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dendritic drainage system to the south combined with 
its typical texture and physical resistance of the 
surface materials clearly indicates the presence of 
the Southern Mountain zone (Figure:5). The Bandung 
zone, on the other hand, occupies most of the valleys 
surrounding the recent volcanoes and volcanic 
materials, This zone is occupied by Tertiary 
sedimentary rocks with the surface topography showing 
bedding, folds, faults and some fractures. The water 
divide lying along the center of the island coincides 
with the radial drainage pattern of the active 
volcanoes. The water divide divides the flowage of 
the water to the South and to the North except in the 
SW section which shows a southwesterly water flowage 
and in the NE-section where the water north of the 
water divide flows to the South instead of to the 
North (Figure:6). The occurence of these flowage 
direction anomalies may be related to geologic 
disturbance in the SW (Sukabumi) section and the NE 
(Leirbang) section where the image processing and 
ground investigation latter were concentrated. 
Figure 6: Regional drainge system, west Java, from 
Landsat imagery. 
The investigation in Sukabumi and the Leirbang area 
was particularly directed toward determining the 
distribution of surface materials and the structural 
features interpreted from several kinds of Landsat 
digital processed imagery. 
COMPARISON OF VARIOUS TYPES OF DIGITALLY PROCESSED 
LANDSAT IMAGERY 
Systematic and comprehensive analysis and 
interpretation of standard product Landsat full-scene 
images rapidly define the regional geologic setting of 
the West Java area and delineate two areas with some 
broadly distinctive geologic terrains. However, 
because of the spatial and spectral resolution 
characteristics of Landsat MSS, the results lack 
detail, particularly concerning the variations in 
sedimentary rock lithologies and of some of the 
geologic structures in the region. Interpretation of 
digitally enhanced Landsat MSS imagery irrproves 
discrimination of lithologic variation and enables one 
to extract more structural geologic details and 
patterns, which in turn, lead to more reliable 
tectonic synthesis. 
Three types of digital image processing were 
conducted in the Sukabumi and Leirbang test site areas 
: Principal Component Transformation, Band Ratioing 
and Image Edge Enhancement. The image processing and 
manipulation in the Sukabumi area were particularly 
intended to discriminate lithologies, to find some 
lithologic contrast to support the structural geologic 
interpretation and to find the relationship between 
its drainage system to the structural geology. For 
the Lembang area, however, these processings were 
conducted with the intention of discriminating 
volcanic materials erupted by different events and to 
establish a firm understanding regarding the 
development of the Lenbang fault. 
The Principal Couponent Transformation (PCT) is a 
linear transformation technique used to minimize data 
redundance, a characteristic of highly correlated 
data, as well as to enhance an area of subtle spectral 
disparity. By rotation and translation, a set of 
eigenvectors and eigenvalues, representing new or 
transformed axes, was formed (Jenson, 1982). Using 
these data, a new imagery - Principal Conponent 
Imagery - can be developed (Figure:7). The 
eigenvectors lie on the new transformed axes and the 
length of the eigenvectors are eigenvalues. The 
longest eigenvector, containing equal loading of Band 
4,5,6,7 and totalling 95% of the total scene, was 
chosen as the first Principal Coprrponent (PC-1) 
(Colwell,1983). The PC-2 covers 4.3% of the total 
scene variance while the PC-4 contains approximately 
0.2% of the total scene variance. 
ORIGINAL 
Figure 7: Model of rotation and translation of Prin 
cipal Conponent Transformation in two dimensions. 
(Jenson & waltz, 1979) 
The Principal Component imagery offers information 
which previously was undetected on the Landsat 
original data. The PC-1 imagery of the Sukabumi area 
(Fig:8) shows very bright tones and coarse textures 
on the recent Quarternary volcanic products (Qr2), 
while the older volcanic products, the Qr4, show a 
darker tone and smoother texture. These older volcanic 
products are mostly weathered with high moisture 
content and are now mostly agricultural fields. The 
limestone of Bojonglopang (Te7) however, shows 
brighter tone which indicates an area with low 
vegetation density and lower moisture content - 
characteristics of a carbonate terrain -, as compared 
to the older Quarternary volcanic materials (Qr4) 
(Figure:8b). The volcanic breccia of the Janpang 
Formation (Te6) is distinguishable from the texture 
and tone on the imagery. It is a highly resistant 
rock formation with some bedding and fractures and is 
easily discriminated from the surrounding materials. 
The tuffaceous sandstone of Bentang Formation (Tpt) is 
separable from the rest of the surface materials by 
its tone as well as by their linear, tilted and folded 
structures. 
The PC-2 imagery (Figure :.8c) of same area shows 
various grey-tones less distinct as conpared to the 
PC-1 imagery. However, this PC-2 imagery is capable of 
discriminating the marl of the Janpang Fm.(Te3) and 
the occurence of the most recent volcanic materials 
(Te8). In PC-2 imagery, with 4.3% of total variance 
are included, the digital data of Band-4 and 5 are 
contrasted against the digital data of Band 6 & 7, 
resulting in tonal variations based on the variations 
in vegetation density. 
Band Ratioing is a digital processing technique 
where pixel brightness values in one band are divided 
by the corresponding pixel brightnes values in a 
different band and from which a new ratio image then 
may be created (Colwell,1983). The ratioing technique 
minimizes the effects on scene brightness that are 
caused by variations in topographic slope and aspect,