Additional USGS Geoscience data can be found by geographic location or by publication series.
Also included in the data set are programs that can retrieve seasonal ice-concentration profiles at user-specified locations. These nongraphical data retrieval programs are provided in versions for UNIX, extended DOS, and Macintosh computers. Graphical browse utilities are included for the same computing platforms but require more sophisticated display systems.
As ancillary data, the ETOPO5 global gridded elevation and bathymetry data (Edwards, 1989) were interpolated to the resolution of the NSIDC data; the interpolated topographic data are included.
Schweitzer, Peter N., 1995, Monthly average polar sea-ice concentration: U.S. Geological Survey Digital Data Series DDS-27, U.S. Geological Survey, Reston, Virginia.Online Links:
- <http://pubs.usgs.gov/dds/dds27/>
- <http://geo-nsdi.er.usgs.gov/metadata/digital-data/27/ice.exe> (Microsoft Windows)
- <http://geo-nsdi.er.usgs.gov/metadata/digital-data/27/ice.bin> (Linux x86)
- <http://geo-nsdi.er.usgs.gov/metadata/digital-data/27/ice.kit> (Tcl/Tk starkit)
- <http://geo-nsdi.er.usgs.gov/metadata/digital-data/27/ice-viewer.dmg.gz> (Mac OSX)
- <http://geo-nsdi.er.usgs.gov/metadata/digital-data/27/dds27.zip> (Source code)
This is a Raster data set. It contains the following raster data types:
The map projection used is Polar Stereographic.
Planar coordinates are encoded using row and column
Abscissae (x-coordinates) are specified to the nearest 25000
Ordinates (y-coordinates) are specified to the nearest 25000
Planar coordinates are specified in meters
The ellipsoid used is Hughes.
The semi-major axis of the ellipsoid used is 6378.273.
The flattening of the ellipsoid used is 1/298.27941.
Value | Definition |
---|---|
-99 | Missing data |
-88 | Land area |
Range of values | |
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Minimum: | 0 |
Maximum: | 100 |
Units: | percent sea-ice cover |
Resolution: | 1 |
Range of values | |
---|---|
Minimum: | -10783 |
Maximum: | 8000 |
Units: | meters |
Resolution: | 1 |
(703) 648-6533 (voice)
(703) 648-6252 (FAX)
pschweitzer@usgs.gov
The purpose of this data set is to provide paleoclimate researchers with a tool for estimating the average seasonal variation in sea-ice concentration in the modern polar oceans and for estimating the modern monthly sea-ice concentration at any given polar oceanic location. It is expected that these data will be compared with paleoclimate data derived from geological proxy measures such as faunal census analyses and stable-isotope analyses. The results can then be used to constrain general circulation models of climate change.
NASA, 1992, Radiances on a North Polar Stereographic Grid 4/1/ 87 - 8/20/87 and Arctic and Antarctic Sea Ice Concentrations 10/25/78 - 8/20/87 volume 7 of Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) Polar Data: Goddard Space Flight Center SMMR Polar Data volume 7.
NSIDC, 1992, DMSP SSM/I ice concentration grids for the polar regions: DMSP SSM/I brightness temperature and sea-ice concentration grids for the polar regions on CD-ROM volume 1, revision 2.
NSIDC, 1993, DMSP SSM/I ice concentration grids for the polar regions: DMSP SSM/I brightness temperature and sea-ice concentration grids for the polar regions on CD-ROM volume 2, revision 2..
Edwards, Margaret H., 1989, Global gridded elevation and bathymetry (ETOPO5): Digital raster data on a 5-minute geographic (lat/long) 2160x4320 (centroid-registered) grid: U.S. National Oceanic and Atmospheric Administration, National Geophysical Data Center, Boulder, Colorado.
The Bourne shell script do_avgs describes the manner in which the program average was used to calculate the monthly and composite monthly average sea-ice concentration files. The program average is given a list of sea-ice-concentration data files in HDF format. For each grid cell in the images, it calculates the arithmetic average of the corresponding cell in the input files and writes the average image into a new file. This program is run once for each month of each year represented in the original data to yield monthly averages. Then the composite monthly averages are calculated using the monthly averages for each year.
Data sources used in this process:
The Bourne shell script do_imgs converts the monthly average and composite monthly average files into GIF and PICT images. This script uses two programs from the freely available PbmPlus toolkit developed by Jeff Poskanzer.
The ETOPO5 global gridded elevation and bathymetry data set describes world topography on a grid whose cells measure 5 minutes of latitude by 5 minutes of longitude. Since the ice-concentration data are given in a polar stereographic projection, the elevation of cells in the ice-concentration grid must be determined by appropriately sampling or interpolating the ETOPO5 data. Because the ETOPO5 grid is finer than the ice-concentration grid, a sampling algorithm was combined with a spatial averaging scheme to derive the desired elevation data. The program that implements this algorithm is called topo.c; its strategy is to find the ice grid cell coordinates of the center of each ETOPO5 cell and to calculate the average depth of all of the ETOPO5 cells that fall within an ice grid cell. The results are two 16-bit images with big- endian byte ordering in which each signed 16-bit word describes the average depth or elevation in meters (sea level is zero) of a cell in the ice-concentration grid.
