Inversion strategy in crosshole radar tomography using information of data subsets

Abstract

Detecting discrete anomalies, such as cavities or tunnels, is an important application of crosshole radar tomography. However, crosshole tomographic inversion results are frequently ambiguous, showing smearing effects and inversion artifacts. These ambiguities lead to uncertainties in interpretation; hence, the size and position of anomalies can only be interpreted with limited accuracy and reliability. We present an inversion strategy for investigating discrete anomalies with crosshole radar tomography. In addition to the full traveltime data set, we use subsets of specified ray‐angle intervals for tomographic inversion. By analyzing inversion results from different ray‐angle intervals, a more accurate interpretation of anomalies is possible. The second step of our strategy is to develop a good inhomogeneous starting model from joint interpretation of the inversion results from different subsets. The third step is to invert the full data set using this new starting model and to evaluate the inversion results by analyzing the distributions of mean square traveltime residuals with respect to the ray angles. We use a synthetic model with two discrete anomalies located roughly at the same depth to demonstrate and evaluate our approach. This inversion strategy is also applied to a field data set collected to investigate karst cavities in limestone. From the inversion results of both examples, we show that horizontal smearing of anomalies can be reduced by eliminating near‐horizontal rays. A good starting model can be obtained based on the joint interpretation of the inversion results of the different subsets; it leads to a high‐resolution final image of the full data set.

High-resolution aquifer characterization using seismic cross-hole tomography: An evaluation experiment in a gravel delta

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Stochastic borehole radar velocity and attenuation tomographies using cokriging and cosimulation

“…Although there exist some full wave form tomography techniques (Cai et al, 1996;Alumbaugh and Newman, 2000;Becht et al, 2004), data acquisition and antenna characteristics limit their applications. Practically speaking, GPR tomography consists in using a transmitting antenna producing a short EM pulse, of radio frequency, in one hole, and recording the voltage produced by the propagated signal at another antenna located in another hole.…”

Resistivity Level Runs to Detect Water-filled Mine Voids between Drill Holes

“…Hammack et al 2004). When a pair of wells are present, crosswell tomographic surveys can be used to detect voids; published examples have used seismic (Rechtien et al 1995), radar (Becht et al 2004), and electrical methods (Maillol et al 1999). Data sets for crosswell tomography consist of hundreds to thousands of data points.…”