BEDMAP gridded data-sets

Sponsored by:
European Ice Sheet Modelling Initiative
Scientific Committee on Antarctic Research

Summary of BEDMAP gridded data sets

In the BEDMAP project a consistent projection, geoid model and geographic framework were used. In accordance with the recommendations of the Scientific Committee on Antarctic Research [SCAR WGGC (Scientific Committee on Antarctic Research Working Group on Geodesy and Cartography), 1961] we used the Polar Stereographic projection with 71°S as the latitude of true scale and 0°E as the central meridian. In this system, coordinates are expressed in metres with the origin at the South Pole. A geopotential model, OSU91A [Rapp et al., 1991], was chosen as the vertical reference system for integration of all the source data. This was chosen to facilitate integration of the bathymetry data (referenced to mean sea level) with the terrestrial data. The minor differences between mean sea level elevation and geoid orthometric height, generally assumed to be around 1.5 m [Bamber and Bindschadler, 1997], were ignored.

To delimit the continent boundary and its physiographic elements (e.g. ice sheet, ice shelf, ice-free ground) we used the 1:1,000,000 scale data set from the Antarctic Digital Database (ADD) [ADD Consortium, 2000] - the best resolution data with complete coverage over the continent. As well as providing an excellent basis for the integration of external source data the ADD also provides important descriptions of rock outcrop polygons, grounding lines, ice shelves and ice rises. The ADD has a maximum error in horizontal position at this scale of around 300 m [Fox and Cooper, 1994].

The integration, manipulation and generation of all products was carried out using the ARC/INFO geographic information system (GIS) supplemented by customised data transformation, error correction and interpolation functions written in the C programming language.

All data sets have a nominal grid spacing of 5 km. The composite bed elevation grid (entire area south of 60°S is a 1334 x 1334 data array with a total elevation range of approximately 11,000 m. In addition to the orthometric DEM, which is referenced to the OSU91A geopotential model, we also constructed an ellipsoidal height DEM relative to the WGS84 ellipsoid by adding the geoidal undulation. In the Antarctic the geoidal undulation ranges from -67 to +42 m [Rapp et al., 1991].

References

ADD Consortium. Antarctic Digital Database, Version 3.0. Database, manual and bibliography. Scientific Committee on Antarctic Research, Cambridge.

Bamber J. L. and R. A. Bindschadler, An improved elevation dataset for climate and ice-sheet modelling: validation with satellite imagery, Ann. Glaciol. , 25, 1997.

Fox A. J. and A. P. R. Cooper, Measured properties of the Antarctic ice sheet derived from the SCAR Antarctic Digital Database, Pol. Rec., 30, 201-206, 1994.

Rapp, Y. M. Wang, and N. K. Pavlis, The Ohio State 1991 Geoptential and Sea Surface Harmonic Coefficient Models, 410, Dept. of Geodetic Sci. and Surv., Ohio State Univ., 1991.

SCAR WGGC (Scientific Committee on Antarctic Research Working Group on Geodesy and Cartography), Standard symbols for use on topographic maps of Antarctica, Division of National Mapping, Canberra, 1961.