Full waveform inversion of surface wave based on instantaneous frequency

Abstract Surface wave has many advantages, such as low attenuation, high signal-to-noise ratio, strong anti-interference ability and dispersion characteristics in layered media. It is widely used in engineering measurement and nondestructive testing. However, the applicability and reliability of surface wave processing methods are severely restricted by velocity inversion or strong heterogeneity of the medium. To overcome these shortcomings, in recent years, scholars have studied full-wave inversion methods including data preprocessing, wave field forward, gradient calculation, and inversion optimization to avoid any assumptions about underground complexity. However, the classical waveform difference mismatch function is apt to fall into a local minimum, which leads to the non-convergence of inversion. At the same time, the existence of surface waves greatly increases the non-linearity of full waveform inversion. Even small perturbations, especially in the S wave velocity structure, can cause dispersion for uniform backgrounds. To overcome this difficulty, a mismatch function based on instantaneous frequency is proposed and the adjoint wave equation is derived. Taking a layered model as an example, the effectiveness of the method is verified.