Monthly average polar sea-ice concentration

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.

This data set represents the results of calculations carried out on sea-ice-concentration data from the SMMR and SSM/I instruments. The original
data were obtained from the National Snow and Ice Data Center (NSIDC). The data set also contains the source code of the programs that made the calculations.
The objective was to derive monthly averages for the whole 13.25-year series (1978-1991) and to derive a composite series of monthly averages representing
the variation of an average year. The resulting file set contains monthly images for each of the polar regions for each year, yielding 160 files for each
pole, and composite monthly averages in which the years are combined, yielding 12 more files. Averaging the images in this way tends to reduce the number of
grid cells that lack valid data; the composite averages are designed to suppress interannual variability.

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.

The data contained in this data set are derived from the Scanning Multichannel
Microwave Radiometer (SMMR) and Special Sensor Microwave/ Imager (SSM/I) data
produced by the National Snow and Ice Data Center (NSIDC) at the University of
Colorado in cooperation with the U.S. National Aeronautics and Space
Administration (NASA) and the U.S. National Oceanic and Atmospheric
Administration (NOAA). The basic data come from satellites of the U.S. Air
Force Defense Meteorological Satellite Program. NSIDC distributes three
collections of sea- ice-concentration grids on CD-ROM: data from the Nimbus-7
SMMR (October 25, 1978 through August 20, 1987) are provided on volume 7 of the
SMMR Polar Data series (NASA, 1992); data from the SSM/I are provided on two
separate volumes, covering the periods from July 9 of 1987 to December 31 of
1989, and from January 1 of 1990 through December 31 of 1991, respectively. The
NASATEAM data from revision 2 of the SSM/I CD-ROM's were used to create the
present data set. SMMR images were collected every 2 to 3 days, whereas SSM/I
data are provided in daily ice-concentration grids. Apart from a number of
small gaps (5 or fewer days) in the record, the only long period for which no
data are available is December 3 of 1987 through January 12 of 1988, inclusive.

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.

The images are provided in three formats: Hierarchical Data Format (HDF), a
flexible scientific data format developed at the National Center for
Supercomputing Applications; Graphics Interchange Format (GIF); and Macintosh
PICT format. The ice- concentration grids are distributed by NSIDC in HDF
format.