Monitoring longwall mine subsidence and far-field displacements using multi-wavelength radar interferometry

This study uses the spaceborne radar interferometry technique to monitor ground subsidence and far-field displacement due to underground longwall mining in the Southern Coalfields of New South Wales, Australia. The radar images acquired by the European ENVISAT/ASAR and the Japanese ALOS/PALSAR sensors were used to compute the terrain deformation. ASAR and PALSAR sensors use microwave signals in the C- and L-band, respectively. The shorter wavelength of C-band (5.6cm) signal is more sensitive to small scale displacement in the far-field; while the longer wavelength of L-band (23.6cm) signal is suitable for measuring large deformations near the centre of the subsidence bowl. In addition, the radar images acquired in both ascending and descending orbits have to be used to measure the vertical and horizontal displacements. During the radar interferometry processing, orbit errors were corrected for by refining the baseline between the locations of the antenna in space during the radar image acquisitions. The atmospheric effects can be accounted for using a low-pass filter. In addition, corner reflectors on the ground are used to calibrate the radar image. The resulting deformation maps were analysed with the aid of a geographic information system (GIS). Possible horizontal movements due to underground mining were identified outside the normal angle of draw.