Performance verification test for the underwater laser Doppler velocimeter in deep-sea area

Currently, we are developing an underwater laser Doppler velocimeter that measures the speed over the water (water-speed) of an underwater vehicle by detecting the Doppler-shift of the laser reflection from suspended matter in the seawater in deep- sea areas. We proposed a monostatic method and a bistatic method as the basic configuration for detecting the Doppler shift for deep-sea area using, and developed an evaluation system that implements both methods until now. As results of evaluating the feasibility and performance of both methods using the evaluation system, we confirmed that the monostatic method has overall advantages for deep-sea use. Therefore, a deep-sea demonstration system of the underwater laser Doppler velocimeter that adopts the monostatic method, was reconstructed. In September 2024, the demonstration system was mounted on an underwater vehicle and its performance was verified by that the underwater vehicle cruised in deep-sea areas. As the result, good Doppler-shifts that satisfied the design performance was detected, and this successfully measured the appropriate water-speed of the underwater vehicle.