GPR radar imaging of water table, salty water, and sand stratigraphy in a coastal zone in Rio de Janeiro

Abstract

A study using GPR has been carried out at Itaipuacu beach,Marica, Rio de Janeiro with the aim of reconstructing and analysing the environment of depositing sediments. Fifty profiles were made using a 200 MHz bistatics antennas (nominal frequency). These profiles generated a 3D cube. In the same way, we obtained an estimation of propagation velocity of the signal in the subsoil (by CMP technique) using two 80 Mhz antennas. The analysis of the radargrams allows to recognize the stratigraphic sequence and its progradation. Through core drill sampling in the investigation site, it has been possible to establish a correlation between some reflections and the presence of organic matter, and to make evident that the salt content of water below the water table increases with depth. With these profiles we can see the progradations, and under the water table, a reflector which seems to be caused by the combination of organic matter, together with a sharp increase in the salt content of the water. This interpretation agrees with the model "Ghyben-Herzberg fresh-water lens" Hagrey & Muller,( 2000), as well as other results obtained by these authors.