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

Summary

This data set provides daily, near-real-time Special Sensor Microwave/Imager (SSM/I) and 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 270 days of near-real-time data. The spatial resolution is 25 km for all channels. Data are contained in flat binary files and are available via FTP.

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.

Citing These Data

The following example shows how to cite the use of this data set in a publication. 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.

Brodzik, M. J. and R. L. Armstrong. 2008, updated daily. Near-Real-Time DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures, [list dates of data used]. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.

Overview Table

Category	Description
Data format	Brightness Temperature Files: Flat binary, little-endian, 2-byte unsigned, compressed (Gzip) Time Files: Flat binary, little-endian, 2-byte signed, compressed (Gzip) Note: The data format information in this document represents the data in its native format as it is archived at NSIDC. If you have downloaded the data using Polaris, please consult the 00README file located in the tar file for information on the data format operations that were performed on this data set.
Spatial coverage and resolution	Northern and Southern Hemispheres 25 km resolution for all channels (19, 22, 37, 85 and 91GHz) Note: The high-frequency 85.5 GHz channel on SSM/I has been replaced by a 91 GHz channel on SSMIS.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.
Temporal coverage and resolution	Past 270 days Resolution: Daily
Tools for accessing data	IDL Tools
Grid/projection description	Northern Hemisphere EASE-Grid Southern Hemisphere EASE-Grid
File naming convention	ID2-Fxx-HHYYYYDDDP.CCC.gz
File size	Gzipped Brightness Temperature Files: 133 KB - 417 KB per file Gzipped Time Files: 9.7 KB - 30 KB per file
Parameter(s)	Brightness temperatures (0.1 K precision)
Procedures for obtaining data	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

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

Technical Contact

2. Detailed Data Description

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.

File and Directory Structure

Data are available on the FTP site and all files reside within one directory, the nsidc0342_nrt_ease_grid_tbs directory.

File Naming Convention

Files are named according to the following convention and as described in Table 1:

ID2-Fxx-HHYYYYDDDP.CCC.gz

Where:

Table 1. File Naming Convention

Variable	Description
ID2	Indicates that this data was interpolated with an inverse distance squared method.
Fxx	DMSP satellite ID (f13: DMSP-F13; f17: DMSP-F17)
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

File Size

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

Spatial Coverage

These 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.

Temporal Coverage and Resolution

This data set provides near-real-time SSM/I and SSMIS brightness temperatures for the past 270 days with a one day lag period. The resolution is daily.

Parameter or Variable

The parameter of this data set is brightness temperature.

Parameter Description

Please refer to the Parameter or Variable section of the DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures guide document for more information on the parameters in this data set.

Quality Assessment

Due to the near-real-time nature of this data set, no quality assessment is performed.

3. Data Access and Tools

Data Access

Data are available via FTP.

Software and Tools

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

Related Data Collections

• DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures

4. Data Acquisition and Processing

Sensor or Instrument Description

These data were acquired using the SSM/I instrument on the DMSP-F13 platform and the SSMIS instrument on the DMSP-F17 platform. For more information about the these instruments, please see the SSM/I Instrument Description and SSMIS Instrument Description Web pages.

Theory of Measurements

The DMSP SSM/I and SSMIS instruments measure passive microwave radiances. For a detailed description of how the instruments obtain these measurements, refer to the SSM/I Instrument Description and SSMIS Instrument Description Web pages.

Data Acquisition Methods

Input data are acquired via FTP. The F13 input data were acquired from NASA's Global Hydrology Research Center (GHRC) and F17 input data are acquired from NOAA's National Environmental Satellite, Data, and Information Service (NESDIS).

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 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 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. Any such products should be evaluated for the impact of the different frequency and adjustments may be necessary for consistent products.

Derivation Techniques and Algorithms

These data have been interpolated with an inverse distance-squared (ID2) interpolation.

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. Data processing is the same as for DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures with the following exceptions:

1. Input data source of SSM/I swath data is from GHRC rather than Remote Sensing Systems (RSS).
2. Input data source of SSMIS swath data is from NESDIS rather than Remote Sensing Systems (RSS).
3. Gridding interpolation method is ID2 instead of Backus-Gilbert.

For information on the processing of these data, please see the Processing Steps section in the DMSP SSM/I Pathfinder Daily EASE-Grid Brightness

5. References and Related Publications

Brodzik, M. J. and K. W. Knowles. 2002. "EASE-Grid: A Versatile Set of Equal-Area Projections and Grids" in M. Goodchild (Ed.) Discrete Global Grids. Santa Barbara, California USA: National Center for Geographic Information & Analysis.

Table 2 lists related documents that are available from NSIDC.

Table2. Related Documents

Document	Description	URL
All About EASE-Grid	Web page that describes EASE-Grid.	http://nsidc.org/data/ease/index.html
EASE-Grid: A Versatile Set of Equal-Area Projections and Grids	Technical Report on EASE-Grid	http://nsidc.org/data/ease/ease_grid.html
NSIDC's EASE-Grid Geolocation Tools	Web page that provides descriptions of each EASE-Grid geolocation tools for the various data sets.	http://nsidc.org/data/ease/tools.html
Special Sensor Microwave Imager (SSM/I)	Web page with SSM/I instrument description	http://nsidc.org/data/docs/daac/ssmi_instrument.gd.html
EASE-Grid Image Gallery	Sampler image gallery of SSM/I Level 3 Brightness Temperatures.	http://nsidc.org/data/docs/daac/nsidc0032_ssmi_ease_tbs/gallery/index.html
Frequently Asked Questions	NOAA/NASA Pathfinder SSM/I Level 3 EASE-Grid Brightness Temperatures FAQs	http://nsidc.org/data/docs/faqs/ssmi_ease_faq.html

6. Document Information

Acronyms

Table 3 lists acronyms that are used in this document.

Table 3. Acronyms

Acronym	Description
DMSP	Defense Meteorological Satellite Program
EASE-Grid	Equal-Area Scalable Earth-Grid
EOS	Earth Observing System
FAQ	Frequently Asked Question
FTP	File Transfer Protocol
GHRC	Global Hydrology Research Center
ID2	Inverse Distance-Squared
NASA	National Aeronautics and Space Administration
NESDIS	National Environmental Satellite, Data, and Information Service
NOAA	National Aeronautics and Space Administration
NSIDC	National Snow and Ice Data Center
RSS	Remote Sensing Systems
SSM/I	Special Sensor Microwave/Imager
SSMIS	Special Sensor Microwave Imager/Sounder
URL	Uniform Resource Locator

Document Creation Date

September 2008

Document URL

http://nsidc.org/data/docs/daac/nsidc_0342_nrt_ssmi_ease_tb/index.html