This study considers the limitations associated with ground conductivity surveys performed with a frequency-domain electromagnetic (EM) instrument. The EM-31 computes an apparent conductivity based on a simplified function linearly relating conductivity to the ratio between two induced magnetic fields. This simplification assumes the low induction number approximation is true; however, direct well measurements in a mangrove forest in southeast Florida indicate pore water conductivities ranging from that of freshwater to hypersaline. Furthermore, varying degrees of clay are present as indicated from borehole logs, which complicates the relationship between terrain conductivity and groundwater conductivity. Understanding the complexities in EM field data in such an environment requires modeling the EM response of a three-dimensional heterogeneous Earth. APhiD is EM modeling software capable of quickly handling heterogeneities on a wide range of scales. We simulate the electromagnetic response for a variety of subsurface conditions potentially representative a mangrove forest on a barrier island and compare the expected response to that measured by a field instruments. Subsurface conditions include a clay layer at variable depths, hypersaline porewater immediately surrounding mangrove roots, presence/lack of salt pans and surface water. Model results will be used to semi-quantitatively interpret EM data previously collected at the study site mentioned above with the ultimate goal of producing high-resolution EM images of salinity structures around vegetation. Synthetic datasets will be also inverted for a 1D Earth and compared with the “true” synthetic 3D Earth.
Presented at the AGU Fall Meeting on December 12, 2016 in San Francisco, CA.
Available at: http://works.bepress.com/christine-downs/8/