Monday, 04 January 1999
From: Matthew Lythe, BEDMAP Database Manager

Compilation exceeds 1 million data points
Over the past few months several substantial data sets have been added to the BEDMAP database pushing it over the milestone of 1 million data points. The compilation now includes ice thickness data from seismic, radio-echo sounding (RES) and gravimetric surveys conducted by 10 nations in almost 80 expeditions carried out during the last fifty years. Although some areas, notably parts of central East Antarctica, still have only limited coverage, the number of data points in BEDMAP is already two orders of magnitude greater than the only comparable compilation, the SPRI Folio 'The Bedrock Surface of Antarctica' published in 1983. Data added to BEDMAP since our last update include;

• seismic, gravity, RES observations collected by Belgian scientists in Dronning Maud Land between 1959 and 1992;
• ground based and airborne RES survey over Dome C carried out by the Italian Antarctic Program in 1992-93;
• airborne RES data collected by British Antarctic Survey over the Brunt Ice Shelf, Dronning Maud Land and Ellsworth Land between 1995 and 1998.
• Airborne RES data collected by the US during the 1987/88 & 1988/89 seasons in gridded blocks covering the upstream parts of Ice Streams A,B and C and the downstream parts of Ice Stream B and C.
• Soviet Antarctic Expedition airborne RES surveys over the Lambert Glacier, Amery Ice Shelf and the surrounding mountains.

Data Density Map
A density map describing the number of data points per 100km square grid cell has been produced from this database. The results indicate that over 36% of cells have more than 100 data points while almost 70% of grid cells have at least 10 observations. Most of the cells with zero data points lie in inland Dronning Maud Land, Queen Mary Land and the region south of the Lambert Glacier. This map may be viewed on the BEDMAP web site at;
http://www.nerc-bas.ac.uk/public/aedc/bedmap/density.html
Some of the gaps, particularly in Victoria Land and coastal regions, will be filled with the incorporation of rock outcrop data while we are confident that many of the larger gaps in East Antarctica will be filled with several data providers promising data over the next few months.

Current activities
Over the next period the focus will switch from the recovery and reformatting of data to comply with the BEDMAP database format to the evaluation, validation and quality assurance of these data. Several QA checks will be carried out on all data sets in order to identify spurious data points and any systematic errors. These checks will include the removal of gross outliers, along track QA to determine isolated data spikes, an analysis of cross-over errors on overlapping or very close data points and cross validation to identify subtle errors not picked up with the previous checks. Meanwhile a number of new data sets are scheduled to be added to the compilation.

Second BEDMAP workshop
At this stage we are planning towards holding a two-day workshop in Cambridge immediately after the 22nd General Assembly of the International Union of Geodesy and Geophysics to be held at the University of Birmingham, UK, 18th to 30th July 1999. As this conference includes a symposium that focuses on ice sheets we expect there to be a number of attendees with an interest in BEDMAP in the UK at this time. We will release the first circular for this workshop in the near future. We do of course welcome any comments or suggestions relating to the timing, possible location or content of this workshop.