Mine subsidence monitoring: A comparison among Envisat, ERS and JERS-1

ABSTRACT This paper reports the progress of the Envisat CAL/VAL Project No 1078. Subsidence in an underground coal mining region southwest of Sydney, Australia, has been monitored using ERS and JERS-1. Seven Envisat images have been acquired in various imaging modes from both ascending and descending passes over the same mining region. More Envisat images have been scheduled and will be acquired in the future. This paper demonstrates that the mine subsidence have been measured by utilising differential interferometric synthetic aperture radar (DInSAR) technique with the C- and L-band SAR images from ERS and JERS-1 satellites. Tandem differential InSAR analysis has revealed 1 cm subsidence in 24 hours with a resolution of +/- 3 mm. The RMS error for DInSAR measured subsidence against ground survey data is 1.4 cm using the JERS-1 repeat-pass images. 1. INTRODUCTION Australia is one of the leading mineral resource extraction nations in the world. However, the complexity of the environmental issues and the potentially damaging consequences of both open-cut and underground mining have attracted public attention and political controversy. Currently the majority of subsidence surveys are performed using total stations, digital levels and GPS, with a height resolution of a few millimetres on a point-by-point basis. This would be, however, very time consuming and expensive when a dense survey is required over a large area. Differential interferometric synthetic aperture radar (DInSAR) has been considered as a competitively cost-effective technique for ground surface displacement mapping. It has been increasingly used to monitor ground surface deformations due to such occurrences as fluid extraction [1], earthquake [2, 3] and volcanic activities [4]. For mine subsidence monitoring, DInSAR has demonstrated its feasibility in the studies in the UK [5, 6], France [7, 8] and Germany [9, 10]. The ERS-1/2 satellite images were primarily used in those studies. Underground mining subsidence normally has a magnitude of tens of centimetres over a short period of time and the results from the studies showed that the phase ambiguity becomes difficult to be resolved due to the strong phase noise caused by unfavourable vegetated cover and/or high gradient of phase fringes for long time span between the interferometric image pairs. This paper shows the outcomes of the project for mine subsidence monitoring using the integration of DInSAR and Geographic Information Systems (GIS) in the region southwest of Sydney, Australia. This project is supported by ESA (Envisat CAL/VAL) and Australian Coal Association Research Program (ACARP). Both ERS (C-band) and JERS-1 (L-band) images have been processed and analysed. The results are presented in the later sections.