Objective Accurate retrieval of the vertical profile of atmospheric aerosol and cloud extinction coefficients is essential for understanding climate change, improving weather forecasting accuracy, and monitoring air quality. However, traditional lidar inversion algorithms such as the Fernald algorithm rely on several simplifying assumptions, including a constant lidar ratio, a fixed calibration height with known aerosol backscatter, and predefined integration paths. These assumptions introduce significant errors, particularly under complex atmospheric conditions where cirrus clouds coexist with varying aerosol layers. This study aims to address these limitations by proposing a stratified iterative inversion algorithm that improves the accuracy and stability of lidar-based atmospheric extinction profile retrievals. Methods The proposed approach builds upon the classic Fernald inversion framework by introducing a stratified iterative refinement strategy. First, cloud layers are automatically identified using a combination of slope analysis and an adaptive threshold method applied to smoothed lidar backscatter signals. The slope algorithm detects cloud base heights by searching for regions with consecutively increasing signal slopes over at least five adjacent bins, while the adaptive threshold distinguishes cloud tops based on background noise levels. Once cloud boundaries are established, the algorithm applies a bisection-based iterative adjustment of the lidar ratio within the cloud regions. The iterative process minimizes discrepancies in backscatter coefficients between cloud base regions under cloudy conditions and reference values obtained from adjacent clear-sky measurements. This approach ensures consistent aerosol backscatter estimates while adaptively refining cloud lidar ratios without requiring external multi-wavelength or Raman lidar data. To quantify error sources in the traditional Fernald algorithm, detailed sensitivity analyses were conducted. Simulated lidar signals were generated by combining measured extinction profiles with known lidar system parameters, including background radiation and photon-counting noise. Retrieval errors were analyzed by systematically varying three key parameters: integration direction (forward vs. backward), calibration backscatter coefficient errors, and lidar ratio settings. For forward integration, calibration near the surface often leads to amplified errors due to strong aerosol concentration variability, while backward integration from high-altitude low-aerosol regions exhibits better error convergence properties. Results and Discussions Experimental results demonstrate that the proposed stratified iterative algorithm significantly improves retrieval accuracy in mixed aerosol-cloud scenarios. When applied to high-concentration aerosol layers (0?5 km altitude), the relative inversion error decreased from a maximum of 50% (using the traditional Fernald method) to only 5%. For low-concentration aerosol regions near cloud bases (5?7.5 km), errors reduced from 60% to 2%, while in cloud regions (7.5?9 km), errors decreased from 90% to 8%. These improvements are attributed to the algorithm's ability to automatically identify cloud positions and iteratively optimize the cloud lidar ratio. Moreover, the algorithm maintains high retrieval stability even under noisy conditions, thanks to its use of backward integration, which inherently suppresses error propagation. Compared with traditional approaches that apply a single, fixed lidar ratio throughout the profile, the proposed algorithm dynamically adjusts cloud-region lidar ratios in response to local scattering properties while preserving reference backscatter consistency. In addition to simulation experiments, real lidar measurements collected over Anhui Province on 20 January 2017 further validate the algorithm. The stratified iterative algorithm successfully identifies thin cirrus layers at around 8 km altitude, avoiding misclassification of near-surface aerosol layers as cloud. The retrieved extinction coefficient profiles show uniform, physically realistic aerosol and cloud distributions, free from the unphysical negative extinction values observed in traditional Fernald inversions without lidar ratio refinement. Conclusions This study develops and validates an atmospheric stratified iterative inversion algorithm based on the classic Fernald algorithm. By combining slope analysis, adaptive thresholding, and iterative lidar ratio optimization, the algorithm enables accurate retrieval of aerosol and cloud extinction profiles even under complex atmospheric layering. Key advantages include error convergence via backward integration, adaptive lidar ratio estimation without auxiliary instruments, and reduced sensitivity to calibration uncertainties. The approach reduces inversion errors by an order of magnitude compared to traditional algorithms and is particularly suited for real-time, single-wavelength elastic lidar applications in operational atmospheric monitoring. Future work will explore extending this framework to multi-wavelength inversions and integrating machine learning approaches for real-time lidar ratio estimation, further enhancing the capabilities of atmospheric remote sensing.

