Athos Ribeiro dos Santos

Evaluating the discrimination of Cu-mineralized rock alteration products from simulated MAPSAR Images in the Curaçá Valley, Brazil

L‐band images simulating MAPSAR satellite sensor data were used to identify Cu‐mineralized rock alteration products in the Curaçá Valley, Brazil. The area is characterized by a semi‐arid terrain, with residual soils and xerophytic vegetation. The mineralizations are mainly associated with pyroxenites but are also found in norites, gabbro‐norites, and anorthosites. These mafic–ultramafic rocks produce characteristic Vertisols. A quantitative analysis for the rock discrimination was based on JM distances derived from training samples (amplitude values of L‐HH, L‐VV, and L‐HV). The investigation showed the possibility of the discrimination of ore‐bearing intrusives from the host rocks, with the exception of amphibolite. Variations in the surface moisture affected the SAR responses, prior to the data acquisition, and caused the higher returns created by wet Vertisols, favouring the discrimination of the rock alteration products.

Applying persistent scatterer interferometry for surface displacement mapping in the Azul open pit manganese mine (Amazon region) with TerraSAR-X StripMap data

Abstract. The Azul mining complex, located in the Carajás Mineral Province, Amazon region, encompasses the most important manganese mine in Brazil. Vale S.A. company operates three simultaneous open pit excavations (mines 1, 2, and 3) in the area, which are conducted on rock alteration products of low geomechanical quality related to sandstones, siltstones, and a lateritic cover. In order to monitor ground deformation, 33 TerraSAR-X (TSX-1) StripMap images covering the period of March 2012–April 2013 were used in the investigation. An advanced differential interferometric synthetic aperture radar (A-DInSAR) approach based on persistent scatterer interferometry (PSI) using an interferometric point target analysis algorithm was applied, and the results showed that most of the area was considered stable during the time span of the synthetic aperture radar acquisitions. However, persistent scatterers (PS) with high deformation rates were mapped over a waste pile, probably related to settlements, and also along the north flank of mine 1, indicative of cut slope movements toward the center of the pit. A spatial relationship of geological structures with PS was observed for this sector of the mine, given by PS showing deformation rates concentrated along a structural corridor with faults, fractures, and folds related to the Carajás fault system. Though only ground-based radar measurements for wall benches of mine 1 were available for a short time period of the TSX-1 coverage, the PS movement patterns showed concordance with geotechnical field measurements. The investigation emphasized the important role that satellite-based A-DInSAR can play for deformation monitoring and risk assessment in this kind of mining area.

Monitoring of surface deformation in open pit mine using DInSAR time-series: a case study in the N5W iron mine (Carajás, Brazil) using TerraSAR-X data

We present an investigation of surface deformation using Differential SAR Interferometry (DInSAR) time-series carried out in an active open pit iron mine, the N5W, located in the Carajás Mineral Province (Brazilian Amazon region), using 33 TerraSAR-X (TSX-1) scenes. This mine has presented a historical of instability and surface monitoring measurements over sectors of the mine (pit walls) have been done based on ground based radar. Two complementary approaches were used: the standard DInSAR configuration, as an early warning of the slope instability conditions, and the DInSAR timeseries analysis. In order to decrease the topographic phase error a high resolution DEM was generated based on a stereo GeoEye-1 pair. Despite the fact that a DinSAR contains atmospheric and topographic phase artifacts and noise, it was possible to detect deformation in some interferometric pairs, covering pit benches, road ramps and waste piles. The timeseries analysis was performed using the 31 interferometric pairs, which were selected based on the highest mean coherence of a stack of 107 interferograms, presenting less phase unwrapping errors. The time-series deformation was retrieved by the Least-Squares (LS) solution using an extension of the Singular Value Decomposition (SVD), with a set of additional weighted constrain on the acceleration deformation. The atmospheric phase artifacts were filtered in the space–time domain and the DEM height errors were estimated based on the normal baseline diversity. The DInSAR time-series investigation showed good results for monitoring surface displacement in the N5W mine located in a tropical rainforest environment, providing very useful information about the ground movement for alarm, planning and risk assessment.

