One-dimensional focusing inversion of the semi-airborne transient electromagnetic method and its application

The semi-airborne transient electromagnetic method (SATEM) is an emerging flexible and efficient geophysical exploration method using ground launch and air reception. The present inversion methods applied to the SATEM produce very smooth inversion results since they apply the maximum smoothing criterion, thus failing to effectively identify the information of specific layer interfaces. This study introduced the focusing inversion theory to the one-dimensional inversion of the SATEM. First, a focusing inversion stabilizer was determined by selecting appropriate focusing and regularization factors. Then, the inversion objective function including the focusing inversion stabilizer was solved to allow the inversion results to effectively identify the abrupt interfaces of layered strata. Furthermore, multiple layered geoelectric models were built to verify the reliability of the focusing inversion. Moreover, the focusing inversion results were compared with the Occam inversion results to highlight the advantages of the focusing inversion in interface identification. This study conducted the focusing inversion calculation of actual data on groundwater detection of a certain area. The calculation results were then combined with the hydrogeological and logging data for comprehensive analysis. Finally, this study determined the locations and spatial distribution of underground aquifers in the area, verifying the feasibility of the SATEM for groundwater detection.