GPR full-waveform inversion, recent developments, and future opportunities

Ray-based, or approximate, forward modeling techniques have often been used to reduce computational demands for inversion purposes. Due to increasing computational power and possible parallelization of inversion algorithms, accurate forward modeling can be included in advanced inversion approaches such that the full-waveform can be exploited. Here, recent developments of full-waveform ground penetrating radar (GPR) inversions are discussed that yield higher resolution of quantitative medium properties compared to conventional approaches, because of the use of accurate modeling tools that are based on Maxwell's equations. For a limited number of parameters, a combined global and local search using the shuffled complex evolution (SCE) can be used for inversion. For a large number of unknowns, gradient-based optimization methods are commonly used that need a good starting model to prevent them from being trapped in local minima. An overview of the methodological developments for surface and crosshole GPR full-waveform inversion will be given and several applications will be presented. Finally, recent developments and future opportunities will be discussed.