Slope Monitoring within Open-Pit Mines by Ground-Based Radar: Methodology, Data Processing and Case Studies Review

Open-pit mines are widely exploited to provide increasing-demand materials around the world. The peculiar extraction methods carried out during mining operations create steep slopes that need to be constantly monitored to ensure the safety of workers and machinery. Methods to reliably measure slope movements and possibly predict impending failures are paramount and constantly under study and improvement. Reliability allows in fact to reduce the false alarm events that cause stopping of the operations with impact on the productivity. Radar interferometry is a technique that has been widely demonstrated in the past to be able to measure millimetric deformations over a wide area (when the radar is mounted on space-borne platforms) or, more, recently, at a local scale with Ground-based radars. Radar interferometry needs two main conditions to work well: the imaged targets should provide sufficient back-scattered signal and this signal remains coherent in time. Open-pit mines offer very often the two conditions above, as the vertical walls ensure a good level of backscattered signal and the poor presence of vegetation, subject to random movement, ensures a huge number of measurement points. Also if these conditions are satisfied, the digital processing of the radar signal is fundamental to eliminate artifacts caused by the variability of the atmospheric conditions, that have to be removed from the raw data in order to obtain accurate displacement measurements and reliable alarms. The paper deals with the monitoring of the slope movements over a wide areas of open pit mines up to millimetric precision, presenting the radar technology, the data processing method and some real case studies. The key parameters and boundary conditions that impact the quality of the measurements are discussed and the results for different cases of movement (fast, slow, distributed or concentrated) are analyzed and presented.