A Land-Based Controlled-Source Single-Component Electromagnetic Exploration Method With Finite Scalar Reference Stations

Traditional scalar controlled-source audio-frequency magnetotellurics (CSAMTs) typically calculate Cagniard apparent resistivity based on the amplitude ratio of the horizontal electric field component parallel to the source ( <tex-math notation="LaTeX">Eₓ </tex-math>) to the horizontal magnetic field component perpendicular to the source ( <tex-math notation="LaTeX">Hy </tex-math>). However, when conducting surveys in areas with magnetic metal installations and dense electromagnetic noise, the <tex-math notation="LaTeX">Hy </tex-math> component is more prone to severe data distortion compared to the <tex-math notation="LaTeX">Eₓ </tex-math> component. In the far-field of a horizontal electric dipole in a uniform medium model, <tex-math notation="LaTeX">Eₓ </tex-math> is also more sensitive to underground medium resistivity than <tex-math notation="LaTeX">Hy </tex-math>. Recording only <tex-math notation="LaTeX">Eₓ </tex-math> can enhance the interference resistance and exploration efficiency of the observation system. However, despite the more concise definition of <tex-math notation="LaTeX">Eₓ </tex-math> apparent resistivity compared to Cagniard apparent resistivity, its susceptibility to source effects is pronounced. Therefore, we have developed a land-based single-component electromagnetic exploration method with finite scalar reference stations. We simulated source effects using several 2-D models and analyzed their impact on <tex-math notation="LaTeX">Eₓ </tex-math> and Cagniard apparent resistivity. To mitigate source effects associated with using only the Ex component for exploration, we strategically placed a finite number of discrete scalar reference stations to simultaneously measure <tex-math notation="LaTeX">Eₓ </tex-math> and <tex-math notation="LaTeX">Hy </tex-math>. An improved far-field formula for <tex-math notation="LaTeX">Eₓ </tex-math> apparent resistivity was derived based on reference observations. Scalar reference stations were positioned in interference-weak areas to ensure data reliability, especially for <tex-math notation="LaTeX">Hy </tex-math>. Through 3-D model simulations and a field case study in Shandong Province, China, the practicality and advantages of the proposed exploration technology were demonstrated.