Inversion of Underground Structure Based on Time-domain Full Waveform Conjugate Gradient Method

This paper introduces the full waveform inversion algorithm of ground penetrating radar, which can make full use of the travel time, phase, amplitude and other echo signal information carried by echo signals, thus its imaging resolution is much higher than the other algorithms. The full waveform inversion algorithm has a large amount of computation, so the conjugate gradient method is used to simplify the calculation of gradient, which can avoid to calculate Hessian matrix directly and can greatly improve the efficiency of the algorithm. This paper first introduces the background and significance of the full waveform inversion about ground penetrating radar. Then it introduces the principle of the full waveform inversion algorithm. Finally, the effectiveness about FWI (full waveform inversion) is verified by numerical simulation. In the paper, time-domain finite difference method is used to calculate the wave field about electromagnetic waves propagating in underground media. Based on the adjoint matrix method, the iterative step length and the gradient for each point in the underground media are calculated, and the initial model can be updated by the gradient matrix and the step length until the terminal condition is reached. Numerical simulation experiments can prove that full waveform inversion algorithm has a higher resolution than direct time-domain imaging method. At the end, the development trends of GPR are put forward.