Hybrid lidar-radar for enhanced underwater detection

Conventional air-to-underwater lidar systems are contrast limited in the detection of small, shallow underwater targets. This is due to the backscatter of the transmitted optical beam from water particles within the receiver field of view. In response to this shortcoming, a hybrid lidar-radar detection scheme has been developed by combining the sophisticated detection and signal processing techniques of radar with the underwater transmission capability of lidar. The work in this thesis focuses on evaluating the ability of this new technique to reduce backscatter clutter and to improve the detection sensitivity of underwater targets.; The feasibility of this novel detection scheme was investigated through laboratory experiments. An ocean mass simulator was designed and constructed to test the effect of the water on a modulated optical pulse. An analytical model based on the ocean mass simulator was developed to predict experimental outcomes. The results of the theoretical study and corresponding laboratory experiments confirmed the ability of the hybrid detection scheme to reduce backscatter clutter and improve the contrast of underwater targets.; Due to the limitations of the laboratory environment in determining the effects of lidar system variables on the hybrid system performance, an ocean experiment was designed and conducted. A theoretical model was developed to predict experimental results, and a hybrid lidar-radar system was designed and fabricated for ocean experimentation. The field test results established the merits of the hybrid system in improving the contrast of small, shallow underwater targets which remain contrast limited in conventional lidar systems. Significantly, the observance of microwave interference effects verified that the microwave signal integrity was preserved and provided confidence that the implementation of more sophisticated modulation and detection schemes may further improve the system performance.