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National Antarctic Data Coordination Center
Products and Services
Publications
NSIDC DAAC
Personnel

NSIDC Notes

Issue 23, December 1997

NATIONAL ANTARCTIC DATA CENTER AT NSIDC

Following discussions this Fall between the National Antarctic Data Coordination Center (NADCC) staff and the National Science Foundation Office of Polar Programs (NSF/OPP), OPP is developing a policy requiring that all grantees submit data descriptions as part of the grant reporting process. These data descriptions will be in the form of Directory Interchange Format (DIF) entries, and will be posted on electronic data directories (such as the Committee on Earth Observing Satellites/International Directory Network (CEOS/IDN) nodes, including the Antarctic Master Directory (AMD). A data description will be due as part of the Final Project Report (NSF 98A), usually three months after the end of the grant.

In order to facilitate the writing of data descriptions (DIFs), NADCC recommends that researchers refer to the Global Change Master Directory Data Documenter.

For more information, please contact NSIDC User Services.

PRODUCTS AND SERVICES

Digital SAR Mosaic and Elevation Map of the Greenland Ice Sheet is now available on CD-ROM

Jakobshavn Glacier, West Coast of Greenland

This image shows the Jakobshavn Glacier on the West Coast of Greenland near the town of Ilulissat. It is the fastest moving glacier in the world, moving at approximately 22 meters per day and unloading 20 million tons of ice every year. The image is displayed with limb software, developed at NSIDC, and distributed with the mosaic on CD-ROM.

The Digital SAR Mosaic and Elevation Map of the Greenland Ice Sheet is now available from NSIDC. This CD-ROM combines the most detailed synthetic aperture radar (SAR) image mosaic available with the best current digital elevation model (DEM) of the ice sheet. Further, the CD-ROM comes with software to enable quick viewing of the data.

The mosaic image shows both the location of the ice edge and the distribution of melt-related "scatterers" on the surface. These scatterers include ice lenses and complex layered structures in the percolation zone, and bare ice in the ablation zone. Other melt-related features that can be seen include lake and surface meltwater stream channels at lower elevations, as well as ice-marginal lakes at the edge of the ice sheet.

This characterization of the ice sheet provides a reference against which future change can be measured. Changing conditions resulting from climatic variation should show up as changes in the ice margin and shifts in the hydrologic zones. It is hoped that the standard reference provided by this data set can facilitate activities aimed at change detection and promote other work aimed at understanding the processes operating on the ice sheet.

The SAR image data are derived from swaths acquired by the ERS-1 satellite during August of 1992. The mosaic was assembled at the Jet Propulsion Labora tory (JPL) and Goddard Space Flight Center (GSFC). Its component images are a copyrighted product of the European Space Agency. The DEM is a recent product of the Danish Geodetic and Cadastral Agency (Kort-og Matrikelstyrelsen, or KMS, in Danish), compiled from elevation data from a number of sources, including field surveys, aerial photographs, and the ERS-1 radar altimeter. Included with the data is NSIDC's Limb (large image map browser) software, which was developed in- house and allows Unix users to easily select and view portions of the mosaic image with elevation contours derived from the elevation data overlain. The image following was generated using this software. Limb is provided as "freeware" for general use.

The Digital SAR Mosaic and Elevation Map of the Greenland Ice Sheet data set is available at no charge, but for research-oriented purposes only. A signed research agreement must be received by NSIDC User Services before the data can be shipped. You may also contact NSIDC User Services for a copy of the agreement.

Just in Time to Capture the Colorado Blizzard of '97

Now up and running in hands-off mode, the NSIDC Near Real-Time Ice and Snow Extent (NISE) product has produced images of snow extent in the western United States for the days before and after October's blizzard. NISE will soon provide similar global snow extent and sea ice concentration data to NASA EOS instrument teams, including TRMM (the Tropical Rainfall Measuring Mission), MISR (the Multiangle Imaging SpectroRadiometer), and CERES (the Clouds and the Earth's Radiant Energy System).

The NISE product is currently restricted to the EOS instrument teams noted above for use as ancillary data for their standard products including top-of- atmosphere and surface radiative fluxes, aerosol mapping, and surface albedo. As of now we have no plans to make the product generally available.

Generated using passive microwave data from the Defense Meteorological Satellite Program F13 Special Sensor Microwave/Imager (SSM/I), NSIDC produces the NISE product each day, within two to four days of the satellite overpass. The data, brightness temperatures, are in swath format and originate at the Lightning Imaging Sensor Enhanced Science Computing Facility at NASA/Marshall Space Flight Center.

The global maps are in a 25-km azimuthal, equal- area gridded format (EASE-Grid) and, for the first time, show both dry snow and melting snow, as well as sea ice concentrations. Two data grids cover the Northern Hemisphere and Southern Hemisphere (see examples following). The sea ice coverage currently includes all Arctic and Antarctic sea ice areas poleward of 35 degrees latitude. Sea ice concentration percentage is derived using the NASA Team "total" sea ice (first year ice plus multiyear ice) algorithm (Cavalieri et al., 1992). The snow extent product is global; however, wet snow and dry snow ex- tents will be mapped separately. Wet snow extent is derived from a modified version of a polarization difference algorithm developed by Walker and Goodison (1993), while dry snow extent is derived from the algorithm described in Goodison and Walker (1993).

