Interpretation of some anomalies in the shape of lidar signals from upper sea-water layers

Abstract

In a series of laser sounding experiments the registered shapes of retroreflected light pulses demonstrate an anomalously high levels of signals from isolated sea-water layers. We propose here an interpretation for such peculiarities of echo-signal shape with the use of developed theory of backscattered light pulse kinetics in turbid medium. Our approach is based on the accounting of the angular anisotropy of the scattering in the back hemisphere and the geometrical conditions of typical lidar experiment, which determine the small angle divergence of collected light beam from the retro-reflection direction. According to the analysis presented below, the enhanced backscattering from isolated depth levels may be caused by high concentration of large biological particles (alga cellscoccolitophorids, diatoms, etc.) in the corresponding water layers. The explanation is shown to be consistent with the known unique measurements of volume scattering phase function in the vicinity of backward direction.