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DMSP SSM/I- Microwave Imager

The SSM/I is a seven-channel, four frequency, linearly-polarized, passive microwave radiometric system which measures atmospheric, ocean and terrain microwave brightness temperatures at 19.35, 22.235, 37.0 and 85.5 GHz. The data are used to obtain synoptic maps of critical atmospheric, oceanographic and selected land parameters on a global scale. The SSM/I archive data set consists of antenna temperatures recorded across a 1,400 km conical scan, satellite ephemeris, earth surface positions for each pixel and instrument calibration. Electromagnetic radiation is polarized by the ambient electric field, scattered by the atmosphere and the Earth's surface and scattered and absorbed by atmospheric water vapor, oxygen, liquid water and ice. The SSM/I instrument consists of an offset parabolic reflector that is 24 x 26 inches fed by a seven- port horn antenna. The reflector and feed are mounted on a drum which contains the radiometers, digital data subsystem, mechanical scanning subsystem and power subsystem. The drum assembly rotates about the axis of the drum. A small mirror and a hot reference absorber are mounted on the assembly. The instrument sweeps a 450 cone around the satellite velocity vector so that the Earth incidence angle is always 540. Data are recorded during the 102.40 of the cone when the antenna beam intercepts the Earth's surface. The channel footprint varies with channel energy, position in the scan, along scan or along track direction and altitude of the satellite. The 85 GHz footprint is the smallest with a 13 x 15 km and the 19 GHz footprint is the largest at 43 x 69 km. Because the 85 GHz footprint is so small, it is sampled twice as often, i.e., 128 times a scan. One data cycle consists of 4 85 GHz scans and 2 scans of the 19, 22 and 37 GHz channels. The complete cycle takes 28 seconds and it must be complete to process the data. The SSM/I processor is queried once a second by onboard computer and the data are placed into the "TS SSP" data field. Data is ingested as sent from AFWA on a T-1 line. At NGDC, the "TS SSP" data are decommutated, deinterleaved, bit flipped, reordered and restructured into orbits beginning with the equatorial crossing as the satellite travels from south to north. Satellite ephemeris are computed using a physically-based, orbital mechanics model. SSM/I pixels are geolocated using the satellite ephemeris and satellite attitude corrections. Antenna temperatures are computed from instrumental counts by a linear equation, i.e., the conversion is reversible. In the decommutation step, we encountered bit reversals that occurred 1.8 - 3.4% of the time and are probably caused by ionospheric scintillation. These are identified through careful checking procedures and corrected. Archive files contain metadata by orbit and geolocated antenna temperatures.

Cite this dataset when used as a source.

Dataset Information
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Distribution Formats
  • ASCII
Distributor DOC/NOAA/NESDIS/NGDC > National Geophysical Data Center, NESDIS, NOAA, U.S. Department of Commerce
Point of Contact Data Manager
DOC/NOAA/NESDIS/NGDC > National Geophysical Data Center, NESDIS, NOAA, U.S. Department of Commerce
(303) 497-6126
ngdc.dmsp@noaa.gov
Documentation links not available.
Originator
  • DOD/USAF/AFWA > Air Force Weather Agency, U.S. Air Force, U.S. Department of Defense
Originator
  • DOC/NOAA/NESDIS/NGDC > National Geophysical Data Center, NESDIS, NOAA, U.S. Department of Commerce (comp)
Publisher
  • National Geophysical Data Center
Date(s)
  • publication: 1992-01-01
Edition: First
Dataset Progress Status Under development
Data Update Frequency: Daily
Supplemental Information: Entry ID: G01123 Sensor Name: SSM/I > Microwave Imager Source Name: DMSP > Defense Meteorological Satellite Program
Purpose: Maps-Critical Atmosphere, Ocean, & Land Parameters
Use Limitations
  • While every effort has been made to ensure that these data are accurate and reliable within the limits of the current state of the art, NOAA cannot assume liability for any damages caused by any errors or omissions in the data, nor as a result of the failure of the data to function on a particular system. NOAA makes no warranty, expressed or implied, nor does the fact of distribution constitute such a warranty.
Time Period: 1974-04-01  to  Present
Spatial Bounding Box Coordinates:
N: 90
S: -90
E: 180
W: -180
Spatial Coverage Map:
Themes
  • EARTH SCIENCE > Spectral/Engineering > Microwave
  • EARTH SCIENCE > ATMOSPHERE > ATMOSPHERIC DYNAMICS > Temperature
  • EARTH SCIENCE > ATMOSPHERE > ATMOSPHERIC DYNAMICS > Precipitation
  • EARTH SCIENCE > RADIANCE OR IMAGERY > Microwave > Brightness Temperature
  • EARTH SCIENCE > OCEANS > DYNAMICS > Wind
  • EARTH SCIENCE > OCEANS > DYNAMICS > Sea Ice
  • EARTH SCIENCE > OCEANS > DYNAMICS > Brightness Temperature
  • EARTH SCIENCE > ATMOSPHERE > HYDROLOGICAL PARAMETER > Water Vapor
  • EARTH SCIENCE > BIOSPHERE > GEOGRAPHY AND LAND COVER > Ice
  • EARTH SCIENCE > BIOSPHERE > GEOGRAPHY AND LAND COVER > Snow
  • EARTH SCIENCE > BIOSPHERE > GEOGRAPHY AND LAND COVER > Surface Water
  • Snow Cover
  • Brightness Temperatures
  • Antenna Temperature
  • DMSP/SSMI
  • Sea Ice
  • Polar Orbiters
  • Satellite Meteorology
  • Ocean Surface Wind Speeds
Places
  • Global
Use Constraints
  • Use Constraints: None
Access Constraints
  • Access Constraints: No Constraints
Fees
  • Download available for no cost
Source Datasets
  • DMSP Raw Data Records (RDR)
    • Description of Source: Source Contribution: Used the Raw Data Records Source Type: digital database file
    • Temporal extent used:  1992-01-01  to  present
Lineage Statement Lineage statement not available.
Processor
  • DOC/NOAA/NESDIS/NGDC > National Geophysical Data Center, NESDIS, NOAA, U.S. Department of Commerce
Processing Steps
  • The SSM/I processor is queried once a second by onboard computer and the data are placed into the "TS SSP" data field. Data is ingested as sent from AFWA on a T-1 line. At NGDC, the "TS SSP" data are decommutated, deinterleaved, bit flipped, reordered and restructured into orbits beginning with the equatorial crossing as the satellite travels from south to north. Satellite ephemeris are computed using a physically-based, orbital mechanics model. SSM/I pixels are geolocated using the satellite ephemeris and satellite attitude corrections. Antenna temperatures are computed from instrumental counts by a linear equation, i.e., the conversion is reversible.

Metadata Last Modified: 2011-11-09

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