The Correlation of the Landsat TM Images Characteristic with the
Geologic Information : A Preliminary Result of a Case Study in
Langkawi Islands, Malaysia
Data and study area
Satellite Data
Satellite data (Landsat TM) used in this study are parts of frame 128/56 in the international reference system which were recorded in 1989, covering most of Langkawi Islands which is situated in the north-west of Malay Peninsula. The data were recorded and kep in computer compatible tape (CCT).
General Geology and Strartigraphy
The geology (rocks distribution) in Langkawi Islands and general stratigraphy (rock sequence) of the area is shown in Figure 1. The oldest rock formation in this area is known as Machinchang Formation, consists of mainly sandstone (quartzite), conglomerate and greywacke in the upper parts and shale, mudstone and subgreywackes in the lower parts of the sequence. This rock formation outcrops in the north-western part of the Langkawi mai island. The age of this formation is assigned as Late Cambrian (Jones, 1981) or Cambro-Ordovician (Lee, 1983). This rock formation forms medium textured to quite rugged topography and well defied ridges. The area is moderate to densely covered by vegetation.
Figure 1 Geology and general stratigraphy of Langkawi Islands. Malaysia.
Mechinchang Formation is conformably overlain by Setul Formation which is consists of mainly limestone (marble) and characterized by karst topography. Towards the top of the sequence of the formation, two detritus strata are present and known as the Lower and the Upper Detrital member. This formation outcrops in the east of Machinchang Formation near Teluk Kuban Badak and the eastern parts of Langkawi Islands including Pulau Dayang Bunting (eastern part), in the south, Pulau Tuba, Pulau Timun, Pulau Tg. Dendang and Pulau Langgun in the north. The age of the formation is interpreted as Ordovician to Early Devonian. This limestone area froms karstic topography, characterized by isolated, steep slope and very rugged topography surrounded by alluvium. The area is covered by thin soil and barren to slightly covered by vegetation especially in dry season.
Singa Formation unconformably overlain the lower paleozoic rock. It consists of mainly black mudstone and siltstone with interbedded-sandstone layer of late Ordovician to early Permian (Jones, 1981). This formation is outcropped in the east of Gunung Raya and many small islands including Pulau Rebak, Pulau Kentut, Pulau Tepur, Pulau Beras Basah and Pulau Singa in southern part of Langkawi Islands. This rock formation ios characterized by rolling and quite smooth topography. Generally the area is covered by thick soil and dense to very dense vegetation.
Chuping Formation conformably overlain Singa Formaion. It consists of relatively pure, lighter colour and thickly bedded to massive limestone of Permian age. This rock formation was metamorphosed to marble and outcrops in the western part of Pulau Dayang Bunting. This rock formation is gently dipping towards east and relatively developed thicker soil as compared to the limestone area of Setul Formation.
Other than the rock formations mention above, igneous rock granite is also present. The main intrusion forms the highest peak in Langkawi Island known as Gunung Raya. Other granite forms a prominent ridge align in north east direction from Teluk Borau in south-west to Pasir Hitam (north-east), a small ridge east of Kuah town, circular hill north of Pulau Dayang Bunting and western part of Pulau Tuba to Pulau Bumbon. A low undulating hill near south of Padang Mat Sirat is also consists of granite. Generally the granite areas show relatively smooth topography with granite to moderate slope gradient . This type of topography is covered by thick soil and dense vegetation.
Alluvium, mainly of marine origin is occupying the south-western part (Pantal Cenang and Pantal Tengah), around Kuah town and the area in between the limestone hill in the north-east of Langkawi main island. Alluvium is also present in the middle part of Pulau Tuba and some parts of Pulau Rebak Beesar. Most of alluvium areas around Kulah and Pantai Chenang in Langkawi main island and Pulau Tuba were developed into residential or agricultural. The alluvium area in the north-east of Langkawi main islands is relatively untouched and covered by thick mangrove.
Data processing and image products
It is quite difficult to detect the difference of grey tone in black and white image which could be related to he differences in near surface material and other geological information. As a result the materials or rocks with slight different in colour may give same appearance in grey tone image. The same information, if it is displays as colour image is possible detected by our eyes since the sensitivity of our eyes to colour is much higher than the grey variation scale. For that reason, in this preliminary study, a special emphasis is given to the production of colour composite images by combining any three bands of Landsat TM data.
Based on colour variation and the geological information which is displayed, three colour composite images were selected for this study, i.e., colour composite TM bands 432, 452 and 457 . The data of every bands were corrected for the atmospheric effect before the composite images are produced for this study.
