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MOUNT PINATUBO LAHAR DAMAGE ASSESSMENT 
USING ERS-1 SYNTHETIC APERTURE RADAR DATA 
Epifanio Lopez”, Jean Chorowicz?, Jean-François Parrot“, Ernesto Corpuz’, Randy John 
Vinluan', Fredy Garcia’ 
! Department of Geodetic Engineering, University of the Philippines, Diliman, Quezon City, Philippines, Tel 632 920 5301 
Local 5275/5535, Fax 632 922 4714, E-mail: edi@engg.upd.edu.ph or rinv@engg.upd.edu.ph 
? Laboratoire de Geologie, Geomorphologie Structural et Teledetection, Universite Pierre et Marie Curie, 4, Place Jussieu, 
75252 Paris Cedex 05, France, Tel 1 43 26 82 46, Fax 1 44 27 50 89, E-mail: choro@lgs.jussieu.fr 
* Philippine Institute of Volcanology and Seismology, Hizon Building, Quezon Avenue, Quezon City, Philippines, Tel 632 712 
6110, Fax 632 732 7592, E-mail:toti@x5.phivoles.dost.gov.ph 
ABSTRACT 
The development of an integrated plan to 
rehabilitate the mudflow-affected areas surrounding 
Mount Pinatubo is hampered by the lack of 
comprehensive, accurate and timely information on 
landcover and mudflow boundaries. Efforts to use 
conventional aerial photography and satellite imagery 
in the visible-infrared portions of the electromagnetic 
spectrum are limited by the adverse effects of bad 
weather and clouds on the imagery. The use of radar 
imagery, particularly the ERS-1 satellite synthetic 
aperture radar data, for providing the much-needed 
basic information in monitoring changes in the lahar- 
covered landscape surrounding Mount Pinatubo is 
assessed in this study. Two approaches in the data 
analysis are made. First, ERS-1 SAR data alone, as a 
single image and as multitemporal sets, are analyzed 
‚to provide the basis for developing relationships 
between radar backscatter and lahar-affected terrain 
surfaces; and, second, ERS-1 SAR data are combined 
with Landsat Thematic Mapper multispectral imagery 
to provide synergy and complementarity analysis 
between radar and  visible-infrared ^ imagery 
particularly for perennially cloud-covered tropical 
areas. 
1.0 INTRODUCTION 
Considered as one of the largest volcanic 
events of this century, the violent eruption of Mount 
Pinatubo on June 15, 1991 caused rain-induced 
massive mudflow, sediment deposition and flooding 
that buried population centers and destroyed roads 
and bridges, crops, buildings and agricultural lands. 
An estimated six billion cubic meters of pyroclastic 
Material and volcanic ash were deposited over a 
4000-square kilometer area including the eight river 
basins that drain the volcano. The pyroclastic deposits 
ranged in thickness from a few meters in the valley 
Areas to as deep as 100-200 meters in river gullies; 
While the volcanic ash ranged from a few centimeters 
437 
in areas about 40-50 kilometers from the volcano to 
about a half-meter near the crater. 
Every year, particularly during the wet 
season, heavy rainfall continues to erode the 
pyroclastic material deposited on the slopes of the 
volcano causing fast-moving lahar to wreak havoc 
and severe damage on an estimated 300,000 hectares 
comprising mostly residential and agricultural 
communities (Figure 1). With the major rivers and 
drainage systems filled up by sediments, widespread 
lahar-induced flooding provides another hazard to 
these communities. Furthermore, the possible 
breakout of temporary lakes formed by the blocking of 
pyroclastic debris on the upstream portions of river 
channels poses another continuing hazard. The 
potential threat of the still-unleashed lahar deposits 
on the slopes of Mount Pinatubo within the next 10- 
15 years makes the study area an appropriate location 
for image analysis studies that can provide input for a 
geographic information system with emphasis on 
monitoring and modelling the rate of mudflow spread 
and damage assessment. 
Sensitive environmental issues and concerns 
within the study area include the potential effects of 
prolonged flooding due to the destruction of the 
drainage systems, extensive damage to vast tracts of 
sugarland, fishpond and riceland in Central Luzon 
(once considered as the rice granary of the 
Philippines), and discharge of ashfall- and sediment- 
laden rivers into coastal areas which support 
aquaculture and fisheries resources. 
The ERS-1 synthetic aperture radar data, 
with its all-weather sensing and cloud-penetrating 
capability, has the potential to provide accurate and 
timely information on the extent of damage in 
perennially cloud-covered tropical areas such as the 
Philippines, in general and Central Luzon, in 
particular, which badly needs a master plan to save its 
once-productive provinces. 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996