Measurement of a Small-scale Subsidence in a Reclaimed Land using RADARSAT-1 SAR

Chang-Wook Lee(1) , Hyung-Sup Jung(1) , and Sang-Wan Kim(2)

(1) Yonsei University, 134 Shinchon-dong, Seodaemoon-ku , 120-749 Seoul, Korea, Republic of
(2) Univ. of Miami, RSMAS-MGG 4600 Rickenbacker Causeway Miami, Florid, Miami, 33149-1098, United States

Abstract

Subsidence rate in a reclaimed coastal land of Noksan industrial complex, Korea, was measured by C-band SAR differential interferometry (DInSAR). Subsidence rate in the area had successfully been measured in a previous study by using L-band DInSAR. Surface conditions of the reclaimed land are very rough without vegetation with respect to C-band, which makes strong radar returns. However, artificially loaded top soil is subject to change within a short period so that it is difficult to obtain coherent interferometric pairs by using C-band in a reclaimed land. Seven RADARSAT-1 data sets of fine beam mode (F4) had been obtained between September 2002 and October 2003, and 4 coherent interferograms were generated from them. A large incidence angle (about 41 degree) of RADARSAT-1 F4 fine-beam mode is not favorable for observing flat areas. To obtain coherent interferograms, we used pairs of short temporal and perpendicular baselines. AIRSAR C-band DEM and a DEM constructed from an ERS tandem pair were used to eliminate topographic phase from the interferograms. Estimated interferometry-based subsidence was evaluated by using in-situ data that had been obtained by magnetic probe extensometers with an accuracy of a few millimeters. The DInSAR measurements correlated well with the field measurements with an average correlation coefficient R2 of 0.75. A two-dimensional DInSAR subsidence map derived from the measurements enabled us to map unstable foundation in detail. The results reveal about 2-3 cm subsidence for a year at the southern area of Noksan industrial complex. Compaction process of the newly filled soil is considered as a main cause of the subsidence. This DInSAR application is very useful to determine construction period for industrial buildings. The results prove that DInSAR technique using RADARSAT-1 fine-beam mode SAR is a useful tool in the field of geotechnical engineering.

 

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