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Proceedings Paper

Application of self-correcting tomographic inversion to a borehole radar test survey
Author(s): Mihu Rucareanu; Michel Chouteau; Gilles Bellefleur
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Paper Abstract

Variations of transmitter power and instrumental time drift often observed during borehole radar surveys are not usually monitored by the commercially-available acquisition systems. These variations may create artifacts in tomograms and lead to erroneous interpretation if not taken into account. The Self- Correcting Tomographic Inversion (SCTI) is a technique that jointly recovers these source variations together with the velocity or attenuation distribution. It assumes that the transmitting time To and the 'source strength' Ao may be considered constant only at each transmitter position. The problem results in a linear system of equations where the usual Jacobian matrix should be augmented by sparse columns with non-null elements corresponding to the respective transmitter positions only; thus the parameter vector (slowness or attenuation coefficient distribution) can be appended with the to (or log Ao) values for these transmitter positions. Synthetic and survey data examples demonstrate that the conventional inversion algorithm produces artifacts mainly located along the transmitter and the receiver boreholes and towards the corners of the tomogram. The magnitude of the artifacts depends on the distance between transmitter and receiver boreholes. The SCTI technique reduces the amplitude of these artifacts while recovering the transmitter drift. Two crosshole surveys with inter-changed transmitter-receiver positions were also performed to evaluate reciprocity. The resulted tomograms are slightly different, but the overall images seem to be improved. However, the SCTI seem to diminish the discrepancy between the reciprocal values. Meanwhile, the SCTI also recovers a very suitable variation for the transmitter parameters. We have also attempted to monitor the drift of these transmitter parameters by control measurements at the ground surface at different times during the survey with different antenna separations. It shows that the variation of to and Ao is of the same order as resulted from the SCTI method.

Paper Details

Date Published: 27 April 2000
PDF: 6 pages
Proc. SPIE 4084, Eighth International Conference on Ground Penetrating Radar, (27 April 2000); doi: 10.1117/12.383624
Show Author Affiliations
Mihu Rucareanu, Ecole Polytechnique de Montreal (Canada)
Michel Chouteau, Ecole Polytechnique de Montreal (Canada)
Gilles Bellefleur, Ecole Polytechnique de Montreal (Canada)

Published in SPIE Proceedings Vol. 4084:
Eighth International Conference on Ground Penetrating Radar
David A. Noon; Glen F. Stickley; Dennis Longstaff, Editor(s)

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