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Data Set ID:
NSIDC-0342

Near-Real-Time DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures, Version 2

This data set provides daily, near-real-time Special Sensor Microwave Imager/Sounder (SSMIS) brightness temperatures in the Equal-Area Scalable Earth-Grid (EASE-Grid). The data set consists of gridded data in two projections: Northern Hemisphere and Southern Hemisphere. The data lag by one day and provide 365 days of near-real-time data. The spatial resolution is 25 km for all channels. Data are contained in flat binary files.

Version Summary:

For this Version 2 data set, NSIDC has switched its SSMIS processing stream from the DMSP-F17 satellite to SSMIS data from the DMSP-F18 satellite.

Geographic Coverage

Parameter(s):
  • Microwave > Brightness Temperature
Spatial Coverage:
  • N: 90, S: -90, E: 180, W: -180

Spatial Resolution:
  • 25 km x 25 km
Temporal Coverage:
  • 1 March 2018
Temporal Resolution: 1 day
Data Format(s):
  • Binary
Platform(s) DMSP 5D-3/F17
Sensor(s): SSMIS
Version: V2
Data Contributor(s): Richard Armstrong, Mary Brodzik

Data Citation

As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.

Brodzik, M. J. and R. Armstrong. 2018. Near-Real-Time DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures, Version 2. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/K7VT6D6Y2SO6. [Date Accessed].

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Detailed Data Description

This data set provides daily, near-real-time Special Sensor Microwave Imager/Sounder (SSMIS) brightness temperatures on the Equal-Area Scalable Earth-Grid (EASE-Grid). The data set consists of gridded data in two projections: Northern Hemisphere and Southern Hemisphere. The data lag by one day and provide 365 days of near-real-time data. The spatial resolution is 25 km for all channels. Data are contained in flat binary files.

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.
Format

Brightness Temperature Files

Brightness temperature data are contained in flat binary files (little-endian) with one array per file consisting of 2-byte integer arrays of brightness temperatures in tenths of kelvins.

Each brightness temperature file contains gridded data for a single sensor channel and polarization; they are derived from either ascending or descending orbits (for example, 37 GHz, horizontal, ascending) for one day. There are 18 brightness temperature files per day for each projection. There are two files for each day (ascending and descending orbits) for each projection and for each sensor channel (frequency and polarization).

Time Files

Time data are contained in 2-byte, signed integer arrays. Time data are minutes since 00:00 Coordinated Universal Time (UTC) of the date of the enclosing file. Each time file represents the corresponding time of the swath sample used for the interpolation of the given grid cell, for either ascending or descending orbits for that day. There are two time files per day (ascending and descending passes) for a given projection, both at 25 km resolution.

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File and Directory Structure

Data are available on the HTTPS site at: 

https://daacdata.apps.nsidc.org/pub/DATASETS/nsidc0342_nrt_ease_grid_tbs/

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File Naming Convention

Files are named according to the following convention, which is described in Table 1:

ID2-Fxx-HHYYYYDDDP.CCC.gz

Table 1. File Naming Convention
Variable Description
ID2 Indicates that this data was interpolated with an inverse distance squared method.
Fxx DMSP satellite ID (F17: DMSP-F17, F18 DMSP-F18)
HH Hemisphere (NL: Northern, SL: Southern)
YYYY 4-digit year
DDD 3-digit day of year
P Direction of pass (A: ascending, D: descending)
CCC Indicates channel and polarization or time file:

19H: 19 GHz Horizontal
19V: 19 GHz Vertical 
22V: 22 GHz Vertical
37H: 37 GHz Horizontal
37V: 37 GHz Vertical
85H: 85 GHz Horizontal (SSM/I data only)
85V: 85 GHz Vertical (SSM/I data only)
91H: 91 GHz Horizontal (SSMIS data only)
91V: 91 GHz Vertical (SSMIS data only)

tim: Time file
gz Indicates that this is a gzipped file
 
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File Size

Gzipped Brightness Temperature Files: 133 KB to 417 KB per file 
Gzipped Time Files: 9.7 KB to 30 KB per file

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Spatial Coverage

Data files are provided in two different spatial coverages: Northern Hemisphere and Southern Hemisphere. Please see the Grid Extent Table on the EASE-Grid: A Versatile Set of Equal-Area Projections and Grids web page for specific latitude and longitude values.

