Ground water targeting using digitally enhanced imagery
Previous Work
The work of S. K. Sharma (1986) shows that there is definite relation between morphology of features (density and frequency) and permeability of the formation in bard rock terrain based on the infilteration number, which is the product of fracture density and frequency. Stephen and Myner ( 1985) used five image enhancement techniques to LNADSAT digital data for lineament detection namely, Mean Value of Four Bands reflectances, Principal Component (PC), Analysis, band retioing, Histogram equalization and High pass Filtering. They found that all the five techniques identified significant amount of lineament features.
Study Procedure
The present study was carried out in two phases. The first phase was to extract the various geological features related to the ground water through digital image process and the second phase involved the mapping of the ground water potential area.
In the study emphasis was given enhance the geological features. The enhancement used can be classification into three categories:
- Contrast manipulation by Histogram equalization and other stretching techniques.
- Multi Image Manipulation by Multi Band addition and Band Rationing.
- Spatial Feature Manipulation by Image Smoothing through low pass filtering and edge enhancement through high pass filtering.
Results
Fig. 2 shows the Landsat MSS band 4 subimage with 15 grey levels before histogram equalization and Fig. 3. Gives after histogram. Qualization. Fig. 4 shows the effect combining or adding Band 1 and Band 2 on the depiction of drainage pattern and Fig. 5 shows the result of combination of Band 3 and Band 4 bringing out clearly the fracture zones. Fig. 6 shows the results of all four MSS bands combined which results in much better depiction of lithological units.
Fig. 7 shows the results of low pass filtering for Band 4 (with equal weights). Fig. 8 shows the Digital Thermatic Map obtained with elysian Classifier. The structural map obtained as a result of the comparison between existing geological map and the imagery obtained as result of enhancement, making use of the regions targeted as A, B, C & D on the structural map and suitably interpreting the enhanced imagery a map showing the ground water potential zones was prepared. This is shown in Fig. 10. The ground water data of about 10 observations well above map. All the targeted water-bearing zones have been marked on Fig. 10. The limited amount of ground data confirm, the results obtained in their investigation.
Conclusions
- The Density Slicing and histrogram equalization methods used to generate the digital image with sixteen colours at a time on the graphic terminal proved that the graphical terminals could be for displaying the remote sensed images. The contrast of the displayed images is greatly increased by suing the maximum available sixteen colours at a time throught he histrogram equalization method.
- Band 4 image shows relatively more geological features i.e., discrimination between lithological units, lineaments and surface water bodies are comparatively more clear after histogram equalization technique.
- The combination of Band 3 and Band 4 has enhanced fractures in granite terrain considerably. The image obtained by combining all the four bands shows clear demarcation between different lithological units.
- While the advantage of two pass Band Ratioing method gives better resolution the one pass may be preferred.
- Low Pass Filter is found to be useful to enhance the sharpness of the iamge. By using this technique the fracture zones, lineaments and linear details, i.e. roads and railways which are generally not visible in the raw image can be clearly seen.
- Baye's Classifier was utilized to obtain the data in four classes viz. water, granite rocks, sedimentary rocks and vegetation. While the earlier three classes fully conformed to the image obtained through enhancement technique, the vegetation ground water potential zones.
References
- Stanley. N, , Dewitt, J.M. 1986, "Hydrogeology" John Wiley & Sons.
- Stephen. J, 1986., "Landsat Digital Enhancement for Lineament Detection", Environmental Geology Vol. 8 No. 3 pp. 123-128.
- William P., M. Karalick & Jeffersion, A. Stephen Whartan. 1987, "A Methodology for evaluation of an interactive multispectral Image Processing System, Photogrammetric Engineering & Remote Sensing",
