Experimental study of simultaneous velocity and distance measurement near air/sea surface based on 632 nm frequency modulated continuous wave laser

In rough sea conditions and complex environments, for safe landing of unmanned aerial vehicles (UAVs) on unmanned surface vehicles (USVs), it is necessary to accurately measure the distance and speed between UAV and USV simultaneously. In response to this requirement, this paper proposes a frequency modulated continuous wave (FMCW) lidar system that uses a visible light wavelength (632 nm), which is low absorption in humid environments, enabling simultaneous measurement of speed and distance. The system directly modulates a 632 nm semiconductor distributed Bragg reflector (DBR) laser with a triangular wave current modulation signal. The modulated laser output features continuous frequency tuning and is divided into two beams. One beam serves as the reference light, while the other beam is used as the detection light and incident on the measurement target. The detection light reflected (scattered) by the target is collected by a photodetector (PD) and mixed with the reference light for coherent heterodyne detection. The beating signal carries information about the distance and velocity of the target. The system has been experimentally verified to simultaneously measure distance within a detection range of 5 cm to 350 cm and a velocity range of 0.5 cm/s to 850 cm/s. Moreover, the system’s capability for simultaneous distance and velocity measurement under humid conditions has also been demonstrated. This lidar system would have broad application in the precise measurement of distance and velocity simultaneously in humid environment.