UAV-Enabled Subsurface Characterization Using Multichannel Analysis of Surface Waves

Abstract

The implementation of unmanned aerial vehicles (UAVs) in civil engineering has primarily focused on remote sensing using optical cameras, light detection and ranging (LiDAR), and communicating with other sensing systems such as wireless sensor networks. However, UAV-enabled methods for subsurface characterization are still at their naissance. In this study, a UAV was used to lift and drop a mass onto the ground surface. The mass’s impact on the ground was used as the impulsive source for multichannel analysis of surface waves (MASW) testing. For this implementation, a hexarotor UAV was modified to lift and drop 4–7 kg masses to generate Rayleigh surface waves. The frequency domain characteristics of the seismic waves generated by UAV-dropped masses were compared to conventional MASW testing using a sledgehammer. The MASW method using a UAV-deployed source developed herein was applied to a soil site and a solid waste site. It was demonstrated that the UAV-dropped mass can generate Rayleigh surface waves below 10 Hz more effectively than the sledgehammer and could therefore support shear wave velocity profiling to greater depths in the subsurface, possibly without the need for signal stacking. Recommendations for drop mass selection and a discussion of observations made by the authors are also provided. Contributions made in this study are intended to contribute toward remote, fully autonomous subsurface mapping coupled with image-based surface mapping that will be critical for remote site characterization in postearthquake geotechnical reconnaissance and will allow the acquisition of more extensive subsurface data than presently feasible.