SELECTION OF THE OPTIMUM LANDSAT THEMATIC MAPPER BANDS FOR AUTOMATIC LINEAMENTS EXTRACTION, WADI NATASH AREA, SOUTH EASTERN DESERT, EGYPT

摘要

Utilization of the digital Landsat TM bands for automatic lineaments extraction and selection of the optimum bands are the main objects of this article. The classical method for lineament extraction was manually performed through aerial photographs and satellite imagery. Nowadays several commercial softwares are developed to deal with the automatic linear features extraction using the optical and radar data. In this research, GeoAnalyst PCI EASI/PACE software is used for lineaments extraction from Landsat TM data under the default parameters. Two case studies (East Gabal Nuqra and Gaziret Khashm Natash) represent different terrain categories have been investigated. Subsets covering these areas were obtained from the original Landsat TM imagery. Lineament is defined as straight or somewhat curved feature in the image. It is distinguished by sharp change in variance across its length as compared to the variance along it. The lineament extraction algorithm consists of three remarkable steps: edge detection, thresholding and linear extraction. Analyses of the results obtained in this study led to the coming conclusions: 1) Visible bands (1, 2 & 3) produced higher lineaments number (frequency) compared with SWIR bands (5 & 7). In the first study area, band-1 produced the highest lineaments number (1423) compared with band-5 (787) while in the second study area, band-2 scored the highest frequency (99) compared with band-7 (65). 2) The regional pattern of the extracted lineaments is characterized by a high degree of preferred orientation. The main trends of the extracted lineaments of band-1 in East Gabal Nuqra area are NW, NNE and N-S constituting 39.5%, 34.8% and 15% of the total number of lineaments. ENE, E-W and WNW are subordinate trends with 4.9%, 4.85% and 0.7% of the total number of lineaments, respectively. In Gaziret Khashm Natash area the main trends of the extracted lineaments of band-2 are NE, NNW, NW and NNE constituting 30.5%, 21%, 14.7% and 13.6% of the total number of lineaments. N-S and E-W are subordinate trends with 13.6% and 6.4% of the total number of lineaments, respectively. 3) In matching with the published data it revealed that the extracted lineaments are coinciding largely with the structural lines mapped by (Madani, 2000). 4) Careful inspection of panchromatic TM images of the study areas showed that the drainage lines are clearly observed in visible bands and faintly observed in SWIR bands. Most of these lines are structurally controlled and follow the main trends of the study areas. 5) Analysis of different structural elements in Gaziret Khashm Natash area revealed that the presence of a relationship between the lineament trends and the distribution of the ring dykes. In the author opinion the emplacement of the ring dykes is controlled by the intersection of the NE, NNE and NW trending faults.