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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.
Data Set ID:
NSIDC-0342
Near-Real-Time DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures, Version 2
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
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Geographic Coverage |
Other Access Options
Other Access Options
Close
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. Earthdata Search: This application allows you to search, visualize, and access data across thousands of Earth science data sets. Additional customization services are available for select data sets, including subsetting, reformatting, and reprojection. |
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:
30 September 2020
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
| 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 Horizontal19V: 19 GHz Vertical 22V: 22 GHz Vertical37H: 37 GHz Horizontal37V: 37 GHz Vertical85H: 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.
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Geographic Coverage
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Northern Hemisphere
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Southern Hemisphere
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|---|---|---|
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Geographic coordinate system
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Unspecified datum based upon the Hughes 1980 ellipsoid
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Unspecified datum based upon the Hughes 1980 ellipsoid
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Projected coordinate system
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NSIDC Sea Ice Polar Stereographic North
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NSIDC Sea Ice Polar Stereographic South
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Longitude of true origin
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-45
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0
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Latitude of true origin
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70
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-70
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Scale factor at longitude of true origin
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1
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1
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Datum
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Not_specified_based_on_Hughes_1980_ellipsoid
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Not_specified_based_on_Hughes_1980_ellipsoid
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Ellipsoid/spheroid
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Hughes 1980
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Hughes 1980
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Units
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meter
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meter
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|
False easting
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0
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0
|
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False northing
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0
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0
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EPSG code
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3411
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3412
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PROJ4 string
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+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
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+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
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Reference
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| 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
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| 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
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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 Summary.
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 Summary.
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.
| 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. |
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| V1 |
01 September 2009 |
Changes to this version include:
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| 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
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
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