This has been superceded by GeoCat 71670

bathymetric grid of the Heard Island-Kerguelen Plateau Region (Longitudes 68 E - 80 E, Latitudes 48 S - 56 S) is produced. In doing so, the individual datasets used have been closely examined and any deficiencies noted for further follow up or have been rectified immediately and the changes documented. These datasets include modern multibeam data, coastline data obtained from the World Vector Shoreline, echosounder data from research, fishing and Customs vessels and satellite derived bathymetric data. A hierarchical system was employed whereby the best and most extensive datasets were gridded first and applied as a mask to the next best dataset. A new masking grid would be formed from these datasets to pass non-overlapping data in the next best dataset. This procedure was employed until finally the satellite data were masked. All the various levels of masked data were then brought together by the gridding algorithm (Intrepid Desmond Fitzgerald Associates) and an ERMapper format grid produced. A grid cell size of 0.005? (nominal 500m) was used with many iterations of minimum curvature gridding and several passes of smoothing. The final grid is available in ERMapper, ArcInfo and ASCII xyz formats.

This dataset has been put together for the Australian Tsunami Warning System Project. Data for the dataset has been collected from a variety of international sources including the International Commission for the Geological Map of the World, Smithsonian Institution's Global Volcanism Program, GNS Science (New Zealand), Geological Survey of Indonesia, and the Geological Survey of Japan. A brief description of each dataset used is listed below, along with how the data was modified. Each dataset has been kept as individual ArcInfo coverages because of the differing scales and projections of the source data. Due to the variety of digital source data most items in the dataset do not comply with the current Geoscience Australia data dictionary or metadata standards.

The Geological and Oceanographic Model of Australia's Territory (GEOMAT- Harris et al., 2000) developed at Geoscience Australia provides maps indicative of the Australian seabed exposure. GEOMAT v.1 proposed a classification of the Australian under water territory based on sediment mobility induced by distinct processes such as tidal currents and gravity waves (Porter-Smith et al., 2004). GEOMAT v.2 proposed an improved classification of the continental shelf area based on a seabed exposure index (Hemer, 2006). The seabed exposure index was derived from the statistical distribution of the sediment transport rate, which reflected the strength and frequency of the combined wave-current bed shear stress. The bed shear stress was derived from a bottom boundary layer model (SEDTRANS - Li and Amos, 2001), which integrated the combined action of tidal currents (Egbert et al., 1994), oceanic currents (OCCAM : Webb et al., 1998), and gravity waves (AUSWAM - Greenslade, 2001) over a given mean sediment fraction (MARS : Geoscience Australia, 2006).

The Global Digital Elevation Model (ETOPO2v2) represents gridded (2 minute by 2 minute) elevation and bathymetry for the world. Two versions of the grid exist, a cell centred version and a grid centred version. As the cell centred version (ETOPO2v2c) is considered to be the authoritative source, this version was used at GA to make the extract. As a result, the depth/elevation values are centred on intersections of lines of odd minutes of latitude and longitude. An extract of this dataset was made for use in the Australian Region. The extract extends from 5°S to 80°S and from 45°E to 180°E.

The GEBCO "One-Minute Grid" is based on the most recent version of the GEBCO Digital Atlas (GDA) bathymetric contours. Additional control contours and sounding data were used in many regions, particularly shallow water areas and semi-enclosed seas, to constrain the gridding process. It is a continuous digital terrain model for ocean and land, with land elevations derived from the Global Land One-km Base Elevation (GLOBE) database. As GA is only interested in the bathymetry in the Australian Region, the downloaded file was edited so that only the values in the Extents Box remained. The extract extends from 5°S to 80°S and from 45°E to 180°E. It must be stressed that although the GEBCO One Minute Grid is presented at one minute intervals of latitude and longitude, this does not imply that knowledge is available on sea floor depth at this resolution. It is important to note that, in most places, many miles exist between adjacent ship tracklines and that the grid is an interpolation based upon the input data. Further details of the data compilation and GEBCO grid construction are available from the 'User guide to the GEBCO One Minute Grid' ( http://www.bodc.ac.uk/data/online_delivery/gebco/documents/gridhelp.pdf).

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