Waldir Renato Paradella

An Assessment of the Altimetric Information Derived from Spaceborne SAR (RADARSAT-1, SRTM3) and Optical (ASTER) Data for Cartographic Application in the Amazon Region

Difficulties in acquiring a complete aerial photography coverage on a regular basis in the Brazilian Amazon due to adverse environmental conditions affect the quality of the national topographic database. As a consequence, topographic information is still poor, and when available needs to be up-dated or re-mapped. In this research, altimetric information derived from RADARSAT-1 (Fine and Standard modes), SRTM3 (3 arc-seconds) and ASTER (band 3N-3B) was evaluated for topographic mapping in two sites located in the region: Serra dos Carajás (mountainous relief) and Tapajós National Forest (flat terrain). The quality of the information produced from Digital Elevation Models (DEMs) was evaluated regarding field altimetric measurements. Precise topographic field information acquired from Differential Global Positioning System (DGPS) was used as Ground Control Points (GCPs) for the modeling of the stereoscopic DEMs (RADARSAT-1, ASTER) and as Independent Check Points (ICPs) for the calculation of accuracies of the products. The accuracies were estimated by comparison of the DEMs values and real elevation values given by ICPs. The analysis was performed following two approaches: (1) the use of Root Mean Square Error (RMSE) for the overall classification of the DEMs considering the Brazilian Map Accuracy Standards (PEC) limits and, (2) calculations of trend analysis and accuracy based on a methodology that takes into account computed discrepancies and standard deviations. The investigation has shown that for flat relief, the altimetric accuracy of SRTM3 and Fine RADARSAT-1 DEMs fulfilled the PEC requirements for 1:100,000 A Class Map. However, for mountainous terrain, only the altimetry of SRTM3 and ASTER fulfilled these requirements. In addition, the performance of ASTER was slightly superior to SRTM3. However it is important to consider the difficulties in the acquisition of good stereo-pairs with optical data in the Amazon and the additional cost (GCPs) to produce ASTER DEMs. Despite showing systematic errors, the findings justify the usage of SRTM3 as a primary elevation source for semi-detailed topographic mapping in the region. It is suggested a combination of altimetry derived for SRTM3 and planimetry extracted from high-resolution SAR (ALOS/PALSAR, TerraSAR-X, RADARSAT-2) or if available optical data for semi-detailed topographic mapping programs in the Brazilian Amazon, where terrain information is seldom available or presents low quality.

Mapping recent deforestation in the Brazilian Amazon using simulated L-band MAPSAR images

Brazilian Amazon Forest biomes are presently under intensive land cover conversion from natural vegetation to agriculture. Timely detection of recent deforestation through orbital remote sensing is a critical requirement for an operational land cover monitoring system in order to provide information to the regulatory systems and decision makers. Optical images present drawbacks for operation in the moist tropics and synthetic aperture radar (SAR) data are a real alternative. The feasibility of using multipolarized L‐band images simulating the Multi‐Application Purpose SAR (MAPSAR) satellite was examined for the detection of recent deforestation in the Tapajós region. The discrimination of recent deforestation from other land cover classes was evaluated through a quantitative analysis based on Jeffreys–Matusitas (JM) distances derived from training samples using amplitude values and supported by field survey. The investigation confirmed the possibility of the discrimination of recently deforested classes from other classes based on the L‐band images as proposed in the MAPSAR.

Spectroradiometric discrimination of laterites with principal components analysis and additive modeling

