SMEX03 SSM/I Brightness Temperature Data

Summary

This data set provides brightness temperature data acquired during the Soil Moisture Experiment 2003 (SMEX03) by the Special Sensor Microwave/Imager (SSM/I). The study was conducted between 29 April 2003 and 29 September 2003 in the SMEX03 Alabama/Georgia study area, between 29 April 2003 and 23 September 2003 in the SMEX03 Oklahoma study area, and between 29 September 2003 and 28 February 2004 in the SMEX03 Brazil 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

We kindly request that you cite the use of this data set in a publication using the following citation example. For more information, see our Use and Copyright Web page.

Jackson, T. 2008. SMEX03 SSM/I Brightness Temperature Data. [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 (.txt)
Spatial coverage and resolution Alabama / Georgia:
Southernmost Latitude: 28.0 N
Northernmost Latitude: 38.0 N
Westernmost Longitude: 90.0 W
Easternmost Longitude: 80.0 W

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

Brazil:
Southernmost Latitude: 20.0 S
Northernmost Latitude: 0.0 S
Westernmost Longitude: 60.0 W
Easternmost Longitude: 40.0 W
Temporal coverage and resolution 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
File naming convention TDmmddyyyysstttt.rr.txt and reg_SSMI.tar.gz
File size 41 MB to 188 MB
Parameter(s) Brightness Temperature (Tb)
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

Investigator(s)

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

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 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
Column
Parameter
1
Latitude in degrees North
2
Longitude in degrees West
3
Tb 19 v-pol
4
Tb 19 h-pol
5
Tb 22 v-pol
6
Tb 37 v-pol
7
Tb 37 h-pol


Table 2. Column Headings for High Frequency Data Files
Column
Parameter
1
Latitude in degrees North
2
Longitude in degrees West
3
Tb 85 v-pol
4
Tb 85 h-pol


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.

Top Level Directory Structure - SMEX03 SSMI
Figure 1. Top Level SMEX03 SSM/I Directory Structure.


File Naming Convention

Data files are named according to the following convention.

TDmmddyyyysstttt.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)

Example File Name: TD04292003132345.hi.txt


Tarred and gzipped files are named according to the following convention.

reg_SSMI.tar.gz

Where:

reg = SMEX03 special region

The special regions are designated as follows:

ALGA = Alabama and Georgia
BZ = Brazil
OK = Oklahoma

Example File Name: ALGA_SSMI.tar.gz


File Size

41 MB to 188 MB

Spatial Coverage

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

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

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

Spatial Resolution

Spatial resolution varies depending on the scanning frequency used as shown in Table 3.

Table 3. SSM/I Spatial Resolution
Frequency (GHz)
Spatial Resolution (km)
19.3
70 x 45
22.2
60 x 40
37.0
38 x 30
85.5
16 x 14


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.

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

3. Data Access and Tools

Data Access

Data are available via FTP

Volume

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

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

Related Data Collections

4. Data Acquisition and Processing

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 4 lists the characteristics of the relevant platforms that were in operation during SMEX03.


Table 4. SSM/I Satellites
Satellite
Launch Date
Supported Through
Ascending Equatorial Crossing Time (local time)
F13
March 1995
present
18:15
F14
May 1997
present
20:21
F15
December 1999
present
21:31

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.

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.

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.

5. References and Related Publications

Heymsfield, G. A. and R. Fulton. 1992. Modulation of SSM/I Microwave Soil Radiances by Rrainfall. Remote Sensing of Environment. 29:187-202.

Hollinger, J. P., J. L. Peirce, and G. A. Poe. 1990. SSM/I Instrument Evaluation. IEEE Transactions 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. International Journal of Remote Sensing. 14:2483-2500.

6. Document Information

Acronyms

The following acronyms are used in this document.

AMSR-E Advanced Microwave Scanning Radiometer - Earth Observing System
ASCII American Standard Code for Information Interchange
DMSP Defense Meteorological Satellite Program
EASE-Grid Equal-Area Scalable Earth-Grid
FTP File Transfer Protocol
GHz Gigahertz
H-POL Horizontal Polarization
IEEE Institute of Electrical and Electronics Engineers
K Kelvin
NSIDC National Snow and Ice Data Center
SMEX Soil Moisture Experiment
SSM/I Special Sensor Microwave/Imager
Tb Brightness Temperature
TDR Temperature Data Record
UTC Coordinated Universal Time
V-POL Vertical Polarization

Document Creation Date

1 April 2008

Document Revision Date

N/A

Document URL

http://nsidc.org/data/docs/daac/nsidc0338_smex03_ssmi.gd.html