Objective Real-time, high-precision, and high spatiotemporal resolution atmospheric wind field data from the near-surface to the lower stratosphere has significant applications in improving climate models, advancing atmospheric thermodynamic and dynamic research, enhancing weather forecast accuracy, ensuring the safety of aerospace takeoffs and landings, and optimizing wind energy utilization. However, wind field detection within this altitude range remains one of the challenging problems in atmospheric observation. Current methods primarily rely on a hybrid approach, combining coherent detection for lower altitudes and direct detection for higher altitudes, resulting in complex system structures and high costs. This paper addresses the critical challenge of simultaneously achieving high-precision detection of wind fields, temperatures, and aerosol backscatter ratios from the near-surface to the lower stratosphere. By thoroughly considering the impacts of Brillouin scattering, aerosol scattering, and atmospheric temperature on wind field measurements, a novel triple-frequency molecular Doppler lidar technology based on single dual-pass Fabry-Perot interferometer (FPI) is proposed and studied. Methods Firstly, the detection principles for wind speed, temperature, and aerosol backscatter ratio of the triple-frequency molecular Doppler lidar technology with a single dual-pass FPI are thoroughly analyzed. By employing a three-Gaussian superposition model for molecular scattering spectra, analytical formulas for the transmittance of atmospheric aerosol Mie backscattered light and molecular Rayleigh-Brillouin backscattered light incident on the dual-pass FPI are theoretically derived. A nonlinear iterative method for joint retrieval of the three parameters of wind field, temperature, and aerosol backscatter ratio is proposed, and the theoretical formulas for these three parameters measurement errors are derived. Ultimately, the theoretical framework of this technology is constructed. Secondly, the structure of the Doppler lidar system is designed based on the detection principle, and key parameters including the frequency difference of the triple-frequency laser, the free spectral spacing and the bandwidth of FPI are optimized for simultaneously measuring the near-ground to low stratospheric wind field, temperature and aerosol backscatter ratio by using the developed parameter optimization program. Thirdly, simulation experiments under near-realistic scenarios are conducted to verify the detection performance of the Doppler lidar system designed in the paper, which can achieve high-precision measurement of atmospheric wind field, temperature, and aerosol backscatter ratio from near ground to low troposphere. Finally, through the comparative analysis of the detection performance simulation results with the traditional triple-FPI based Rayleigh Doppler lidar, it is verified that the technology proposed in the paper has significant superiority compared with the traditional technology. Results and Discussions The overall structure and parameters of the Doppler lidar system based on proposed technology are presented, with the emitted laser frequency alternating between the peak and the two wings of the FPI transmittance, while the backscattered light passes through the FPI twice. The optimal frequency difference, free spectral range and bandwidth of FPI for simultaneously measuring the wind field, temperature and aerosol backscatter ratio from the near ground to the lower troposphere are 3 GHz, 12 GHz and 2 GHz, respectively. Under simulated atmospheric conditions, with the daytime sky background light brightness of 0.3 W.sr(-1) .m(-2).nm(-1) @ 355 nm, using a 350 mJ pulse energy, 50 Hz repetition rate laser and a 0.3 m aperture telescope, with a detection zenith angle of 30 degrees, a vertical resolution of 26 m @ 0-10 km and 78 m @ 10-20 km, and a temporal resolution of 3 min, the simulation results of the detection performance of the designed Doppler lidar show that within the 0-20 km altitude range, the system achieves measurement errors of less than 1.2 m/s for radial wind speed, 5.2 K for temperature, and 1.3 & times;10(-2) for aerosol backscatter ratio under all-weather conditions (excluding cloud regions); when clouds appear at 5 km altitude, the radial wind speed error slightly decreases and remains largely unaffected by clouds, whereas the temperature error and aerosol backscatter ratio error abruptly increase to 1.2 K and 2.3 & times;10(-2), indicating significant cloud influence. Compared with the traditional triple-FPI based Rayleigh Doppler lidar technology, the proposed technology has a more compact structure, stronger Mie signal suppression ability and higher accuracy of the inversion algorithm, and can achieve joint high-precision measurement of high and low altitude wind fields, temperature and aerosol backscatter ratio. Conclusions This paper presents a triple-frequency molecular Rayleigh-Brillouin scattering Doppler lidar technology based on a single dual-pass FPI, which can effectively suppress the influence of low-altitude aerosols and clouds on wind speed and temperature measurements, and achieve joint high-precision measurements of wind speed, temperature and aerosol backscatter ratio from near the ground to the low stratosphere. This technology effectively addresses the issue of large wind speed inversion errors that may be caused by unknown temperature and aerosol backscatter ratio during the wind speed inversion process in traditional single-parameter wind speed measurement methods, ensuring the accuracy of wind speed inversion. The paper adopts the three-Gaussian superposition model to describe the Rayleigh-Brillouin scattering spectrum of atmospheric molecules more accurately. Through principal analysis and formula derivation, the theoretical framework of this technology is constructed, and the system structure is further designed and the key parameters are optimized. The detection performance simulation results of this new molecular Doppler lidar show that compared with the traditional triple-FPI based Rayleigh Doppler lidar technology, the technology proposed in this paper has obvious advantages, which can simultaneously and precisely measure the wind field, temperature and aerosol backscatter ratio from the near-ground to low stratospheric atmosphere, and has a good application prospect.

