High quality pre-stack migrated radar images of several fixed-offset passes along a shore-normal profile on Marambaia Barrier Island

Abstract

We show high quality images of constructed multi-offset radar data along a shore-normal profile on Marambaia Barrier Island. The multi-offset data is constructed assembling traces from seven collinear fixed-offset passes with a 100MHz bistatic equipment. The traces are binned and stacked as sparse 7-trace common-source gathers along the profile. We deal with the severe alias on each gather through trace interpolation, yielding adequately sampled, unaliased, dense common-source gathers. With the interpolated gathers we have produced a stack section and estimated a 2-D velocity model spanning over the whole profile. All images obtained through from the common-source gathers have a degree of quality far beyond what would be possible to obtain with a usual fixed-offset survey, eventually complemented with a limited number of multi-offset gathers, aiming at estimation of 1-D velocity models. Moreover we show here that a CMP gather is unable to accurately estimate a 1-D velocity distribution at its central point. The multi-offset data yielded not only a 2-D velocity model but also pre-stack time and depth migrated images of the subsurface, products which are well beyond the reach of the usual GPR data acquisition. The pre-stack migrated images provide a clear glimpse on the stratigraphic framework, a result from the interplay of base-level changes and sedimentation at the shoreline of Marambaia Barrier Island. Two unconformities probably correlated to the last process of marine regression, provide chronological markers allowing a qualitative correlation with a sea level variation curve for the last 12,000calyBP on the coast of the State of Rio de Janeiro.