Analysis on the phase perturbation of a dual-frequency wind LiDAR caused by the propagation effect through turbulence

Random fluctuation of refractive index induced by atmospheric turbulence trends to deteriorate laser coherence, making it unfeasible for traditional single-frequency LiDAR (SFL) to obtain the Doppler velocity through inter-pulse echo processing. While dual-frequency LiDAR (DFL) simultaneously transmits two coherent laser signals with small frequency difference into space to detect wind velocity by monitoring the difference of Doppler shift corresponding to the two frequencies, the impact of turbulence propagation effect on the phase perturbation remains unclear. This study establishes the variance of dual-frequency phase difference as a critical factor to indicate the performance of DFL. The results provide quantitative correlations between phase perturbation and turbulence intensity, propagation distance and dual-frequency difference, demonstrating that DFL can effectively mitigate the atmospheric turbulence effects and maintain superior velocity estimation error performance compared to SFL even under strong turbulence and long-distance conditions. This makes it possible for DFL to calculate the Doppler velocity of wind through inter-pulse coherent processing achieving good range resolution and velocity resolution simultaneously.