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SMEX02 SSM/I Brightness Temperature Data, Iowa

Summary

This data set provides brightness temperature data, acquired during the Soil Moisture Experiment 2002 (SMEX02) by the Special Sensor Microwave/Imagery (SSM/I). SSM/I is a seven-channel, four-frequency, linearly polarized passive microwave radiometric system. The brightness temperatures are given by channel: 19.3, 22.2, 37.0, and 85.5 GHz. The study was conducted between 29 April and 13 July 2002 in the SMEX02 Iowa study area. Data are provided as ASCII text files and are available via FTP.

These data were collected as part of a validation study for the Advanced Microwave Scanning Radiometer - Earth Observing System (AMSR-E). AMSR-E is a mission instrument launched aboard NASA's Aqua Satellite on 04 May 2002. AMSR-E validation studies linked to SMEX are designed to evaluate the accuracy of AMSR-E soil moisture data. Specific validation objectives include assessing and refining soil moisture algorithm performance; verifying soil moisture estimation accuracy; investigating the effects of vegetation, surface temperature, topography, and soil texture on soil moisture accuracy; and determining the regions that are useful for AMSR-E soil moisture measurements.

Citing These Data

Jackson, T. and J. Wen. 2003. SMEX02 SSM/I Brightness Temperature Data, Iowa. [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center.

Overview Table

Category Description
Data format ASCII text files.
Spatial coverage and resolution 34.5°N, 44.5°N, 100.0°W, 90.0°W.
Temporal coverage and resolution 29 April and 13 July 2002.
File naming convention TDmmddyysstttt.rr.txt
where:
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)
File size File sizes range from 33 bytes to 244 KB.
Parameter(s) Brightness temperatures (TBs)
Procedures for obtaining data Data are available via FTP.

Table of Contents

1. Contacts and Acknowledgments
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. References and Related Publications
6. Document Information

1. Contacts and Acknowledgments

Investigators Names

Thomas J. Jackson
Jun Wen

US Department of Agriculture (USDS) Agricultural Research Service (ARS) Hydrology Lab.

Technical Contact

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

2. Detailed Data Description

Format

Data are provided in ASCII text format.

File Naming Convention

The data files use the following convention:
TDmmddyysstttt.rr.txt

where:

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)

For example, the file "TD04302002150312.lo.txt" was acquired on April 30, 2002 from the F15 satellite at 3:12 AM, and the frequency is low. Low-frequency files contain brightness temperatures for 19.3, 22.22, and 37.0 GHz, while high-frequency files contain brightness temperatures for the 85.5 GHz channel.

File Size

File sizes range from 33 bytes to 244 KB.

Spatial Coverage

Southernmost Latitude: 34.5°N
Northernmost Latitude: 44.5°N
Westernmost Longitude: 100°W
Easternmost Longitude: 90.0°W

Temporal Coverage

Data were acquired from 29 April and 13 July 2002.

Temporal Resolution

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

Parameter or Variable

Parameter Description

The following table describes the data columns for the low frequency (.lo.txt) files:

Column Parameter
1 Latitude in degrees North
2 Longitude in degrees West
3 19 GHz V TB
4 19 GHz H TB
5 22 GHz V TB
6 37 GHz V TB
7 37 GHz H TB

The following table describes the data columns for the high frequency (.hi.txt) files:

Column Parameter
1 Latitude in degrees North
2 Longitude in degrees West
3 85 GHz V TB
4 85 GHz H TB

Unit of Measurement

Unit of measurement is brightness temperature (TBs).

Sample Data Record

The following is a sample from the file "TD04302002141607.lo.txt."

   44.46  -99.63  268.11  261.98  268.53  266.66  263.45
   44.36  -99.92  263.14  254.22  264.36  262.16  255.76
   44.45  -99.17  271.20  264.89  269.96  268.66  264.65
   44.35  -99.46  268.16  261.98  268.36  266.83  263.48
   44.24  -99.75  264.23  254.94  263.38  260.59  254.14

The next sample is from the file "TD04302002141607.hi.txt."

   44.46  -99.87  265.55  262.71
   44.46  -99.63  265.66  263.68
   44.41  -99.78  262.97  260.78
   44.36  -99.92  261.02  257.87
   44.45  -99.40  267.14  263.88
   44.40  -99.55  264.68  262.11

3. Data Access and Tools

Data Access

Data are available via FTP.

Volume

Total volume is 175 MB.

Related Data Collections

4. Data Acquisition and Processing

Sensor or Instrument Description

The SSM/I instrument package has been available on at least one Defense Meteorological Satellite Program (DMSP) satellite since 1987. It is a conical scanning microwave radiometer system operating at a look angle of 53°. The following table summarizes the key features of the instruments. The nominal swath width is 1400 km. Data are collected at 128 locations across track on every scan at 85 GHz. Only 64 observations are made across track on every other scan at the other frequencies.

Frequency (GHz) Polarization Spatial Resolution (km)
19.3 H and V 69 x 43
22.2 V 60 x 40
37.0 H and V 37 x 28
85.5 H and V 15 x 13

The next table lists the characteristics of the various platforms that were in operation during SMEX02. For a given satellite, coverage is possible twice a day, approximately 12 hours apart, on the ascending and descending passes.

Spacecraft Launch Date Supported Through Ascending Equatorial Crossing Time (LTZ)
F13 March 1995 present 18:15
F14 May 1997 present 20:21
F15 December 1999 present 21:31

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

Data Acquisition Methods

Data were available to the investigators as antenna temperatures. Latitude and longitude coordinates for each pixel were included with these records. Each orbit consisted of about 5 mb of data in compressed mode. When a study area was specified in the data search procedure, all orbits that cross that area were extracted. For an individual satellite, two orbits might cover parts of the study area. On a given day, it was possible to have coverage by each of the three satellites twice a day. It was also possible to have no coverage. During the SMEX02 period from April 29 to July 13th, SSM/I overpasses were available.

Processing Steps

The raw SSM/I data sets were acquired and further processed by reducing the data set size by eliminating scans without coverage in the SMEX02 region, 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. Data are provided as separate files for low- (19.3, 22.2, and 37.0) and high-frequency channels (85 GHz) because the frequency of measurement is higher for 85 GHz.

5. References and Related Publications

Heymsfield, G. A. and R. Fulton. 1992. Modulation of SSM/I microwave soil radiances by rainfall. Remote Sensing of Environment. 29:187-202.

Hollinger, J. P., J. L. Peirce, and G. A. Poe. 1990. SSM/I instrument evaluation. IEEE Trans. on Geoscience and Remote Sensing, 28:781-790.

Jackson, T. J. 1997. Soil moisture estimation using SSM/I satellite data over a grass land region. Water Resources Research. 33:1475-1484.

Teng, W. L., J. R. Wang, and P. C. Doraiswamy. 1993. Relationship between satellite microwave radiometric data, antecedent precipitation index, and regional soil moisture. Int. J. of Remote Sensing. 14:2483-2500. 1993.

6. Document Information

Acronyms and Abbreviations

The following acronyms and abbreviations are used in this document.

ASCII American Standard Code for Information Interchange
DMSP Defense Meteorological Satellite Program
FTP File Transfer Protocol
LTZ Ascending Equatorial Crossing Time
SSM/I Special Sensor Microwave/Imagery
TBs Brightness Temperatures

Document Creation Date

December 2003

Document URL

http://nsidc.org/data/docs/daac/nsidc0200_smex_ssmi.gd.html