Along with the 16-bit depth data files, displayable images are created using depthppm.c in portable pixmap format, and from that intermediate stage, GIF and PICT images are created using the PbmPlus toolkit. Depthppm reduces the complexity of the depth data by assigning one color to a range of depths. The relationship between depth ranges and colors is given in the source-code file depthppm.c.
The Bourne shell script do_topo carries out these operations.
Data sources used in this process:
One of the principal derivative products of this data set is a set of ice-concentration grids in which the grid cell size and position match those produced by the USGS PRISM project for its reconstruction of the climate of the Pliocene, a warm interval about 3 million years before present. These grids are tab-delimited ASCII files suitable for use in spreadsheet programs; each cell of the spreadsheet represents the ice-concentration value of one grid cell measuring 2 degrees latitude by 2 degrees longitude. This calculation is carried out by the Bourne shell script do_tabs.
The procedure is to use a list of the geographic coordinates of the grid cell centers as the request file for the program u_rtrv. The result is a table where each row is a grid cell, and columns 3 through 14 represent the ice-concentration profile for each grid cell (columns 1 and 2 reiterate the grid cell coordinates).
The grid cell centers are given in the files grid_n.2x2 and grid_s.2x2 for the Northern and Southern Hemispheres, respectively. The output of u_rtrv is stored in the files arctic.2x2 and antarctic.2x2.
By using the UNIX cut command, the columns themselves were isolated in separate files, and the program table.c was used to rearrange each column into a tab-delimited ASCII table suitable for entry into a spreadsheet.
Schweitzer, Peter N. , 1993, Modern Average Global Sea-Surface Temperature: U.S. Geological Survey Digital Data Series DDS-10.Online Links:
Calculation of sea-ice-concentration values from brightness temperatures is described extensively in the user's guides of the source data products and in the NASA publication dealing with the SMMR data.
The grids provided in the source data (supplied by NSIDC) are described in the user's guides of the relevant products, and the positional accuracy of the pixels is dealt with both in the user's guides and in the NASA report on the SMMR data.
Included in the data set is a table enumerating the days for which sea-ice-concentration data were available in the source material. In general, images were available every 2 days during the time period from 781025 through 870709, when the SMMR was used, and images were available every day during the period 870709 through 911231, when the SSM/I was used. A large gap (871202 through 880113) occurred when the SSM/I became temporarily inoperative. Other gaps in the SSM/I record were not longer than five consecutive days.
Included in the data set are the UNIX shell scripts and makefiles that were used to derive the averages and create the tables and images. Source code is provided for all programs written by the author.
Are there legal restrictions on access or use of the data?
- Access_Constraints: none
- Use_Constraints: none
(703) 648-6533 (voice)
(703) 648-6252 (FAX)
pschweitzer@usgs.gov
U.S. Geological Survey Digital Data Series DDS-27
Although all data and software published on this CD-ROM have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials or the functioning of the software. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data, software, or related materials.
Data format: | Sea-ice concentration in format GIF (version 89a) Size: 1.5 megabytes |
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Network links: |
<http://geo-nsdi.er.usgs.gov/metadata/digital-data/27/dds27.zip> |
Data format: | Sea-ice concentration display application in format starkit Stand-alone runtime (Tcl/Tk starkit, usable with Linux x86, Microsoft Windows, and MacOSX, requires tclkit to run) Size: 1.5 megabytes |
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Network links: |
<http://geo-nsdi.er.usgs.gov/metadata/digital-data/27/ice.kit> |
Data format: | Sea-ice concentration display application in format EXE Stand-alone runtime (Tcl/Tk starpack executable, UPX compressed) for Microsoft Windows Size: 1.5 megabytes |
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Network links: |
<http://geo-nsdi.er.usgs.gov/metadata/digital-data/27/ice.bin> |
Data format: | Sea-ice concentration display application in format ELF Stand-alone runtime (Tcl/Tk starpack executable, UPX compressed) for Linux x86 Size: 1.5 megabytes |
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Network links: |
<http://geo-nsdi.er.usgs.gov/metadata/digital-data/27/ice.bin> |
Data format: | Sea-ice concentration display application in format Compressed disk image Compressed disk image containing the application Size: 1.5 megabytes |
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Network links: |
<http://geo-nsdi.er.usgs.gov/metadata/digital-data/27/ice-viewer.dmg.gz> |
(703) 648-6533 (voice)
(703) 648-6252 (FAX)
pschweitzer@usgs.gov