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This data set provides a near real-time map of sea ice concentrations for both the Northern and Southern Hemispheres. Near real-time passive microwave brightness temperature data from the Defense Meteorological Satellite Program (DMSP) F13 Special Sensor Microwave/Imager (SSM/I) are received daily from the Marshall Space Flight Center (MSFC) and gridded onto a polar stereographic grid. Investigators generate sea ice concentrations from these data using the NASA Team algorithm.
These data are stored as one-byte flat scaled binary arrays with one byte per pixel, at a resolution of 25 km. For each data file, a corresponding PNG image file is provided. These data are available via FTP for the most recent three to six months, and are retained on the FTP site until NSIDC's Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data (preliminary data) become available for the same time period.
These data are primarily meant to provide a best estimate of current ice and snow conditions based on information and algorithms available at the time the data are acquired. Near real-time products are not intended for operational use in assessing sea ice conditions for navigation and should be used with caution in extending the sea ice time series in NSIDC's Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data.
To broaden awareness of our services, NSIDC requests that you acknowledge the use of data sets distributed by NSIDC. Please refer to the citation below for the suggested form, or contact NSIDC User Services for further information. We also request that you send us one reprint of any publication that cites the use of data received from our Center. This helps us to determine the level of use of the data we distribute. Thank you.
Please use caution if using this data set to extend the sea ice time series in NSIDC's Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data. Any such use should be explicitly stated within any publication, presentation, or other application. 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 used (for example, 01 January to 15 March 2006), publishers (NSIDC), and digital media.
Maslanik, J., and J. Stroeve. 1999, updated daily. Near real-time DMSP SSM/I daily polar gridded sea ice concentrations, [list dates of data used]. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.
| Category | Description |
|---|---|
| Data format | One-byte flat scaled binary (preceded by a 300-byte header); a PNG image is provided with each data file |
| Spatial coverage and resolution | North and south polar regions; 25 km resolution |
| Temporal coverage and resolution | Most recent three to six months; daily |
| Tools for accessing data | Software and tools to display and extract the data are available via FTP. |
| Grid type and size | See Polar Stereographic Projections
and Grids. Grid size varies by region: North: 304 columns x 448 rows South: 316 columns x 332 rows |
| Data range | 0 to 250 (fractional coverage scaled by 250; percentage scaled by 2.5) |
| File naming convention | nt_yyyymmdd_f13_nrt_R.bin |
| File size | File size varies by region: North: 136492 bytes South: 105212 bytes |
| Parameter | Sea ice concentration |
| Procedures for obtaining data | Data are available via FTP. |
Jim Maslanik
University of Colorado
Boulder, Colorado USA
Julienne Stroeve, Ken Knowles, Walt Meier
National Snow and Ice Data Center (NSIDC)
Boulder, Colorado USA
Donald J. Cavalieri
NASA Goddard Space Flight Center (GSFC)
Greenbelt, Maryland USA
NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org
This near real-time sea ice concentration (NRTSI) data set is created using brightness temperatures from NASA's Global Hydrology Resource Center (GHRC) at Marshall Space Flight Center (MSFC), in order to provide the product within one to two days following data acquisition. See the Quality Assessment section for more information.
The NRTSI data processing is as close as possible to that used for NSIDC's Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data (SMMR-SSM/I Sea Ice). Table 1 compares some of the major processing features for these two data sets.
| Processing | NRTSI | SMMR-SSM/I Sea Ice |
|---|---|---|
| Weather filter | Same | Same |
| Sea ice algorithm | Same | Same |
| Land-to-ocean spillover correction | Same | Same |
| Brightness temperature tie points | Same | Same |
| Residual weather effects and associated subjective filtering | Maximum ice extent climatology | Sea surface temperature-based climatology |
| Missing data | Flagged as missing | Filled by spatial or temporal interpolation |
For more information about processing, see the Data Acquisition and Processing section in the documentation for NSIDC's Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data.
The NRTSI files are stored as flat scaled binary data with one byte per pixel. The file format consists of a 300-byte descriptive header followed by a two-dimensional array of one-byte values containing the data. For each data file, a corresponding graphics file in PNG format is provided.
For more information about the data format, see the Format section in the documentation for NSIDC's Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data.
The directory structure on the FTP site is shown below. These data are in the near-real-time directory; data for the north polar region are in the north directory, and data for the south polar region are in the south directory. Browse images (PNG files) are in the browse directory.
The binary data files and browse image files are named according to the following convention and as described in Table 2:
| Binary: | nt_YYYYMMDD_f13_nrt_R.bin |
| Images: | nt_YYYYMMDD_f13_nrt_R.png |
where:
| Variable | Description |
|---|---|
| nt | Indicates this was created with the NASA Team algorithm |
| YYYY | 4-digit year |
| MM | 2-digit month |
| DD | 2-digit day |
| f13 | Indicates that data are from the F-13 sensor |
| nrt | Indicates that data are near real-time |
| R | Region (n = north; s = south) |
| .bin | Identifies this as a binary data file |
| .png | Identifies this as a browse image file (.PNG format) |
For example, nt_20060115_f13_nrt_n.bin holds data for the north polar region for the date 15 January 2006.
File size varies by region:
North: 136492 bytes
South: 105212 bytes
North and south polar regions (defined by the Polar Stereographic Projections and Grids spatial coverage map).
25 km
Data are in a polar stereographic projection.
Grid
size varies by region:
North: 304 columns x 448 rows
South: 316 columns x 332 rows
Most recent three to six months.
