Camit, Rex 
  
  
LEGEND: 
[_] Quaternary Alluvium - 
Quaternary Volcanics 
Tertiary Volcanics 
Tertiary Clastics 
Tertiary Limestone 
Cretaceous Ultramafics 
   
  
  
ü 10000 
Figure 2. 1999 general geology based on Landsat TM and SAR imagery. 
  
Previous geothermal studies were conducted at SLGP by Bureau of Energy Development together with Electroconsult 
of Italy (BED-ELC, 1979). This was followed by a series of integrated geoscientific studies by PNOC Energy 
Development Corporation (PNOC EDC, 1989; Leynes et al, 1997; and Catane and Apuada, 1998). These latest 
geoscientific studies postulate the presence of a neutral-pH resource located between Hugpa and Kapakuhan Kaipohan 
with a temperature range of 188 - 205 °C (Leynes et al., 1997). Resistivity surveys, on the other hand, delineated 
distinct low resistivity anomalies to the west (Nava-Magcasa anomaly) and northeast (Mainit-Mahalo anomaly) of Mt. 
Cabalian which are indicative of outflowing geothermal fluids. 
This study aims to: (1) supplement the previous structural and other geologic interpretations and (2) assess the location 
of the proposed (i.e. Hugpa) and additional drilling target in the area through the application of remote sensing 
technique using Landsat TM and Radar imageries. 
2 METHODOLOGY 
The study utilizes a 30-m resolution Landsat TM image and a < 10-m resolution Radar image georeferenced to a 
1:50,000 scale topographic map. The images were radiometrically- and geometrically-corrected wherein the general 
geology and regional structural lineaments were drawn by heads-up digitizing. The results initially were delineated 
from the enhanced false color composite of Landsat TM bands 7, 5 and 2 (Figure 2). In combination with the 
interpreted Synthetic Aperture Radar (10-m resolution) data, spatial discrimination of said lithologic units and 
lineaments were confirmed. Processing of the Landsat TM and Radar imageries were performed using the Integrated 
Land and Water Information System (ILWIS) version 2.1 and Environment for Visualizing Images (ENVI) version 3.0 
(evaluation software), respectively. 
In addition, the combined use of the Normalized Difference Vegetation Index (NDVI) and Principal Component 
Analysis (PCA) methods were applied to the Landsat TM image to pinpoint bare grounds as probable hydrothermal 
signatures. Landsat TM bands 1, 4, 5, and 7 were inputted in the PCA method while Landsat TM 4 and 5 were set in the 
NDVI method. The NDVI method initially classifies the various ground classes (e.g. bare, vegetated, rocky grounds, 
water bodies, etc.) while the PCA method filters the previously identified bare grounds as probable hydroxyl-bearing 
surfaces indicative of hydrothermal alteration. The resulting principal component 3 image obtained the highest 
eigenvector loading (0.55, -0.49) which represents hydroxyl-bearing surfaces associated with either epithermal or 
hydrothermal areas. This theory works mainly on “strained” vegetation/ground where hydrothermal activity is believed 
evident. The ILWIS 2.1 software was used in processing said Landsat TM imagery. 
Interpretations done in this study were based mainly on integrating Remote Sensing (RS) data with the Geographic 
Information System (GIS) data. Interpreted remotely-sensed altered grounds/thermal springs mostly coincide with the 
locations of ground-validated thermal manifestations of SLGP 
  
222 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000.