Estimating Penetration Depth of the CHTEM‐I System by the Diffusive Electric Field Method

Penetration depth is one of key technical parameters in the airborne time-domain electromagnetic system (ATEM), which plays an important role in system design as well as data interpretation. When the difference of conductivity between the target layer and host rock is small or the anomaly response of the target layer is not obvious, the conventional method for estimating penetration depth is no longer applicable. To overcome this drawback, this study suggests a new approach. It simulates the diffusion processes of the induced electric field in a uniform half-space model or a layering model and determines the transient position of the field with the largest amplitude in the subsurface. Then it defines that the depth of this position is the penetration depth of the system, where the measured response value is equal to the given noise level. Taking the China helicopter time-domain electromagnetic system I (CHTEM-I), developed independently by our own forces, as the example, this work presents the application of this new method. It compares calculation results under various conditions, produces relation curves of penetration depth, flight height and noise level, and explores how to enhance the penetration depth of the system. The results show that the system can probe down depth 300 m in the case that noise level is proportional to t−05 when the half-space model has conductivity in 0.000295∼0.0422 S/m. This depth estimation method is not affected by factors such as layer thickness and magnitude of conductivity difference between the target layer and host rock, and thus very applicable. It is of significance to design including estimation of penetration depth for various time-domain airborne electromagnetic systems.