International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B7. Istanbul 2004
MONITORING DEFORMATION
AT MIYAKE-JIMA VOLCANO
Miyakejima is a volcanic island, about 10 km across, located
150 km south of Tokyo on the Izu-Mariana arc (Figure 2a).
This basaltic composite volcano has erupted every 15-20 years
during the past 500 ycars. According to the Geological Survey
of Japan, the most recent activity started with the collapse of the
crater on July 8, 2000. A large eruption occurred on August 18
with a plume height of over 12 km. The crater grew to the size
of L6 km wide and 500 m deep as of early September.
(Kazahya et al, 2001). All residents were evacuated in
September 2000. Electrical failures during the eruption resulted
in the malfunction of all in-situ monitoring instruments. Under
these conditions, SAR interferometry was the only useful
technique to monitor surface deformation of the volcano.
Since the eruption volcanic gases have been released
intensively. The volcano is still active. Routine monitoring of
SO, emission is done the by the airborne COSPEC Monitoring
Team of the Japan Meteorological Agency. SO, emissions
average about 10,000 tons/day compared to 100,000 tons/day
during the late June eruption (Figure 2b). Our InSAR
investigation is aimed at providing deformation information
related the post eruption behaviour.
Although L-band InSAR produces higher coherence over a
vegetated area than C-band SAR imagery, we used
RADARSAT C-HH because of its availability, high resolution
and suitable viewing geometry. We selected RADARSAT fine
mode images (F3f: 41.8-44.3 degrees) with a spatial resolution
of 8 m to detect and monitor surface deformation on the small
(6 km diameter) island (Figure 2d). Since most of the island is
covered with vegetation, a special filter was used to enhance the
raw interferogram in areas of poor coherence and speckle. This
filter, useful for InSAR analysis in vegetated areas, was
developed by Okhura and Shimada (2000). The filter is based
on a moving average attached to Atlantis Scientific Inc InSAR
software. After each filtering the portion in which the
interferogram becomes clear is superposed on the output
interferogram. The data of GPS stations installed after the
eruption were used for baseline adjustment.
Of the fifteen RADARSAT images acquired from August to
December 2000, we selected the November 10^ and December
4^ InSAR result for this paper (Figure 2c). Our results from the
other interferograms (August to December) provided a more
complete picture of deformation during this period.
CONCLUSION
e GPS and D-InSAR measurements are providing an
integrated monitoring system of post eruption shrinkage
rates at the Miyake-Jima volcano, after the severe August
2000 eruption. Our differential InSAR results show
Miyake-jima crater subsided 4.7 cm between November
10^ to December 4", 2000.
e The D-InSAR image shows deformation along an existing
fault lines at the Frank Slide. This information is used to
understand the post failure mechanism and mobility of the
slide and target in the location of in-situ monitoring
sensors
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