U.S. GEOLOGICAL SURVEY DIGITAL DATA SERIES DDS-27 Monthly Average Polar Sea-Ice Concentration By Peter N. Schweitzer U.S. Geological Survey 1995 U.S. DEPARTMENT OF THE INTERIOR Bruce Babbitt, Secretary U.S. GEOLOGICAL SURVEY Gordon P. Eaton, Director -------------------------------------------------------------------------- DESCRIPTION OF THE DATA SET -------------------------------------------------------------------------- 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 the NSIDC data and 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 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 (one for each month from October 1978 through December 1991 except December 1987, and two each for July and August of 1987), 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. -------------------------------------------------------------------------- DIRECTORY STRUCTURE -------------------------------------------------------------------------- Contents/ Text files describing the data set and its contents. Core/ Essential elements of the data set. meta/ Documentation needed to understand the data set. raw/ Essential observations and data files. north/ Sea-ice-concentration data for the Arctic region. south/ Sea-ice-concentration data for the Antarctic region. Derived/ Data and software requiring specific computer systems, and results of calculations on the raw data. dos/ MS-DOS-specific source and executable code. mac/ Macintosh-specific source and executable code and data. unix/ UNIX-specific source and executable code. images/ Images of the data in GIF and PICT formats. grids/ 2-degree by 2-degree gridded modern average sea-ice data used as the basis for a model of sea-ice distribution during the Pliocene warm interval at 3.0 Ma. -------------------------------------------------------------------------- SYSTEM REQUIREMENTS -------------------------------------------------------------------------- This data set is intended for use on MS-DOS, Macintosh, and UNIX computer systems. Included in the data set are simple programs to extract numerical values from the data files and more elaborate graphical display programs, which require more sophisticated hardware to use. Listed below are the minimum system requirements for each of the supported platforms; the additional memory and display capabilities required by the graphical software are noted. MS-DOS - IBM or compatible personal computer - 80386 or 80486 CPU - MS- or PC-DOS version 3.3 or later - Microsoft MSCDEX version 2.1 or later - CD-ROM drive with ISO 9660 software driver The graphical display software requires the following: - 4 megabytes of available RAM configured as extended memory - Super VGA graphics system with at least 640x400 pixels in 256 colors Video adapters based on the following chips are supported: Paradise Video 7 ATI Wondercard, ATI VGA Wonder Oak Technologies Trident Genoa 6400 and 6600 Tseng Labs ET3000 and ET4000 Chips and Technologies S3 Cirrus Logic VESA software interface Macintosh - Macintosh computer - System 7.0 or later - CD-ROM drive The graphical display software requires the following: - 4 megabytes of RAM - 256-color display UNIX - ANSI-conformant C-language compiler - CD-ROM drive with ISO 9660 software driver The graphical display software requires the following: - 8 megabytes of RAM - X Window System version 11, release 4 or later -------------------------------------------------------------------------- HOW TO GET STARTED -------------------------------------------------------------------------- MS-DOS users: To read the documentation: Make the CD-ROM the active drive. Type RUNME To print the documentation on a PostScript printer: Type PRINT DERIVED\REPORT.PS To run the graphical display program: Change directory to the subdirectory \DERIVED\DOS, then type SEE_ICE n or SEE_ICE s where n indicates the Arctic, and s indicates the Antarctic region. If the program runs out of memory, look carefully at your CONFIG.SYS file to determine how extended memory is being used. You may need to disable SMARTDRIVE, and if you use EMM386, you will need to specify NOEMS and NOVCPI as its arguments. On the author's system, the first 3 lines of CONFIG.SYS are as follows: DEVICE=C:\DOS\HIMEM.SYS DOS=HIGH,UMB DEVICE=C:\DOS\EMM386.EXE NOEMS NOVCPI Macintosh users: To read the documentation: Open the folder DOCFILES Use TeachText to view the text files there. The documentation is provided as MS-DOS text files, so small boxes will appear at the beginning of each line of text following the first line. Ignore the small boxes. To print the documentation on a LaserWriter: Run the application "LaserWriter Font Utility", which is on the Tidbits diskette distributed with System 7. Select the menu option "Download PostScript File..." Choose "report.ps", in the folder "Derived". To run the graphical display program: Open the folder "Derived". Open the folder "mac". Open the folder "See Ice". Double-click the application "See Ice". See Ice asks you to locate a file containing a list of data files to read. The files you want are named n for the Arctic and s for the Antarctic. UNIX users: To read the documentation: Documentation files are contained in DOCFILES/*.doc; these can be viewed with your favorite editor; vi will do. The documentation is provided as MS-DOS text files, so ^M may appear at the end of every line of text. Ignore these extra characters. To print the documentation: Send the PostScript file "Derived/report.ps" to your PostScript printer. To run the graphical display program: You must compile the program for your local system. If you have X11R4 or X11R5 and are using gcc or another ANSI-conformant C compiler and if the X Windows header files reside in /usr/include/X11, then the proper command is similar to gcc Derived/unix/see.c -o $HOME/see -lX11 -lm Following successful compilation, change directory to Derived/unix and enter $HOME/see n & or $HOME/see s & The files n and s are text files listing the data files of composite monthly average sea-ice concentration for the Arctic and Antarctic regions, respectively. -------------------------------------------------------------------------- DISCLAIMER -------------------------------------------------------------------------- This Compact Disc-Read Only Memory (CD-ROM) publication was prepared by an agency of the United States Government. Neither the United States Government nor any agency thereof nor any of their employees makes any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. Any views or opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. 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. This CD-ROM has been produced in accordance with the ISO 9660 CD-ROM standard and is therefore capable of being read on any computing platform that has appropriate CD-ROM drive hardware and software installed. (end)