Multi-channel observation experiments of audio-frequency magnetotelluric technology in shallow water

Abstract

Geophysical electromagnetic (EM) surveys for imaging the subsurface structure under lakes, rivers, or other water bodies have attracted increasing attention. Based on forward modeling and field experiments, a boat-towed audio-frequency magnetotelluric (AMT) multi-channel observation system for shallow fresh water was developed preliminarily. Through the development of water electrodes and the streamer cable, a boat-towed multi-channel data acquisition cable was developed. We carried out a variety of different comparative experiments, such as water- and land-AMT experiments, different polar-distances, and acquisition time-length experiments, and observation experiments at different time, in ditches or rivers around the Qilihai Wetland, Tianjin, China. We also carried out profile detection experiments using this system in southern Baiyang Lake, Xiongan New Area, China. The experimental results demonstrate that the proposed water–AMT system can be utilized to characterize subsurface structure underneath shallow water areas, advancing the potential of geophysical surveys on rivers or lakes.