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The Arctic and Antarctic Research Center: Support for research during 1996-1997

Robert H. Whritner, Elizabeth Nelson, and Dan Lubin, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, California 92093-0214

During 1996 and 1997, the Arctic and Antarctic Research Center (AARC) at the Scripps Institution of Oceanography provided satellite remote sensing data and data-analysis services to polar researchers worldwide. The AARC receives high-resolution picture telemetry (HRPT) data from the National Oceanographic and Atmospheric Administration (NOAA) and Defense Meteorology Satellite Program (DMSP) telemetry from the U.S. Air Force polar orbiters (Van Woert et al. 1992). The numerous uses of these remote-sensing data for polar research and operations in all disciplines are discussed by Massom (1991) and by King and Turner (1997).

These data are collected by National Science Foundation-maintained antennas at two land-based antarctic sites (Palmer and McMurdo Stations). The AARC also receives data from the U.S. Coast Guard icebreakers Polar Sea and Polar Star when these ships are operating north or south of 50 latitude. The data are sent to the AARC periodically as raw digital telemetry on magnetic media, but much of the AARC's work is also done by logging directly into the satellite-tracking computer at McMurdo via the T1 line. The satellite-tracking facilities, as well as the AARC image-processing laboratory at the Scripps Institution of Oceanography, are based on the SeaSpace Corporation (San Diego, California) TeraScan and TeraVision hardware and software. The AARC also (and primarily) supports researchers who do not themselves possess this specialized software. The AARC's involvement with polar research has encompassed a wide variety of disciplines, including atmospheric sciences (26 percent of all AARC users as of late 1997), polar oceanography (7 percent), sea-ice research (25 percent), glaciology (7 percent), geophysics (5 percent), polar biology (23 percent), and space science (7 percent). The table lists the total number of HRPT and DMSP overpasses in the AARC archive.

The number of HRPT and DMSP overpasses archived at the AARC as of 19 September 1997
Year HRPT DMSP
1985 44 0
1986 78 0
1987 130 0
1988 604 0
1989 612 0
1990 1,954 0
1991 3,008 1,264
1992 5,151 3,502
1993 6,083 4,187
1994 6,195 6,769
1995 6,819 5,263
1996 6,887 6,704
1997 4,238 3,418

Between the two land-based sites, geographic coverage of the continent is nearly complete, with some gaps on the Indian Ocean side. The table is complete as of 2 August 1997 for McMurdo HRPT data, 8 June 1997 for McMurdo DMSP data, and 19 September 1997 for all Palmer data. There is a total of 72,910 satellite overpasses in the archive. For the earlier years, some of the table entries have changed from our last report (Whritner, Nelson, and Lubin 1995), because some data have been rescued from older media, as discussed below. In addition to providing this historical archive, the AARC has maintained the real-time data-processing and reduction services described in our last report.

During the past 2 years, the AARC has greatly expanded the use of its World Wide Web page (http://arcane.ucsd.edu). The entire AARC data catalog can be accessed through a graphical search program, which will provide the user with the number and specific listings of satellite overpasses for a specific antarctic region and time period. Sample images are available at http://arcane.ucsd.edu/aarc.pages/img.html . Also, many of the specialized data-reduction and -analysis projects provided to the international community have been delivered over the World Wide Web. One example during 1997 was a large advanced very-high-resolution radiometer (AVHRR) image processing project completed for Antarctica New Zealand (ANZ).

ANZ wanted 9 years' worth of clear-sky scenes over the Cape Roberts area, to determine seasonal dependence in sea-ice conditions. This information was necessary to plan geological drilling operations, because ANZ is heading an international field program, the Cape Roberts Project. For the years 1987-1997, clear-sky image data were provided covering May through September. AARC personnel inspected all available overpasses to find clear sky scenes, and an example is shown in figure 1.


Figure 1. Example of HRPT support given by the AARC to Antarctica New Zealand. This clear-sky AVHRR infrared image was obtained on 7 July 1989 and shows the structure of the ice floes in the Cape Roberts region at 2-kilometer spatial resolution. (GMT denotes Greenwich mean time.)

