Jorge Luís Porsani

Ground-penetrating radar profiles over multiple steel tanks: Artifact removal through effective data processing

This paper describes some ground-penetrating radar (GPR) results to characterize steel tanks buried in the subsoil of an urban center. Tanks were installed in the first Brazilian geophysical test site located at the Institute of Astronomy, Geophysics, and Atmospheric Science (IAG) of the University of Sao Paulo (USP). This paper also presents an effec-tive procedure for removal of hyperbolic artifacts associated with GPR reflections between multiple steel tanks. One hundred sixty-five GPR profiles of 200 MHz , 400 MHz , and 500 MHz (shielded bistatic antennae) were measured. The work was done in two distinct places: on the geophysical test site of the IAG/USP in the city of Sao Paulo, Brazil, and in an area formerly occupied by a truck cleaning, refueling, and maintenance facility, located in Oscoda, northeastern Michigan, USA. Predictive deconvolution and Kirchhoff migration were first used to improve vertical and lateral resolution. To minimize the hyperbolic artifacts caused by reflections between tank...

Investigações geofísicas de superfície e de poço no sítio controlado de geofísica rasa do IAG-USP

This paper presents the results obtained from surface and borehole geophysical investigations carried out at the Shallow Geophysical Test Site of IAG-USP. The main objective was to characterize the sediments and the top of basement. The area is constituted by sandy-clay sediments of Sao Paulo Basin (Sao Paulo and Resend Formations) on the granite-gneiss basement with different degrees of weathering. In the area of studies, three boreholes were drilled for geological and geophysical research purposes (pioneer in Brazil). These boreholes were used to verify the stratigraphy, to collect the sample for laboratory measurements, to calibrate the results of surface geophysics and to carry out well logging. The surface methods used were: seismic (reflection and refraction), electric-resistivity (profiling and vertical electric sounding) and GPR-Ground Penetrating Radar. The integration of results show excellent agreement and allow constructing a geological-geophysical model for the site which is at the border of Sao Paulo sedimentary basin. Moreover, the various geophysics methods, commonly used in geological, geotechnical and environmental researches, have been tested under controlled conditions.

O sítio controlado de geofísica rasa do IAG/USP: instalação e resultados GPR 2D-3D

The data interpretation from shallow geophysical survey can be complex because the uncertainty about subsurface targets. To reduce the ambiguity and help in the interpretation of geophysical data, the Shallow Geophysical Test Site of IAG-USP (Sitio Controlado de Geofisica Rasa-SCGR do IAG-USP) was installed inside the campus at USP. Different targets at various depths were installed along seven lines. The targets buried in the Test Site simulate targets found in geotechnical, archaeological, and environmental studies. In this article, the construction methodology of the Test Site and some GPR results along a line characterized by empty metallic tanks are presented. The geophysical characterization in controlled field condition allowed the calibration of geophysical responses due to known targets, such as, metallic tanks. 250 MHz GPR profile showed an excellent agreement with a GPR 2D model determined by finite difference in time domain method. Fk-migration improved the resolution and the spatial position of the metallic tanks. GPR 3D results, such as 3D cube, fence diagrams, and depth slices, were very important to improve the characterization of the targets in subsurface. SCGR-IAG revealed itself as important tool for teaching, research and extension activities in university related to Geophysics, and it will be very important to our community. With the installation of this Test Site, an important step was done in searching the State of Art in Shallow Geophysics in Brazil, were the development of news equipment, modeling and inversion software could be tested and its response calibrated.

Microwave Tomography-Enhanced GPR in Forensic Surveys: The Case Study of a Tropical Environment

Ground penetrating radar (GPR) is a geophysical tool currently adopted by police forces to locate buried objects and missing human bodies. However, a systematic assessment of its achievable imaging capabilities is still an open issue. In addition, sometimes, conventional data processing tools do not provide accurate and reliable information, thus leading to a misinterpretation of the location and geometry estimation of the target. In this framework, this paper deals with a case study referred to a tropical environment, and investigates the imaging capabilities offered by a linear microwave tomography approach. The results of three experiments, referred to the same organic target and carried out at different times by means of 270- and 900-MHz antennas, are presented. The comparison between the microwave tomographic approach and the widely used Kirchhoff migration suggests that the former procedure allows improved performances in locating both the target and the grave.

Estudos geofísicos integrados no lixão de Cuiabá, MT, Brasil: resultados preliminares

One of the major concerns in geoenvironmental projects is the soil and water contamination caused by the waste disposal. The geophysical methods applied are a good way to get some information required in a site characterization program. This work shows some results obtained through resistivity, EM inductive and GPR surveys in the search of informations about the impact caused by a waste disposal area in Cuiaba, State of Mato Grosso, Brazil.

Automatic classification of metallic targets using pattern recognition of GPR reflection: a study in the IAG-USP Test Site, Sao Paulo (Brazil)

In this work, a methodology to automatically classify of metal targets using pattern recognition techniques on GPR reflection data is presented. The methodology consists of designing a multilayer perceptron (MLP) classifier based on features extracted from the targets in the subsoil, and then using it to classify hyperbolas diffraction indicating their position and depth. The classification of reflections allows a high resolution reconstruction of the subsurface with reduced computing time. The system was developed in MATLAB and applied to GPR data obtained at IAG-USP test site, located in the city of Sao Paulo, Brazil, where metallic drums were studied under controlled field conditions. This site contains different targets of variable sizes buried under different depths and it served as a model for the computational experiment. The results indicate that the automatic classification of the metallic targets in the subsoil is efficient, contributing for the reduction of the ambiguities in the geophysical data interpretation, besides having application on the subsoil mapping of utilities.

