第29回日本情報地質学会講演会 講演要旨集 039-040頁 2018年

SBAS-InSAR for detecting and characterizing topographic change in ageothermal plant area
Panggea G. Sabrian*, Katsuaki Koike*, Asep Saepuloh**, and M.N. Heriawan****Graduate School of Engineering, Kyoto University, Katsura C1-2-215, Kyoto 615-8540, Japan.
Email: sabrian.ghiyats.57n@st.kyoto-u.ac.jp**Faculty of Earth Sciences and Technology, Bandung of Institute Technology, Bandung, Indonesia.
***Faculty of Mining and Petroleum Engineering, Bandung of Institute Technology, Bandung,Indonesia.

Key Words: Geothermal resource, SBAS, coherence, deformation, uplift, Wayang Windu

Introduction
Geothermal potential in Indonesia is estimatedapproximately as 28,100 MW with potential resources of
13,440 MW and reserves of 14,473 MW at the 265
locations throughout the country. Currently only about
1,189 MW (4%) is utilized to generate electricity.
Geothermal energy has advantages of being renewable
andenvironmentallyfriendly.
Thus,intensiveexploration and clarification of geothermal potential areindispensable to develop this huge renewable energy.
One of the regions that has high potential of geothermal
resource is the Wayang Windu field, West Java. Thegeothermal system in this area is known to be atransition between vapor domination and water
dominance with four upwelling centers. The system
becomes young and more dominated by water towards
the south (Bogie et al., 2008).
Surface deformation has been prevalent in many
geothermal fields around the world, especially alreadyoperated geothermal fields in Indonesia. This requires
many sets of spatial technologies to precisely detect andmonitor the deformation. One of the effective
technologies for this is Interferometric Synthetic
Aperture Radar (InSAR). Based on those background,
this study focus on the use of InSAR technique fordetecting and characterizing the surface deformation inthe Wayang Windu field (Figure 1).

criteria to reduce “ link” the separate small baseline
subsets, clearly increasing the temporal sampling rate.

Methods
To analyze the surface deformation in the Wayang
Windu field, seven scenes of ALOS PALSAR image (Lband) in the period of 2009-2011 and a method, Small
Baseline Interferometric Synthetic Aperture Radar(SBAS-InSAR) were used. This method can provide
accurate result and minimize the atmospheric effect.
The SBAS-lnSAR algorithm was firstly demonstrated
by Berardino et al. (2002) as a method to reduce theatmospheric effect and topographic error. Then, thisalgorithm was improved to clarify the time-series
deformation by using interferograms generated by image
pairs of small baselines only, because such pairs canreduce the spatial decorrelation. The atmospheric effectcan be removed through applying the temporal high-passand low-pass spatial filters to the interferograms.
Because there are temporal gaps in the image pairs (i.e.,their acquisition dates are more or less different), SBASlnSAR uses the Singular Value Decomposition (SVD)
approach based on the minimum deformation standard

Figure 1. Location of the Wayang Windu geothermal field and ageological map around the field by Malik and Rustadi (2012)
and Masri et al. (2015).

After that, the SBAS algorithm has been improved to(1) suppress errors caused by temporal decoration andother noise effects, (2) increase the estimate of linear
deformation by reducing the phase unwrap error, (3)reduce furthermore the atmospheric effect andtopographic errors, and (4) reduce the orbital errors byusing specific reference points and interferogram phase40values in the other pixels. For example, Lee et al. (2010)
improved the SBAS algorithm to increase the estimation
accuracy of the time-series deformation by the following
four methods. First, the error of unwrap phase wascorrected under an assumption that the atmosphericeffect was generally correlated spatially and temporally.
After the removal of atmospheric effect, the time series
deformation was again calculated by applying the SVD
approach and other methods (Schmidt and Biirgmann,2003) to furthermore suppress the noise effect. Thirdly,
the applied procedure eliminated the possibility of aphase bias at reference points caused by the orbital andatmospheric effects (Lee et al., 2010). Finally, those
reductions of the atmospheric effect and topographic
errors and the accuracy time-series measurements ofdeformation were enhanced through the iteration
procedures of the three steps.

InSAR analyses are in progress to enhance thedeformation accuracy using more SAR data pairs.
Acknowledgement: We sincerely thank Star Energy
Geothermal (Wayang Windu) Ltd. for the collaborationof the Science and Technology Research Partnership for
Sustainable Development (SATREPS) Program with JST,JICA, and Institute Technology of Bandung.

Result and Discussion
The coherence values among the seven scenes were
low in general (Figure 2), which may originate from thethick vegetation in the study area. Coherence is anindicator for the level of noise in phase and describes allproperties of the correlation between physical quantities
of several SAR images by a value between 0 (high phasenoise) and 1 (low phase noise). Because of the low
coherence, the resultant SBAS-InSAR deformation map(Figure 3) shows that the detected deformation areas
were limited in flat topography with sparse vegetation.
The most noteworthy feature of the deformation
pattern is that the deformation is different between thenorthern and southern regions: the northern region is
generally subside, while the southern region is uplift.
This different pattern may be caused by the movement of
the Bandung Basin boundary fault (Figure 1). The
deformations at the production wells of geothermal plant
were estimated to subside between 2 mm to 17 mm
except for one well, WWT well at which the 16 mm uplift
was estimated. This is likely due to the large uplift inthe south region.

Figure 2. Coherent value over the Wayang Windu field in thesingle looking.

Conclusion
The results of SBAS-InSAR analysis suggested thedeformation pattern was different between the northernand southern regions of the Wayang Windu geothermal
field, subsidence or uplift pattern, respectively, due tothe movement of the Bandung Basin boundary fault. Inaddition, geothermal reservoirs are known to be different
between the two regions, vapour or liquid dominatedreservoir. This physical different may also be a cause of
the difference in deformation pattern. More detailedFigure 3. Deformation velocity estimated over the study field.

References
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