1,721,042 research outputs found
Rock fracture characterization with GPR by means of deterministic deconvolution
No full textIn this work I address GPR characterization of rock fracture parameters, namely thickness and filling material. Rock fractures can generally be considered as thin beds, i.e., two interfaces whose separation is smaller than the resolution limit dictated by the Rayleigh's criterion. The analysis of the amplitude of the thin bed response in the time domain might permit to estimate fracture features for arbitrarily thin beds, but it is difficult to achieve and could be applied only to favorable cases (i.e., when all factors affecting amplitude are identified and corrected for). Here I explore the possibility to estimate fracture thickness and filling in the frequency domain by means of GPR. After introducing some theoretical aspects of thin bed response, I simulate GPR data on sandstone blocks with air- and water-filled fractures of known thickness. On the basis of some simplifying assumptions, I propose a 4-step procedure in which deterministic deconvolution is used to retrieve the magnitude and phase of the thin bed response in the selected frequency band. After deconvolved curves are obtained, fracture thickness and filling are estimated by means of a fitting process, which presents higher sensitivity to fracture thickness. Results are encouraging and suggest that GPR could be a fast and effective tool to determine fracture parameters in non-destructive manner. Further GPR experiments in the lab are needed to test the proposed processing sequence and to validate the results obtained so far
Seismic noise data and processing software used to test a low-cost 3C seismometer
No full textThis dataset contains data and matlab routines used to generate the figures included in the manuscript titled "Lab and Field Tests of a Low-Cost 3-Component Seismometer for Shallow Passive Seismic Applications", submitted by D. Arosio, A. Aguzzoli, L. Zanzi, L. Panzeri, and D. Scaccabarozzi to Journal of Geophysical Research - Solid Earth for peer review (February 2023)
A microseismic approach to locate survivors trapped under rubble
No full textThe detection of microseismic noise generated by survivors trapped by debris is a method already used by Search and Rescue (S&R) teams. Present seismic S&R equipment works exclusively on energy analysis whilst ignoring information associated with propagation delays. We explore the potential of using traveltime analysis compared to energy analysis for both 2D and 3D location. Results obtained from three different debris field scenarios used for training S&R teams demonstrate that using travel-time information is more reliable than using energy information alone. A joint analysis of both signal parameters is suggested as an appropriate strategy to improve the reliability of locating survivors. Traveltimes can also potentially extend the location into the third dimension by returning an approximate estimate of the survivor depth below ground level. The main obstacles to achieving this goal are the inhomogeneity of the debris pile, the need for a real-time response and the limited spatial extension of the sensor array. Despite these difficulties, results obtained in the field, with an algorithm based on energy focusing by means of cross-correlation and semblance operators, show an accuracy within the limit of the seismic resolution. A new searching strategy is defined and the procedure reduces the investigation time taken by current seismic S&R systems by a factor of three. © 2010 European Association of Geoscientists & Engineers
Sensitivity and accuracy in rebar diameter measurements from dual-polarized GPR data
No full textAccording to some authors, high-frequency GPR (Ground Penetrating Radar) can provide on-site non-destructive measurements of the diameter of concrete reinforcements. The procedure should be based on the analysis of radar energy scattered by reinforcements when illuminated with parallel and perpendicular polarization. The theory of Radar Cross Section (RCS) supports this assumption. However, laboratory test performed on concrete specimens indicate that many practical problems must be solved to obtain reliable and stable measurements from real data. Synthetic data were used to analyze the problem. A data processing sequence was optimized to obtain the best fit between synthetic results and theoretical expectations. Results on real data processed with the same sequence were less encouraging. The comparison with synthetic data was essential to understand that background subtraction is the most critical issue. This problem is of larger importance than the fact that commercial GPR systems generate wide band radar pulses while RCS theory is frequency dependent. Once identified, the problem was directly addressed and results improved significantly. Although delicate, the methodology is potentially showing a high sensitivity which is proportional to wavelength. An optimal selection of antenna frequency versus rebar diameter range is proposed to preserve the highest sensitivity. Accuracy is related with sensitivity but also with stability and repeatability of the measurements. On-site experiments performed to explore this issue suggest that the problem must be addressed statistically. This makes the procedure more complex but the use of dual-polarized antennas might be the solution to save efficiency and cost-effectiveness. © 2012 Elsevier B.V. All rights reserved
Predicting slope collapse using Slope Stability Radar deformation data
No full textWe selected six open-pit wall collapses, representing a variety of failure sizes, failure types and rock mass characteristics, in order to assess the accelerating creep theory by Voight and Fukuzono as an early forecasting tool. Time-displacement monitoring data were collected shortly before ultimate failure using the GroundProbe Slope Stability Radar (SSR), a ground based interferometric radar able to detect surface displacements with a sub-millimetre accuracy. Non-linear estimation techniques were employed to relate slope displacement behaviours to Voight's empirical relationship in order to investigate the trend of its controlling parameters and possibly identify a time window where forecasting output were found to be stable. Analyses were performed taking into account different amounts of survey points involved in the failure mechanism and various values of the velocity at time of failure parameter. Finally we evaluated Fukuzono's inverse velocity approach paying particular attention to update linear fits whenever a trend change was identified. © 2010 Taylor & Francis Group, London
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