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.

This is the most recent version of these data.

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.

COMPREHENSIVE Level of Service

Data: Data integrity and usability verified; data customization services available for select data

Documentation: Key metadata and comprehensive user guide available

User Support: Assistance with data access and usage; guidance on use of data in tools and data customization services

See All Level of Service Details

Parameter(s):
  • MICROWAVE > BRIGHTNESS TEMPERATURE
Data Format(s):
  • Binary
Spatial Coverage:
N: 90, 
S: -90, 
E: 180, 
W: -180
Platform(s):DMSP 5D-3/F17, DMSP 5D-3/F18
Spatial Resolution:
  • 25 km x 25 km
Sensor(s):SSMIS
Temporal Coverage:
  • 2 April 2018
Version(s):V2
Temporal Resolution1 dayMetadata XML:View Metadata Record
Data Contributor(s):Richard Armstrong, Mary Brodzik

Geographic Coverage

Once you have logged in, you will be able to click and download files via a Web browser. There are also options for downloading via a command line or client. For more detailed instructions, please see Options Available for Bulk Downloading Data from HTTPS with Earthdata Login.

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].
Created: 
23 July 2019
Last modified: 
23 July 2019

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.

Parameters

The parameter of this data set is brightness temperature. 

File Information

Format

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. 

Time data are contained in 2-byte, signed integer arrays.

Extensible Markup Language (.xml) files with associated metadata are also provided.

File Contents

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 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.

Directory Structure

Data are available on the HTTPS site at: https://daacdata.apps.nsidc.org/pub/DATASETS/nsidc0342_nrt_ease_grid_tbs/

Naming Convention

Files are named according to the following convention and as 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

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 Information

Coverage

Data files are provided in two different spatial coverages: Northern Hemisphere and Southern Hemisphere. 

Spatial Resolution

The spatial resolution for all channels is 25 km.

Geolocation

The following tables provide information for geolocating this data set.

Table 2. Geolocation Details
Geographic Coverage
Northern Hemisphere
Southern Hemisphere
Geographic coordinate system
Unspecified datum based upon the Hughes 1980 ellipsoid
Unspecified datum based upon the Hughes 1980 ellipsoid
Projected coordinate system
NSIDC Sea Ice Polar Stereographic North
NSIDC Sea Ice Polar Stereographic South
Longitude of true origin
-45
0
Latitude of true origin
70
-70
Scale factor at longitude of true origin
1
1
Datum
Not_specified_based_on_Hughes_1980_ellipsoid
Not_specified_based_on_Hughes_1980_ellipsoid
Ellipsoid/spheroid
Hughes 1980
Hughes 1980
Units
meter
meter
False easting
0
0
False northing
0
0
EPSG code
3411
3412
PROJ4 string
+proj=stere +lat_0=90 +lat_ts=70 +lon_0=-45 +k=1 +x_0=0 +y_0=0 +a=6378273 +b=6356889.449 +units=m +no_defs 
+proj=stere +lat_0=-90 +lat_ts=-70 +lon_0=0 +k=1 +x_0=0 +y_0=0 +a=6378273 +b=6356889.449 +units=m +no_defs 
Reference

Table 3. Grid Details
Grid cell size (x, y pixel dimensions) 25.0 km
Number of rows Northern Hemisphere: 448
Southern Hemisphere: 332
Number of columns Northern Hemisphere: 304
Southern Hemisphere: 316
Geolocated lower left point in grid Northern Hemisphere: 33.92° N, 279.26° W
Southern Hemisphere: 41.45° S, 225.00° W
Nominal gridded resolution 25 km by 25 km
Grid rotation N/A
ulxmap – x-axis map coordinate of the center of the upper-left pixel (XLLCORNER for ASCII data) Northern Hemisphere: -3850 projected km
Southern Hemisphere: -3950 projected km
ulymap – y-axis map coordinate of the center of the upper-left pixel (YLLCORNER for ASCII data) Northern Hemisphere: 5850 projected km
Southern Hemisphere: 4350 projected km

Temporal Information

Coverage

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

Resolution

Daily

Data Acquisition and Processing

Background

The DMSP SSMIS instrument measures passive microwave radiances. For details regarding the SSMIS instrument, refer to the SMMR, SSM/I, and SSMIS Sensors page.

Acquisition

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

Processing

These data are intended as a near-real-time extension of the DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures data set. Processing are identical between the two, except that the input data source for this product comes from the NOAA CLASS system rather than Remote Sensing Systems (RSS). Users should refer to the DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures user guide for more details.

Quality, Errors, and Limitations

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

Instrumentation

Description

These data were acquired using the SSMIS instrument on the DMSP-F18 platform. For more information about the instrument and platform, refer to the SMMR, SSM/I, and SSMIS Sensors page.

Software and Tools

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

Version History

Table 4 provides a summary of the version history of this product.

Table 4. 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, 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,  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.

Related Data Sets

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

Related Websites

Special Sensor Microwave Imager/Sounder (SSMIS)

NOAA/NASA Pathfinder Equal-Area Scalable Earth Grid (EASE-Grid)Brightness Temperatures Image Gallery

Contacts and Acknowledgments

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

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

Access complete Knowledge Base

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