A multimode Doppler lidar based on a quadri-channel Mach–Zehnder interferometer (QMZI) is investigated in this study. The effects of laser frequency pulling, ambient temperature variation, low-frequency vibration, phase defects, atmospheric temperature uncertainty, Brillouin scattering, and other factors on its detection performance are analyzed. The results indicate that laser frequency pulling has a negligible effect on wind field and aerosol measurements. When the ambient temperature varies by 10 K and low-frequency vibration causes a relative change of 1‰ in the optical path difference between the two arms of the QMZI, the resulting deviations in wind speed and backscatter ratio are negligible. The mismatch between the interferometer spectrum and the laser mode spacing also has a negligible influence under these conditions. The influence of phase defects or phase differences introduced by the quarter-wave plate coating can be compensated for by modifying the inversion method. Atmospheric temperature uncertainty has no effect on wind speed inversion accuracy, but it influences backscatter ratio inversion accuracy. When the optical path difference is 50 cm, the inversion deviation of the backscatter ratio is negligible. When the optical path difference is 3 cm and the atmospheric temperature uncertainty is 10 K, the relative deviation of the backscatter ratio inversion reaches 3.2

The importance of acquiring source images using Differential Image Motion LiDAR (DIM LiDAR) system for detecting atmospheric coherence length is investigated. Based on error propagation theory, the effect of jitter variance of the center of mass of the spot image was derived and simulated, identifying it as the dominant error. This underscores the importance of source image acquisition. Multiple simultaneous out-of-field experimental comparisons were conducted using the DIM LiDAR and an ultrasonic anemometer. The consistency of the comparison results is related to the quality of the source image. Furthermore, the probability of the maximum pixel value of the spot image is proposed as a reference for parameter settings prior to measurement with DIM LiDAR. The study concludes that the probability of the maximum pixel value of the captured source image should be less than 8%. Accordingly, the quality of the source image is active controlled to measure the atmospheric coherence length using DIM LiDAR. Multiple parameters can be adjusted simultaneously to ensure that the probability of the maximum pixel value of the image is satisfied. Blind adjustment of a single parameter and the mutual impact of parameters are avoided to ensure the accuracy of r0 measurement using DIM LiDAR.

Since aerosols are rare above the boundary layer, Mie Doppler lidar can generally only detect lowaltitude wind speed. Therefore, for wind-field detection at altitudes of 0.1-20 km a molecular Doppler lidar technology, using a fixed air-gap dual Fabry-Perot etalon as the frequency discriminator and a tunable ultra-violet (UV) laser as the emission source, is proposed. The Rayleigh-Brillouin scattering spectrum of atmospheric molecules is described by a three-Gaussian model, and the parameters of the dual Fabry-Perot etalon are optimized. Simulation results show that in the absence of dust and clouds, the inversion deviation of radial wind speed is less than 0.08 m/s within the radial-wind-speed dynamic range of +/- 10 m/s at 100 m of altitude; The deviation is less than 0.1 m/s within the radial-wind-speed dynamic range of +/- 50 m/s above 1.2 km of altitude. By using a 355-nm ultraviolet laser with a pulse energy of 400 mJ and repetition frequency of 50 Hz, and a telescope with a 300-mm aperture, vertical resolution of 26 m @ 0.06-10km and 78 m @ 10-20 km, and temporal resolution of 1 min, the system has an allday radial-wind-speed measurement error of less than 1.8 m/s between 0.1 to 20 km of altitude, and a radial-wind-speed error less than 0.54 m/s at 10 km of altitude.

