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Summary of Proposal LAN0452

TitleAdvanced Differential Interferometry for Geohazard assessment in South Africa
Investigator Engelbrecht, Jeanine - Council for Geoscience, Western Cape
Team MemberNo team members defined
SummaryThis research proposes the development of advanced DInSAR techniques for applications related to geohazard assessment in South Africa. The geohazards to be investigated include the monitoring of mining subsidence associated with the Witbank Coalfields. The availability of ground-based measurements of subsidence will provide the ideal test case for methodology development of advanced DInSAR approaches, including the polarimetric interferometry (PolInSAR) technique. Successful application of the technique in this study area will imply that the methodology can be applied to areas where deformation is expected, but not proven. Such deformation includes the detection of movement as a result of isostatic adjustment and associated movement along faults. If movements along faults are detected, the risk of an area to be affected by earthquake activity can be established. This will imply that the technique could function as an early warning system and would be invaluable for decision-making strategies on current and future infrastructure. Following a broad hypothesis, we aim to answer the following specific research questions: 1) Can DInSAR techniques be employed to study surface subsidence associated with mining activities in South Africa?, 2) Can fault movement and differential movement due to isostatic adjustment be detected and, consequently, seismic hazards assessed using DInSAR and PolInSAR techniques?, and 3)What advances can be achieved by using PolInSAR techniques that could not be achieved by using traditional interferometry approaches? The ultimate objective of this research is to establish the use of DInSAR techniques for the study of geohazards in South Africa. The known limitations of traditional DInSAR approaches will be addressed by testing PolInSAR techniques for its ability to enhance interferometric coherence and to detect surface movement in the areas of interest. The investigation approach will start with an evaluation of the availability of interferometric image pairs for the proposed study areas. This will include X-, C- and L-band data at a variety of polarisations. Traditional differential interferometry techniques will be applied to the data sets with the aim of testing its ability to map and monitor surface deformation associated with mining activities in the Witbank Coalfields. Expected problems associated with traditional DInSAR approaches include the temporal decorrelation (resulting in incoherence) of data as a result of changing landcover conditions over time. This effect will be particularly limiting in the presence of vegetation. To curb the problems associated with decorrelation by vegetation and landcover conditions, the polarimetric interferometry approach will be tested for its ability to detect the surface deformation associated with mining activities. Polarimetric radar interferometry (PolInSAR) improves the performance of InSAR by exploiting the wave polarisation, allowing for a more sophisticated interpretation of SAR interferograms. The combination of polarimetry and interferometry allows for the retrieval of the height of different scattering mechanisms present in a resolution cell, even if one scattering mechanism dominates over another. The separation of scattering mechanisms is based on selecting those polarisation states in both images that maximise the interferometric coherence. In this study polarimetric decomposition techniques will be applied to identify the different scattering mechanisms for the purpose of optimising interferometric coherence for geohazard assessment. The data used will include historical single polarization ERS 1 and 2 SAR data as well as single polarizarion ALOS PALSAR data. The hope for future acquisitions of interferometric TerraSAR-X and ALOS PALSAR data in fully polarimetric mode will be invaluable for determining the ability of the PolInSAR technique to enhance interferometric coherence and subsequent deformation monitoring.

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