High Resolution Digital Elevation Models - A New Data Source

High resolution digital elevation models (DEMs) can now be produced for large areas of Australia. This paper will describe the method of producing DEMs and some of the applications.

The change in technology which has made possible routine generation of height data for large areas, is soft photo-grammetry. In the past, the method of determining height was by matching points on two airphoto stereopairs. This was accomplished manually which made for a tedious and time consuming process. The advent of computer software that can match features on stereopairs has meant that DEMs can be created much more quickly.

The procedure is to scan the diapositives of the air photographs with a geometrically accurate scanner at high resolution (15-30 microns). This will give a pixel size of 1.5 metres for a 1:50,000 scale photo. Internal and external distortion is then removed from the scanned images by internal, relative and absolute orientation procedures. The images are then resampled as epipolar pairs. The final procedure is to automatically match common features on both of the stereopairs. Changes in the X parallax give the height or Z value.

The DEMs are accurate to within +/-1 pixel i.e. 1.5 metres for standard 1:50,000 scale photography or 25 cm for 1:10,000 photography. This high resolution allows for a number of novel applications, including:- identify topographic anomalies associated with mineralisation (e.g. kimberlite lows, silicified highs)

- georectify photographs to produce orthophotos

- 3D visualisation, 3D Photomaps, and terrain draping

- structural analysis using shaded relief images

- landform analysis including palaeo surface reconstruction

- slope vector maps for soil sampling and geochemical dispersion

- drainage maps and drainage divides for stream sampling programs

- height corrections for high resolution gravity surveys

Images for these applications will be shown for the Laverton 1:50,000 sheet area in Western Australia.