To suppress the influence of aerosols scattering on the double-edge detection technique and achieve high-accuracy measurement of the wind field throughout the troposphere to the lower stratosphere, an ultraviolet 355 nm Rayleigh–Brillouin Doppler lidar technology based on a dual-pass dual Fabry–Perot interferometer (FPI) is proposed. The wind speed detection principle of this technology is analyzed, and the formulas for radial wind speed measurement error caused by random noise and wind speed measurement bias caused by Mie scattering signal contamination are derived. Based on the detection principle, the structure of the lidar system is designed. Combining the wind speed measurement error and measurement bias on both sides, the parameters of the dual-pass dual-FPI are optimized. The free spectral range (FSR) of the dual-pass dual-FPI is selected as 12 GHz, the bandwidth as 1.8 GHz, and the peak-to-peak spacing as 6 GHz. Further, the detection performance of this new type of Rayleigh–Brillouin Doppler lidar with the designed system parameters is simulated and analyzed. The simulation results show that at an altitude of 0–20 km, within the radial wind speed dynamic range of ±50 m/s, the radial wind speed measurement bias caused by aerosol scattering signal is less than 0.17 m/s in the cloudless region; within the radial wind speed dynamic range of ±30 m/s, the bias is less than 0.44 m/s and 0.91 m/s in the simulated cumulus cloud at 4 km where aerosol backscatter ratio Rβ = 3.8 and cirrus cloud at 9 km where Rβ = 2.9, respectively; using a laser with a pulse energy of 350 mJ and a repetition frequency of 50 Hz, a 450 mm aperture telescope, setting the detection zenith angle of 30°, vertical resolution of 26 m@0–10 km, 78 m@10–20 km, and 260 m@20–30 km, and a time resolution of 1 min, with the daytime sky background brightness taking 0.3 WSr−1m−2nm−1@355 nm, the radial wind speed measurement errors of the system during the day and night are below 2.9 m/s and 1.6 m/s, respectively, up to 30 km altitude, below 0.28 m/s at 10 km altitude, and below 0.91 m/s at 20 km altitude all day.

Through theoretical calculations and field experiments, the setting of gate width in distance gating technology has been optimized in DIM LiDAR. The mathematical relationship between gate width and detection distance has been derived. The relationship curves between gate width and image signal-to-noise ratio(SNR), as well as gate width and atmospheric refractive index structure constant \(C_n^2\) were obtained. The results indicate that at a constant detection distance, there is a gradual increase in the SNR of the image with increasing gate width, followed by a saturation point. The higher the SNR, the closer the inverted $C_n^2$ is to the ultrasonic anemometer. Meanwhile, if the SNR is similar, the inverted $C_n^2$ is similar. Finally, the appropriate gate width for this system is given.

A denoising method applied to atmospheric coherent length lidar is proposed. Wavelet decomposition (WD) and the adaptive median filter (ADMF) are combined in this method. In this research, the effectiveness of the WD-ADMF has been verified through simulation and measurement. The results show that this filter algorithm, when applied to lidar data, improves the average peak signal-to-noise ratio (PSNR) and centroid error while maintaining data integrity such that the measurement of coherence length or the inference of C n 2 from coherence length more closely matches simulated truth and measured data.

Through theoretical calculations and field experiments, the setting of gate width in distance gating technology has been optimized in DIM LiDAR. The mathematical relationship between gate width and detection distance has been derived. The relationship curves between gate width and image signal-to-noise ratio(SNR), as well as gate width and atmospheric refractive index structure constant C_n^2 were obtained. The results indicate that at a constant detection distance, there is a gradual increase in the SNR of the image with increasing gate width, followed by a saturation point. The higher the SNR, the closer the inverted C_n^2 is to the ultrasonic anemometer. Meanwhile, if the SNR is similar, the inverted C_n^2 is similar. Finally, the appropriate gate width for this system is given.