Throughout 1996-1997, the AARC continued to provide regular sea-ice mapping support to the antarctic research vessels Polar Duke and Nathaniel B. Palmer. Sea-ice maps were provided at 30-kilometer spatial resolution using the National Aeronautics and Space Administration (NASA) team algorithm (Cavalieri et al. 1991) and also at 12.5-kilometer spatial resolution using the 85.5-gigahertz channels of the DMSP special sensor microwave imager (SSM/I). The 85.5-gigahertz SSM/I brightness temperatures are influenced by tropospheric cloud cover more than those from the lower frequency channels used by the NASA team algorithm. As a result of our participation in the 1994 Arctic Ocean Section (Aagaard et al. 1996), however, we have gained more confidence and experience with the use of 85.5-gigahertz data for sea-ice mapping (Lubin et al. 1997). Generally speaking, our 85.5-gigahertz SSM/I sea-ice maps provide better location of the ice edge for cruise-planning purposes, whereas the NASA team algorithm provides more accurate estimates of total sea-ice concentration over large geographic areas (e.g., Cavalieri et al. 1997). Figure 2 shows an example of an 85.5-gigahertz SSM/I sea-ice map generated at the AARC for Scripps Institution of Oceanography research scientist Gregory Mitchell, in support of the 1997 Joint Global Ocean Flux Study (JGOFS) antarctic cruises of the research vessels Nathaniel B. Palmer and Roger Revelle.


Figure 2. Example of a total sea-ice concentration image provided by the AARC to the Joint Global Ocean Flux Study (JGOFS). The ice concentration is mapped at 12.5-kilometer spatial resolution using the 85.5-gigahertz (GHz) channels of the SSM/I instrument aboard the U.S. Air Force polar orbiters.

The AARC has also taken important steps to safeguard the large archive of antarctic satellite data. By the end of 1996, all of the AARC data had been migrated to modern 4-millimeter (mm) Hewlett-Packard compression format tapes. Prior to 1996, digital satellite telemetry at the AARC resided on two types of 4-mm media (Hewlett-Packard and WangDat compressions), 8-mm (Exabyte) tapes, and old 9-track tapes, depending on the original source in the Antarctic. Migration to a common format has (most important) rescued older data from loss through media deterioration and has made access to all data more efficient. In total, 1,327 WangDat tapes, 569 8-mm tapes, and 100 9-track tapes were copied over to accomplish this. The AARC has also been making copies of raw telemetry for the National Snow and Ice Data Center (NSIDC) on a regular basis for specific regions and time periods as requested by NSIDC. The AARC's mandate is to provide satellite data and support with interpretation to interested researchers at no cost to the user, although for large data requests, the user is asked to cover the cost of magnetic media.

Support for the AARC commenced with National Science Foundation grant DPP 88-15818 and continued with subsequent supplements. The AARC presently operates with support from National Science Foundation grant OPP 94-14276.

References

Aagaard, K., L.A. Barrie, E.C. Carmack, C. Garrity, E.P. Jones, D. Lubin, R.W. Macdonald, J.H. Swift, W.B. Tucker, P.A. Wheeler, and R.H. Whritner. 1996. U.S., Canadian researchers explore Arctic Ocean. EOS, Transactions of the American Geophysical Union, 77(22), 209 & 213.

Cavalieri, D.J., J.P. Crawford, M.R. Drinkwater, D.T. Eppler, L.D. Farmer, R.R. Jentz, and C.C. Wackerman. 1991. Aircraft active and passive microwave validation of sea ice concentration from the Defense Meteorological Satellite Program Special Sensor Microwave Imager. Journal of Geophysical Research, 96, 21989-22008.

Cavalieri, D.J., P. Gloersen, C.L. Parkinson, J.C. Comiso, and H.J. Zwally. 1997. Observed hemispheric asymmetry in global sea ice changes. Science, 278, 1104-1106.

King, J.C., and J. Turner. 1997. Antarctic meteorology and climatology. Cambridge, United Kingdom: Cambridge University Press.

Lubin, D., C. Garrity, R.O. Ramseier, and R.H. Whritner. 1997. Total sea ice concentration retrieval from the SSM/I 85.5 GHz channels during the arctic summer. Remote Sensing of Environment, 62, 63-76.

Massom, R. 1991. Satellite remote sensing of the polar regions. New York: Lewis.

Van Woert, M.L., R.H. Whritner, D.E. Waliser, D.H. Bromwich, and J.C. Comiso. 1992. ARC: A source of multi-sensor data for polar science. EOS, Transactions of the American Geophysical Union, 73, 65 & 75-76.

Whritner, R.H., E. Nelson, and D. Lubin. 1995. The Arctic and Antarctic Research Center: Support for research during 1994-1995. Antarctic Journal of the U.S, 30(1-4), 10-12.