Problems affecting the sea ice concentration algorithm accuracy include atmospheric water content, ocean roughening and spray, presence of thin ice, and formation of melt ponds on the sea ice cover. To minimize weather-induced errors over open ocean, a filter is applied to detect these atmospheric effects. Designating mixed pixel areas containing coastline as coastal pixels minimizes further "false" ice concentration estimates.

For the snow extent product, when the snow is wet, the surface becomes primarily an emitter, and much of the signal is lost, greatly limiting algorithm accuracy. To reduce the frequency of observations over wet snow, only data from the descending orbits (early morning) are used as input to the algorithm.

Northern Hemisphere

NISE image, Northern Hemisphere

Southern Hemisphere

NISE image, Southern Hemisphere

References

Cavalieri, D.J., et al. (1992) NASA sea ice validation program for the DMSP SSM/I: Final report. NASA Technical Memorandum, no.104559.

Goodison, B.E.; Walker, A.E. (1993) Use of snow cover derived from satellite passive microwave data as an indicator of climate change. Annals of Glaciology, vol.17, p.137-142.

Walker, A. E.; Goodison, B.E. (1993) Discrimination of a wet snow cover using passive microwave satellite data. Annals of Glaciology, vol.17, p.307-11.

Passive Microwave Derived Polar Sea Ice Concentration Time Series

NSIDC is distributing "Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data." These data were announced in NSIDC Notes no.21, Spring 1997, as the "Passive Microwave Derived Polar Sea Ice Concentration Time Series."

Data are expected to be available on CD-ROM in March 1998, and are currently available via anonymous ftp. The data set has been updated to include the F13 sensor and extends from October 1978 through December 1996. Please contact NSIDC User Services if you would like to be placed on the mailing list to receive the data on CD-ROM when they become available, or if you have downloaded the data via ftp and would like to be a registered user so that we may notify you of updates and corrections.

The data may accessed from NSIDC's Data Catalog as Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data, or by contacting NSIDC User Services.

Great Lakes Ice Data

The winter of 1996/97 marked the last Great Lakes ice season for which NSIDC is collecting daily ice observations at the NOAA/National Ocean Service (NOS) water level gauge sites. Available on the Web or via ftp, the 42-year time series of observations (1955/56 1996/97) provides a snapshot of the ice type from the viewpoint of an observer on the shore, in 8 different categories (open water, solid ice, honeycombed ice, windrowed ice, slush ice, drifting ice, ice gorge) as well as codes indicating the first and last dates of reported ice. The observers have been recruited by NOAA/NOS to maintain a network of water level gauges around the Lakes and along the connecting rivers. We have learned that the water level gauges are being phased to automatic operation, which effectively eliminates the "piggyback" ice observation opportunity. Since we are unable to support the 30-40 observers, we regret that we must terminate the collection of new data for this data set.

The 43 years of observations will remain in the NSIDC archive, accessible and freely available for anyone to use. See the NSIDC Data Catalog for Great Lakes Daily Ice Observations at NOAA Water Level Gauge Sites.

Publications

Snow Cover of the Arctic Basin

The Polar Science Center at the University of Washington Applied Physics Laboratory has published an English translation of Snow Cover of the Arctic Basin, by V.F. Radionov, N.N. Bryazgin, and E.I. Alexandrov (APL-UW TR 9701, 1997, 95 p.). This report is the final version of a draft that was distributed by NSIDC on the CD-ROM Arctic Ocean Snow and Meteorological Observations from Drifting Stations, 1937, 1950-1991. The technical report is available in hard copy from the Polar Science Center. If you have previously requested a copy of the CD- ROM from NSIDC you may already have received the technical report in a separate mailing from the Polar Science Center. To receive a copy of the report, contact Ignatius Rigor, e-mail (igr@apl.washington.edu) or Fax: (206) 543-3521. For more information or to request a copy of the CD-ROM, contact NSIDC User Services.

Personnel

Farewell to Claire

Claire Hanson leaves her position as User Services Manager, after 19 years at NSIDC, at the end of November. She is "retiring" from the cryospheric data world to seek a new career direction in Santa Fe, New Mexico, where her husband has accepted a new position. From Claire: "It has been a pleasure and a privilege to work with all our wonderful requesters and others in the polar and cryospheric community. I thank you all for sharing with us the interesting work you are doing, and for being patient during our busy times when we may have put you "on hold" for a while. I leave you all in good hands with Michelle Holm as the new User Services Manager, and with Diana Starr and Jason Wolfe staffing the e-mail and phones on a daily basis."

NSIDC DAAC

EOSDIS Ombudsman

The NASA EOSDIS project is structured such that each DAAC (Distributed Active Archive Center, of which NSIDC is one) has a User Services group that provides information and support for users of the EOSDIS data and information products. At NSIDC, the User Services group also provides information and support for users of all the other products available from NSIDC. We encourage you to let the User Services group know if you are not satisfied with a product or service, and if your complaint is not addressed to your satisfaction, you are invited to contact NSIDC User Services. If you experience difficulty with NSIDC DAAC or another EOSDIS DAAC or DAAC service and are unable to resolve the problem with the User Services group at that DAAC, call the EOSDIS Ombudsman at 1-800-461- 0075.