Analysis of affecting factors for laser underwater transmission echo signals based on semi-analytic Monte Carlo

Abstract

ABSTRACT In order to design an economical and reliable LiDAR, it is necessary to quantify the influence of different factors on the attenuation of laser propagation in water. Although these factors have been widely investigated, a complete understanding is still few. In addition, a comparative analysis between the measured data and the simulation results of LiDAR to build the design of LiDAR is still lacking. For these reasons, a semi-analytical Monte Carlo method was applied to establish a simulation model of the underwater laser echo signal propagation. The control variable method was quantified with the three major types of influencing factors: 1) LiDAR system parameters, 2) water optical characteristics and 3) external conditions. The effects of these different influencing factors on laser underwater echo signal transmission were investigated. With the experimental results, the attenuation rate of laser transmission in turbid harbour was 7.1 and 19.2 times higher than that in coastal water and clean ocean. Compared with other influencing factors, the optical characteristics of water have the most significant influence on underwater laser transmission. The laser echo signals in water with different concentrations of suspended solids were investigated in a laboratory tank using a LiDAR prototype developed by our research group. The results were compared with that from the semi-analytical Monte Carlo simulation to further explore the influence of the inherent optical characteristics of water on laser energy attenuation. The experimental results showed that with increasing water turbidity, the light beam diverged by strong scattering, the size of the light spot increased, the energy of the echo signal decreased as a whole and the backscattering signal of the water changed significantly. The determination coefficients and relative errors of the measured echo signals and the normalized simulation results were 0.99 and 0.01, respectively, which demonstrate the reliability of LiDAR prototype.