This abstract was part of a paper published in Geophysics, v. 66 no. 6, p. 1781-1792, Copyright 2001 by Society of Exploration Geophysicists.  This paper is also available in a pdf-version.

Application of Alford rotation to Ground Penetrating Radar data.

Jean-Paul Van Gestel, Paul L. Stoffa, Department of Geological Sciences, and Institute for Geophysics, The University of Texas at Austin, 4412 Spicewood Springs Road, #600, Austin, TX, 78759-8500.

Traditionally, Ground Penetrating Radar (GPR) measurements are conducted using two co-polarized antennas oriented perpendicular to the line of data collection. Configurations where the antennas are held parallel to the direction of propagation or cross-polarized to each other are rarely used. In this study we show that collection of this kind of data increases our knowledge of buried objects with a distinct orientation. By recording the reflected field using four different configurations and applying Alford rotation, we can extract information about the orientation of objects that have angle-dependent reflectivity.

We show that in theory this method can be successfully applied to dipping layers, cylinders and vertical fractures. Theoretically it is even possible to predict the exact origin of a reflection, which can be used for migration purposes. Modeling results show angle-dependent reflections in all three cases. Therefore, Alford rotation can be successfully applied to obtain an exact prediction of the angle of orientation of objects with a distinct orientation. A GPR survey was conducted at a controlled GPR testing site in Scheveningen, The Netherlands. Reflections were collected of an elongate cylinder, buried in a homogenous background. The results of this survey show good prediction of the angle of orientation of the cylinder and confirm the expected theoretical results.

To obtain a better understanding of the practical application of this method an error analysis was studied. Three sources for error were examined and we conclude that with accurate data acquisition this method is effective in practice. However, exact knowledge of the radiation pattern of the antennas is required and better understanding and measurement of this radiation pattern under different circumstances is essential.

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