Spatial Resolution

The spatial resolution for all channels is 25 km.

Projection/Grid Description

The SSM/I azimuthal EASE-Grids are equal-area projections: one for the Northern and one for the Southern Hemisphere. Please see the EASE-Grid: A Versatile Set of Equal-Area Projections and Grids for more information on the EASE-Grid.

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Temporal Coverage and Resolution

This data set provides near-real-time SSMIS brightness temperatures for approximately the past 365 days with a 1-day lag period. The resolution is daily.

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Parameter

The parameter of this data set is brightness temperature. Refer to the Parameter section of the DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures user guide for details regarding this parameter.

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Quality Assessment

Due to the near-real-time nature of this data set, quality assessment is not performed.

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Software and Tools

Geolocation tools for this data set are available via the EASE-Grid Data Geolocation Tools web page.

Related Data Collections
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Data Acquisition and Processing

Theory of Measurements

The DMSP SSMIS instrument measures passive microwave radiances. For a detailed description of how the instrument obtains these measurements, refer to the SSMIS Instrument Description web page.

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Data Acquisition Methods

Input data are acquired via HTTPS from the Comprehensive Large Array-data Stewardship System (CLASS) at the National Oceanic and Atmospheric Administration (NOAA).

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Derivation Techniques and Algorithms

These data have been interpolated using an inverse distance squared (ID2) interpolation method.

Processing Steps

These data are intended as a near-real-time extension of the DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures data set. The input data source for this product comes from the NOAA CLASS system rather than Remote Sensing Systems (RSS), and all processing is identical.

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Sensor or Instrument Description

These data were acquired using the SSMIS instrument on the DMSP-F18 platform. For more information about this instrument, see the SSMIS Instrument Description web page.

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Version History

Table 2 provides a summary of the version history of this product.

Table 2. Summary of Version History
Version Release Date Description of Changes
V2
28 March 2018

Switched the SSMIS processing stream from the DMSP-F17 satellite to SSMIS data from the DMSP-F18 satellite.

V1
 
01 September 2009

Changes to this version include:

  • Swtiched the SSM/I processing stream from the DMSP-F13 satellite to SSMIS data from the DMSP-F17 satellite.
  • Changed the gridding interpolation method from Backus-Gilbert (BG) to inverse distance squared (ID2) to maintain consistency between this data set and the DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures data set.
  • SSMIS swath data, the input data source for this product, is obtained from the NOAA CLASS system rather than RSS.
2008 Initial release of this data product using SSM/I on the DMSP-F13 satellite.

Version 2 Update Notice

28 MARCH 2018

As of 06 March 2018, NSIDC switched its SSMIS processing stream from the DMSP-F17 satellite to SSMIS data from the DMSP-F18 satellite. Data prior to this date will overlap with DMSP-F17 and remain available via HTTPS until they age off (approximately 9 months). An assessment of the data comparing the results from SSMIS DMSP-F17 and SSMIS DMSP-F18 showed that, for any given day, about half of the F17 and F18 observations overlap identical grid cells with a time separation of less than two hours. Through linear regression testing, observations from the two satellites align with very high correlation. Lower frequency channels generally have offsets of less than 5 Kelvin with r2 correlations above 0.98, and higher frequency channels show biases less than 10 Kelvin with r2 correlation values above 0.95.

Version 1 Update Notice

01 September 2009

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 01 September 2009, NSIDC 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 August 2009 to allow for a one-month overlap period for the two sensors. The F13 data will remain available via FTP until they age off and are eventually replaced by the F17 data. However, NSIDC recommends using the F13 near-real-time data for intercomparison purposes only. SSMIS data from the DMSP-F17 satellite are used for the current near-real-time product.

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.

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References and Related Publications

Contacts and Acknowledgments

Mary J. Brodzik 
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
(303) 492-6199

Document Information

DOCUMENT CREATION DATE

September 2008

DOCUMENT REVISION DATE

March 2018

No technical references available for this data set.
No FAQs or How Tos available for this data set.

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Questions? Please contact:
NSIDC User Services
Phone: 1 303 492-6199
Email: nsidc@nsidc.org