Effects of External Digital Elevation Model Inaccuracy on StaMPS-PS Processing: A Case Study in Shenzhen, China

Yanan Du,Jianjun Zhu,Zhiwei Li,Zhengyong Ren,Xing Peng,Guangcai Feng

doi:10.3390/rs9111115

Abstract

External Digital Elevation Models (DEMs) with different resolutions and accuracies cause different topographic residuals in differential interferograms of Multi-temporal InSAR (MTInSAR), especially for the phase-based StaMPS-PS. The PS selection and deformation parameter estimation of StaMPS-PS are closely related to the spatially uncorrected error, which is directly affected by external DEMs. However, it is still far from clear how the high resolution and accurate external DEM affects the results of the StaMPS-PS (e.g., PS selection and deformation parameter calculation) on different platforms (X band TerraSAR, C band ENVISAT ASAR and L band ALOS/PALSAR1). In this study, abundant synthetic tests are performed to assess the influences of external DEMs on parameter estimations, such as the mean deformation rate and the deformation time-series. Real SAR images, covering Shenzhen city in China, are also selected to analyze the PS selection and distribution as well as to validate the results of synthetic tests. The results show that the PS points selected by the 5 m TanDEM-X DEM are 10.32%, 4.25% and 0.34% more than those selected by the 30 m SRTM DEM at X, C and L bands SAR platforms, respectively, when a multi-look geocoding operation is adopted for X band in the SRTM DEM case. We also find that the influences of external DEMs on the mean deformation rate are not significant and are inversely proportional to the wavelength of the satellite platforms. The standard deviations of the mean deformation rate difference for the X, C and L bands are 0.54, 0.30 and 0.10 mm/year, respectively. Similarly, the influences of external DEMs on the deformation time-series estimation for the three platforms are also slight, except for local artifacts whose root-mean-square error (RMSE) ≥ 6 mm. Based on these analyses, some implications and suggestions for external DEMs on StaMPS-PS processing are discussed and provided.

Highlights

Multi-temporal InSAR (MTInSAR) technique, an enhanced differential InSAR technique, has been widely applied in deformation mapping for urban surface, volcanos, mines and earthquakes [1,2,3,4,5,6,7]
MTInSAR can be divided into three categories [8]: the single-master MTInSAR, such as PSInSAR, STUNS, and StaMPS-PS [1,9,10,11]; the multi-master MTInSAR, for instance, SBAS, NSBAS, TCPInSAR, and StaMPS-SBAS [1,12,13,14]; and the combination of the previous two categories [15,16]
For high resolution X band SAR images, the increasing rates of PS number is 10.32% if multi-look geocoding of SRTM-1arc Digital Elevation Models (DEMs) is adopted, while − 0.37% if for median high resolution SAR images, with the increasing rates of PS number for C band (4.25%) and L band (0.34%)

Summary

Introduction

Multi-temporal InSAR (MTInSAR) technique, an enhanced differential InSAR technique, has been widely applied in deformation mapping for urban surface, volcanos, mines and earthquakes [1,2,3,4,5,6,7]. The quality of differential interferometric phase (referred to as “original phase” hereafter) is directly affected by the external DEM, such as the phase unwrapping error caused by incorrect external DEM in mountainous areas [17,18], the aliasing of deformation signal, and topographic residues [19,20,21]. It affects the deformation estimation of MTInSAR, for example, the influences of incorrect topographic residuals on the calculation of time-series deformation [18,22,23].

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Discussion

Conclusion