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Spatial data are nowadays commonly used in engineering practice to support geohazard managements, identify and classify possible instabilities, and monitor their activity. Terrestrial laser scanners and ground-based radar systems, often implemented in mobile vehicles, are widely used within the mining sector to conduct periodic surveys of extended areas of hazardous access, and track deformations in almost real time. While such systems are very accurate and can operate in various weather conditions, their utilisation could incur substantial costs and require high technical expertise. Photogrammetry is considered as a viable and cost-effective alternative to traditional slope monitoring techniques. This paper presents recent improvements of a low-cost, autonomous terrestrial stereo-pair photogrammetric monitoring system specifically developed by the authors to monitor highly hazardous areas in surface mining environments and its application to the monitoring of a highwall face located in a mine site in New South Wales (Australia). The system is used to identify the sources of block instabilities (detachments) over several months to estimate the volumes of rock detached and their frequency over the period of observation.

The system consists of two units. Each unit includes a box containing a high-resolution digital single-lens reflex (DSLR) camera (Nikon D850) controlled by a Raspberry Pi microcomputer. The system allows the collection of synchronised images at different periods. The images are downloaded remotely and processed automatically on a server to obtain a 3D model (eg 3D point cloud and mesh). The system also includes a …