The detection principle of a multi-longitudinal-mode (MLM) Doppler lidar based on a quadri-channel Mach-Zehnder interferometer (QMZI) was analysed. The measurement error formulas for the radial wind speed and backscatter ratio of this type of Doppler lidar system were derived. The advantages of this detection technology were thoroughly analysed based on the principle. The optical path difference (OPD) 'l' between the two interference arms of the QMZI was optimised. For a detection height of 0-20 km, 'l' was selected as 50 cm to balance the detection of radial wind speed and backscatter ratio. The overall structure of the MLM Doppler lidar based on QMZI was designed, and detailed design parameters of the system were provided. Further simulation was conducted to evaluate the detection performance of the designed QMZI- based MLM Doppler lidar system. The simulation results showed that when using a pulse laser with a power of 17.5 W@355 nm and a telescope with an aperture of 25 cm, a detection zenith angle of 30 degrees, a vertical resolution of 26 m@0-10 km and 52 m@10-20 km and a pulse accumulation time of 1 min, the radial wind speed measurement errors of the system during the day and night were less than 2.1 m/s and 2.5 m/s; the backscatter ratio relative measurement errors were less than 0.81% and 0.97%.

A novel Rayleigh Doppler lidar technology based on a quadruple dual-pass Fabry-Perot interferometer (FPI) that can accurately measure wind field, temperature and aerosol backscatter ratio from the troposphere to lower stratosphere is proposed. This study aims to analyse the detection principle of wind speed, temperature and aerosol backscatter ratio in detail and obtain their measurement error formulas. The structure of this type of lidar is studied and designed. The FPI consists of two edge channels FPI-1 and FPI-2, aerosol channel FPI-M and locking channel FPI-L. FPI-1, FPI-2 and FPI-M use a dual-pass optical path, whereas FPI-L uses a single-pass optical path. The parameters of FPI are optimised as follows: the free spectral spacing (FSR) is 12 GHz, the FWHM of FPI-1 and FPI-2 are both 2.2 GHz, the peak-to-peak interval of FPI-1 and FPI-2 is 5.8 GHz, the FWHM of FPI-M and FPI-L are both 1.2 GHz, the peak-to-peak interval of FPI-M and FPI-1 is 2.9 GHz and the peak-to-peak interval of FPI-L and FPI-1 is 2.3 GHz. Under simulated atmospheric conditions, for a daytime sky background brightness of 0.3 Wsr- 1m- 2nm- 1 at 355 nm, using a laser with a pulse energy of 350 mJ and a repetition fre-quency of 50 Hz and a telescope with a 0.45-m aperture, with a vertical range resolution of 30 m at 0-10 km, 100 m at 10-20 km and 500 m at 20-35km, temporal resolution of 30 min, zenith angle of 0 degrees for temperature and aerosol backscatter ratio detection and temporal resolution of 3 min and zenith angle of 30 degrees for radial wind speed detection, the detection performance of the designed Rayleigh Doppler lidar is determined. The simulation re-sults show that the measurement errors of aerosol backscatter ratio, temperature and radial wind speed of the lidar system in the daytime and night-time are less than 4.36 x 10-3 and 3.32 x 10-3 (excluding cirrus cloud area), 4.0 K and 3.0 K and 3.8 m/s and 1.9 m/s, respectively, from an altitude of 0.06 to 35km.

提出了基于双法布里-珀罗干涉仪（FPI）的多纵模米散射多普勒激光雷达技术，分析了探测原理，并导出了径向风速和后向散射比测量误差公式。该技术要求多纵模激光源的纵模间隔与双FPI的自由谱间距相匹配，并将各纵模的中心频率锁定在双FPI周期性频谱曲线的交叉点附近。详细分析了频率匹配误差引起的风速测量误差。在低风速区域，由频率匹配误差造成的风速测量误差增加的百分数E V 随匹配误差的增大而迅速增大；频率匹配误差不变时，E V 随风速增大而缓慢减小；当频率匹配误差小于10MHz时，E V 将小于5%。设定合理的大气模式和系统参数，对基于双FPI的多纵模米散射多普勒激光雷达的探测性能进行了仿真分析。结果表明：在0～10km高度、0～50m/s的径向风速范围内，当距离分辨率为30m、时间分辨率为30s、激光发射天顶角为30°时，系统白天和晚间的径向风速测量精度分别优于1.50m/s和1.02m/s；在无云条件下，系统白天和晚间的后向散射比相对测量精度分别优于6.57%和4.53%。

