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Data Set ID:

SMEX03 SSM/I Brightness Temperature Data, Alabama, Version 1

This data set provides brightness temperature data acquired during the Soil Moisture Experiment 2003 (SMEX03) by the Special Sensor Microwave/Imager (SSM/I) conducted in the SMEX03 Oklahoma, the Alabama/Georgia, and Brazil study areas.

Geographic Coverage

  • Microwave > Brightness Temperature
Spatial Coverage:
  • N: 38, S: 28, E: -80, W: -90

Spatial Resolution: Not Specified
Temporal Coverage:
  • 29 April 2003 to 29 September 2003
Temporal Resolution: Not specified
Data Format(s):
  • ASCII Text
Platform(s) DMSP, DMSP 5D-2/F13, DMSP 5D-2/F14, DMSP 5D-2/F15
Sensor(s): SSM/I
Version: V1
Data Contributor(s): Thomas Jackson
Data Citation

As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.

Jackson, T. 2008. SMEX03 SSM/I Brightness Temperature Data, Alabama, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: [Date Accessed].

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Detailed Data Description


Data are provided in ASCII text files (.txt).

The following tables describe the column headings for the low (*.lo.txt) and high (*.hi.txt) frequency data files.

Table 1. Column Headings for Low Frequency Data Files
Latitude in degrees North
Longitude in degrees West
Tb 19 v-pol
Tb 19 h-pol
Tb 22 v-pol
Tb 37 v-pol
Tb 37 h-pol

Table 2. Column Headings for High Frequency Data Files
Latitude in degrees North
Longitude in degrees West
Tb 85 v-pol
Tb 85 h-pol
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File and Directory Structure

The top directory level contains tarred and gzipped files containing the data for each SMEX03 study region and the readme file as shown in Figure 1.

Figure 1. Top Level SMEX03 SSM/I Directory Structure.
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File Naming Convention

Data files are named according to the following convention. Table 3 describes the naming convention variables.

File Naming Convention
Example File Name

Table 3. File Name Description
Variable Description
mm month
dd day
yyyy year
ss satellite number
tttt start time of swath (hour and minute of local standard time)
rr frequency set (lo or hi)

Tarred and gzipped files are named according to the following convention, where reg indicates the SMEX03 special region. Table 4 lists the regions

File Naming Convention
Example File Name

Table 4. SMEX03 Regions
Region Code Region Name
ALGA Alabama and Georgia
BZ Brazil
OK Oklahoma

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File Size

41 MB to 188 MB

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Total volume is approximately 275 MB for all data. Volume by region is approximately:

Alabama / Georgia: 42 MB
Oklahoma: 188 MB
Brazil: 45 MB

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Spatial Coverage

Alabama / Georgia:
Southernmost Latitude: 28.0° N
Northernmost Latitude: 38.0° N
Westernmost Longitude: 90.0° W
Easternmost Longitude: 80.0° W

Southernmost Latitude: 30.0° N
Northernmost Latitude: 40.0° N
Westernmost Longitude: 103.0° W
Easternmost Longitude: 93.0° W

Southernmost Latitude: 20.0° S
Northernmost Latitude: 0.0° S
Westernmost Longitude: 60.0° W
Easternmost Longitude: 40.0° W

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Temporal Coverage

Alabama / Georgia: 29 April 2003 to 29 September 2003

Oklahoma: 29 April 2003 to 23 September 2003

Brazil: 29 September 2003 to 28 February 2004

Temporal Resolution

For a given satellite, coverage is possible twice a day, approximately 12 hours apart, on the ascending and descending passes.

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Parameter or Variable

Brightness Temperature (Tb) in units of kelvin (K)

Parameter Description

The brightness temperatures are given by channel: 19.3, 22.2, 37.0, and 85.5 GHz.

Sample Data Record

Low Frequencies: The following is a sample from the file TD04292003132343.lo.txt. The first three lines are shown. See Format for column headings.

        28.04  -85.46  212.17  157.06  246.36  224.99  174.41
        28.08  -85.20  212.98  158.99  248.69  227.32  178.99
        28.12  -84.95  211.80  156.60  247.29  228.85  183.20

High Frequency: The following is a sample from the file TD04292003132343.hi.txt The first three lines are shown. See Format for column headings.

        28.01  -84.92  270.57  258.45
        28.02  -84.79  267.10  252.69
        28.03  -84.66  267.13  250.93
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Software and Tools

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Data Acquisition and Processing

Data Acquisition Methods

Data are first acquired as antenna temperatures in Temperature Data Record (TDR) format. Latitude and longitude coordinates for each pixel are included with these records. When a study area is specified in the data search procedure, all orbits that cross that area are extracted. On a given day, it is possible to have coverage by each of the three satellites twice a day. It is also possible to have no coverage.

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Derivation Techniques and Algorithms

Processing Steps

Additional processing consists of eliminating scans without coverage in the SMEX03 study regions, converting the antenna temperatures to brightness temperatures, and reformatting the data into ASCII files. The processed data files include a latitude and longitude assigned to each data point.

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Sensor or Instrument Description

SSM/I is a seven-channel, four-frequency, linearly polarized passive microwave radiometric system. It is a conical scanning total power microwave radiometer system operating at a look angle of 53 degrees. The nominal swath width is 1400 km. Data are collected at 128 points across track on every scan at 85 GHz. Only 64 points of observation are made across track on every other scan at the other frequencies.

SSM/I is flown aboard Defense Meteorological Satellite Program (DMSP) satellites F8, F10, F11, F12, F13, F14, and F15. Table 5 lists the characteristics of the relevant platforms that were in operation during SMEX03.

Table 5. SSM/I Satellites
Launch Date
Supported Through
Ascending Equatorial Crossing Time (local time)
March 1995
May 1997
December 1999

The SSM/Is orbit the earth about 14.1 times per day with an orbital period of about 102 minutes. The minimum data unit, an orbit, consists of two passes. These are pole-to-pole swaths, one ascending (south to north) and one descending (north to south). The first pass of a Coordinated Universal Time (UTC) day is defined as the first complete pass of the day.

For more information, see the Special Sensor Microwave Imagery (SSM/I) Web page.

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References and Related Publications

Contacts and Acknowledgments

Thomas J. Jackson
USDA ARS Hydrology and Remote Sensing Lab
Bldg. 007, Rm. 104, BARC-West
Beltsville, MD 20705

Document Information


1 April 2008


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