Characterize Basin‐Scale Subsurface Using Rocket‐Triggered Lightning.

This paper exploits triggered lightning as a point source for the basin‐scale electromagnetic tomographic survey to image 3‐D subsurface electrical properties in basins. This paper further develops a new temporal moment approach, overcoming the difficulties in forward and inverse modeling of 3‐D Maxwell's equations with heterogeneous parameter fields. Using this approach, we find that the influence of a single triggered lightning strike covers a radius of 20–70 km with detectable signals. The cross‐correlation analysis between the moment difference of the electric and electric/magnetic property field indicates that the approach is suitable for mapping subsurface electric conductivity (σ $\sigma $) heterogeneity. A numerical experiment with 3‐D spatially random parameter fields demonstrates that the method captures the spatial distribution of electric conductivity over large areas with a sparse monitoring network. It reveals the potential of using triggered lightning as a basin‐scale electric/magnetic tomography survey. Plain Language Summary: Triggered lightning experiments traditionally aim at adverse impacts of lightning phenomena on near‐surface structures (such as buildings, power, communication, and transportation networks). Magnetotellurics surveys have exploited electromagnetic (EM) waves from thunderstorm activities and the interaction of solar wind with the Earth's magnetosphere to map the subsurface structure, assuming that electromagnetic waves are planar and propagate vertically into the Earth. This paper, in contrast, explores the EM waves generated by flashes of lightning triggered by a lightning rocket at designated locations as EM point sources and their measurements at different depths and distances in the subsurface. Such experiments are tantamount to an EM tomographic survey, viewing the subsurface from different perspectives. This paper further develops a new stochastic methodology to analyze the propagation of EM waves in heterogeneous geologic media over hundreds of kilometers. These accomplishments permit harvesting the lightning signals to image the subsurface over greater depths and areas and address the image's uncertainty. Numerical experiments confirm the robustness of this proposed concept, which could be a new technology to explore subsurface processes and natural resources in basins and mountain terrains. Key Points: An efficient 3‐D forward and inverse model based on the temporal moment is developed to solve Maxwell's equations in random parameter fieldsTriggered lightning tomography yields an excellent subsurface electric conductivity spatial distribution in a basin of several kilometersDeep lightning rods in the subsurface improve vertical resolution and depth of investigation [ABSTRACT FROM AUTHOR]