Assessing the impact of optical vortex spatial filtering in underwater LiDAR systems

Area of Science:

• Ocean Optics
• Remote Sensing
• Optical Physics

Background:

• Blue-green underwater lidar offers high spatial resolution but suffers from scattering in turbid waters, limiting range and accuracy.
• Optical vortices have been explored as spatial filters to combat scattering by exploiting coherence differences.
• Underwater turbulence and target surface roughness can degrade the spatial coherence of lidar echoes, potentially hindering vortex filter performance.

Purpose of the Study:

• To investigate the impact of turbulence and target surface roughness on the effectiveness of optical vortex spatial filtering in underwater lidar.
• To develop a simulation model accounting for scattering, turbulence, and surface roughness for laser beam transmission in water.
• To analyze the combined effects of these factors on spatial filtering efficiency using signal-to-clutter ratio and transmittance.

Main Methods:

• Developed a multiple random phase screen model to simulate laser beam propagation through scattering, turbulent water with rough surfaces.
• Evaluated spatial filtering efficiency by measuring the improvement in signal-to-clutter ratio and spatial filter transmittance.
• Conducted simulations and experiments to validate the model and analyze the impact of environmental factors.

Main Results:

• The combined effect of turbulence and surface roughness significantly reduces the spatial filtering effectiveness of optical vortices, more so than individual factors.
• When one factor (turbulence or roughness) is dominant and negates the filter's function, the influence of the other factor becomes negligible.
• Simulation and experimental results corroborated the detrimental combined impact on filter performance.

Conclusions:

• The effectiveness of optical vortex spatial filtering in underwater lidar is substantially diminished by the combined presence of turbulence and surface roughness.
• Understanding these combined effects is crucial for optimizing lidar system design and spatial filtering strategies in challenging underwater conditions.
• The proposed simulation model provides a valuable tool for predicting and mitigating performance degradation in diverse underwater environments.