Abstract Bidirectional reflectance factor determinations in the visible and near-infrared of mineralized laterite samples collected at the surface of the alkaline / ultramafic rocks-carbonatite complex of Maicuru, northern Brazil, were evaluated for iron, phosphate, and titanium content. Nineteen spectra were subjected to principal components analysis in order to get a better insight into the factors affecting spectral discrimination. The spatial distribution in a PC1 vs. PC2 plot is related to the overall reflectance (albedo) along the PO axis and to the spectral inversion around 1100 nm along the PC2 axis. The latter can be characterized by any spectral ratio of reflectance values taken before and after the inversion wavelength. Two major groups were thus identified: titanium-rich (anatase, ilmenite) laterites and aluminum phosphate laterites. The former presented spectra with low to intermediate albedos and lower near-infrared / visible and very near-infrared reflectance ratio values. The phosphate-rich samples presented intermediate to high albedos and higher reflectance ratios. Titaniferous laterites have a greater content of opaques than the phosphates which are usually richer in iron oxides. The presence of titanium lowers the albedo whereas iron oxides absorb only in the visible and very near-infrared. Binary mixtures of Fe 2 0 3 and carbon provided spectral variations analogous to the ones observed in the titaniferous laterites. Such modeling helped in evaluating the effects of opaques. As a practical result, a band radiometer could conceivably identify the titanium mineralized areas in the field.

Integrating airborne SAR, Landsat TM and airborne geophysics data for improving geological mapping in the Amazon region: the Cigano Granite, Carajas Province, Brazil

This study examines the value of integrating airborne C‐band Synthetic Aperture Radar (SAR), Landsat Thematic Mapper (TM) and airborne gamma spectroradiometric data with field, petrographic and geochemical data for geological mapping of the Cigano batholith, an important representative of the Paleoproterozoic granitic magmatism in the Carajás Mineral Province (CMP), Amazon region. Distinct schemes for the integration of radar/optical and radar/optical/gamma data were evaluated and the geological information derived from the integrated products was verified in the field. The investigation allowed the re‐evaluation of previous geological information and the definition of distinct domains within the Cigano pluton and country rocks. The importance of brittle structures related to the tectonic evolution of the area and the location of intensely altered zones in the pluton was emphasized, favouring new insights into current geological and exploratory models of the area. The application of a similar approach as operational routine in exploration programmes in the Amazon region is justified considering the limited geological information, the availability of aerogeophysical data and airborne/spaceborne remote sensing data (radar, optical) and the high costs of field mapping in this kind of terrain.

Detection and Monitoring of Surface Motions in Active Open Pit Iron Mine in the Amazon Region, Using Persistent Scatterer Interferometry with TerraSAR-X Satellite Data

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, Para 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.

Relationship Between PALSAR Backscatter and Surface-Roughness Parameters From Iron Laterites in CarajÁs, Amazon Region

The objective of this investigation was to evaluate the influence of micro- and macrotopography on PALSAR fine-beam dual backscattering in the characterization of iron laterites in Carajas Province, Amazon Region. The moderate linear correlation between sigma0 and surface roughness indicated that, only for L-HH polarization, sigma0 was modulated by the morphology of the geological surfaces.

Operational use of RADARSAT-1 fine stereoscopy integrated with Landsat-5 thematic mapper data for cartographic application in the Brazilian Amazon

The feasibility of topographic mapping through orbital remote sensing was investigated for the Brazilian Amazon. The study area is in a region of low topographic terrain within the Tapajós National Forest. Two kinds of radargrammetric digital elevation models (DEMs), one based solely on satellite ancillary data and one calibrated with ground control points (GCPs), were produced based on a fine RADARSAT-1 stereopair (F2/F5) and evaluated regarding accurate field planialtimetric measurements. The geometric modeling for the DEM extractions was based on the RADARSAT-1 specific model from OESE software (PCI Geomatics Inc.). The planimetric features were extracted from integrated fine and Landsat thematic mapper (TM) products. Precise topographic field information from a differential global positioning system (DGPS) was used as GCPs for the modeling of the DEMs and for the orthorectification of the synthetic aperture radar (SAR) and optical data and as independent check points (ICPs) for the calculation of planialtimetric accuracies of the products. The investigation has shown that the accuracy of the topographic map met the requirements for a 1 : 100 000 scale map (class A) as requested by the Brazilian Standard for Cartographic Accuracy. The approach is a realistic alternative for topographic mapping at a semi-detailed scale in similar environments of the Amazon, where terrain information is seldom available or is of low quality.

