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Issue 26, September 1998


SSM/I Sea Ice Data from Bootstrap Algorithm

NSIDC announces the release of 25-km gridded sea ice concentrations derived from SSM/I passive microwave data using the Bootstrap algorithm. Data processed for the DMSP F8 time period using both the NASA Team and Bootstrap algorithms were previously released on a 2 CD-ROM set. The Bootstrap algorithm has since been updated, and data processed using both algorithms should be accessed from NSIDC's ftp site for the entire time period, currently July 1987 through March 1998, to ensure that users are working with the most recent release of the data. Sea ice products from the SMMR sensor (1979-1987) provided by GSFC are also available at NSIDC.

The Bootstrap algorithm utilizes the basic radiative transfer equation and a mixing formulation that makes use of reference brightness temperatures (for ice and open ocean) based on results from cluster analysis of sea ice emissivity data (Comiso, 1983; Comiso, 1986). Only two channels are needed to estimate ice concentration but this algorithm uses two sets of channels to minimize errors associated with spatial variations in emissivity and ice temperature (Comiso, 1995). One set is the 19 and 37 GHz channels at vertical polarization, used in the Antarctic and in the seasonal regions of the Arctic, while the other set is the 37 GHz channels at both polarizations, used in the perennial ice region of the Arctic. The assumptions in the algorithm have been confirmed using aircraft overflight data in the Arctic and data from several cruises in the Antarctic (Grenfell et al., 1994).

A comparison of ice concentration maps from NASA Team and Bootstrap algorithms show good agreement in ice edge location but substantial disagreement in the inner regions of the Antarctic and in seasonal regions of the Arctic (Comiso et al., 1996).

For example, in large areas of the ice pack in the Weddell, Ross, and Amundsen Seas, the ice concentrations from the NASA Team Algorithm are lower by as much as 30 percent than those derived from the Bootstrap Algorithm. Preliminary results show that ice concentrations derived from Landsat and OLS data are very high in these areas and are generally in good agreement with the Bootstrap results. In the coastal areas around the continent, the NASA Team values are often higher than the Bootstrap values, partly due to the presence of ice bergs and partly due to coastal polynyas, where new and young ice are dominant and the temperature of the emitting part of the ice can be extremely low. NSIDC will attempt to update users regarding further validation and intercomparisons of the various sea ice products. The Bootstrap sea ice data are available on the NSIDC ftp site and detailed data set documentation may be accessed from the NSIDC online catalog. See Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I.


Comiso, J.C. 1983. Sea Ice Microwave Emissivities from Satellite Passive Microwave and Infrared observations. Journal of Geophysical Research, 88(C12), p.7686-7704.

Comiso, J.C. 1986. Characteristics of Winter Sea Ice from Satellite Multispectral Microwave Observations. Journal of Geophysical Research, 91(C1), p.975-994.

Comiso, J.C. 1995. SSM/I Concentrations using the Bootstrap Algorithm. NASA RP, 1380, 40p.

Comiso, J.C.; Cavalieri, D.; Parkinson, C.; Gloersen, P. 1997. Passive microwave algorithms for sea ice concentrations. Remote Sensing of the Environment, 60(3), p.357- 384.

Grenfell, T.C.; Comiso, J.C.; Lange, M.A.; Eicken, H.; Wenshahan, M.R. 1994. Passive microwave observations of the Weddell Sea during austral winter and early spring. Journal of Geophysical Research, 99(C5), p.9,995-10,010.

EOSDIS Data Sampler Now Available on CD-ROM

NSIDC is now distributing the "EOSDIS Data Sampler" on CD-ROM. It provides examples of information, images, and animations that introduce the Earth science data sets supported by the NASA Earth Observing System Data and Information System (EOSDIS). An overview of the EOSDIS program is provided along with a summary of the Information Management System (IMS), a web-based tool for accessing EOSDIS products. Data are archived and distributed at various Distributed Active Archive Centers (DAACs), with each DAAC representing a specific scientific discipline such as atmospheric chemistry, snow and ice, oceanography, etc.

Images include the El Niño phenomenon and the stratospheric aerosol concentrations following the Mount Pinatubo eruption. Animations include the Antarctic ozone hole season, weekly snow cover and sea ice extent of the Northern Hemisphere, Pacific winds and typhoons, and global lightning flash rates. This CD-ROM was designed as a resource for the general science and education communities, and is supported by PC and Macintosh platforms. Contact information for the various DAACS is provided for people interested in learning more about EOSDIS data. To receive a free copy of the EOSDIS Data Sampler, please contact NSIDC User Services.

