Method Research Of Building An Initial Model For Full Waveform Inversion

With the development of geophysical exploration research,people have a higher demand for high precision inversion technology.Full waveform inversion shows its attractive application foreground and practical application value.The full waveform inversion theory system is almost perfect,but it is a highly "ill-posed" nonlinear problem in the mathematical angle,so that the misfit function of the full waveform inversion has many local extreme points,which seriously affect the convergence results of full waveform inversion,this is the reason of the strong dependence of the full waveform inversion on the initial model.In this paper,the high-order staggered-grid finite difference method based on acoustic equation is used as forward modeling.Aiming at the problem of the strong dependence on the initial model,the envelope of the seismic signal is extracted by the Hilbert transform to obtain the low-frequency information,and a new envelope inversion method based on the global-correlation objective function is chosen to recover the large-scale structure of the model.The gradient of this method is derived and compared with the conventional envelope inversion method based on the least-square objective function.The sensitivity of this method to complex structures and the computational efficiency are higher than those of conventional envelope inversion.Then,the two methods of envelope inversion based on least-square combines with least-square full waveform inversion and envelope inversion based on global-correlation combines with global-correlation full waveform inversion are tested respectively.Experiments are carried out to prove the effectiveness of the method of global-correlation envelope inversion combines with the global-correlation full waveform inversion and this method has a better performance than the method based on least-square in some parts of the model.