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Near-Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures

Summary

The Near-Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperature product provides near-real-time brightness temperatures for both the Northern and Southern Hemispheres. These brightness temperatures are used to generate Near-Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Sea Ice Concentrations. Near-real-time passive microwave brightness temperatures are received daily from the Special Sensor Microwave Imager/Sounder (SSMIS) on board the Defense Meteorological Satellite Program (DMSP) F17 satellite, and are gridded onto the SSM/I polar stereographic grid. The SSMIS instrument is the next generation Special Sensor Microwave/Imager (SSM/I) instrument. SSMIS data used for this data set are received from the Comprehensive Large Array-data Stewardship System (CLASS) at the National Oceanic and Atmospheric Administration (NOAA). Two-byte scaled integer data are available via FTP at a resolution of 25 km for the 19, 22, and 37 GHz channels, and at 12.5 km resolution for the 85 GHz and 91GHz channels. NSIDC plans daily updates to the data. These data will be retained on the FTP site until NSIDC's standard brightness temperature product, DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures, is available.

Typically, NSIDC receives the standard SSM/I brightness temperatures from Remote Sensing Systems, Inc. (RSS), who derive them from SSM/I antenna temperatures, between three and six months after the initial satellite overpass. NSIDC chose to provide near-real-time brightness temperatures to facilitate time-sensitive research dependent upon precise detection of seasonal polar sea ice formation and break up. Daily brightness temperatures consist of seven files, one for each channel and polarization, for each hemisphere.

Possible differences between the standard and near-real-time products remain to be determined. The near-real-time data do not supplant the standard products, but instead fill the gap in time between present-day and the delivery of the RSS data. Users are therefore cautioned to be aware of potential data differences and should continue to use the standard products derived from the RSS data for time series analyses.

These data may contain errors and are not suitable for time series, anomalies, or trends analyses. Near-real-time products do not undergo quality assessment and are therefore not intended for operational use.

Near-real-time data will remain on-line and available to users for three months after receipt of NSIDC's standard products from RSS. The file naming convention allows users to easily distinguish the near-real-time data from the standard SSM/I brightness temperatures.

For general information about these data, please see the DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures. Users interested in understanding how the near-real-time data were acquired and processed should review the Near-Real-Time SSM/I-SSMIS EASE-Grid Daily Global Ice Concentration and Snow Extent documentation.

Detailed Data Description

Format

The near-real-time brightness temperature files are stored as 2-byte scaled integer data.

Data Access and Directory Structure

The data are available via FTP. All files reside in the same directory. Note: The F17 and F15 files are located after the F13 files.

Software and Tools

Table 1 lists the tools that can be used with this data set. For a comprehensive list of all polar stereographic tools and for more information, see the Polar Stereographic Data Tools Web page.

Table 1. Tools for this Data Set
Tool Type Tool File Name(s)
Data Extraction extract.pro
Data Display dataviewer.tar.gz
Geocoordinate dataviewer.tar.gz
locate.for
mapll.for and mapxy.for
psn12lats_v3.dat and pss12lats_v3.dat
psn12lons_v3.dat and pss12lons_v3.dat
psn25lats_v3.dat and pss25lats_v3.dat
psn25lons_v3.dat and pss25lons_v3.dat
Pixel-Area psn12area_v3.dat and pss12area_v3.dat
psn25area_v3.dat and pss25area_v3.dat
Land Masks gsfc_12n.msk and gsfc_12s.msk
gsfc_25n.msk and gsfc_25s.msk
Land Overlays coast_12n.msk and coast_12s.msk
coast_25n.msk and coast_25s.msk
ltln_12n.msk and ltln_12s.msk
ltln_25n.msk and ltln_25s.msk


File Naming Convention

The data files are named according to the following convention and as described in Table 2:

tb_fxx_YYYYMMDD_nrt_RCCP.bin

where:

Table 2. File Naming Convention Variable Description
Variable Description
tb Indicates this file contains brightness temperature data
fxx Indicates which DMSP satellite the data came from (f13: DMSP-F13; f15: DMSP-F15; f17: DMSP-F17)
Note: DMSP-F13 and -F15 data currently retained in the FTP directory should be used for intercomparison purposes only.
YYYY 4-digit year
MM 2-digit month
DD 2-digit day
nrt Indicates that data are near-real-time
R Region (n: north; s: south)
CC Channel (19: 19 GHz, 22: 22 GHz, 37: 37 GHz, 85: 85 GHz, or 91:91 GHz)
P Polarization (h: horizontal, v: vertical)
.bin Identifies this as a binary data file

Data Acquisition and Processing

The DMSP-F13 satellite that has been central to our brightness temperature products for the past several years is nearing the end of its mission and is no longer a reliable resource for our brightness temperature products. As is standard data practice, we have transitioned to a newer sensor. As of 02 June 2009, NSIDC has switched its SSM/I processing stream from the DMSP-F13 satellite to SSMIS data from the DMSP-F17 satellite. For data continuity, F17 data have been acquired and processed back to 01 April 2008.

One year earlier, on 02 June 2008, NSIDC switched its SSM/I processing stream from the DMSP-F13 satellite to the DMSP-F15 satellite due to a failing recorder on F13. For continuity, F15 data were acquired and processed from 01 January 2008 until 25 February 2009. On 16 February 2009, however, NSIDC switched its SSM/I processing stream back to the DMSP-F13 satellite due to an issue with the DMSP-F15 SSM/I 22 GHz frequency brightness temperature fields. NSIDC continued to produce the F13 products until further degradation of the SSM/I instrument on 11 May 2009. Processed F13 data are available for the 01 July 2008 through 11 May 2009 time period.

However, although you may choose to use data from either the F13 or F15 satellites, NSIDC recommends using these data for intercomparison purposes only. SSMIS data from the DMSP-F17 satellite are used for the current near-real-time product. Regarding the F13 and F15 data, you should be aware of the following differences:

Regarding the F17 data, users should note a difference in the high frequency channel. The SSMIS sensor is similar to the SSM/I sensor and has the same low frequency channels: dual-polarized 19 GHz and 37 GHz channels, and a vertically polarized 22 GHz channel. However, the high-frequency 85.5 GHz channel on SSM/I has been replaced by a 91 GHz channel on SSMIS. Users should note that the different frequency will affect any products that employ a high frequency channel. Any such products should be evaluated for the impact of the different frequency and adjustments may be necessary for consistent products. For more information regarding the SSMIS instrument, refer to the SSMIS Instrument Description Web page.


Document Information

Document Revision Dates:
20 June 2009
02 June 2009
13 January 2009
27 May 1999

Document ID: nsidc-0080

Citation:

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.

The following example shows how to cite the use of this data set in a publication. List the principal investigators, year of data set release, data set title, dates of data you used, publisher (NSIDC), and digital media.

Cavalieri, D. J., P. Gloersen, and H. Zwally. 1999. Near-Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures. [indicate subset used]. Edited by J. Maslanik and J. Stroeve. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center.