Entry_title: Monthly Average Polar Sea-Ice Concentration
Start_date: 1978-10
Stop_date: 1991-12
Sensor: SMMR>Scanning Multichannel Microwave Radiometer
Sensor: SSM/I>Special Sensor Microwave/Imager
Source: Nimbus-7, DMSP F series
Group: Technical_contact
  Last_name: SCHWEITZER
  First_name: PETER
  Phone: (703) 648-6533
  Email: SMTP>pschweitzer@usgs.gov
  Group: Address
    Mail Stop 955, National Center
    U.S. Geological Survey
    Reston, VA 22092
  End_Group
End_Group
Originating_center: USGS
Storage_medium: CD-ROM
Parameter: Ocean Dynamics> Sea Ice
Discipline: Earth Science> Ocean> Hydrography
Group:  Coverage
  Minimum_latitude=  90S
  Maximum_latitude=  90N
  Minimum_longitude= 180E
  Maximum_longitude= 180W
End_Group
Location: Global> Sea Surface
Keyword: SMMR
Keyword: SSM/I
Keyword: Sea Ice
Keyword: Seasonality
Group: Summary
  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.

  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.

  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.

  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.

  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.
End_Group