Full Waveform Inversion of Ground Penetrating Radar Data

by Jan van der Kruk

*Please note: This course is not available for in-house training.

Duration: One-day

Intended Audience: Entry and Intermediate levels

Prerequisites (Knowledge/Experience/Education required): The course is designed to be followed by anyone with some background in Ground Penetrating Radar or seismic processing. A basic understanding of the physics of wave propagation is required.

Summary:
This one-day course provides a thorough overview of full-waveform inversion of ground penetrating radar (GPR) data, which is a promising technique that fully utilizes all of the information content present in high-frequency GPR and is capable of yielding sub-wavelength resolution images. The course includes a theoretical background, synthetic examples, and several case histories using crosshole, on-ground and off-ground GPR.

Course Outline: 

Maxwell's equations: full-waveform modeling

  • Radiation patterns in homogeneous space/halfspace
  • Vectorial character of EM waves
  • Horizontally layered, 2D and 3D media
     

Ray-based inversion: which approximations are made?
Full-waveform inversion

  • Combined global-local minimization for a limited number of unknowns
  • Gradient-based approach for a large number of unknowns
  • Simultaneous permittivity and conductivity updating
  • Influence of non-linearity
  • Reducing non-linearity by frequency filtering of the data
  • Importance of the used start model
  • Comparison of raybased and FWI of several synthetic data sets
     

Application of FWI in following Case Studies: 

1. Chloride and water content estimation in concrete
    System calibration measurements: Phase center estimation and effective wavelet estimation
    Model parameterisation: frequency dependent conductivity
    FWI of homogeneous lossy concrete slabs
    FWI of concrete slabs with chloride gradients due to the use of different saline solution
    Different exposure length

2. FWI of on-ground GPR data measured at a fine-texture soil
    Source wavelet estimation
    Simultaneous source wavelet and medium property estimation
    Comparison of obtained permittivity and conductivity results with theta probe, ERT
    EMI measurements

3. FWI of crosshole GPR data measured at the Boise hydrogeophysical research site
   3D to 2D conversion
   Source wavelet estimation
   Gradient calculation
   Steplength calculation
   Influence of assuming a scalar wavefield
   Influence of using a sequential permittivity and conductivity updating
   Comparison of obtained results with neutron neutron measurements

4. FWI of crosshole GPR data measured at the gravel aquifer Widen, Switzerland
    Ray-based inversion results
    Source wavelet estimation
    Gradient analysis
    Analysis of low-velocity waveguide present in inverted data
    Interpretation of low-velocity waveguide: high porosity layer: preferential flowpath
    Low-velocity waveguide characteristics: elongated high amplitude wavetrains

Learner Outcomes:

  • Recognize the need for full waveform inversion (FWI) and its potential
  • Understanding of the vectorial wave propagation of electromagnetic waves
  • Understanding of theory and implementation of FWI
  • Understanding of the approximations, potential and limitations of FWI compared to other methods

Instructor Biography:
Jan van der Kruk