Monitoring Longwall Mine Subsidence and Far-field Displacements using Multi-wavelength Radar Interferometry

  • Dr Hsing-Chung Chang, School of Surveying and Spatial Information Systems, University of New South Wales, Australia
  • Mr Alex Hay-man Ng, School of Surveying and Spatial Information Systems, University of New South Wales, Australia
  • Mr Kui Zhang, School of Surveying and Spatial Information Systems, University of New South Wales, Australia
  • Dr Yusen Dong, School of Surveying and Spatial Information Systems, University of New South Wales, Australia
  • Mr Zhe Hu, School of Surveying and Spatial Information Systems, University of New South Wales, Australia
  • A/Prof Linlin Ge, School of Surveying and Spatial Information Systems, University of New South Wales, Australia
  • Prof Chris Rizos, Australia

    • This study uses the spaceborne radar interferometry technique to monitor ground subsidence and far-field displacement due to underground longwall mining in the southern coal fields of New South Wales. The radar images acquired by the European ENVISAT/ASAR and the Japanese ALOS/PALSAR sensors are 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) signals is sensitive to small scale displacement in the far-field; while the longer wavelength of L-band (23.6cm) signals 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 can be used to measure the vertical and horizontal displacements.

    During the radar interferometry process, orbit errors will be corrected by refining the baseline between the locations of antenna in space of the radar image acquisitions. The atmospheric effects are reduced using multiple interferograms and a low-pass filter. In addition corner reflectors on the ground are used to calibrate the radar image.

    The resulting deformation maps are analysed with the aid of a geographic information system (GIS). The results have been validated against conventional field survey data, especially over regions which have important infrastructure, such as optical communication cables, gas pipelines, highways, etc.