Daily
For more information, see the Parameter or Variable section in the documentation for NSIDC's Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data.
Sea ice concentration represents an areal coverage of sea ice. For a given grid cell, the parameter provides an estimate of the fractional amount of sea ice covering that cell, with the remainder of the area consisting of open ocean. Land areas are coded with a land mask value.
Data source is the DMSP-F13 SSM/I instrument. Please see the SSM/I Instrument Description for more details.
The sea ice concentration floating-point values (fractional coverage ranging from 0.0 to 1.0) are multiplied by a scaling factor of 250. To convert to the fractional range of 0.0 to 1.0, divide the scaled data in the file by 250. To convert to percentage values, divide the scaled data in the file by 2.5. Data files may contain integers from 0 to 255, as described in the Table 3.
| Data Value | Meaning |
|---|---|
| 0 - 250 | Sea ice concentration (fractional coverage scaled by 250) |
| 251 | Circular mask used in the Arctic to cover the irregularly-shaped data gap around the pole (caused by the orbit inclination and instrument swath) |
| 252 | Unused |
| 253 | Coastlines |
| 254 | Superimposed land mask |
| 255 | Missing data |
This NRTSI data set is created using brightness temperature data from GHRC at MSFC, in order to provide the product within one to two days following data acquisition. These brightness temperatures do not receive the same level of quality control as the DMSP SSM/I Daily Polar Gridded Brightness Temperatures product created at NSIDC.
Additionally, these NRTSI data may:
Data are available via FTP.
Software and tools to display and extract the data are available via FTP. For more information, please see the Software and Tools section in the documentation for NSIDC's Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data.
Please see Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data for general information about these data and the data processing.
Please see Near Real-Time SSM/I EASE-Grid Daily Global Ice Concentration and Snow Extent for more information about how the near real-time data were acquired and processed.
Near real-time passive microwave brightness temperatures from the DMSP F13 SSM/I are received daily from MSFC and gridded onto the SSM/I polar stereographic grid. NSIDC generates sea ice concentrations from these brightness temperature data using the NASA Team Sea Ice Algorithm. These data are updated daily and are retained on the FTP site until NSIDC's Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data (preliminary data) become available for the same time period. Roughly the most recent three to six months of near real-time sea ice concentration data are available.
These data are intended to facilitate time-sensitive research dependent upon precise detection of seasonal polar sea ice formation and break up. These data are primarily meant to provide a best estimate of current ice and snow conditions based on information and algorithms available at the time the data are acquired. Near real-time products are not intended for operational use in assessing sea ice conditions for navigation and should be used with caution in extending the sea ice time series. For historical SMMR and SSM/I sea ice concentration data, please see Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data.
For more information, see the Data Acquisition and Processing section in the documentation for NSIDC's Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data.
Please see the Defense Meteorological Satellite Program (DMSP) Satellite F13 platform description and the Special Sensor Microwave Imager (SSM/I) instrument description and for information about the DMSP-F13 SSM/I platform and instrument.
References include:
Cavalieri, D. J., P. Gloersen, and W. J. Campbell. 1984. Determination of sea ice parameters with the NIMBUS-7 SMMR. Journal of Geophysical Research 89(D4):5355-5369.
Cavalieri, D. J., C. I. Parkinson, P. Gloersen, and H. J. Zwally. 1997. Arctic and Antarctic sea ice concentrations from multichannel passive-microwave satellite data sets: October 1978 to December 1996, User's Guide. NASA Technical Memorandum 104647. 17 pages.
Table 4 lists related documents that are available on NSIDC's Web site.
| Document | Description | URL |
|---|---|---|
| Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data | General information about these data, details about the data processing, and a complete list of references. | http://nsidc.org/data/docs/daac/nsidc0051_gsfc_seaice.gd.html |
| Defense Meteorological Satellite Program (DMSP) Satellite F13 | Platform description | http://nsidc.org/data/docs/daac/f13_platform.gd.html |
| Special Sensor Microwave Imager (SSM/I) | Instrument description | http://nsidc.org/data/docs/daac/ssmi_instrument.gd.html |
| NASA Team Sea Ice Algorithm | Algorithm description | http://nsidc.org/data/docs/daac/nasateam/index.html |
| Polar Stereographic Projections and Grids | Grid definition and details | http://nsidc.org/data/grids/ps_grid.html |
| Near Real-Time SSM/I EASE-Grid Daily Global Ice Concentration and Snow Extent | Information about how the near real-time data were acquired and processed. | http://nsidc.org//data/nise1.html |
Table 5 lists acronyms that are used in this document.
| ANSI | American National Standards Institute |
| ASCII | American Standard Code for Information Interchange |
| DMSP | Defense Meteorological Satellite Program |
| FTP | File Transfer Protocol |
| GHRC | Global Hydrology Resource Center |
| GSFC | Goddard Space Flight Center |
| MSFC | Marshall Space Flight Center |
| NASA | National Aeronautics and Space Administration |
| NRTSI | Near real-time sea ice concentration |
| NSIDC | National Snow and Ice Data Center |
| PNG | Portable Network Graphics |
| SMMR | Scanning Multichannel Microwave Radiometer |
| SSM/I | Special Sensor Microwave/Imager |
| URL | Uniform Resource Locator |
May 2008
April 2001
October 2006
http://nsidc.org/data/docs/daac/nsidc0081_ssmi_nrt_seaice.gd.html