2-D scanning system with double mirrors of a traditional wind light detection and ranging（LiDAR） was large in volume and complex in structure, which was not conducive to the small-scale integration of the system. A new 2-D optical scanning system based on rotating double circular wedge prism was studied. The working principle of the system was analyzed, and the simple forward and inverse functional relationship between the rotation angle of the double circular wedge prism and the azimuth and zenith angle of the outgoing beam was derived. The refractive index and wedge angle of the wedge prism were optimized and designed. The results show that when the working wavelength is 532 nm and the refractive index of wedge prism material is 2.03, the optimal wedge angle is 19.5°. The maximum zenith angle of the outgoing beam depends not only on the refractive index and wedge angle of the wedge prism, but also on the beam compression effect. The system is compact and easy to integrate, and large-scale, fast and high-precision scanning of the outgoing beam can be realized. The wind LiDAR can also work in beam scanning modes such as plane position display and distance height display.

提出了基于双级联法布里-珀罗干涉仪（FPI）的多纵模高光谱分辨率测温激光雷达技术。分析了该技术的温度探测原理，并据此构建温度探测的理论模型，导出了温度和后向散射比测量误差公式。该技术要求多纵模激光发射源的纵模间隔与双级联FPI的自由谱间距相匹配，并将各纵模的中心频率锁定在前级FPI周期性频谱的峰值位置。详细分析了频率匹配误差和锁定误差引起的温度测量偏差，结果表明：后向散射比越大，相同的频率匹配误差和锁定误差引起的温度测量偏差就越大；频率匹配误差对温度测量的影响大，为保证低层大气温度测量准确，频率匹配误差和锁定误差应分别小于5 MHz和10 MHz。进一步给出了采用FPI腔长粗扫和细扫相结合的频率匹配校准方法和步骤。设定合理的系统参数，对基于双级联FPI的多纵模测温激光雷达系统的探测性能进行仿真分析。结果表明：在0～20 km高度范围内，通常匹配误差和锁定误差引起的温度测量偏差很小，在2 km以上可忽略不计；若出现云层、沙尘等，对应高度的温度测量偏差将会较大；垂直距离分辨率取30 m@0～12 km和60 m@12～20 km、时间分辨率取1 min时，白天和晚间由噪声引起的温度测量误差分别小于3.7 K和3.5 K，后向散射比相对测量误差分别小于0.40%和0.38%。

基于扩展标量衍射理论,建立了衍射光学元件的微结构高度与周期宽度和入射角度的理论关系模型,提出了不同入射角度时,利用带宽积分平均衍射效率最大化实现设计波长和微结构高度等结构参数的优化设计方法.以工作在近红外波段的衍射光学元件为例进行分析.结果表明:周期宽度一定时,入射角度的改变会引起基于带宽积分平均衍射效率最大化所确定的结构参数发生变化.该设计方法和结论可以用于指导衍射光学元件的设计.

通过深入分析软件知识产权在创造、保护和应用转化中存在的问题,探索解决之法,寻找软件知识产权全链条保护的可行性路径.针对涉及软件发明的保护范围在权利要求书中难以清晰表述,导致软件专利在侵权纠纷中难以获得有效保护的问题.分析如何简化申请程序、改变权利要求撰写方式、增加司法解释条款等方面开展深入研究,探寻软件方法发明专利保护的改进方法.从软件知识产权保护的源头出发,研究企业如何在初创期整体规划知识产权,主动防范侵权行为.针对软件侵权诉讼时间过长和举证困难以致原告损失惨重的问题,研究侵权发生时如何快速有效地终止侵权.本研究对软件知识产权的全方位保护具有积极的参考价值.

