Three-dimensional geometry of fluvial gravel deposits from GPR reflection patterns; a comparison of results of three different antenna frequencies

Ground-probing radar (GPR) proftles have been recorded in fluvial gravel deposits to investigate the two and three dimensional aspects of inhomogeneities. Because reflection patterns depend strongly on the frequency of the input signal, the measurements have been perfonned with a variety of antenna frequencies: an OYO Georadar 1 system with a pair of 250 MHz antennae and a Sensors & Software Inc. pulseEKKO IV system with pairs of 100 MHz and 200 MHz antennae. The GPR profiles which have been recorded with different frequencies are compared. The reflection patterns on the GPR proftles illustrate different aspects of subsurface inhomogeneities. It is demonstrated that the 250 MHz antennae of OYO and the 200 MHz antennae of pulseEKKO IV portray the small scale variability of the gravel deposit, whereas the reflection proftles recorded with the pulse EKKO IV 100 MHz system show reflection patterns which can be assigned to the principal set-boundaries of the sedimentary units. Recently developed software packages provide some good processing opportunities such as filtering, trace editing and migrating in the time domain. The 3-D representation of GPR sections enables the recognition of the geometry of sedimentary units. This information could be useful in the process of quantification of geophysical data as input in hydraulic models.