The Correlation of the Landsat TM Images Characteristic with the
Geologic Information : A Preliminary Result of a Case Study in
Langkawi Islands, Malaysia
Ibrahim Abdullah & Juhari Mat Akhir
Department of Geology
Faculty of Physical and Applied Sciences
Universiti Kebangssan Malaysia
43600 Ukm Bangi, Malaysia
Tel: 6-03-8292392 Fax. 6-03-8292490
E-mail :iba@pkrisc.cc.ukm.my
Abstract
Satellite data is commonly used in helping the geological mapping and interpretation in arid and semi-arid region. However, in tropical area which is covered by dense vegetation and thick soil, the used of satellite data in such mapping is said generally to be vary difficult to success. To test the perception, Langkawi Islands which is geologically has been mapped in quite detail is selected. The Landsat Thematic Mapper (TM) data of the area is processed digitally to exhibits its geological information. The characteristics of the produced images are carefully studies and correlated to the lithological units in the islands.
The Langkawi Islands consists of four rock formations. The oldest, known as Machinchang Formation consists of mainly quartzite and subordinate flagstone. This formation is conformably overlain by the Setul Formation which is compose of mainly limestone with minor sandstone and shale. The Singa Formation which is consists of mainly mudstone and shale with minor sandstone unconformably overlain the Machinchang and Setul Formations. The youngest rock formation is known as Chuping Formation consists of limestone (dolomitic), conformably overlain the Singa Formation. In addition to these formation, granite is also widespread in the islands.
To test the capability of the satellite data in exhibiting the geological information of the area, the digitally processed Landsat TM images were compared to the published geological map. It is found that the colour composite of the Landsat TM band 432 displays in red, green and blue respectively exhibit the overall best correlation between image characteristics and geological information in the area especially in discriminating the limestone area from other rock units. Further more, the colour composite images of the Landsat TM bands 452 and 457 are also show a quite different characteristics in terms of colour and texture which could directly be correlated to the lithological units of the area. Other than lithology, the Landsat TM images are also exhibit a number of major lineaments which represent faults. The results from the preliminary study show that it is clear the characteristics of remote sensing data, in this case the Landsat TM images are well correlated with most geological information (lithology and structure), and have a great potential to be used in general geological mapping of the area which is largely still covered by naturally vegetation and less disturbed by the development.
Introduction
Satellite image which shows a wide coverage of certain area permits the recognition of big scale geological features such as folds, faults and rock formation boundaries. Further, all these features could be traced and mapped. Digitally processed data will provide better images, as compared with hard copy of so-called standard image product for geological interpretations (Anuta, 1977; Condid & Chavez, 1979).
In Malaysia, the use of satellite data for geological interpretations are still lacking compared to other fields. Among other reasons cited is the nature of our tropical terrain with heavy vegetation and thick soil cover. Under this situation, it is difficult to differentiate the rock units of the area especially when the rocks are deeply weathered, covered by near surface material, alluvium, or insitu soil or vegetation of not strata related. Such conditions were used by many people to exclude the used of remote sensing technique in geological interpretation especially to map the rocks distribution in tropical area including Malaysia. They believed, it will be very difficult for this technique to produce any satisfactory result. However, the vegetation anomalous and the geomorphological appearance which are related to the rock types, quite frequently could be seen or detected in satellite image. Under these circumstances, the lithologic unit of the area could be differentiated. In these relations, some of the positive results about the use of satellite data for geological interpretation in Malaysia were already shown (Juhari, 1990 and 1996; Nor Bakri, 1993; Azli Kamil et. al., 1996 and Noraini Surip et. al., 1996).
One of the purpose of this study is to test the general perception that the use of remote sensing images for geological study in tropical area is very difficult to reach a satisfactory result. Langkawi Islands is selected as the study area since the geology of the area is already established. Therefore, it is very convenience to complete the satellite data characteristic of the area with the geological information observed in the field.
