Ground subsidence observation of solid waste landfill park using multi-temporal radar interferometry

Land subsidence on landfill parks needs to be consistently and periodically measured because the landfill areas tend to subside unexpectedly. Although in-situ measurements have been adopted in general, these have a number of limitations of spatial and temporal resolutions because of the high cost. However, the use of interferometric synthetic aperture radar (InSAR) can overcome these disadvantages. In this study, we carried out two experiments using the InSAR method. We then compared the interferometric coherence between ALOS PALSAR and TerraSAR-X data and measured the ground subsidence using multi-temporal TerraSAR-X data acquired from ascending and descending paths. The mean coherences from the ALOS PALSAR and TerraSAR-X interferograms were 0.26 and 0.54, respectively. The coherence from TerraSAR-X was nearly 2 times higher than that of ALOS PALSAR, despite its shorter wavelength of radar signal. These results showed that the data with the shorter temporal baseline is appropriate to monitor the ground subsidence on landfill park areas. As a result of measuring surface deformation, the mean line-of-sight (LOS) deformation rates estimated from the small baseline subset (SBAS) method were −2.4 and −3.2 cm/year for the ascending and descending data of TerraSAR-X, respectively. Also, the mean deformation rate in the vertical and east–west directions were −5.7 and −1.7 cm/year, respectively. The root mean square error (RMSE) of InSAR measurements by comparing with the in-situ measurements was about 1.2 cm/year and the coefficient of determination ($R^2$R2) was about 0.97. These results indicated good agreements between the InSAR measurements and the in-situ measurements.