U.S. GEOLOGICAL SURVEY DIGITAL DATA SERIES DDS-27

               Monthly Average Polar Sea-Ice Concentration

                         By Peter N. Schweitzer


                             ACKNOWLEDGMENTS


    This project was supported by the Global Change and Climate History
    Program, U.S. Geological Survey.

    The original Scanning Multichannel Microwave Radiometer (SMMR) and
    Special Sensor Microwave/Imager (SSM/I) data from which this data set
    was derived can be obtained from

        National Snow and Ice Data Center
        CIRES, Box 449
        University of Colorado
        Boulder, CO 80309
        Tel: (303) 492-1834 or (303) 492-5171
        FAX: (303) 492-2468
        email: nsidc@kryos.colorado.edu

    The SMMR data are provided on volume 7 of the Nimbus-7 SMMR Polar Data
    series (NASA, 1992).

    The SSM/I data are provided on two CD-ROM's, one spanning the time
    period 870709 (that is, July 9, 1987) through 891231, the other
    spanning 900101 through 911231 (National Snow and Ice Data Center,
    1992, 1993).  The data are encoded using the Hierarchichal Data Format
    developed by the National Center for Supercomputing Applications.
    DDS-27 was creating using Revision 2 of the SSM/I data.

    The gridded elevation and bathymetry data were interpolated (using the
    program getdepth whose source getdepth.c is included) from the ETOPO5
    data set of Edwards (1989), available from the National Geophysical
    Data Center (NGDC) of the National Oceanic and Atmospheric
    Administration (NOAA) on CD-ROM.  The full data set citation is
    described in the NOAA Global Ecosystems Database documentation manual
    as follows:

    NOAA/NGDC. 1992. Integrated Global Elevation and Bathymetry. Digital
    Data. NOAA/NGDC/WDC-A, Boulder, Colorado. Digital raster data on a
    5-minute geographic (lat/long) 2160x4320 grid. In: Global Ecosystems
    Database Version 1.0: Disc A. Boulder, Colo.: NOAA National Geophysical
    Data Center. 1 independent single-attribute spatial layer on CD-ROM.
    18.6 MB. [first published in 1989]

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