The fluctuation of acoustic signals scattered from the ocean bottom displays a beat or interference characteristic when the source and/or receivers are in motion. Beat rates obtained statistically from observed data are shown to vary with velocity of source and receiver, as well as with transmitted frequency and acoustic geometry. Data obtained with a conical beam at a frequency of 19.5 kc/sec are compared with a simple physical model. Experimental results of a method for controlling the heat rate by linear frequency modulation of the transmitted signal are illustrated. Implications of the observations relative to reflection and scattering theory are discussed.