Effect of microtopography on RADARSAT-1 and PALSAR backscattering from rock alteration products in the Curaçá Valley, Brazil.

This paper addresses the influence of microtopography (root mean square height HRMS and correlation length LC) on RADARSAT-1 and phased array L-band synthetic aperture radar (PALSAR) backscattering coefficient (σ0) values from distinct rock alteration products of the Cu-rich district of Curaçá Valley, northeastern Brazil. The area is characterized by a semiarid environment, flat topography with rock outcrops and residual soils, and low to moderate Caatinga vegetation cover. The lithologies consist of Archean gneisses and granulites interbedded with mafic-ultramafic intrusives and upper Proterozoic marbles, schists, and phyllites. The images were acquired under distinct look azimuth and incidence angles and corresponded to four RADARSAT-1 images (F2, S2, and S7 ascending and S7 descending) and one PALSAR image (fine beam dual (FBD) descending). The research was based on the use of linear regression analyses, which showed a weak to moderate linear correlation between σ0 and HRMS and LC for both SAR data. HRMS was the most important microtopographic parameter influencing σ0, whereas LC played a secondary role. Regarding RADARSAT-1, the highest regression coefficient (R2) values were obtained for shallower incidence angles (S7), and this dependence increased from steeper to shallower incidence, regardless of changes in the look azimuth. For PALSAR, R2 was slightly higher than that for RADARSAT-1 and was related to cross-polarization. The investigation showed that backscattering for synthetic aperture radar (SAR) data from both RADARSAT-1 and PALSAR is not modulated in a predominant manner by the microtopographic variations of the geological surfaces.

Characterization of Renders and Plasters from a 16th Century Portuguese Military Structure: Chronology and Durability

In coastal areas of Portugal, many historical buildings and fortresses still exist that were constructed in masonry with aerial lime mortars. These mortars are often found to be in good condition, showing appropriate cohesion and adhesion to the background, although usually they show surface degradation as a result of the aggressive marine environment. The aim of this paper is to present and characterize the mortars used for the renders and plasters of one of these fortresses, that of Nossa Senhora da Luz which was constructed and modified over several centuries. The study of the mortars permitted to identify a construction period chronology improving the knowledge of the changes in formulation of the aerial lime mortars thus allowing to select compatible repair solutions.

Results of the application of persistent scatterers interferometry for surface displacements monitoring in the Azul open pit manganese mine (Carajás Province, Amazon region) using TerraSAR-X data

Brazil has 10% of global Mn reserves with its most important mine located in the Amazon region. The Azul deposit is related to sandstones and siltstones of the Águas Claras Formation (Archean), situated in the central portion of the Carajás Strike-Slip System. Vale S.A. mining company operates the Azul mining complex with three simultaneous excavations (mines 1, 2 and 3) conducted on rock materials of low geomechanical qualities. Mining operations are openpit, with 4-8 m-high benches and depth of 80 m. A stack of 19 TerraSAR-X (TSX) images was used for the investigation covering the period of March 20-October 4, 2012. In order to minimize the topography phase error in the interferometric process, a high resolution DEM was generated based on a panchromatic GeoEye-1 stereo pair. Persistent Scatterers Interferometry (PSI) analysis was carried out using the IPTA (Interferometric Point Target Analysis) software and led to the detection of 40,193 point-wise persistent scatterers (PS), with an average density of 5,387 PS/km2. It was concluded that most of the mining area can be considered stable during the TSX coverage. High deformation rates related to settlements were mapped over a waste pile, while small deformation rates were detected along the north and south flanks of mine 1and were interpreted as cut slope movements toward the center of the pit. Despite only ground-based radar measurements were available for a short time period during the TSX coverage, and covering a sector of bench walls along the south flank of mine 1, the PSs movement patterns showed concordance with the field measurements. The investigation emphasized the important role that PSI technique can play in planning and risk assessment in this mining area. Monitoring of this type of deformation by PSI can usefully complement other commonly used field geotechnical measurements due to the synoptic SAR coverage over a dense grid, providing ground deformation data independently of field access and with millimeter accuracy.

