Estimating horizontal and vertical movements due to underground mining using ALOS PALSAR

In this paper, the capability of determining the three dimensional (3D) ground displacements due to underground mining using the multiple ALOS PALSAR interferometric pairs acquired with different viewing geometries has been investigated and validated in the area of West Cliff colliery, New South Wales (NSW), Australia. Four ALOS PALSAR interferometric pairs acquired with two different incidence angles from both ascending and descending orbits were used in this study. Three different approaches were used to derive the 3D displacement maps. The first two approaches utilised SAR data only, while the third approach required a one dimensional measurement by using other surveying techniques as inputs. The results were compared with the GPS field survey data obtained between April and May 2008. The obtained results and the GPS data agreed well with each other in the vertical and the east–west directions. However, the precision of displacement measured in the north–south direction was much poorer for the first two approaches compared to the third approach. This was due to two reasons: (1) the lack of viewing geometries, and (2) the poor temporal overlap in the interferometric combination datasets. The results suggested that it is possible to use other one dimensional surveying techniques to assist the InSAR measurements in order to enhance the accuracy of the 3D deformation derived. The horizontal movements in transverse and longitudinal directions were calculated from the 3D deformation results, in order to derive the subsidence parameters that have been caused by mining activities. The subsidence parameters derived matched well with the GPS-derived parameters. The results suggested that an accurate 3D displacement vectors can be derived by combining InSAR-measurement with measurement from other equipment such as extensometer and optical fibre which may carry out measurement in one direction only (ideally north–south direction).