New Data Sets Available from NSIDC

Submarine Upward Looking Sonar Ice Draft Profile Data and Statistics are now available from NSIDC. This data set includes recently declassified submarine data collected in the Arctic Ocean from Navy cruise L2-92, in April, 1992. This data set will be augmented by data from approximately 19 additional cruises dating back to 1986, as the data become available.

The upward looking sonar data are interpolated and processed for release as unclassified data at the U.S. Army's Cold Regions Research and Engineering Labora tory (CRREL) in Hanover, New Hampshire. Data in this data set are saved in two types of files, one for ice draft profiles and the other for statistics derived from the profile data. Ice draft files include a header that gives date and location information followed by a sequential list of drafts spaced at 1.0 m intervals that comprise the bottom-side sea-ice roughness profile. The length of the profile in any given file can be up to 50 km, but may be shorter if data dropouts create gaps greater than 0.25 km, or if changes in course cause deviations from a straight-line track.

Statistics files that include information concerning ice draft characteristics, keels, level ice, leads, and undeformed- and deformed-ice are provided for all draft profiles that exceed 10 km in length.

The data, in ASCII text format are available via ftp. Data set documentation can be accessed online at:Submarine Upward Looking Sonar Ice Draft Profile Data and Statistics

For more information on this new data set please contact NSIDC User Services.

Nenana River Ice Annual Breakup Dates. This archive, obtained from the The Nenana Ice Classic in Alaska, consists of annual date and time of ice breakup on the Nenana River. Data currently span 1917-1997. Ice breakup dates and times will be added yearly.

The data, in ASCII format, are available via ftp. Data set documentation can be accessed online at: Nenana River Ice Annual Breakup Dates.

For more information on this new data set please contact NSIDC User Services.

EASE-Grid Brightness Temperature Data Survey

During the past few months, NSIDC has been surveying all registered EASE-Grid Brightness Temperature users to determine if they would like to continue their subscription to the EASE-Grid data and to evaluate the preferred medium. If you have not responded to this survey and would like to continue to receive the EASE-Grid data, please contact User Services as soon as possible. If we do not hear from you, we will assume that you would like to cancel your subscription. NSIDC staff members are currently working out distribution details.

We will let EASE-Grid users know as soon as we have finalized a plan.

Greenland Summit Ice Cores CD-ROM mailing

NSIDC has completed mailing the Greenland Ice Sheet Project 2 (GISP2) and the Greenland Ice Core Project (GRIP) CD-ROMs to principal investigators and subscribers. This collection represents all data archived from the two campaigns, as well as information on the drilling procedures, core analysis, and scientific results. Please contact NSIDC User Services if you would like to receive this CD-ROM.

Circumpolar Active-Layer Permafrost System (CAPS) CD-ROM mailing

The Circumpolar Active-Layer Permafrost System (CAPS) CD-ROM has been sent to all June 1998 International Conference on Permafrost attendees and others who have requested this CD-ROM. The CD-ROM is intended for a broad audience including the scientific and engineering communities, educators, and policy makers.

Please contact NSIDC User Services if you would like to receive this CD-ROM.

West Antarctica Ice Velocity Data Now Available on the Web

A preliminary set of ice velocity data from the ice streams and perimeter glaciers of West Antarctica is now available on the NSIDC web site. The data consists of over 100,000 vectors from the Siple Coast area, covering parts of Ice Stream B, catchment areas of C, Siple Dome, and large portions of Ice Streams D, E, and F, the Prestrud Inlet and Sulzberger Bay. We are currently asking the scientific community for velocity data for the Antarctic Peninsula, Northern West Antarctic Coast, Filchner/Ronne Ice Shelves, and Amery Ice Shelf/Lambert Glaciers to add to this archive.

A large JPEG image map of the Siple Coast study area provides links to each of the smaller regional study areas and their respective velocity contour and data point maps, as well as tabular data (latitude, longitude, speed, bearing, estimated errors for speed and bearing). A short text section accompanies the data tables, describing the specific images or other sources the data was derived from, pertinent references, and estimated locational accuracy.

For further information, please visit our online data catalog at:Antarctic Ice Velocity

Please contact NSIDC User Services for further assistance.


