Identifying underground utilities and predicting their depth are fundamental when it comes to civil engineering excavations, for example, to install or repair water, sewer, gas, electric systems and others. The accidental rupture of these systems can lead to unplanned repair costs, delays in completing the service, and risk injury or death of workers. One way to detect underground utilities is using the GPR-Ground Penetrating Radar geophysical method. To estimate depth, the travel time (two-way travel time) information provided by a radargram is used in conjunction with ground wave velocity, which depends on the dielectric constant of materials, where it is usually assumed to be constant for the area under investigation. This procedure provides satisfactory results in most cases. However, wrong depth estimates can result in damage to public utilities, rupturing pipes, cutting lines and so on. These cases occur mainly in areas that have a marked variation of water content and/or soil lithology, thus greater care is required to determine the depth of the targets. The present work demonstrates how the interval velocity of Dix (1955) can be applied in radargram to estimate the depth of underground utilities compared to the conventional technique of constant velocity applied to the same data set. To accomplish this, synthetic and real GPR data were used to verify the applicability of the interval velocity technique and to determine the accuracy of the depth estimates obtained. The studies were carried out at the IAG/USP test site, a controlled environment, where metallic drums are buried in known positions and depths allowing the comparison of real to estimated depths. Numerical studies were also carried out aiming to simulate the real environment with variation of dielectric constant in depth and to validate the results 727with real data. The results showed that the depths of the targets were estimated more accurately by means of the interval velocity technique in contrast to the constant velocity technique, minimizing the risks of accidents during excavation.
In this paper, the Ground Penetrating Radar (GPR) method was used to characterize concrete tubes and steel/plastic tanks buried in IAG/USP test site. The microwave tomography was used to improve the GPR images, aiming to retrieve the geometry of the targets. The numerical modeling studies also were done in order to predict the GPR results of the buried targets and to give more reliability to the results interpretation. The targets were installed in the first shallow geophysical test site of the Brazil located at Institute of Astronomy, Geophysics, and Atmospheric Science (IAG) of the University of São Paulo (USP). GPR profiles of 200 MHz (shielded bistatic antennas) were acquired along three lines containing concrete tubes and steel/plastic tanks buried in subsoil. The concrete tubes show a hyperbolic reflector for the top, and the vertical tube also presented a reflection on its bottom. The horizontal steel tanks were characterized by a strong GPR reflection on their top. The empty plastic tank shows a strong reflector for the top with normal polarity. On the other hand, the plastic tank filled with water shows a weaker reflector for its top characterized by the inverted polarity of GPR signal when compared with empty plastic tank. The plastic tank filled with water also went characterized by the strong reflection to its bottom, being a good indicative to interpret GPR data on target in subsoil with some types of fluid inside of tank. The results of polarity difference for the top of tank can be used as guide pattern to identify buried tank empty or filled with water. The application of microwave tomography to the GPR data permitted to determine the position and get a good identification of the edges of the targets studied. The numeric modeling presented a good accordance with real data reducing the ambiguities in interpretation of results. These results can be used as a reference, and they can be extrapolated for areas where there is no subsurface information.
A reforma e a requalificação de centros históricos -como construção, saneamento, pavimentação, entre outras -requerem que uma pesquisa arqueológica seja realizada antes de qualquer intervenção. Nesse contexto, busca-se um equilíbrio entre o que pode sofrer impactos negativos e o que deve ser estudado e preservado arqueologicamente, sempre buscando atender à necessidade do melhoramento dos locais públicos. O Largo da Igreja Nosso Senhor do Bonfim, Marechal Deodoro, Alagoas, ofereceu oportunidade de empregar o método geofísico GPR (Ground Penetrating Radar ou Georadar) para orientar escavações, identificar áreas para preservação e informar engenheiros civis sobre possíveis desafios para a execução do projeto civil. Os resultados foram interessantes, proporcionando um bom argumento para a incorporação de metodologias geofísicas em projetos de Arqueologia Urbana similares. Palavras-chave: GPR-Ground Penetrating Radar; Geofísica arqueológica; Arqueologia Urbana. ABSTRACTBrazilian urban renewal projects in historic districts require that archaeological research be conducted prior to any intervention, such as excavations for sanitation, construction, pavement, among others. In such a context, a balance must be struck between what might suffer impacts and what should be studied and preserved archaeologically, while attending the need to improve these public spaces. The Largo da Igreja Nosso Senhor do Bonfim, a public square dating to the early 17th century, offered the opportunity to use Ground Penetrating Radar to guide excavations, identify areas for preservation and to inform civil engineers of possible challenges for the project generally. The results were mixed, but provide a strong argument for the incorporation of geophysical methods in similar projects.
ABSTRACT:We compare the performance of some available atmospheric models for the atmosphere of Sao Paulo (Brazil) to be used in case of absence of radio-sounding data for the given day. We developed our own model (SPm) from historic radio-sounding data in order to create a local model. By performing inversions of lidar signals (distributed over a year), we could benchmark the performance of the models against radio-sounding data. SPm and ISA-15N show the smallest deviation and represent, therefore, the best fallback models for this southern latitude.
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