Abstract
Persistent Scatterer interferometry (PSI) represents a powerful tool for the detection and monitoring of tiny surface deformations in vast areas, allowing a better understanding of its triggering mechanisms, planning of mitigation measures, as well as to find better solutions for social and environmental issues. However, there is no record hitherto of its use in active open pit mine in tropical rainforest environment. In this paper we evaluate the use of the PSI technique for the detection and monitoring of mine slope deformations in the N4W iron mine and its surroundings, Pará State, Northern Brazil. The PSI processing was performed with 18 ascending SAR scenes of the TerraSAR-X satellite acquired in the dry season of 2012. The results showed a significant number of widely distributed persistent scatterers. It was observed that most of the study area was stable during the time span. Nevertheless, high deformation rates (312 mm/year) were mapped over the mine waste piles, but do not offer any hazard, since they are expected displacements of meters in magnitude for these manmade land structures. Additionally, it was mapped tiny deformation rates in both the east and west flanks of pits 1 and 2. The main underlying reasons can be assigned to the accommodation phenomena of very poor rock masses, to the local geometric variations of the slope cuts, to the geological contact between ironstones and the country rocks, to the exploitation activities, as well as to the major geological structures. This study showed the applicability of the PSI technique using TerraSAR-X scenes in active open pit mines in tropical moist environment. However, the PSI technique is not capable in providing real-time warnings, and faces limitations due to SAR viewing geometry. In this sense, we strongly recommend the use of radar scenes acquired in both ascending and descending orbits, which would also provide a more complete understanding of the deformation patterns.
Highlights
One of the most important open pit iron mines in Brazil is the N4W, located in the Carajás MineralProvince, Amazon Region (Figure 1)
Both geometric distortions limit the use of the Persistent Scatterer interferometry (PSI) technique
As one can see through the visual inspection of the SAR scenes, over the waste pile W, mining activities are not the only factor affecting coherence
Summary
One of the most important open pit iron mines in Brazil is the N4W, located in the Carajás Mineral. In spite of being known for having a high precision, these traditional techniques present operational, logistical, and economic disadvantages, such as the cost against the size of the monitored area [3,4,5] In this sense, the persistent scatterer technique, PSI [6,7], which uses the phase information (proportional to the sensor-target distance) of SAR (Synthetic Aperture Radar) scenes acquired at different times (from the past to the present depending on the availability of the scenes), provides a synoptic view of the distribution and the activity status of unknown surface motions [8,9,10,11,12,13,14]. This study is part of an innovative research among INPE-FAPESP-Vale that aims for the application of orbital radar imaging to the detection of possible surface displacements affecting the active open pit iron mines of the Carajás Mineral Province, Pará State, Northern Brazil
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