SCAR-COMNAP Joint Committee on Antarctic Data Management

NSIDC participated in the Scientific Committee on Antarctic Research-Council of Managers of the National Antarctic Programs (SCAR-COMNAP) Joint Committee on Antarctic Data Management (JCADM) meeting in Concepcion, Chile, July 20-24, 1998. As part of NSIDC's Antarctic Data Coordination Center, sponsored by NSF, Greg Scharfen and Rob Bauer represented the U.S. at the JCADM meeting.

JCADM consists of representatives of countries which are participating in the Antarctic Data Directory System (ADDS) which was established by SCAR and COMNAP. The ADDS consists of a network of National Antarctic Data Centers (NADCs), similar to the effort underway at NSIDC, responsible for collecting descriptions of Antarctic data sets (metadata records) and then submitting these to a central Antarctic Master Directory (AMD). The AMD provides a single point of contact for information on Antarctic data sets and is part of the International Directory Network.

Twelve countries participated in the JCADM meeting: Australia, Chile, China, Germany, Italy, Japan, Netherlands, New Zealand, Spain, United Kingdom, the U.S. and Uruguay, plus representatives of the AMD Host and the International Directory Network Global Change Master Directory (GCMD). The AMD is hosted at ICAIR, Christchurch, New Zealand and is funded by a consortium of four nations (the U.S., Italy, France, and New Zealand).

The key issues addressed at the meeting include:

JCADM identified several benefits of submitting metadata records to the AMD:

As of July 1998 there are 504 metadata records held in the Antarctic Master Directory (approximately 380 of these were submitted by the U.S.), 300 of which have been added within the past 12 months (the directory effort began 2 years ago).

The full report from the meeting is available as the Second Report of the Joint Committee on Antarctic Data Management (JCADM), Concepcion, Chile, July 20-24 1998.


ARCSS Web Site Gets Overhaul

The Arctic System Science (ARCSS) Web site at NSIDC has undergone a major redesign and is now available to the research community. Chris McNeave, the ARCSS Data Coordinator, is the architect for the new web site. Pages of importance can now be located easily on the left side navigation bar. The navigation column includes a convenient section for scientists interested in acquiring ARCSS data, as well as a section specifically for ARCSS investigators who wish to submit data and in formation to the ARCSS archive. This design was implemented in conjunction with the anticipated increase in use of the web site by non-ARCSS investigators as well as a planned increase in data and information to be received in the future.

Please visit the new Arctic System Science (ARCSS) Coordination web site

All comments would be appreciated and can be registered on the web site through the "Feedback" link at the bottom of each page.


AMI-Wind and NSCAT Sea Ice Backscatter Grids

Since the launch of ERS-1 in 1991, the Department of Oceanography from Space at the French Research Institute for the Exploitation of the Sea (IFREMER) has been producing backscatter grids from the AMI in Wind mode, the C-band scatterometer on ERS Satellites, over both polar oceans, on a weekly basis.

Ku-band backscatter grids over the lifetime of NSCAT on ADEOS 1 have been produced using the same Polar Stereographic grids that NSIDC uses to process SSM/I brightness temperatures and sea ice concentration data. Taking advantage of the fact that NSCAT was a two-swath instrument, these grids were produced every three days, from September 1996 to June 1997.

Both data sets are now distributed on a WWW server: Institut Français de Recherche pour l'Exploitation de la Mer WWW pages for the CEO-project Integrated use of new microwave satellite data for improved sea ice observation.

Through a friendly browser, the grids can be visualized and the selected data extracted for more detailed analysis. From August 1998, grids will be placed on the server with a two week delay. This work was financed through the European Community Centre for Earth Observations project, IMSI (Integrated use of new Microwave Satellite data for Improved sea Ice observation).

In the future, it is planned to continue production of such grids, using QUIKSCAT then SEaWinds at Ku-band, the AMI-Wind then the ASCAT at C-band.

Alain Cavanie, IFREMER, Department of Oceanography from Space, B.P. 70, 29280 PLOUZANE, FRANCE, IFREMER.

Weekly Ice Thickness and On-Ice Snow Depth Measurements for Canadian Stations

Archived at the Canadian Ice Service (CIS), this data collection contains ice thickness and snow depth measurements for 195 sites, going back as far as 1947 for the first established stations in the Canadian Arctic. For more information or to download data from the CIS web site, please visit their URL at: Weekly Ice Thickness and On-Ice Snow Depth Measurements for Canadian Stations.