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Geology
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A case study of the Khorat plateau and its vicinity in Thailand using high resolution satellite imagery
Tokio Kachi, Yoshio Akiyama, Jiroh Komai
Earth Resources Satellite Data Analysis Center, Tokyo, Japan
S. Yaemniyom, K. Kuntawang, T. apakasetr
Economic Geology Division Department of Mineral Resources
Thailand
Abstract
Landsat TM and SPOT imagery of Nam Phong area and the surrounding areas were used to map surface geology. SPOT color composite images integrated with high resolution panchromatic data resulted in enhancing spectral differences in the vegetation at the surface. Vegetation patterns according to the subtle difference of topography clearly revealed several circular features.
Field spectra were acquired with hand held spectrometer fitted with seven spectral bands coinciding with the Japanese ERS-1 bands to with seven spectral difference in vegetation according determine the cause of the spectral difference in vegetation according to the difference of landuse observed in SPOT color composite images.
On the circular features extracted from the satellite imagery of the Khorat Plateau, the verification by the newly developed PLMT (Power Line Magnetotelluric) method was carried out in order to acquire the distribution of subsurface rock resistivities concordant to the working hypothesis that that the surface uneven terrain reflects the difference of subsurface lithology, resulting in being expressed as a circular structure.
Landsat TM image clearly revealed the north south trending phetehabun infra mountain basin as a garben type basin, where the inside Cenozoic sediments and the outside Paleozoic / Mesozoic rocks are bounded on both sides by two parallel lineaments, although no fault on the surface has been found to prove those lineaments to be large displacement faults. PLMT method and "Fingerprint" geochemical method were carried out at eh eastern boundary lineament and verified the existence f large displacement fault.
Introduction
In the Khoral Plateau area,(Fig.1) surface circular features on the Jurassic (Cretaceous terrain are particularly conspicuous (CCOP 1983). At the Nam Phong structure in the Western edge of the Khorat plateau, the surface subtle uneven terrains are adjusted to several types of landuse. Judging from this surface condition, it is possible to extract a circular feature caused by subsurface geological structure in spite of no outcrop at the surface (ERDAC, 1988). Fro the verification of this analytical result, field checking with portable spectra radiometer (Yamaguchi et al 1988) is necessary so that colors on the false color image of the Nam Phong structure can be compared to real field spectra of vegetation patterns.
Figure.1 LANDSAT TM false-color composite mosaic(bands 2,3,and 4)showing the khorat Plateau and the Phetchabun graben
At the south of Nam Phong structure located approximately 20km southwest of Khon Kaen City, a circular feature extracted from high resolution SPOT color composite image is also inferred to reflect subsurface differential rock resistivities. One of the magnetotelluric tools, PLMT method is thought to be convenient for the certification of such lithological differences in shallow under guard (Tsubota et al 1987).
Further more, at the Petchabun graben in the Central Thailand. North south trending intra mountain basin with 30 km in width flanks on Permian rock mountains on the both sides. Lineaments extracted from the Landsat TM image also have to be surveyed with the PLMT method as well as "Fingerprint" method, which is useful to verify the existence of deep-seated faults.
The purpose of this paper is to verify previously predicted geological hypothesis on circular features and large scale lineaments extracted from high-resolution satellite imagery.
Satellite data and processing
The data used in this case study were 9 Landsat MSS data, 7 Landsat TM data 6 SPOT multi spectral and 1 SPOT HRV Panchromatic data. All data except HRV Panchromatic one were enhanced by linear stretch processing method to produce full scene false color images. It subscene data in the interesting areas were also processed of principal component analysis techniques to elucidate the effectives of multisepctral data applied to the discrimination of surface objects.
Two HRD subscene composite images were also produced to obtain high resolution (10m) color images. As for HIS (Hue, Saturation, intensity) transformed multi spectral data (20m), intensity was replaced by panchromatic band (10m), and then it was inverse transformed to false color of HRV composite images.
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