Wiskin, J. W., D. Borup, and S. Johnson. “Fast and Accurate 3D Acoustic Propagation and Inversion in Layered Media Environments”. Canadian Acoustics, vol. 26, no. 3, Sept. 1998, pp. 38-39, https://jcaa.caa-aca.ca/index.php/jcaa/article/view/1146.