater than 320. 0 K) were replaced with the average of the two closest in bound brightness temperatures along the same scan. Beginning with F11 data (January 1992) we eliminated this treatment, and set the out of bounds value to an invalid brightness temperature. The Backus-Gilbert interpolation for any EASE-Grid pixel was only performed if both of the following conditions were true:
   1. the interpolation coefficient corresponding to any missing T_B must have been smaller than a "missing coefficient threshold" of 0.0005.
   2. the sum of the interpolation coefficients corresponding to valid T_Bs must have been within plus or minus 0.0005 of 1.0000 (which is the sum of all 16 coefficients).
4. There are no 85 GHz data for the 1 February 1989 through 31 December 1991, see related note.

Errors

Please read the ERROR ALERT.

Quality Assessment

Measurement Error for Parameters

Geolocation errors in input Wentz data are no more than 10 km, "although there may be exceptions" (Sharon Tremble, e-mail to M.J. Brodzik, 18 January 1996). Additional error introduced by nearest-neighbor interpolation from the over-sampled array is approximately 6 km for the 25 km grids and 3 km for the 12.5 km grids.

Additional Quality Assessment

Each T_B and time file is visualized and manually inspected by data center operators before being archived and distributed.

6. Notes and Plans

• Please see EASE-Grid: A Versatile Set of Equal-Area Projections and Grids or All About EASE-Grid.
• For more information, see Frequently Asked Questions.

Note to users of SSM/I EASE-Grid data for 1994 through April 1995:

Substantial amounts of swath data over Alaska, Greenland, and the Canadian Prairies are missing beginning early in 1994 until May 1995. During this period the data tape recorder on the DMSP-F11 failed. As a result, it was necessary to download data to ground stations more frequently than usual. Data download and acquisition could not occur simultaneously, consequently data gaps exist in the EASE-Grid data for Alaska, Greenland, and the Canadian Prairies from early 1994 until data acquisition by the DMSP-F13 SSM/I began in May 1995.

7. Products and Access

Procedures for Obtaining Data

Data are available free of charge. Data are available via FTP as processing is completed. The data are in the ftp://sidads.colorado.edu/pub/DATASETS/brightness-temperatures/easegrid/ssmi/ directory on the FTP site. There is one directory for each projection (global, north, and south); within each of the projection directories are subdirectories for each year for which data are available (new year subdirectories are added as needed). The directory structure is illustrated below.

Beginning with data from January 2005, data are no longer distributed via CD-ROM. Instead, data will be made available on our public FTP site as the data are produced. Users who are currently registered to receive data on CD-ROM will continue to do so for data through December 2004. Users may order historical data on CD-ROM, while supplies last.

The Graphical Interface for Subsetting, Mapping, and Ordering (GISMO) allows users to select specific temporal and spatial subsets of gridded data from NSIDC, including DMSP SSM/I Pathfinder Daily EASE-Grid Brightness Temperatures. Subsetted data from GISMO ordered prior to July 2005 have a big-endian byte order; GISMO data ordered after July 2005 are little-endian. Users can request data by FTP. The GISMO was designed to allow users to order spatial and temporal subsets of data. It is not an appropriate tool for ordering entire data sets or entire grids for long time series. Users who wish to order a full time series, or several years' worth of SSM/I EASE-Grid data, should contact NSIDC User Services. Large orders will be fulfilled as resources allow.

Please contact NSIDC User Services for more information:

Software on the CD-ROM

This section applies only to data distributed on CD-ROM.

A "TOOLS" directory accompanies the data on CD-ROM, with 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.

GZIP

The /TOOLS/GZIP/ directory contains copies of the latest available GZIP Unix source code, two versions of executables (for Sun and SGI platforms), and a self-extracting archive file, /TOOLS/GZIP/MSDOS/GZIP*.EXE, for DOS systems. The copyright and distribution information are in the file /TOOLS/GZIP/README.GNU.

Sun/SGI platforms -

1. Users with IDL need only set the environment variable EASE_GZIP to the location of the executable on the CD. The IDL EASE Tools will do the rest.
2. Users without IDL, if you do not already have gzip, copy the executable version you need to a directory on your machine, renaming the files using lower case characters, and remember to add its location to your appropriate path environment variable. Type 'gzip -h' for help on using it.

PC platforms - 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 in installation for your platform.

Other Unix platforms - If you do not already have gzip, copy the tar file /TOOLS/GZIP/SOURCE/GZIP.TAR to your machine, and use the command 'tar xvf GZIP.TAR', which will expand the file into the directory gzip-x.x.x and its contents, then follow the instructions in the INSTALL file. 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.

You may also obtain GZIP directly over the Internet, via anonymous ftp, from prep.ai.mit.edu, in subdirectory /pub/gnu/.

Once you have obtained a copy of gzip (which includes gunzip after installation), copy the files you want from the CD to a target directory on your own system, then you may uncompress any single file with the .GZ extension, using the command:

% gunzip -v /target_path/DATAFILE.GZ

The -v switch stands for "verbose" output.

Alternatively, you may uncompress multiple files by using shell wildcards for pattern matching. Be careful to calculate the necessary disk space for the files you are uncompressing.

