Date of Defense

4-30-2026

Date of Graduation

5-2026

Department

Physics

First Advisor

Mine Dogan

Second Advisor

Mohamed Sultan

Abstract

The Very Low Frequency Electromagnetic (VLF-EM) method is a geophysical method that utilizes remote military radio communication stations as sources of primary EM fields to map the electrical resistivity distribution of the subsurface materials. These radio stations broadcast radio signals in the 15-30 kHz frequency range, which falls within the VLF band of the EM spectrum and enables worldwide long-distance and submarine communication.  A common VLF-EM receiver used in geophysical surveys consists of three coils that operate similarly to a portable radio, detecting and recording magnetic field components at the target frequency. As the primary EM field propagates through the subsurface, it induces secondary EM fields within electrically conductive materials, in accordance with Maxwell’s equations. These secondary fields allow geophysicists to delineate electrically conductive subsurface targets. However, other EM field sources, especially anthropogenic sources such as metal structures (fences, railroads, etc.) containing ferromagnetic alloys, other radio and GSM communication stations, and transmission lines act as EM noise sources. Due to their generally higher amplitudes, these signals can obstruct the detection of weaker secondary EM fields originating from the geological targets. In this study, the effects of high-voltage transmission lines on VLF-EM geophysical data were examined using computer models developed in COMSOL Multiphysics software. This work was designed as a supporting study for a recent field campaign conducted in the Mojave Desert to assess the influence of the Helendale fault system on the regional groundwater regime. A new vehicle-mounted data acquisition rig was developed by the WMU Near Surface Geophysics Laboratory (Dept. of Geological and Environmental Sciences) to collect VLF-EM data at the site. Although the VLF-EM probe used for the data collection was originally designed for UAV-based data collection, the geographic conditions, site scale, and sensitivity required to detect the anomalies originating from the faults led the team to deploy the system on a vehicle. This approach significantly increased survey efficiency and improved signal quality; however, anthropogenic noise remained a major challenge. Transmission lines running parallel and across the survey roads posed a particularly significant source of interference. To address this issue, the study focused on identifying the effects of transmission lines with varying geometric properties, current strengths, and current phases. A synthetic geophysical survey site was modeled in COMSOL Multiphysics, and the influence of parameters such as transmission line current, phase, wire diameter, and tower height were systematically evaluated. Although the model could not perfectly replicate the observations at the Mojave Desert site, it provides valuable insight into the general effects of transmission lines on VLF-EM data and can inform data interpretations and survey design in similar settings.

Access Setting

Honors Thesis-Restricted

Restricted to Campus until

6-4-2028

Download

Available for download on Saturday, June 03, 2028

Share

COinS