An assessment of the use of RADARSAT-2 for detailed topographic mapping in a tropical semiarid terrain of Brazil

In this paper, the feasibility of using planialtimetric information derived from RADARSAT-2 (RST-2) ultra-fine (UF) stereo pairs and fine quad-pol (FQP) images for detailed topographic mapping was investigated for a semiarid terrain in the Curaçá Valley, northeast of Brazil. Precise topographic field information acquired from a global positioning system was used for ground control points for the modeling of the stereoscopic digital surface models (DSMs), ortho-images, and as independent check points for the calculation of planialtimetric accuracies. The analysis was performed with the following two approaches: (i) the use of root mean square error for the overall classification of the DSMs and ortho-images considering the Brazilian Map Accuracy Standard limits, and (ii) calculations of systematic errors (bias) and accuracy based on a methodology that takes into account computed discrepancies and standard deviations. Thematic information was extracted from FQP data through the use of an unsupervised terrain and land-use classification scheme based on the Freeman–Durden decomposition and the Wishart classifier. The investigation showed that the planialtimetric accuracies of UF DSMs and ortho-images and the thematic information of the FQP data fulfilled the requirements compatible to detailed topographic mapping (1:50000). Thus, the use of RST-2 data can be considered a real alternative as a primary source for detailed topographic mapping programs in similar environments of Brazil, where terrain information is limited or of a poor quality.

Spatiotemporal monitoring of surface motions using DInSAR techniques integrated with geological information: a case study of an iron mine in the Amazon region using TerraSAR-X and RADARSAT-2 data

Instabilities are extremely common in the iron open-pit mines located in the Carajás mineral province, the world´s largest iron reserves located in the Brazilian Amazon. Due to deep excavations in rock products of low geomechanical quality, heavy precipitation, and blasting practices, mining operations in the area present surface displacements that potentially lead to slope instabilities with several risks (personnel, equipment, mining infrastructure, etc.). This paper presents the results related to the N5E mine based on DInSAR Time Series (DTS) and Persistent Scatterer Interferometry (PSI) using a temporal series of 33 StripMap TerraSAR-X (SM TSX) images, and geological information provided from a 3D photointerpretation of an SM TSX and Ultra-Fine RADARSAT-2 (UF RST) stereo-pair, calibrated with field data. Measurement point (DTS, PSI) results were compared with in situ geodetic survey information (total station/prism measurements) and showed good agreement indicating that most of the mine can be considered stable during the period of the TSX coverage. The highest accumulated displacements were spatially related to a thematic unit mapped as a landfill. For other sectors of the mine, lower deformation rates were related to photointerpreted lineaments related to the Carajás fault system suggesting that geological structures can play a key role in controlling some surface displacements. The investigation demonstrated that the strategy based on the use of DTS and PSI techniques integrated with geological data provided a synoptic view of the deformation process that affected the mine. The approach was relevant for ground displacements monitoring of the study area with DInSAR results compared with in situ geodetic measurements showing good statistical correlation.

Monitoring subsidence of waste piles and infrastructures of active open PIT iron mine in the Brazilian Amazon Region using SBAS interferometric technique and TerraSAR-X data

This paper presents the results of applying SBAS (Small Baseline Subset) differential interferometric technique using 33 Stripmap mode images from the TerraSAR-X satellite, over a 1-year monitoring, Stripmap mode, for detection of ground deformation processes in five Carajas open pit iron mines in the state of Pará/Brazil in Amazon region, characterized by torrential rains. The SBAS algorithm was used for the interferometric processing, with coherence threshold of 45%, 4 looks, Delaunay Minimum Cost Flow (MCF), with a reference GeoEye-1 DEM, which allowed obtaining a synoptic view of the mine complex, covering the infrastructure and benches, as well as detecting the deformation in one mine (N5W). In order to monitor the waste piles, a lower coherence value (30%) was necessary. The results obtained were consistent with field work data, including topographic surveying, showing that this technique can be very useful for ground movement alert, planning, and risk assessment.