Evaluation of Digital Classification of Polarimetric SAR Data for Iron-Mineralized Laterites Mapping in the Amazon Region

This study evaluates the potential of C- and L-band polarimetric SAR data for the discrimination of iron-mineralized laterites in the Brazilian Amazon region. The study area is the N1 plateau located on the northern border of the Carajas Mineral Province, the most important Brazilian mineral province which has numerous mineral deposits, particularly the world’s largest iron deposits. The plateau is covered by low-density savanna-type vegetation (campus rupestres) which contrasts visibly with the dense equatorial forest. The laterites are subdivided into three units: chemical crust, iron-ore duricrust, and hematite, of which only the latter two are of economic interest. Full polarimetric data from the airborne R99B sensor of the SIVAM/CENSIPAM (L-band) system and the RADARSAT-2 satellite (C-band) were evaluated. The study focused on an assessment of distinct schemes for digital classification based on decomposition theory and hybrid approach, which incorporates statistical analysis as input data derived from the target decomposition modeling. The results indicated that the polarimetric classifications presented a poor performance, with global Kappa values below 0.20. The accuracy for the identification of units of economic interest varied from 55% to 89%, albeit with high commission error values. In addition, the results using L-band were considered superior compared to C-band, which suggest that the roughness scale for laterite discrimination in the area is nearer to L than to C-band.

Evaluating the quality of the Digital Elevation Models produced from ASTER stereoscopy for topographic mapping in the Brazilian Amazon Region

Brazilian Amazon is a vast territory rich in natural renewable and non-renewable resources. Due to the adverse environmental condition (rain, cloud, dense vegetation) and difficult access, topographic information is still poor, and when available needs to be up-dated or remapped. In this paper, the feasibility of using elevation generated from orbital ASTER- stereo-pairs images for topographic mapping was investigated for the mountainous relief in the Serra dos Carajas, Para. The quality of information derived from these optical images was evaluated regarding field altimetric measurements. Precise topographic field information acquired from Global Positioning System (GPS) was used as Ground Control Points (GCPs) for the modeling of the stereoscopic Digital Elevation Models (DEMs) and as Independent Check Points (ICPs) for the calculation of elevation accuracies. The analysis was performed following two approaches: (1) the use of Root Mean Square Error (RMSE) and (2) calculations of trend analysis and accuracy. The investigation has shown that the altimetric accuracy from ASTER fulfilled the Brazilian Map Accuracy Standards elevation requirements for 1:100,000 A Class. In addition, ASTER can provide up-dated planimetric information that is also necessary for cartographic production. Thus, when the environment condition allows the acquisition of stereo-pairs, the use of ASTER can be considered an alternative for semi-detailed topographic mapping in similar environments of the Brazilian Amazon.

Mapping iron-mineralized laterite environments based on textural attributes from MAPSAR image simulation - SAR-R99B (SIVAM/SIPAM) in the Amazon region

The use of remote sensing is a valuable method for geological mapping as it provides synoptic coverage at relatively low cost. In the Amazon region, radar imagery has a potential for geological applications due the enhanced sensitivity to topography (macrotopography), surface roughness (microtopography), and dielectric properties of materials, independent of weather, sun angle, and illumination conditions. As the roughness is highlighted, SAR textural attributes can be used for mapping iron-ore mineralized laterites in N1 deposit, located in the Carajas Province. For mapping the lateritic cover, the airborne SAR was used from Surveillance of the Amazon System (SIVAM/SIPAM, L-hh, L-hv, L-vv) to simulate orbital Multi-Application Purpose SAR (MAPSAR). The images were analyzed through textural classifications derived from second-order measure (GLCM) with the objective of mapping the mineralized laterites for iron ore. Differences are highlighted when comparing the classified maps and the ground information. Not all classes were separated, but a high performance for textural attributes was presented by the hematite class. This class was sensitive to the sensor and target parameters, especially macrotopography and physics characteristics. The results showed that for mineral exploration, the radar images at L-band can be used as a practical tool for a preliminary mapping, and as a guide for field-based verification.