Comparative study of a novel arithmetic amplitude-phase weighted beamforming method in vector and tensor CSAMT

Abstract

Abstract Vector controlled-source audio-frequency magnetotellurics (CSAMT) emits electromagnetic waves with a low directivity coefficient using a grounded horizontal electric dipole (HED). During observations in the far-field region (FfR), only a fraction of radiation energy is used. To improve the signal-to-noise ratio (SNR) in the FfR, it is necessary to increase the power of the transmitter or shorten the transceiver distance, but it will restrict the development of vector CSAMT. Comparatively, the tensor CSAMT uses HEDs in two directions to measure geological bodies in every direction. If the geological conditions of two HEDs are vastly different, it is easy to cause issues, such as an imbalance of the SNR in two directions of the receiving point. This paper presents a comparative study of a novel arithmetic amplitude-phase (AAP) weighted beamforming method (BFM) in vector and tensor CSAMT, which uses multiple HEDs to transmit signals with controlled amplitude ratio and phase difference to modulate the wavefront, thereby achieving beam steering and other additional functions (such as amplitude compensation). By concentrating the radiation energy in the area of interest (AoI) using BFM, the SNR can be largely regulated. The comparative simulation and analysis demonstrate that the BFM has advantages in improving energy utilization and beam steering in vector and tensor CSAMT. On the premise of same power and transceiver distance, using the AAP-weighted BFM, the SNR received in the AoI can meet the requirements better than that received via the traditional method.