Determination of sea-water cut-off frequency by backscattering transfer function measurement

The temporal frequency response of water supplemented with scattering parti cles was deduced from the measurement of the optical backscattering of a sh ea (100 ps) blue-green (532 nm) optical pulse given by a frequency-doubled Nd:YAG laser. Indeed, this backscattering measurement gave the water impuls e response from which the transfer function was computed by taking the powe r spectrum. This backscattering frequency response had a low-pass filter-li ke response which enabled us to estimate the medium cut-off frequency. As t he backscattered signal shape depends on the value of the water attenuation coefficient, the ocean water cut-off frequency varies with the amount of s cattering particles its contains. The aim was to define the variations of t he cut-off frequency as a function of the attenuation coefficient.