Bobe, Christin

Van De Vijver, Ellen

Van Meirvenne, Marc

Ghent University Academic Bibliography

Geophysical Research AbstractsVol. 21, EGU2019-5756, 2019EGU General Assembly 2019© Author(s) 2019. CC Attribution 4.0 license.Proposing a statistical interpretation for the depth of investigationChristin Bobe, Ellen Van De Vijver, and Marc Van MeirvenneDepartment of Environment, Ghent University, Gent, BelgiumWhen inversion results from electrical or electromagnetic surveys are interpreted, the depth of investigation(DOI) is a crucial quantity. The DOI is conventionally defined as the smallest depth below which surface dataare insensitive to the investigated physical property of the subsurface. Most of the DOI approaches described inliterature rely on thresholding the measurement sensitivity with depth. Measurement sensitivity can be derivedin different ways, with a perturbation of the estimated inversion parameters in the forward model as the moststraightforward approach. For probabilistic inversion, we propose the correlation between prior model parametersand measurement data as a proxy for measurement sensitivity. The DOI is placed where correlation approachesthe zero function.Probabilistic inversion procedures start from sampling a prior probability density function (PDF), desirablydrawing a high number of samples to allow an exhaustive search of the model space. If Gaussian prior PDFsare assumed, the PDFs are fully defined by their mean and standard deviation (STD). Computing the forwardresponses for the samples from the prior PDF, we calculate the covariance between the prior and the forwardresponse. In the Gaussian case, the covariance can be normalized using the STD of the prior PDF to achieve thecorrelation between the prior PDF of each discrete model layer or cell and the corresponding forward responses.We propose to interpret the derived correlation as a statistical measure for sensitivity. Correlations are restrictedto the interval from minus one to one, which has two advantages: (1) correlations from all measurement signalsare directly comparable, and (2) the depth at which the correlation curve approaches the zero function gives anintuitive measure for the DOI.We show how this correlation-based DOI can support the assessment of frequency-domain electromagnetic(FDEM) inversion results and how this DOI relates to measurement sensitivity and commonly used DOIapproaches. Furthermore, we show how the results from the correlation-based DOI computation can be readilyintegrated in a probabilistic inversion of FDEM data, jointly deriving subsurface electrical conductivity and mag-netic susceptibility without requiring additional forward model runs than the one performed to estimate correlation.This project has received funding from the European Union’s EU Framework Programme for Research andInnovation Horizon 2020 under Grant Agreement No 721185.

Proposing a statistical interpretation for the depth of investigation

https://biblio.ugent.be/publication/8603694/file/8603697.pdf

Proposing a statistical interpretation for the depth of investigation

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