An optical instrument for use in the study of wind induced ripple on the water surface of a wind and wave tank is described. The instrument measures the tip angle of the projected surface normal vector in the down-wind and the cross-wind vertical planes independent of water height, thereby allowing studies of wind induced ripple on lower frequency, mechanical waves. Underwater hardware is reduced to one mirror. Each projected angle appears on a separate output channel as an analog voltage. An in situ calibration technique used prior to recording calibrates the over-all system. Sample output records are shown, and system performance is discussed.
G. Tober, R. C. Anderson, and O. H. Shemdin, "Laser Instrument for Detecting Water Ripple Slopes," Appl. Opt. 12, 788-794 (1973)