The use and abuse of image analysis in geophysical potential field interpretation
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Images of geophysical potential field data are becoming more common as a result of the increased availability of image analysis systems. These data are processed using techniques originally developed for remotely sensed satellite imagery. In general, geophysicists are not familiar with such techniques and may apply them without due consideration. This can lead to abuses of the geophysical data and reduce the validity of the interpretation. This paper describes some critical processes which can introduce errors to the data. The production of a regular grid from scattered data is fundamental to image processing. The choice of cell size is paramount and must balance the spatial distribution of the data. The necessary scaling of data from real values into a byte format for display purposes can result in small anomalies being masked. Contrast stretching of grey level images is often applied but can alter the shape of anomalies by varying degrees and should be avoided. Filters are often used to produce shaded relief images but without due regard to their frequency response and the effect on images expanded to fill the display space. The generation of spurious numerical artefacts can be reduced by ensuring that the filter is applied at real precision to the original data grid. The resultant images can then be processed for display. The use of image analysis systems for data integration requires careful consideration of the sampling strategy and information content of each dataset. It is proposed that such procedures are more appropriately conducted on a geographic information system.
KeywordsImage Analysis System Satellite Imagery Regular Grid Data Grid Scattered Data
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- Aarnisalo, J.: 1984, ‘Image Processing and Integration of Geophysical, Landsat and Other Data as a Tool for Mineral Exploration in Glaciated Precambrian Terrain’, inERIM Proceedings of International Symposium on Remote Sensing for Exploration Geology 1, 107–128.Google Scholar
- Billingsley, F. C.: 1983, ‘Data Processing and Reprocessing’, in R. N. Colwell (ed.)Manual of Remote Sensing (2nd edn) American Society of Photogrammetry, Falls Church, Virginia, pp. 719–792.Google Scholar
- Davis, J. C.: 1973,Statistics and Data Analysis in Geology, John Wiley & Son, New York.Google Scholar
- Drury, S. A.: 1987,Image Interpretation in Geology, Allen & Unwin, London.Google Scholar
- Drury, S. A. & Walker, A. S. D.: 1987, ‘Display and Enhancement of Gridded Aeromagnetic Data of the Solway Basin’,Int. J. Remote Sensing 8, 1433–1444.Google Scholar
- Dynamic Graphics: 1988,Interactive Surface Modeling User's Guide Release 6.93, Dynamic Graphics Inc., Berkely, California.Google Scholar
- Gaál, G. (ed.): 1988, ‘Exploration Target Selection by Integration of Geodata Using Statistical and Image Processing Techniques: an Example from Central Finland’,Geological Survey of Finland, Report of Investigation 80.Google Scholar
- Greenbaum, D.: 1987, ‘Lithological Discrimination in Central Snowdonia Using Airborne Multispectral Scanner Imagery’,Int. J. Remote Sensing 8, 799–816.Google Scholar
- Pratt, W. K.: 1975,Digital Image Processing, John Wiley & Sons, New York.Google Scholar
- Turnbull, G.: 1987, ‘Gravity Data Bank on the Keyworth GEC 4090 and VAX 8600 Computers at March 1987’,Regional Geophysics Research Group Project Note PN 87/5, British Geological Survey, Keyworth.Google Scholar
- Uniras: 1986,UNIMAP Users Guide Version 5.4, Uniras A/S, Copenhagen.Google Scholar