R. D. Purrington, "Bottom scattering in acoustic propagation modeling," J. Comput. Acoust. 2, 147-160 (1994).
R. D. Purrington, "Scattering kernal approach to bottom loss and scattering in a parabolic equation model," Theoretical and Computational Acoustics, 385-398 (1996).
R. D. Purrington, Physics in the Nineteenth Century, Rutgers University Press. (1997)