We have developed an algorithm for joint inversion of full-waveform ground-penetrating radar (GPR) and electrical resistivity (ER) data. The GPR data are sensitive to electrical permittivity through reflectivity and velocity, and electrical conductivity through reflectivity and attenuation. The ER data are directly sensitive to the electrical conductivity. The two types of data are inherently linked through Maxwell’s equations, and we jointly invert them. Our results show that the two types of data work cooperatively to effectively regularize each other while honoring the physics of the geophysical methods. We first compute sensitivity updates separately for the GPR and ER data using the adjoint method, and then we sum these updates to account for both types of sensitivities. The sensitivities are added with the paradigm of letting both data types always contribute to our inversion in proportion to how well their respective objective functions are being resolved in each iteration. Our algorithm makes no assumptions of the subsurface geometry nor the structural similarities between the parameters with the caveat of needing a good initial model. We find that our joint inversion outperforms the GPR and ER separate inversions, and we determine that GPR effectively supports ER in regions of low conductivity, whereas ER supports GPR in regions with strong attenuation.
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The role of electrical conductivity in radar wave reflection from glacier beds
Abstract. We have examined a general expression giving the specularreflection coefficient for a radar wave approaching a reflecting interfacewith normal incidence. The reflecting interface separates two homogeneousisotropic media, the properties of which are fully described by three scalarquantities: dielectric permittivity, magnetic permeability, and electricalconductivity. The derived relationship indicates that electricalconductivity should not be neglected a priori in glaciological investigations ofsubglacial materials and in ground-penetrating radar (GPR) studies of saturated sediments and bedrock,even at the high end of typical linear radar frequencies used in suchinvestigations (e.g., 100–400 MHz). Our own experience in resistivitysurveying in Antarctica, combined with a literature review, suggests that awide range of geologic materials can have electrical conductivity that ishigh enough to significantly impact the value of radar reflectivity.Furthermore, we have given two examples of prior studies in which inclusionof electrical conductivity in calculation of the radar bed reflectivity mayprovide an explanation for results that may be considered surprising if theimpact of electrical conductivity on radar reflection is neglected. Thecommonly made assumption that only dielectric permittivity of the two medianeeds to be considered in interpretation of radar reflectivity can lead toerroneous conclusions.
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- Award ID(s):
- 1644187
- NSF-PAR ID:
- 10293050
- Date Published:
- Journal Name:
- The Cryosphere
- Volume:
- 14
- Issue:
- 12
- ISSN:
- 1994-0424
- Page Range / eLocation ID:
- 4495 to 4506
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/tc-14-4495-2020
