# Data Processing and Analysis of Eight-Beam Wind Profile Coherent Wind Measurement Lidar
## 1 Introduction  
The real-time measurements of the space atmospheric wind field not only have an impact on our daily lives but also have important applications in aerospace and civil engineering. Atmospheric wind field detection plays an important role in theoretical studies of the space atmosphere [1, 2], wind farm performance evaluation [3, 4], aviation meteorological safety [5], weather warnings [6], and environmental monitoring [7, 8]. Early wind measuring devices included pilot balloons, high-altitude detectors, radio theodolite, and microwave radar. Due to the near detection range, low detection accuracy, and low spatial resolution, these methods cannot meet the actual demand. In 1964, [PERSON] and [PERSON] proposed a laser Doppler velocimetry method. In 1968, [PERSON] and [PERSON] proposed a Doppler Light Detection and Ranging (Lidar) method using the Velocity Azimuth Display (VAD) [9] method to obtain wind profiles, in which the measurements of the radial velocity (also called the line-of-sight velocity) at different azimuth angles are combined to deduce the wind field components. In 1987, a team led by [PERSON] et al. was the first to develop a 1.06-\(\upmu\)m Nd: YAG coherent Doppler wind measurement Lidar. In 1998, [PERSON] et al. introduced coherent Doppler Lidar measurements for boundary layer wind statistics [10]. Subsequently, [PERSON] et al. [11], [PERSON] et al. [12], [PERSON] et al. [13], and [PERSON] et al. [3] confirmed that wind Lidar is a very useful tool for the measurement of wind profiles. The concept of low-coherent Doppler meteorological wind Lidar with a continuous reference wave formed from part of the amplified radiation transistor-transistor-logic (TTL)-modulated Distributed Feedback (DFB)-laser, passing through the fiber ring delay, was proposed for the first time in 2011 [14]. Since then, all-fiber lasers with wavelengths of 1.5-1.6 \(\upmu\)m have been used to improve the compactness and efficiency of coherent Lidar systems [2, 15]. The data from Lidar wind measurements can be used to retrieve the windturbulence parameters [16; 17; 18], identify weather conditions [19], and improve wind energy efficiency. Recently, wind profile Lidar has been demonstrated to have the advantages of high spatial and temporal resolutions, a high measurement accuracy, a long detection range, and strong anti-interference, and it has been widely used for the real-time detection of three-dimensional wind fields in the space atmosphere. Wind profile Lidar mainly takes clear air as the detection object [20]. In the process of atmospheric propagation, the electromagnetic wave emitted by the laser telescopes is scattered due to the uneven refraction distribution caused by the atmospheric turbulence, and the backscattered energy is received by the wind profile radar [21; 22]. The velocity component of the airflow along the direction of the radar beams is determined according to the Doppler effect, and the echo position is determined according to the roundtrip time of the echo signal. Wind profile Lidar has been used on ground-based [23], vehicle-based [24], and airborne platforms [25; 26]. [PERSON] et al. demonstrated the possibility of using a two-beam method for wind profile estimation using pulsed coherent Doppler Lidar [27]. In previous studies, three-beam [28], five-beam, and six-beam Lidar [29] were more common. Because the echo signal is weak, the Lidar detection has been shown to be easily affected by various jamming issues. In the case of heavy rainfall, the Lidar will have a large amplitude interference spectrum peak in the echo power spectrum measured by one or more beam pointing, which will drown the echo signal, resulting in a large error in the wind measurement calculation results [30]. In this study, wind profile coherent wind measurement Lidar was used to transmit eight electromagnetic beams in different directions to detect the upper wind field by driving the exiting telescope with the rotation of the head [31; 32].