Abstract
In this paper, the authors developed the methodology of vegetation cover ratios using multiple types of optical sensor data and clarified microwave backscattering characteristics on vegetation and environments acquired by Synthetic Aperture Radar (SAR). These data are used to analyze the effects of eruption from Mt. Pinatubo, the Philippines over a time period from 1991 (eruption time) to present (1997). By this satellite image analysis, chronological changes from vegetation damage in the term of decrease rate of vegetation cover caused by volcanic ash fall and suffered area by mudflows. Through satellite image analysis, changes in vegetation damage over time is assessed from the decrease in vegetation cover to volcanic ash and mudflows.

Introduction
Satellite remote sensing is only one method of monitoring vegetation changes. However it is very difficult to acquire optical remote sensing data at the coast and island in Asia monsoon area, because of the cloud cover. For the reason, we cannot perform using only one optical sensor to monitor vegetation for suitable interval and long term observation. We must use multi optical sensors and/or Synthetic Aperture Radar (SAR) sensors. Mt. Pinatubo that located the northern part of Luzon Island erupted hugely on June 15, 1991, and agriculture land and first in this area were suffered much damage owing to the eruption10. We monitored this area and estimated vegetation damage by ash falling and mudflows from Mt. Pinatubo using MOS-1/MESSR, LANDSAT/TM, JERS-1/OPS as optical sensors, and JERS-1/SAR and ERS-1/SAR as macro-wave sensors.

Optical Sensor Data
We used MOS-1/MESSR data that were before and after Mt. Pinatubo eruption, and LANDSAT/TM and JERS-1/OPS that were after the eruption. Table 1 shows the characteristics of used optical sensors and table 2 indicates list of used optical satellite sensor data.

Table 1 Characteristic of used optical sensors


Table 2 List of used optical satellite sensor data

SAR Data
Table 3 shows characteristics of SAR instruments and Table 4 shows the list of SAR data used in this study

Sensor	Wavelength	Incident angle	Polarization	Spatial resolution	Swath
JERS-1	L-band (1.275GHz 23.5cm)	38.5	HH	18 m(3 looks)	75 km
ERS-1	C-band (5.3 Ghz 5.66cm)	23	VV	15 m(3 looks)	100km

Table 3 Characteristics of used SAR instruments

Name of Senser	Date(YYYY/MM/DD)	Orbit	Treatment Level
JERS-1/SAR	1993/03/23	Descending	2.1 Geometry correction
"	1995/02/25	"	"
ERS-1/SAR	1993/08/29	Ascending	1.0 Raw image
ERS-1/SAR	1995/11/19	Descending	0 Raw signal data
ERS-2/SAR	1995/11/20	"	0     "
ERS-1/SAR	1996/04/21	Ascending	0     "
ERS-2/SAR	1996/04/22	"	0     "

Table 4. List of used SAR data