Detection of subsidence affecting civil engineering structures by using satellite InSAR

Abstract

Satellite interferometric synthetic aperture radar (InSAR) is an operational remote sensing technique for monitoring ground deformation. Advanced techniques to process radar data like persistent scatterer interferometry (PS-InSAR) combined with recently available high-resolution radar modes such as StripMap (SM) and spotlight, permit detection and measurement of vertical displacements in a range of subcentimetre to millimetre and unprecedented ground range resolution. Such features open up new fields of application in civil engineering projects. Now many objects distributed over large areas may be monitored, typically on an object size scale of 2 to 20 m, with high measurement density and adequate accuracy. We present an application of this technique on a navigation lock that was constructed in a karst region where bedrock is locally dissolved by groundwater flow, occasionally leading to sinkholes, surface subsidence and displacement of structures. For that reason, the lock complex has been under terrestrial geodetic survey for several decades. This set of readily available geodetic data has been used to validate the processed satellite InSAR data, acquired by two satellites (ERS and Envisat) during the time period ranging from 1992 to 2010. Encouraged by good agreement of the geodetic and satellite measurements, in a second step TerraSAR-X data taken in SM mode has been processed to increase ground resolution. To assess further improvements in resolution the newly available TerraSAR-X High-Resolution Spotlight (HS) mode is investigated. It can be concluded that InSAR data (ERS and Envisat) reaching back to 1991/1992 may be used to gain information on subsidence effects like using a rear view mirror. However, significant limitations in resolution need to be taken into account. Comparing remotely sensed data using TerraSAR-X (SM) mode to in situ measurements of deformation, it is too early for a 1:1 validation of the very small deformation measured in situ based on 17 months of observation. Nevertheless, it can be stated that no conflicting measurements have been observed and that several areas associated with larger deformations were clearly detected. In our opinion, such approaches may improve the quality of site investigation by focusing further terrestrial geodetic and geotechnical monitoring on such pre-selected locations, especially for operational monitoring of civil engineering applications.

Hybrid Georeferencing, Enhancement and Classification of Ultra-High Resolution Uav Lidar and Image Point Clouds for Monitoring Applications

“…As discussed by Kauther & Schulze (2015) our test area is subject to potential subsidence in the order of 10 mm/year. Thus, for the time frame between our measurement epochs in November 2018 and March 2019, changes in height in the order of 3 mm are expected, which are still beyond detectability while using our current sensor setup.…”

“…The area of interest stretches over 570 m (east-west) × 780 m (north-south) and includes the ship lock facilities, the river and the riparian area as well as vegetated areas, farmland, and residential areas of the surrounding village. In that test area subsidence of about 1-10 mm/a relative to the stable surroundings have been observed over the past few years (Kauther & Schulze, 2015). For area-covering monitoring of such changes, 3D point clouds at mm-accuracy have to be provided twice a year.…”