The SNR for an underwater optical heterodyne detection system is defined and an equation for this ratio is derived. The equation allows computation of the SNR when the fields to be mixed have nonuniform irradiance profiles and are partially coherent. Effects of backscattered light on the SNR are considered. Curves showing the effect of backscattered light on the SNR are presented.
S. G. Varnado, "SNR Concept in Underwater Optical Heterodyne Detection Systems," Appl. Opt. 11, 2037-2039 (1972)