Revision of 1:50,000 Topographic Sheet Using Satellite Imagery Preliminary Studies

Abstract

Topographic map coverage of Ghana is a costly project, considering both acquisition of the aerial photographs and the mapping that covers the entire country It has therefore often gone as a bilateral project. It becomes therefore imperative, considering the rate of development in the country, to revise these ageing maps consistently rather than allow them to get outdated and unattended to. Though revision by aerial photographs would have been the best method by reason of their resolution, reflying large areas for revision would be a costly project. Reflying to obtain new aerial photographs for revision is also costly. Considering the fact that revision must often be selective, the use of satellite imagery may be a good alternative and must be exploited. The study limits itself in this stage to the Landsat TM with a pixel size of 30m and the SPOT XS also with a pixel size of 20m. In this paper, a level III SPOT XS imagery at 20 m pixel and a Landsat Thematic Mapper of pixel size of 30m are rectified to a Transverse Mercator Projection using control points (Map coordinates) and a digitizer with a resolution of 0.03mm. Performance of the imagery with regard to accuracy (geometric fidelity) feature identification and the economic applications are discussed. Alternative proposals are also outlined.