Note that the file name 'L213A19H.GZ' will exist on at least 3 separate CDs (one for each projection, and more for separate years). If you plan to use data for the same dates from more than one projection remember to either reproduce the year directory and the NORTH-SOUTH-GLOBL directory structure on your machine, or change your local file names so that they are unique.

A sample C Shell script, /TOOLS/SOURCE/GET_EASE_DATA.CSH, has also been included. This script takes as input a pattern string to determine the names of a number of files that are to be extracted from the CD, for example, '/CDROM/1987/NORTH/D273_277/L274?85H*', and a destination directory to which the uncompressed files are written. Each uncompressed data file name will consist of the file name base from the CD, with no extension, i.e., % get_ease_data.csh '/CDROM/1987/NORTH/D273_277/?274?85H*' ./ will uncompress to the files:

./L274A85H
./L274D85H
./H274A85H
./H274D85H

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. A word of warning: the user should verify, before running GET_EASE_DATA.CSH, that enough local disk space exists for the uncompressed versions of data being extracted.

Note to IDL users: the IDL tools included on the CDs will uncompress gzipped files on the fly. 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.

IDL

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, performing gunzip'ing and byte-swapping on the fly, using the latest version of ssmi_read (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.

SOURCE

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 (when necessary) a number of data files at one time.

8. References

Based on the recommendations of the SSM/I Products Working Team (SPWT), the point of departure for the EASE-Grid interpolation from swath coordinates to earth-gridded coordinates is the methodology of Galantowicz and England (1991) which is based on earlier work by Stogryn (1978) and by Poe (1990). Those interested in the details of the interpolation method used in the EASE-Grid should consult the references listed below.

Brodzik, M. J. 1997. EASE-Grid: A Versatile Set of Equal-Area Projections and Grids. Unpublished report to the National Snow and Ice Data Center, Boulder, CO.

Galantowicz, J. F., England, A. W. 1991. The Michigan Earth Grid: Description, Registration Method for SSM/I Data, and Derivative Map Projections. Radiation Laboratory, Department of Electrical Engineering and Computer Science, Technical Report 027396-2-T. University of Michigan, Ann Arbor.

Galantowicz, J. F. 1995.Microwave Radiometry of Snow-Covered Grasslands for the Estimation of Land-Atmosphere Energy and Moisture Fluxes. PhD Thesis, Department of Electrical Engineering and Computer Science and Department of Atmospheric, Oceanic, and Space Sciences. University of Michigan, Ann Arbor.

Knowles, K. W. 1993. Points, pixels, grids, and cells -- a mapping and gridding primer. Unpublished report to the National Snow and Ice Data Center, Boulder, CO.

Poe, G. A. 1990. Optimum interpolation of imaging microwave radiometer data. IEEE Trans. Geosci. Remote Sensing GE-28:800-810.

Stogryn, A. 1978. Estimates of brightness temperatures from scanning radiometer data. IEEE Trans. Antennas Propagat. AP-26:720-726.

Wentz, F. J. 1991. User's Manual SSM/I Antenna Temperature Tapes, Revision 1. Remote Sensing Systems Technical Report 120191. Santa Rosa, CA. 70 p.

Wentz, F. J. 1992. Final Report, Production of SSM/I Data Sets. Remote Sensing Systems Technical Report 090192. Santa Rosa, CA. 9 p.

Wentz, F. J. 1993. User's Manual SSM/I Antenna Temperature Tapes, Revision 2. Remote Sensing Systems Technical Report 120193. Santa Rosa, CA. 13 p.

Special thanks to:

• Dr. Tony England, Dr. John Galantowicz and Ed Kim for their ongoing research efforts, and for consistent support and input during all phases of this project, including prototyping and development; also for producing the Antenna Pattern Correction coefficients used in the interpolation procedure.
• Molly Hardman for software development of the first revisions of the processing software.
• Dr. Ted Habermann, for development of the FREEFORM and makeHDF tool set.
• Ray Kokaly, for technical support and comments.
• Ken Knowles, for technical support, gridding and overlay software support, advice and comments.
• Mark Ohrenschall, for support with the FREEFORM and makeHDF tool set.
• To members of the product team at the NSIDC DAAC, including Renea Ericson, Rachel Hauser, David Hoogstrate, Tracy Thrasher-Hybl, Xiaoming Li, Mike Machowski, Alex Machado, John Maurer, Heidi Schumacher, Annette Varani, I-Pin Wang, Jason Wolfe, Fran Coloma, Dave Korn, Jonathan Kovarik, Peter Gibbons, and Lynn French, whose constant attention to detail and professional energies have made possible the continuing availability of this high-quality data set.
• To members of the User Services Office at the NSIDC DAAC, whose professional attitude and attention to many technical details makes possible continuing responsive, knowledgable user support, and especially to Michelle Holm, for many iterations of technical comments on this document and its earlier incarnations.
• Annette Varani, for documentation support, developing the EASE-Grid Sampler area of the Equinox Sampler, and much patience involved in the packaging artwork.

The following related documents are available on NSIDC's Web site.

9. Document Information

Acronyms and Abbreviations

The following acronyms and abbreviations are used in this document.

Document Revision Date

August 2004
November 2005
January 2007
July 2007

Document URL

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