Performance analysis of dual-frequency coherent lidar for rough target detection in turbulent atmosphere

Abstract

The dual-frequency coherent lidar (DFCL) has advantages of anti-interference, stability, and can obtain low Doppler frequency shift in high-speed dynamic target detection. A performance evaluation model of DFCL is established for remote Gaussian rough object detection. The detection ability is closely related to laser echo characteristics, especially the intensity and coherence. The laser beam radius on the far field increases with the decay of the emitted laser pulse coherence, and the atmospheric turbulence reduces the coherence further. The intensity utilization factor is defined and calculated. The decoherence effects of rough surfaces are calculated via the complex coherence degree under typical roughness parameters and laser wavelength. Moreover, the Doppler frequency shift is proportional to dual-frequency difference ∆f, but the signal-to-noise ratio (SNR) decreases with larger ∆f duo to the coherence reduction of dual-frequency laser, and the optimal dual-frequency difference ∆fm selection criteria is determined for practical applications; and the system efficiency reduction factor are calculated and compared under typical detection parameters. Finally, the combined effects of laser source coherence, atmospheric turbulence, optical parameters and ∆f on the SNR improvements are analyzed considering dual-frequency and single frequency lidar systems. This research is of significance to reveal the dual-frequency coherent detection process and the optimization method of coherent lidar systems.