Using a dual-frequency single-offset ground-penetrating radar for subbottom profiling of a small stream in Hawaii

Abstract

Acoustic sub-bottom profilers are a common instrument for determining the stratigraphy underneath bodies of water. However, the size and weight of acoustic sub-bottom profilers prohibits or complicates their use in smaller bodies of water such as small streams and shallow ponds. Ground penetrating radar (GPR) antennas are significantly lighter and more portable than acoustic sub-bottom profilers. However, their application to bathymetry and sub-bottom profiling has been limited because of lower resolution and sampling depth than acoustic profilers. The recent introduction of real-time sampling and dual GPR, now make it possible to use GPR for sub-bottom profiling more feasible opening up smaller bodies of water to sub-bottom profiling. We used a 70 MHz and 300 MHz center frequency real-time sampling GPR to characterize the stratigraphy underneath a small stream and bank on the Hawaiian island of O'ahu. The 300 MHz antennas proved effective at characterizing the channel bottom and a paleo channel, while the 70 MHz antenna was able to image the bedrock contact and a deeper soil horizon on the bank. This demonstrated that dual-frequency GPR are a suitable tool to characterize the subsurface below shallow bodies or water.