For deciphering a greater amount of geological information from satellite remote sensor data, high spectral resolution 'multi-spectral optical' remote sensor data and high spatial resolution 'panchromatic optical' or 'radar microwave' remote sensor data are conventionally merged by data fusion. In a mature topographic terrain, topographic expression, i.e. variation in surface relief over the area, plays an important role in reflecting lithological variation and exposed/subsurface structural features. If the topographic information from such a terrain is merged with high spectral resolution multi-spectral and higher spatial resolution panchromatic satellite remote sensor data by an appropriate data fusion method, the visual interpretability of geological information in the final image product will be significantly improved. This method may also be useful in identifying linear features that are reflected through subtle variation in topographic elevation, but suppressed in the satellite data due to parallelism of the sun azimuth with the trends of these features or due to high sun elevations. In the present work, surface relief data derived from the existing Survey of India topographic base map have been merged with high spectral resolution Landsat-5 thematic mapper (TM) data and higher spatial resolution IRS-1C panchromatic data of Holenarsipur Supracrustal Belt, Karnataka, India, using a data fusion method. The method employs mainly the Intensity-Hue-Saturation (IHS) technique incorporating the concept of the High-Pass-Filter (HPF) technique of data fusion. In this technique, although the spatial details of the original panchromatic data are not being exploited to their fullest potential, the geological information reflected through subtle topographic expression are highlighted well, for example, boundaries of resistant rock formations, regional fold closures and folded layers in resistant rock formations, intrusive granitic masses and mafic-ultramafic intrusive bodies, and regional trends of the planar structural fabrics (regional foliation, fault and joint planes).
