|Geoscience and Environment|
Penang Island has no sedimentary rocks, which simplifies the geology and makes it a worthwhile subject for geomorphology, the study of landforms and the processes that produce them. However, restrictions placed on topographic maps make such a study almost impossible without satellite imagery. Russian topographical maps do help, but converting a contoured topographic map to a digital elevation model (DEM) means that there will be artifacts at each contour. In this context an artifact is something added to a map by the map-making technology, rather than from nature.
With its two views, downwards (nadir) and backwards, ASTER band 3 makes it possible to process stereo pairs of images to make high resolution DEM's. Such DEM's support the study of landforms. The image below was produced from a file generated by GDS, the Japanese partner in charge of ASTER DEM products, (GDS). The black voids in the image are caused by clouds. The straight line down the edge of the scene is the furthest limit of band 3B, not visible in the browse image. The analyst must take care in selecting an ASTER scene for DEM production to ensure that there is space all around the area of interest to avoid such cut-offs.
The topographic map shows a broad correspondence with the topography shown in the ASTER DEM (Ong Wee Seck, The Geology and Engineering Geology of Pulau Penang, Geological Survey Malaysia, Map Report 7, 1993).