2D Synthetic Emitter Array methodology for improving GPR reflections

BULLO, DARÍO; BONOMO, NÉSTOR

JOURNAL OF APPLIED GEOPHYSICS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2018 vol. 159 p. 285 - 293

0926-9851

Synthetic 1D-arrays of emitters are used in thearea of GPR to improve primary reflections that in single-offset profiles showlow continuity and amplitude due to the interference of clutter and noise. Inthis methodology, at each array position along the survey line, a series ofsingle emitter-receiver measurements is performed, keeping the position of thereceiver constant and placing consecutively the emitter at the positions of thenodes of the array grid. A definite phase relation between the traces thatconstitute each common receiver gather is established and used to shift them intime with respect to the reference-offset trace, and the results are averaged. Thephase relations are defined in order to superpose constructively the primaryreflections, and reduce the random noise and clutter. The 1D synthetic procedureis equivalent to narrowing the transmitted electromagnetic wave-front along thedirection of a real 1D array, which reduces the interference produced by reflectorslocated in formerly illuminated regions of the soil, and directing the fieldalong an emitters-reflector-receiver path that maximizes the amplitude of theprimary reflection at the position of the receiver with respect to the otherreflections.  In this article, a previously developed1D-array method is extended to 2D-arrays, and the results of the 2D extension areanalyzed and compared to the results of the 1D-array, Common-Midpoint andSingle Offset techniques. The proposed 2D procedure considers a rectangular,homogeneous geometry for the array and a simple phase-relation between thecomponent traces. In addition to directing the wave-front towards the target, thesesettings make possible to reduce the width of the wave-front along both axes ofthe array, which is expected to enhance the 1D results. Since the dimensionalityincreases in the 2D geometry, the number of traces in the summation growssignificantly, which should also improve the final result. As a part of the 2Dmethodology, a variable that represents the reflection improvement, withrespect to the Single Offset method, is defined and optimized as a function ofthe phase differences between adjacent traces along both directions of thearray and the position of the emitters-receiver group along the survey line. Afinal data-section is generated from the optimal values found in this step. Toevaluate the results of these methodologies, two basic types of reflections areanalyzed: diffractions produced by small objects and reflections at extensiveinterfaces. Numerical and laboratory data are considered. The effects ofdifferent numbers of emitters and distances between them on the results are investigated,in order to obtain the best result. The 2D method shows noticeable enhancementsof the continuity and amplitude of the primary reflection with respect to theother methods.