GEODATA 9 Second DEM and D8 - Digital Elevation Model Version 3 and Flow Direction Grid : User Guide

Abstract

This dataset and its metadata statement were supplied to the Bioregional Assessment Programme by a third party and are presented here as originally supplied. The GEODATA 9 Second DEM (DEM-9S) Version 3 is a grid of ground level elevation points covering the whole of Australia, with a grid spacing of 9 seconds in longitude and latitude (approximately 250 metres) in the GDA94 coordinate system. The 9 Second Flow Direction Grid (D8-9S) is a corresponding grid describing the principal directions of surface drainage across the whole of Australia. Version 3 of the DEM-9S was calculated by Version 5.2.2 of the ANUDEM procedure (Hutchinson 2007) from comprehensively revised and augmented national GEODATA TOPO-250K (TOPO-250K) topographic source data (AUSLIG 1992, Geoscience Australia 2003, Geoscience Australia 2006). The source data included revised versions of TOPO-250K elevation points, streamlines, cliff lines and waterbodies, trigonometric points from the National Geodetic Database and additional elevation, streamline and sink point data digitised by the Fenner School from 1:100K source material. Version 5.2.2 of the ANUDEM procedure incorporates major upgrades to the modelling of streamlines, lakes, cliff lines and the coastline. The 9 Second Flow Direction Grid (D8-9S) has been released for the first time, with Version 3. This grid was calculated by the ANUDEM procedure as it calculated the DEM-9S. It incorporates the data streamline structure and describes the drainage structure continent-wide. It can be used to delineate streamlines and associated catchment boundaries for the DEM-9S. This is particularly useful in low relief areas where drainage structure is not reliably defined by the DEM elevations alone. The comprehensive revisions and additions to the source data for the DEM-9S Version 3 were completed over a period of 3 years by the Fenner School and Geoscience Australia. This built on the substantial period of source data revision and algorithmic development by the Fenner School over the last 15 years. Comprehensive quality assurance of the DEM-9S and the D8-9S was performed jointly by the Fenner School and Geoscience Australia. The revised version of the ANUDEM elevation gridding procedure was developed and implemented by Professor Michael Hutchinson of the Fenner School. The DEM-9S Version 3 is a model of the terrain in which each data point represents the approximate elevation at the centre of each 9 second by 9 second cell. The density and positional accuracy of the source point elevation data generalises the local terrain, resulting in limited representation of some high points. Version 3 incorporates the improvements made in Version 2 by including with the source data the national trigonometric points from the National Geodetic Data Base. The representation of abrupt changes in landform has been comprehensively upgraded in Version 3 by incorporating, for the first time, the TOPO-250K national cliff line data and by upgrading the modelling of cliff lines by the ANUDEM procedure to minimise conflicts between streamlines and cliff lines. The upgraded procedure maximises the accuracy of the representation of surface shape within the limits imposed by the 9 second grid spacing. Of central importance for the accurate representation of surface drainage structure is the upgrading of the modelling of streamlines by ANUDEM. This improves the positional accuracy of streamlines and explicitly incorporates, also for the first time, the extensive distributary streamline networks that occur in low relief areas of the Australian continent. ANUDEM has also been upgraded to improve the positional accuracy of the coastline and to ensure a smooth transition between land and seabed away from areas with coastal cliffs.