Sound speed measurement with an edge technique

Summary form only given. The edge technique is a powerful method for measuring small frequency variations such as the Brillouin shifts of an ocean backscattering signal from a pulsed laser. Besides yielding a direct measurement of the speed of sound in the ocean, an edge technique has obvious advantages over the heterodyne techniques, which are based on devices such as interference filters or Fabry-Perots, including a much higher solid angle of acceptance and relative insensitivity to mechanical instability and environmental variations. One model of this edge detector based on iodine (/sup 129/I/sub 2/) absorption lines has been implemented in our lab to obtain the first measurements, to our knowledge, of the temperature dependence of the sound speed in fresh water. We provide an illustration of the detection apparatus to measure sound speed (temperature) based on the Brillouin Lidar return. Our laser system is a modified Continuum PowerLite Nd:YAG, which provides 1 joule of pulse energy at 532 nm.