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Discovery of ancient water reservoir in historical town of Phimai , Nakornrathchasima, Thailand: Application of air SAR for archaeology study

Shunji Murai*,Panjai Tantatsanawong** and Surat Lertlum***,
* Asian Center for Research on Remote Sensing (ACRoRS),
Asian Institute of Technology, Pathumthani, Thailand
** Chulachomklao Royal Military Academy, Thailand
*** Silapakorn University
E-Mail: surat @ait.ac.th


Abstract
PACRIM 96 AirSAR flight illustrated the advantage of using SAR data for various applications such as coastal study and oceanography, geology, forestry, and also archaeology. From the characteristics of the AirSAR P L and C bands, AirSAR data can be used for the exploration of archaeology sites as demonstrated in this paper. By analyzing the combination of P, L, and C bands data, we can identify human activities at 800 years ago.

This study illustrate the integration of technology in the field of remote sensing and image processing to discover the world as never been before in Thailand.

Introduction
Remote sensing has a wide range of applications as has been realized for quite sometime. As one of the applications, archaeology has been an application that remote sensing can assist in identification in many area. For example, when NASA launched an imaging system called SIR-A on the Space Shuttle. Archeologist Farouk El-Baz had asked NASA to fly SIR-A over the eastern Sahara desert, hoping it could make sense of the anomalous rock formations he had been studying there. No one was quite prepared for the images that came back. The Sahara is the driest place on earth right now, but SIR-A was able to penetrate the sand and reveal an ancient landscape below that, amazingly, had been carved by running water. (NOVA, 1996)

Background Information
Phimai town had been built during the Khmer empire. The town itself had been established as a region center of the empire. There are many evident exist like stone inscription describing the live during the period. In addition, there was a communication routing from Angkor to Phimai as described in many stone inscriptions.

Location
The location of Phimai is aligned with the location of Angkor as shown in the map (Figure 1).


Figure 1 The map of showing the relationship of Phimai and Ankor

Airsar Data Specification
The AirSAR data has the following specification. According the wave length, P band has the longest wave length of 67 cm.

Bands: P (0.45 Ghz, 67 cm)
L (1.26 Ghz, 23 cm)
C (5.31 Ghz, 5.7 cm)
Polarization Full pol
Bandwidth 20, 40, 80 (Available after May 1998) MHz
Resolution, range 7.5, 3.75, 1.875 (Available after May 1998) m
(without considering the tapering effect.)
Resolution, azimuth 1 m single look (JPL, 1999)


Dataset and Information Usage
  • AirSAR
    The AirSAR data had been taken on Dec 6, 1996 as a part of the PACRIM 96 project. The flight had been organized and supported by JPL and the Royal Thai government.
  • Air Photo
    The air photo taken in 1954 had been used for integration of analysis. The reason to use old air photograph was because during 1954, there was still not have a lot of new infrastructures constructed in the area (Figure 3A).
  • Map
    The map of the scale 1:50,000 had been obtained to study the current transportation network, and rough estimation of the terrain (Figure 3B).
  • Historical Information
    The historical information had been gather from various source that we can find, mostly from archaeological books about Angkor, and the report from the Royal Thai Archaeology Department about the excavation at Phimai and the Northeast region of Thailand.
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