马赫-曾德尔干涉仪(MZI)具有光学能量利用率高、便于视场展宽等优点,在光学滤波、鉴频等方面具有广泛的应用.然而,在实际应用中MZI频谱会受到各种因素的影响而导致性能下降.从理论上导出了在考虑入射光发散角2θ0和谱宽?ν的影响下,MZI干涉频谱的理论表达式,并定量分析了其对MZI频谱的影响.结果表明:MZI的光程差l越大,其频谱受?ν的影响越显著,l与入射光波长λ比值越大,其频谱受θ0的影响越显著;当λ=355 nm,l=3 cm时(第1种情形),?ν=10 GHz和θ0=4.5 mrad将分别使条纹对比度K降至2.8％和16.3％;当λ=532 nm,l=59 cm时(第2种情形),?ν=0.5 GHz和θ0=1.25 mrad将分别使K降至3.2％和15％.为减小发散角的影响,从理论上进一步研究了棱镜式视场展宽技术.结果表明:若补偿棱镜厚度d和折射率n满足d=nl/(n?1),对应第1种情形,θ0=50 mrad时K仍高于93.1％,θ0=70 mrad时K将降至33.3％;在第2种情形下,θ0=25 mrad时K仍高于94.0％,θ0=35 mrad时K将降至37.6％.若d依据不同θ0取不同最优值时,在第1种情形下,θ0=70 mrad时K仍高于92.1％;而在第2种情形下,θ0=35 mrad时K仍高于94.4％.

Objective Wind is a critical variable for applications such as numerical weather prediction and climate study. The direct-detect Rayleigh-Mie Doppler lidar is currently one of the most effective tools for tropospheric to stratospheric wind field detection with high accuracy and spatiotemporal resolution. However, owing to the strong aerosol backscattering and Brillouin backscattering signals in the lower atmosphere, the traditional wind retrieval method for Rayleigh-Mie Doppler lidar yields large retrieval errors of low -altitude atmospheric wind speeds. In this study, we quantitatively analyze the wind speed retrieval error of the traditional wind retrieval method in the low -altitude wind field inversion. Further, we propose a new retrieval algorithm and present its specific steps for Rayleigh-Mie Doppler lidar. The proposed new retrieval method can accurately and simultaneously retrieve wind speeds and aerosol backscattering ratios. We expect that the proposed method can effectively expand the capabilities of the Rayleigh-Mie Doppler lidar for detecting low-altitude wind field and aerosol backscattering ratios. Methods First, factors causing the large retrieval errors in the low-altitude wind field inversion using the traditional retrieval method are analyzed, starting from the principle of wind field detection. Second, considering the influence of Brillouin scattering and Mie scattering, the S6 -model -based Rayleigh-Brillouin scattering spectrum model, which is closer to the reality, is used instead of the Gaussian approximate spectrum model. Furthermore, a nonlinear iterative algorithm is used to separate the Rayleigh-Brillouin backscattering signal from the Mie backscattering signal using the signals of energy channel and two edge channels. After combining the above two points, a new retrieval algorithm based on the S6 model and nonlinear iterative method is established, which can simultaneously retrieve the low-altitude wind field and aerosol backscattering ratio. Third, the effectiveness of the proposed retrieval method is verified using the inversion simulation test of the wind field and aerosol backscattering ratio. Finally, based on the measured data of the Rayleigh-Mie Doppler lidar verification system of Anhui institute of optics and fine mechanics (AIOFM) in a comparison experiment with a sounding balloon, the traditional and proposed methods are used to retrieve the horizontal wind speed. By comparing the retrieval results of the horizontal wind speed obtained by employing the two methods using the measured data of the sounding balloon, the advantages of the proposed method in the actual low-altitude wind field inversion are further analyzed and confirmed. Results and Discussions Based on the U. S. standard atmosphere model and design parameters of the RayleighMie Doppler lidar of AIOFM, the wind speed retrieval error below the 3 -km altitude will reach 4-5 m/s and the relative error will exceed 10% within a wind speed range of 50 m/s using the traditional wind field retrieval method, confirming the necessity of the study on low-altitude wind field retrieval method for Rayleigh-Mie Doppler lidar (Fig. 7). The parameter inversion simulation tests show that the retrieval value of the radial wind speed using the proposed method is obviously closer to the true value than that using the traditional method; additionally, the lower the altitude, the more obvious the advantages of the proposed method ( Fig. 9). Moreover, the proposed method can simultaneously retrieve the aerosol backscattering ratio (Fig. 10). Using the measured raw data of the AIOFM Rayleigh-Mie Doppler lidar verification system in a comparison experiment with a sounding balloon, the horizontal wind speed profile retrieved using the proposed method is more consistent with that measured using the sounding balloon on the whole and this observation is particularly obvious below 6 km ( Fig. 11). The statistical results of the difference in the horizontal wind speed data pairs measured using the two detection devices at the same altitude further verify that the proposed method has obvious advantages in retrieving the low-altitude wind field compared with the traditional method (Fig. 12). Conclusions To address the problem of large retrieval errors yielded by the traditional wind field retrieval method of Rayleigh-Mie Doppler lidar in the low-altitude wind field inversion, a new retrieval algorithm based on the S6 model of Rayleigh-Brillouin scattering spectrum and nonlinear iterative method is proposed and the specific inversion steps are presents. The results of parameter inversion simulation tests show that the proposed method can simultaneously retrieve the wind speed and aerosol backscattering ratio with high accuracy. The inversion results of actual wind fields using the measured data of the AIOFM Rayleigh-Mie Doppler lidar verification system also show that the horizontal wind speed retrieved using the proposed method is obviously more consistent with the measurement results of the sounding balloon in the comparison experiment in the lower altitude. These findings fully verify that the proposed method can more accurately retrieve the low-altitude wind speed than the traditional method. The proposed low-altitude wind retrieval method can effectively expand the detection capability of RayleighMie Doppler lidar and has a high practical application value.

