Three-dimensional multicomponent georadar imaging of sedimentary structures

Multicomponent georadar methods that involve recording data using several different antenna configurations and orientations should provide better constrained information about the subsurface than conventional single-component techniques. We test this hypothesis using three-dimensional (3D) multicomponent data recently acquired across braided river sediments deposited adjacent to the Alpine Fault in New Zealand. Strong reflections were observed in the two pairs of co- and cross-polarized data sets. Relatively high reflection amplitudes in the cross-polarized data were a consequence of the dip and oblique orientation of most sedimentary structures relative to the antennae. Many differences in structural information content and reflection amplitude observed in the different components could be explained on the basis of rather simple wavefield models. To obtain reliable subsurface information, a novel 3D multicomponent imaging (migration) algorithm was applied to the data. This algorithm accounted for the effects of antenna orientation, antenna offset and far-field electromagnetic radiation patterns. In addition to correcting the dips, positions and lengths of reflections, the multicomponent imaging also adjusted their relative amplitudes according to the far-field wavefield model. The contributions of the cross-polarized data to the images were particularly important in our data set, because they selectively enhanced dipping reflections oriented at oblique angles to the antenna axes. Phase characteristics of reflections with certain orientations and dips were not recovered consistently, indicating a need for further investigation.