Néstor Bonomo

Electrical and GPR prospecting at Palo Blanco archaeological site, northwestern Argentina

We conducted a geophysical survey at the Palo Blanco archaeological site located in Catamarca, Argentina. Age estimates from radiocarbon dating indicate first occupation of the site around 1500 years ago. The first description of thesite was done in 1960. At that time, five residential units with different architectural arrangements were reported. These structures had different levels of deterioration caused by exposure and human activities. Some of these original structures have become completely covered by sediments. To aid in the design of efficient excavation plans, detailed maps are required to locate the buried walls. For this purpose, we conducted geophysical surveys over one of the structures. We had poor documentation about the structure at the time of the survey. Only one of the walls described in the earlier report was partially visible. We used two geophysical methods: ground-penetrating radar (GPR) and electrical resistivity. We performed 2D inversion of the resistivity data, together with nu...

Pipe-flange detection with GPR

This paper describes an application of the ground penetrating radar (GPR) method for detecting pipe flanges. A case history is described in which GPR was successfully used to locate pipe flanges along an 8 km metal pipeline, using a fixed-offset methodology, from the ground surface. Summaries of numerical simulations and in situ tests, performed before the definitive prospecting to evaluate the feasibility of detection, are included. Typical GPR signals are analysed and several examples shown. Constant-time sections of data volumes and migration are evaluated with the goal of distinguishing flange signals from rock signals in unclear situations. The applied methodology was effective for detecting the pipe flanges in relatively short times, with accuracies below 10 cm in the horizontal direction and 20 cm in the vertical direction.

Spatial Modifications of Gaussian Beams Reflected at Isotropic-uniaxial Interfaces

The spatial modifications of electromagnetic beams of finite size reflected at plane isotropic-uniaxial interfaces are investigated theoretically. It is shown that the lateral displacement of the beam is a maximum at two angles of incidence : one below and the other above the critical angle of total reflection. These angles are very close to those for which the extraordinary and ordinary waves transmitted into the uniaxial media become evanescent. The analysis of the polarization of the reflected beam shows that both cross-polarized and co-polarized components can exhibit lateral shifts either in the forward or in the backward direction with respect to the incident beam.

Nonspecular reflection of ordinary and extraordinary beams in uniaxial media

We study nonspecular phenomena experienced by two-dimensional ordinary and extraordinary beams propagating in a uniaxial crystal and reflected at a flat uniaxial–isotropic interface. We extend to uniaxial crystals the aberrationless approach used for beams in isotropic media. Analytical expressions for the geometrical nonspecular effects (lateral shift, focal shift, angular shift, and beam waist modification) are given and compared with those predicted by the stationary phase approximation. The theory is applied to the reflection of beams at a flat interface between TiO2 and a vacuum.

Lateral displacement of a beam incident from a uniaxial medium onto a metal

Abstract The reflection of spatially limited beams at the flat boundary between a uniaxial crystal and a metal is studied theoretically. Incident limited beams are expanded in terms of the ordinary and extraordinary plane waves that can be propagated in uniaxial media. The spatial modifications in ordinary and extraordinary reflected field distributions are numerically calculated. Several effects, including polarization conversion between ordinary and extraordinary waves and field enhancement on the interface due to the excitation of surface waves, are discussed. The numerical calculations of the Goos–Hanchen lateral shift in the reflected fields are compared with the results predicted by the extension to uniaxial media of the stationary phase approximation used for limited beams in isotropic media.

GPR investigations at an Inca-Spanish site in Argentina

Fil: Bonomo, Nestor Eduardo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Fisica de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Fisica; Argentina

Electrical imaging for localizing historical tunnels at an urban environment

We performed a geophysical study at a historical site in Buenos Aires, Argentina, corresponding to the location of a Jesuit Mission established during the 17th century, remaining there until the 18th century. The site consisted of a church, cloisters, a school, orchards and a procurator?s office; also several tunnels were built, connecting the mission with different public buildings in the town. In the 19th century the Faculty of Sciences of the University of Buenos Aires was built in a sector of the site originally occupied by an orchard, functioning until its demolition in 1973. At present, this area is a cobbled square. With the aim of preserving and restoring the buried structures, work was carried out in this square looking for tunnels and remains of the basement of the old building.Considering the conductive features of the subsoil, mainly formed by clays and silt, the complex characteristics of the buried structures, and the urban localization of the study area with its consequent high level of environmental electromagnetic noise, we performed pre-feasibility studies to determine the usefulness of different geophysical methods. The best results were achieved from the geoelectrical method. Dipole?dipole profiles with electrode spacings of 1.5 and 3?m provided enough lateral and vertical resolution and the required penetration depth. Reliable data were obtained as long as the electrodes were buried at least 15?cm among the cobble stones. Nine 2D electrical resistivity tomographies were obtained by using a robust inversion procedure to reduce the effect of possible data outliers in the resulting models. The effect on these models of different error estimations was also analyzed. Then, we built up a pseudo-3D model by laterally interpolating the 2D inversion results. Finally, by correlating the resulting model with the original plans, the remains of the expected main structures embedded in the site were characterized. In addition, an anomaly was identified that indicates the presence of a tunnel not previously reported.

Aberrationless approach for diffraction of pulses at linear interfaces

The diffraction of temporally Gaussian shaped light pulses is theoretically studied by means of the aberrationless approach, a theoretical technique previously used for spatially bounded beams of unlimited time extension and which is extended here to time domain. We consider linear interfaces, that is, we assume that the spectral components of the vector field in the diffracted pulse are linearly related with the spectral components of the vector field in the incident pulse. In our analysis pulse deformations are described in terms of the following effects: time delay, focal displacement, waist modification and change in propagation velocity. Expressions for these effects, the time domain analogues of those already reported in the spatial domain, are given and compared with those obtained using the stationary phase method. The theory is used to calculate deformations of a short light pulse at a flat interface near conditions of total internal reflection.

Reflection of light by a slab containing electrically small dielectric spheres

Theoriginal and theenhanced Maxwell-Garnett estimates for the permittivity of a particulate medium are applied to the reflection of light by a composite dielectric slab. The reflection coefficients for incident s and p polarizations are calculated and some curves are plotted and discussed.