The double-square-root (DSR) formula is an integral part of many wavefield based imaging tools. A transversely isotropic medium with a titled symmetry axis (TI) version of the DSR formula is nearly impossible to obtain analytically. As a result, we develop an approximate version of the DSR formula valid for media with the symmetry axis normal to the dip of the reflector (DTI). The accuracy of this approximate solution is enhanced using Shanks transform to a point where the errors are extremely small for practical anisotropic values. Under this assumption, we also do not need to compute the symmetry axis field as it is inherently included in the formulation.
Golikov, P., Alkhalifah, T., & Stovas, A. (2012). Prestack traveltimes for dip-constrained TI media. SEG Technical Program Expanded Abstracts 2012. doi:10.1190/segam2012-0507.1