## 2 Materials and Methods
### Data Acquisition System and Parameters
#### 2.1.1 All-Fiber Coherent Wind Measurement Lidar  
In this study, we used a pulsed CWML system manufactured by Technovo Lidar High Tech Co., Ltd., Hefei, China (model KC-WL-2006 Lidar) [30]. The Lidar system is divided into two sub-systems: laser-transmitting system and laser-receiving system. In this study, the transmitting and receiving modules of telescope are integrated, which could be used to adjust focus. The seed laser produces a narrow linewidth laser with a wavelength of 1.55 \(\upmu\)m. After beam amplification, collimation, and beam expansion, the laser is emitted into the atmosphere using a scanner at specific azimuth and elevation angles. Multiple laser \"lines\" are formed by rotational scanning, thus enabling 3D scanning of the detection area. The transmitted laser experiences Mie scattering in the atmosphere, and the receiving telescope receives the backward-scattered light. Next, the light received by telescope is collimated into parallel light through the optical fiber and reflecting telescope and then converted to photoelectric signal via balance detector. Finally, the data are collected by the acquisition card and stored in the computer. The whole system ensures the coordination of laser transmission and reception, data acquisition, and processing under the control of the computer. The Lidar optical skylight was installed with special optical glass for mobile Lidar operations. The Lidar was placed on a special frame to keep the instrument stationary and reduce the impact of vehicle movement (see Figure 2). Specifically, the vehicle-mounted system hosted a CNS, which consisted of two high-precision GPS antenna, an accelerometer, and a gyroscope (see Figure 3). The first GPS (i.e., the Lidar GPS) was located on top of the Lidar special frame, while the second GPS (i.e., the vehicle GPS) was located on the bottom of vehicle structure, to enable the measurement of the vehicle and Lidar attitude. The system is compact with a size of 835.0 mm \(\times\) 550.5 mm \(\times\) 888.6 mm, and mass of 50 kg. A laptop or PC is used to control the Lidar and store the measured data in each azimuth angle. Moreover, the laser emits a beam with 1.55 \(\upmu\)m wavelength, where the pulse energy is 145 \(\upmu\)J. The single-pulse energy is limited. Noncoherent integration of echo signals is required. The spectral accumulation number is 20,000. The pulse width is \(\tau\) = 400 ns, which corresponds to distance resolution of R = c \(\times\)\(\tau\)/2 = 60 m. The sampling frequency is f\({}_{\rm s}\) = 1 GHz, and N = 1024 points Fast Fourier Transform (FFT) is performed on this signal, so the spectral resolution f = fs/N = 0.98 MHz. To simplify the analysis, a valid section of echo signal power spectrum containing the peak value was intercepted for analysis, i.e., each range gate contained Np = 112 valid points after the interception. In addition, the first 128 range gates were retained, i.e., 14,336 data were collected for subsequent analysis in each radial direction. The power spectrum data is shown in Figure 4 (only the first thirty range gates are shown). The X-coordinate represents frequency, the Y-coordinate represents range gate index, and Z-coordinate represents power spectral density (PSD). The first range gate stores noise data, and the second and third range gates store the mirror data. The mirror data are formed by the reflection and refraction phenomenon of the telescope system itself. The data in the 4 th to the 128 th range gates are valid data. The CNR is an important index used to detect the performance of Lidar. For a CWML system featuring a real-time signal processing function, the CNR is usually estimated from the average PSD data in the frequency domain. Moreover, the frequency-domain wideband CNR of the signal is defined as the ratio of the integration of signal PSD to the integration of noise PSD. As suggested by [PERSON] et al. [31], this study used a CNR of \(-\)20 dB as a threshold. After FFT, if the CNR of range gate is below the threshold, the data of range gate will be rejected.