Born近似层析与Rytov近似层析对比研究

Comparison between Born's approximate tomography and Rytov's approximate tomography.

本文讨论了 Born 近似与 Rytov 近似的相互关系,并对地面反射、VSP、井间和四周观测系统在异常体速度与背景速度相差5%、10%以及15%的条件下,用这两种近似方法作了重建图像的实验。其结果表明,速度差低于10%时,无论 Born 近似或 Rytov 近似,更射层析均优于透射层析。此时,Rytov 近似的透射层析优势消失,这一结论与传统观点相悖。当速度差大于10%时,Rytov 近似透射层析优于 Born 近似。实验结果还说明,在地面激发、四周观测时,波动理论层析效果最佳,此点与射线理论是一致的。

The relationship bet.ween Born's approximation and Rytov's approximation is discussed here.The two.approximations are respectively used to make image recon- struction of the seismic data of surface reflection,VSP,interborehole and four side observation when the velocity contrast between abnormal area and background are 5%,10% and 15% respectively.Consequently,when the velocity contrast is low than 10%,both Born's approximation and Rytov's approximation show that reflec- tion tomography is better than transmission tomography.In other words,in this case,Rytov's approximation loses its advantage on transmission tomography,which is contrary to traditional conclusion,when velocity contrast is higher than 10%,Ry- toy's approximate transmission tomography is superior to Born's approximation. It is also shown that when receivers are on four sides of a surficial source,wave theory tomography is the optimum,which is consistent with ray theory tomogra- phy.