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DMSP SSM/I- Microwave Imager

Metadata Updated: November 12, 2020

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 the NOAA National Centers for Environmental Information (formerly National Geophysical Data Center), 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.

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License: No license information was provided. If this work was prepared by an officer or employee of the United States government as part of that person's official duties it is considered a U.S. Government Work.

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Metadata Date September 18, 2015
Metadata Created Date November 12, 2020
Metadata Updated Date November 12, 2020
Reference Date(s) January 1, 1992 (publication)
Frequency Of Update daily

Metadata Source

Harvested from NGDC STP DMSP

Additional Metadata

Resource Type Dataset
Metadata Date September 18, 2015
Metadata Created Date November 12, 2020
Metadata Updated Date November 12, 2020
Reference Date(s) January 1, 1992 (publication)
Responsible Party Unknown
Contact Email
Guid gov.noaa.ngdc.stp.dmsp:G01123
Access Constraints Use Constraints: None, Access Constraints: No Constraints
Bbox East Long 180
Bbox North Lat 90
Bbox South Lat -90
Bbox West Long -180
Coupled Resource
Frequency Of Update daily
Harvest Object Id 2a22d727-b24b-4d9b-bd48-e2d3a2b6999b
Harvest Source Id e404f77a-c028-47ea-9804-e5967810b42f
Harvest Source Title NGDC STP DMSP
Licence 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.
Metadata Language eng; USA
Metadata Type geospatial
Progress underDevelopment
Spatial Data Service Type
Spatial Reference System
Spatial Harvester True
Temporal Extent Begin 1974-04-01

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