基于逆散射成像条件的最小二乘逆时偏移

最小二乘逆时偏移（LSRTM）相对于常规逆时偏移（RTM）具有分辨率更高、振幅更准确、噪音更少等优势，可以对复杂的地质构造进行有效的成像.这种迭代更新反演成像方法十分依赖目标函数的梯度质量和计算效率.当地质模型中存在强反射界面或者记录中存在折射波时，基于常规互相关成像条件（CCC）的最小二乘逆时偏移梯度会包含很强的低频噪音，从而使反演的收敛速度和成像质量降低.为此，本文在最小二乘逆时偏移的梯度中引进了逆散射成像条件来压制这种低频噪音，并以此提出基于逆散射成像条件（ISC）的最小二乘逆时偏移方法.数值模拟结果表明，两者计算耗时基本一致，但逆散射成像条件能高效压制梯度中的低频噪音，从而使反演过程中收敛加速，成像质量得到显著提高.

Least-squares reverse-time migration enhanced with the inverse scattering imaging condition

Compared with the conventional reverse time migration (RTM), the least-squares reverse-time migration (LSRTM) can effectively image complex geological structures with the advantages of higher resolution, higher fidelity and fewer artifacts. However, when sharp velocity interfaces exist in the model or when seismic records contain strong refraction signals, the gradient of the objective function calculated by using the conventional cross-correlation imaging condition can contain substantial low-frequency noise, leading to significant deterioration of the imaging quality. In this study, we propose an implementation of the least-squares reverse-time migration by incorporating the linear Born inverse scattering imaging condition. Numerical tests indicate that the proposed method can suppress the low-wavenumber imaging artifacts and therefore update the gradient more efficiently. It can accelerate the convergence of the objective function, and hence is more effective in improving the image quality.