Imaging in clear ocean water.

A parametric analysis is given of imaging in backscattered light in clear ocean water characterized by temperature and salinity inhomogeneities whose scale length is large compared to the diameter of the light beam. An expression for the beam pattern of a finite underwater laser beam is derived where the effects of source coherence on the imaging properties of backscattered light are discussed. On the basis of the model assumed here, it is concluded that the resolution cannot be significantly improved by reduction of the camera threshold. This limitation results from the rapid decrease of the modulation transfer function for increasing spatial frequencies, which indicates that image modulation below 2% falls another 10 dB at only negligibly higher spatial frequencies. Thus, a 10-dB improvement in the limiting resolution of the camera will not result in significantly better image quality through ocean water.