A multicomponent GPR survey in Marambaia Isthmus

Abstract

ABSTRACTThis work deals with a multicomponent ground‐penetrating radar data set obtained on Quaternary unconsolidated deposits of eolian, alluvial, lacustrine and marine sands with a choice of two cross‐dipole and two co‐polar antenna configurations. The geophysical response is characterized by strong reflectors observed in both co‐ and cross‐polarized 100 MHz data sets down to a two‐way time (TWT) of 400 ns. With this data set we delineate a given horizon using its overall polarization direction, which is different from that defined by the position of the antennas and of profile direction. That horizon, whose existence was not previously known, represents a more complex situation than an isolated body, e.g., a buried metallic pipe, a situation well studied elsewhere.The polarizing horizon is characterized by linear polarization and a reasonable uniformity of an Alford rotation angle that maximizes the co‐polar responses. With the modal Alford angle we produce improved images corresponding to the two co‐polar components and a conspicuous improvement in the continuity of the reflectors across the polarizing horizon. All goes as if the antennas were oriented parallel and perpendicular to the main polarizing direction of the structure. In addition, the two co‐polar components display a good degree of independence from each other as revealed by their eigenvalues. Our results illustrate how a data set collected with less than optimal field geometry can still satisfactorily reveal the subsurface.