Deconvolução preditiva de dados GPR adquiridos sobre lâmina d'água: exemplo do Rio Taquari, Pantanal Matogrossense

This paper presents results obtained from the acquisition and processing of GPR (Ground Penetrating Radar) data recorded on the water surface of the Taquari River in the Pantanal wetland. This unconventional mode of use of the GPR method has shown to be quite viable and had allowed us to set some optimal parameters for GPR data acquisition on water surface, acting as a guiding tool for future GPR works in similar regions. The obtained GPR sections have allowed the clear identification of some physiographic structures of the riverbed, in addition to primary reflections and events corresponding to multiple reflections. We have applied the Wiener-Levinson predictive deconvolution (PD) method to remove the multiple reflections present in the GPR sections. PD method has been successfully used in the petroleum industry for marine seismic data processing. PD in the mono and multichannel modes were applied on three GPR sections. The deconvolved sections have demonstrated that the attenuation of the multiple reflections in the radargrams has been more efficient in regions where no abrupt variations occur in the riverbed and the thickness of the water surface is greater than two meters. Even though this work has a local feature, the promising results obtained with the Wiener-Levinson PD method, both mono and multichannel, suggest the employment of this methodology as an effective tool in the removal of multiple reflections present in GPR data acquired on the surface of rivers and lakes.

Investigações GPR nos distritos mineiros de Santa Bárbara e Bom Futuro: Província Estanífera de Rondônia

Investigacoes GPR - Ground Penetrating Radar foram realizadas nos distritos mineiros de Santa Barbara e Bom Futuro (Provincia Estanifera de Rondonia), visando averiguar a aplicabilidade do metodo para localizacao de depositos estaniferos primarios e secundarios, bem como otimizar os custos envolvidos na etapa de prospeccao. Os perfis de reflexao GPR foram adquiridos com antenas de 25, 50 e 100 MHz, o que permitiu investigar a subsuperficie ate 30 metros de profundidade. Em relacao aos depositos primarios das minas de Santa Barbara e de Bom Futuro, o metodo GPR permitiu identificar zonas com predominância de corpos de greisens. No deposito secundario aluvionar da mina de Bom Futuro, o metodo GPR permitiu localizar uma estrutura de paleocanal na base do sistema deposicional sedimentar. Os resultados obtidos apresentaram uma excelente concordância com as informacoes geologicas provenientes das sondagens, demonstrando essa nova aplicabilidade do metodo GPR para a exploracao mineral, na qual podera ser extendida para ambientes similares do Craton Amazonico. Alem disso, os custos envolvidos no processo exploratorio poderao ser otimizados, caso as investigacoes GPR sejam realizadas antes da execucao de sondagens.

Investigações geofísicas na borda da bacia sedimentar de São Paulo

This paper shows partial results of geophysical investigations carried out in the border of Sao Paulo Sedimentary Basin, within the Sao Paulo University campus. The main objective of this research is characterizing the sediments and the top of basement rocks using the GPR - Ground Penetrating Radar and Resistivity Methods. The geophysical profiles were carried out along the same line in order to compare results obtained from these methodologies. One GPR profile (216m) was acquired employing 50MHz antennas and one resistivity profile with dipole length of 20m. Besides two verticals electrical soundings (VES) measurements were done on the same line. The analysis of GPR profile permitted to identify the bottom boundary the soil and one coarse sand layer. The result was supported by borehole information. The electrical profile identified one conductivity anomaly zone between 80 and 110m, related probably with a shear zone.

Radarfacies and sedimentological analysis: Study of sedimentary substrate from an archaeological site (shell mound), southern Brazil

Integrated results of GPR (Ground Penetrating Radar) and sedimentological analysis are presented for the Jabuticabeira II archaeological site (shell mound), Santa Catarina, Brazil. By means of radarfacies identification, this study aims to delimit the archaeological site and differentiate the coastal depositional systems that compose its substrates. For these purposes, available models of the temporal–spatial distribution of depositional systems in the area were used and sedimentological analysis (granulometry, quantification of heavy minerals and clay-mineral characterization) were performed on samples spaced at 0.5-m vertical intervals in auger drills cutting the identified radarfacies. GPR data were obtained along a radial grid, which allowed the rapid mapping of a large area (several hundred square metres). The results allowed to characterize an archaeological layer, the soil and two sedimentary layers (palaeolagoon and aeolian) in the substrates under and around the site. The high porosity and the grain size, cementation and heavy mineral segregation contrasts along wind-controlled laminations are for the reflector sharpness in the aeolian deposits. The archaeological site settlement mostly overlies the palaeolagoon, which was a newly emerged land during the epoch of occupation and is situated on the margins of aeolian deposits that formed in the region after the Holocene maximum flooding. This configuration reinforces the sambaquis occupation model of south-central Santa Catarina during the Holocene, strongly controlled by the proximity to lagoon bodies. The resolution of the data in this study was sufficient to advance our understanding of the regional sedimentary evolution and its relation with sambaqui occupation.