Performance analysis of dual-frequency lidar in the detection of the complex wind field

Abstract

Due to short coherent length of the laser, traditional single frequency lidar (SFL) uses echoes of adjacent samples to retrieve Doppler wind velocity, which inevitably brings about a dilemma of high range resolution and velocity resolution. Dual-frequency lidar (DFL), however, with a frequency difference locating at the radar band, can process the laser echoes with a radar processing framework while maintaining a good wind sensing ability in clear air. In this paper, performances of SFL and DFL are analyzed in terms of different conditions like pulse duration, number of sampling points in processing, wind distribution, signal to noise ratio (SNR), etc. It is shown that, for a complex wind field, DFL has the potential to retrieve the Doppler velocity with high velocity and range resolution, even in a relatively low SNR condition.

Coherence analysis of laser pulses based on an external cavity circulation

“…4 In the framework of these applications, range resolution and Doppler resolution directly rely on the coherence time of the microwave-modulated optical pulses, which is supposed to be much longer than the coherence time of laser pulses. 5 Thus, the accurate measurement of the pulse-to-pulse coherence of laser sources, especially the beat-note-carrying ones, is required to characterize signal quality. 6 However, there are few studies in this area due to the difficulties in the coherence measurement of optical pulses: first of all, the linewidth of continuous-wave laser can reach sub-KHz and is even narrower when using the technique of injection locking, which exceeds the resolution of the current finest commercial spectrometer.…”