Semi-analytical Monte Carlo simulation of underwater target echoes from a small UAV-based oceanic lidar

Small unmanned airborne oceanic lidars are becoming increasingly popular for ocean surveys. They typically weigh less than 10 kg and can be mounted on commonly used commercial drones, making them easier to use than traditional large oceanic lidars, which typically weigh up to 80 kg and can only be carried on manned aircraft. Unmanned airborne oceanic lidars typically fly at lower altitudes and use higher laser emission frequencies, making them suitable for detecting underwater targets. However, most of the existing LiDAR underwater echo simulation models are designed for flat terrain and assume that the target fills the LiDAR receiving field of view, and there are few studies on the echoes of suspended targets smaller than the field of view range. Therefore, we combined ray tracing and semi-analytical Monte Carlo to model the laser echo energy of the underwater target. The study investigated the energy change of the target echo in the direction of deviation from the laser outgoing direction, and the impact of absorption and scattering coefficients on it. The difference in echo energy between different fields of view for extended and non-extended targets and the effect of water quality on it were explored. The echo waveforms of the target under different tilt angles were simulated, and it was found that the target echo pattern will be tilted with the change of tilt angle and offset position.