Assessments of land subsidence in the Gippsland Basin of Australia using ALOS PALSAR data

Abstract

In this paper, the land deformation in the Gippsland Basin, Victoria, Australia has been mapped using the interferometric synthetic aperture radar (InSAR) time-series analysis with the ALOS L-band SAR data. Land subsidence in the basin resulting from mining activities has already been known over the past few decades. There has been ongoing concern that irrigation and off-shore oil and natural gas extraction has significantly lowered groundwater levels on-shore, and that this may lead to further subsidence. Therefore it is important to map the land surface change in the basin in order to understand the actual impact of these activities. The total area of Gippsland Basin is approximately 46,000km2, where approximately one-third of the basin is located onshore. Because of the large area of the basin, ALOS PALSAR data from 4 different paths were used to map the land displacement over the basin. The InSAR result suggests that the land displacement at 98% of the measurement points in the basin was between −10mm/year and 10mm/year. The InSAR result has been compared to the ground survey data in several areas, collected with GPS and total station surveys. The comparison of results suggested that the InSAR measurement and the ground survey measurement agree with each other in general.The standard deviation of difference between the InSAR results and the ground survey data is approximately 4mm/year near the coastal area and 15mm/year near the mining sites. Several rapidly deforming areas have been identified at the mining sites and the surrounding areas. Deformation rate at up to −82.9mm/year is observed in these areas. The deformation at the mining sites and the surrounding areas are expected to be resulted from mining activities and associated mine dewatering. Moreover, several minor displacement zones have been observed and investigated in the area between the Loy Yang Mines and the Gippsland coast as well as the area between Yanakie and Wilsons Promontory.