Authors: Sage, E; Holley, R; Carvalho, L; Miller, M; Magnall, N; Thomas, A

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Sage, E, Holley, R, Carvalho, L, Miller, M, Magnall, N & Thomas, A 2022, 'InSAR monitoring of a challenging closed mine site with corner reflectors', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: Proceedings of the 15th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 779-788,

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Slope instability at mine sites is a hazard that may persist long after closure. Stewards of such assets can monitor and assess the associated risks by examining ground displacement over time. Mapping ground displacement through satellite Interferometric Synthetic Aperture Radar (InSAR) is an increasingly common tool for mine site monitoring. The satellite returns image acquisitions at regular time intervals, which are compared to each other to measure displacement. InSAR is a remote sensing technique that can provide wide-area, high-precision data coverage, regardless of cloud cover. However, for InSAR to provide coverage, the radar reflectivity of the ground needs to stay consistent throughout the analysis period. This consistency is hindered by changes on the ground surface, such as construction, excavation, snow or water inundation, and the type, thickness, and seasonal variation of vegetation. These can be challenging variables across active sites, due to ongoing mining activities, and at closed sites, due to deconstruction of infrastructure, revegetation and any other process that alters the ground surface. These challenges are present at one such site, which has been anonymised in this article, where closure activities make conventional InSAR workflows challenging. At this site, to be able to provide critical ground displacement data, more than 100 artificial radar corner reflectors (CRs) were deployed. These are metal structures carefully located and positioned to provide a strong, consistent radar response across desired assets. The use of CRs for InSAR is not new, but they have not been widely adopted for mining applications, especially in large numbers. Our results demonstrate the benefits of using CRs for such applications, including improved precision and enhanced data coverage over key assets, such as the tailings storage facility. The success of the project highlights the importance of a collaborative approach in planning an InSAR monitoring program. Further, this study discusses challenges of InSAR and CR use for closed mine sites and provides alternative InSAR technologies to CRs that could be used for the application of mine closure.

Keywords: monitoring, InSAR, coherence, corner reflectors, mine closure

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