Rayleigh Doppler lidar based on a quad Fabry-Perot etalon (FPE) is proposed that is capable of accurately detecting wind speed, as well as temperature and aerosol from 0.2 to 60km altitude. The structure of lidar is designed and its measurement principle is analyzed. One of the four FPEs, i.e. FPE-L is used for locking and measuring the outgoing laser frequency, and the other three, i.e. FPE-1, -2 and -3 form a three-stage FPE. The first-stage FPE (FPE-1) can effectively filter out Mie backscattering signal, thereby suppressing its effects on wind measurement and measuring the aerosol backscatter ratio as well. The transmission spectra of the second- and third-stage FPEs (FPE-2,-3) form double edge for simultaneous wind and temperature measurements by using Rayleigh backscattering signal. The parameters of the quad FPE are optimized. The FWHM and relative peak position of FPE-1,-2,-3,-L are 0.6, 1.2, 1.2, 0.6GHz and 0, -1, 1, 0.3GHz, respectively. The performance of the proposed lidar is simulated and results show that for 0.3WSr- 1m2nm- 1@355nm sky brightness, by using a 350mJ pulse energy, 50Hz repetition frequency laser and a 0.8m aperture telescope, with temporal resolution of 2min@0.2-20km, 20min@20-60km and vertical resolution of 45m@0.2-10km, 90m@10- 20km, 180m@20-40km, 1km@40-60km, the measurement errors of temperature, aerosol backscattering ratio and vertical wind speed are below 5.3K, 3.0?10-3, 1.1m/s in nighttime and below 14.6K, 8.1?10-3, 2.5m/s in daytime from 0.2 to 60km altitude; the measurement error of two other orthogonal LOS wind speed with fixed zenith angle of 25.8? is below 1.3m/s in nighttime and 3.5m/s in daytime within the LOS wind speed dynamic range of ?50m/s from 0.2 to 60km altitude.

For diffractive optical elements (DOEs) in imaging optical system, oblique incidence is the normal working situation. An additional phase is introduced by antireflection coatings (ARCs) for DOEs, having an effect on diffraction efficiency. In this study, a diffraction efficiency model for DOEs with ARCs at different incident angles is proposed. Based on the relationship between phase function of DOE and incident angle, and the effect of ARCs on incident angle of diffractive microstructure surface at oblique incidence, the diffractive microstructure height is modified, the diffraction efficiency with ARCs at different incident angles are optimized by the proposed model. A theoretical model of the relationship between the comprehensive polychromatic integral diffraction efficiency (PIDE) and the modified microstructure height of DOE working within a certain incident angle range is established. The diffraction efficiency of DOE designed by the traditional method and the optimal method is compared and analyzed with single layer and multilayer ARCs. Results show that with the optimal design method, the diffraction efficiency and PIDE of the DOE working in the visible waveband at different incident angles are improved, as well as the comprehensive PIDE over the whole working incident angle range.