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SAR/InSAR
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A Study On Differential Interferometry In Subsidence
4. Experimental Results:
In this study, the technique of differential interferometry was used to find the displacement field and to estimate the terrain subsidence of a 45 km x 25 km coastal area, Ton-Kang, southwestern Taiwan. The subsidence of this area has 48 GPS measurement points. The distances of GPSs are from 5 Km to 10 Km. The time difference is about 8 months. Over the test area, southwestern region is subsidence while the northeastern region is arising. For comparison, we interpolated and scaled the GPS data same with time difference of test pairs (Figure 5). It is shown from the comparison that the DInSAR results are consistent with GPS measurements, both in the pattern of subsidence and in its magnitude (about 2cm/month).
5. Summary
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We conclude that, given suitable SAR images, the differential interferometry can be a useful tool for monitoring the earth surface displacement even for a subtropical, densely vegetative area like Taiwan.
- Atmospheric effect should be taken into account in forming the interferogram and subsequent process, because, heavy cloud, for example, can cause the phase shifts resulting appreciable error in displacement estimation.
- For long-term and large area subsidence monitoring, DInSAR provides cost-effective and yet practical tool which is complementary and supplementary to ground GPS surveys.
- RADARSAT has more choices of beam modes which can release limitations of ERS series satellites having high incidence angle causing several layovers over mountain area, and should be considered as another data sources.
Acknowledgement
This research was partly supported by NSC 88-2612-E-008-003. CSRSR, National Central University supported ERS1 ¢ ERS2 ¢ SPOT images and assistants. Central Geological Survey supported the GPS data of subsidence over test area.
6. References
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