Fundamental relationships between backscattered power, range, wavelength, and number of scatter centers in the probe volume for the self-aligning, dual-scatter, laser doppler velocimeter are developed. It is shown that not all power scattered from the velocimeter probe volume contributes to a doppler signal. This fact leads to significant deviations in calculations involving signal-to-noise power ratios as compared to the case when only gross backscattered power is considered.
W. M. Farmer and D. B. Brayton, "Analysis of Atmospheric Laser Doppler Velocimeters," Appl. Opt. 10, 2319-2324 (1971)