Meter-scale spatial-resolution-coherent Doppler wind lidar based on Golay coding

Abstract

Generally, the pulse duration of a coherent Doppler wind lidar (CDWL) is shortened to minimize the spatial resolution at the sacrifice of carrier-to-noise ratio, since the peak power of a laser source is limited by the stimulated Brillouin scattering or other nonlinear optical phenomena. To solve this problem, an all-fiber CDWL incorporating Golay coding is proposed and demonstrated. Given the peak power of the laser pulse, the Golay coding method can improve the measuring precision by improving the pulse repetition frequency of the outgoing laser. In the experiment, the Golay coding implementation is optimized by normalizing the intensity of every single pulse of the outgoing laser with a closed-loop feedback, achieving a spatial resolution of 6 m and a temporal resolution of 2 s with a maximum detection range of 552 m. The wind profile in line of sight and the result derived from another noncoding CDWL show good agreement.Doppler wind lidar (DWL) with an all-fiber structure is developed rapidly due to its inherited characteristics, such as high spatial/temporal resolution, high precision, large dynamic range, strong immunity to electromagnetic (EM) interference, and its stability in harsh environments. DWL has been used widely in different applications and scientific researches, such as aviation safety, air force operation in a carrier, wind power generation, and forecast of extreme weather events. Although DWL is mature and commercially available, minimizing the spatial resolution is still a great challenge [1][2][3][4][5][6][7].In order to improve the aviation safety and optimize the aerodynamic design of an aircraft, the impact of small-scale turbulence on aircraft is receiving increasing attention. Aircraft vortex and wakes have also become a serious limitation in managing the efficiency and capacity of airports [8]. The wingspan of the aircraft is about tens of meters. In such a scale, to study and estimate the dynamic influence of the surrounding atmospheric environment (small-scale turbulence, aircraft vortex, and wakes) on the aircraft, DWL with meter-scale spatial resolution is highly demanded.The spatial resolution (ΔR) of a lidar based on the timeof-flight method is defined as ΔR cΔT ∕2, where ΔT is the duration [full width at half-maximum (FWHM)] of the transmitted laser pulse. c is the speed of light in the atmosphere. The lidar equation is used to describe the relationship between the backscatter signal, transmitted laser, and atmosphere, and it is defined as [9]where P s R is the power of the backscatter signal at a distance of R, E T is the energy of a single laser pulse, η T is the transmitter optical efficiency, η R is the receiver optical efficiency, and T is the single-pass transmittance of laser in atmosphere. β is the aerosol backscattering coefficient, and A r is the effective area of the telescope. In principle, the following three problems limit the spatial resolution improvement of a lidar:(1) In coherent Doppler wind lidar (CDWL), the carrierto-noise ratio (CNR) is proportional to ΔT ...

Doppler Wind Lidar From UV to NIR: A Review With Case Study Examples

“…A research group from USTC successfully developed the C-DWL that can simultaneously measure the wind field and depolarization rate of the atmosphere (Wang et al 2017). Then, they proposed to apply the JTFA and the pulse coding technique to increase the spatial resolution (Wang et al, 2018;Wang et al, 2019). The power spectra distribution of non-coding C-DWL and Golay coding C-DWL are shown in Figure 5.…”

“…Since the spatial resolution enhancement of DWL is generally achieved by reducing the pulse duration of the transmitted laser according to the basic lidar equation, it inevitably induces the sacrifice of other properties, such as the SNR, maximum detection range, and realtime data processing of C-DWL. To solve this problem, various methods have recently been developed in the C-DWL, including a joint time-frequency analysis (JTFA) method (Wang et al, 2018), Golay coding technique (Wang et al, 2019), and differential correlation pair (DCP) technique (Zhang et al, 2021). Apart from the derived LOS wind speeds, C-DWL also provides a spectrum information that has been applied for precipitation observation (Wei et al, 2019), cloud identification (Yuan et al, 2020), and other applications (Wei et al, 2021).…”

Turbulence Detection in the Atmospheric Boundary Layer Using Coherent Doppler Wind Lidar and Microwave Radiometer

“…Coherent Doppler wind lidar (CDWL) obtains radial wind speed information by retrieving the frequency shift of the received signal after passing through a distance in the atmosphere [40][41][42]. Its reliable performance has been verified in various areas, such as the following: turbulence parameters [43][44][45][46][47], aircraft wake vortices [48], boundary layer height [49][50][51], cloud seeding [52], gravity waves [53,54], low-level jets (LLJs) [44,55,56], simultaneous wind and rainfall detection [57], identifying different atmospheric environments [58], and others [59,60].…”

A Compact, Flexible, and Robust Micropulsed Doppler Lidar

“…Modern Doppler lidar systems have exploited developments in fiber optics to address a need for compact and accurate instruments that are more easily deployed and cost effective. Though there are commercial systems available (Pearson et al 2009;Wächter et al 2008), many groups are still conducting research on these systems to minimize their volume, maximize their sensitivity, and increase resolved range (Xia et al 2017;Yan et al 2017;Abari et al 2014;Wang et al 2017Wang et al , 2019b. This paper will address a recent push to advance lidar measurements by developing a compact, near-infrared, pulsed Doppler lidar built almost entirely with robust, telecommunications grade equipment that allows rapid and motion stabilized field deployments.…”