Frequency-domain acoustic reverse time migration based on improved NAD method

Reverse time migration imaging has the characteristics of high resolution, and it can improve the efficiency of migration imaging when performed in the frequency domain. Numerically solving the wave equation is a key point of reverse time migration imaging. The pros and cons of numerical algorithm directly determine the computing efficiency of migration processes and the quality of imaging results. In this paper, based on frequency-domain nearly analytic discrete (NAD) method, an improved NAD method is constructed by optimizing the grid stencil coefficients to relieve the ill-posed condition of impedance matrix as well as ensuring the accuracy of numerical discretion. To improve the computing efficiency of frequency-domain forward modeling, this method is used in the frequency-domain reverse time migration. By respectively performing migration imaging of sunken model, Sigsbee2B model, and Marmousi model, and comparing the corresponding results with fourth-order standard NAD method and fourth-order ordinary finite difference method, the advantages of improved NAD method in suppressing numerical dispersion and improving imaging efficiency have been fully reflected.