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A New Technique to Remove false Topographic Perception Phenomenon and its Impacts in Image Interpretation

Abstract


A New Technique to Remove false Topographic Perception Phenomenon and its Impacts in Image Interpretation

Arun K. Saraf


Arun K. Saraf
Email: [email protected]

Sudipta Tapan Sinha


Sudipta Tapan Sinha
Email: [email protected]

Parthapratim Ghosh


Parthapratim Ghosh
Email: [email protected]

Department of Earth Sciences,
Indian Institute of Technology, Roorkee
Roorkee – 247667, India

Abstract
All sun-synchronous remote sensing satellites, during day passes always acquire images when the illumination source (i.e. sun position) is from the SE direction. The typical solar-illumination-source – observer position creates false topographic perception phenomenon (FTPP) in the images of any rugged terrain (e.g. Himalayas, Alps etc.). Due to the presence of FTPP, valleys appear as ridges and vice versa specially in rugged terrain. The correction of FTPP is necessary because it creates confusion in interpreters mind due to inherent inverse topographic perception. This paper explains the development of a new approach to remove FTPP. It has been successfully demonstrated using IRS-1D-LISS-III image of part of Himalayas, which represents highly rugged terrain. In this newly developed image-processing technique; first a RGB image is transformed into IHS channels, then the original intensity channel is inverted and later retransformed back from IHS to RGB image. After this retransformation, the RGB image is then colour balanced with original FCC. The final image product is free from FTPP and also contains almost same image information. This method is an easy and quicker method to remove FTPP in comparison to already available methods (e.g. (a) image rotation by 180°, (b) creating image negative and (c) using opposite illuminated shaded relief model as intensity image during IHS to RGB retransformation) for FTPP correction. Further, this paper discusses the relative advantages of this new method in comparison to previous methods in light of image classification and lineament interpretation done using images with FTPP and without FTPP.