Remote sensing of air pollution incorporating integrated-path differential-absorption and coherent-Doppler lidar

An innovative complex lidar system deployed on an airborne rotorcraft platform for remote sensing of atmospheric pollution is proposed and demonstrated.The system incorporates integrated-path differential absorption lidar(DIAL) and coherent-doppler lidar(CDL) techniques using a dual tunable TEA CO_(2)laser in the 9—11 μm band and a 1.55 μm fiber laser.By combining the principles of differential absorption detection and pulsed coherent detection,the system enables agile and remote sensing of atmospheric pollution.Extensive static tests validate the system’s real-time detection capabilities,including the measurement of concentration-path-length product(CL),front distance,and path wind speed of air pollution plumes over long distances exceeding 4 km.Flight experiments is conducted with the helicopter.Scanning of the pollutant concentration and the wind field is carried out in an approximately 1 km slant range over scanning angle ranges from 45°to 65°,with a radial resolution of 30 m and10 s.The test results demonstrate the system’s ability to spatially map atmospheric pollution plumes and predict their motion and dispersion patterns,thereby ensuring the protection of public safety.

The Application of Sea-Surface Wind Detection with Doppler Lidar in Olympic Sailing

The mobile incoherent Doppler lidar （MIDL）, which was jointly developed by State Key Laboratory of Severe Weather （LaSW） of the Chinese Academy of Meteorological Sciences （CAMS） and Ocean University of China, provided meteorological services during the Olympic sailing events in Qingdao in 2008. In this study, two experiments were performed based on these measurements. First, the capabilities of MIDL detection of sea-surface winds were investigated by comparing its radial velocities with those from a sea buoy. MIDL radial velocity was almost consistent with sea-buoy data; both reflected the changes in wind with time. However, the MIDL data was 0.5 m s-1 lower on average than the sea-buoy data due to differences in detection principle, sample volume, sample interval, spatial and temporal resolution. Second, the wind fields during the Olympic sailing events were calculated using a four-dimensional variation data assimilation （4DVAR） algorithm and were evaluated by comparing them with data from a sea buoy. The results show that the calculations made with the 4DVAR wind retrieval method are able to simulate the fine retrieval of sea-surface wind data--the retrieved wind fields were consistent with those of sea-buoy data. Overall, the correlation coefficient of wind direction was 0.93, and the correlation coefficient of wind speed was 0.70. The distribution of retrieval wind fields was consistent with that of MIDL radial velocity; the root-mean-square error between them had an average of only 1.52 m s-1^.

Correction of temperature influence on the wind retrieval from a mobile Rayleigh Doppler lidar

A mobile Rayleigh Doppler lidar based on double-edge technique is implemented for simultaneously observing wind and temperature at heights of 15 km-60 km away from ground.Before the inversion of the Doppler shift due to wind,the Rayleigh response function should be calculated,which is a convolution of the laser spectrum,Rayleigh backscattering function,and the transmission function of the Fabry-Perot interferometer used as the frequency discriminator in the lidar.An analysis of the influence of the temperature on the accuracy of the Une-of-sight winds shows that real-time temperature profiles are needed because the bandwidth of the Rayleigh backscattering function is temperature-dependent.An integration method is employed in the inversion of the temperature,where the convergence of this method and the high signal-to-noise ratio below 60 km ensure the accuracy and precision of the temperature profiles inverted.Then,real-time and on-site temperature profiles are applied to correct the wind instead of using temperature profiles from a numerical prediction system or atmosphere model.The corrected wind profiles show satisfactory agreement with the wind profiles acquired from radiosondes,proving the reliability of the method.

Comprehensive wind correction for a Rayleigh Doppler lidar from atmospheric temperature and pressure influences and Mie contamination

A correction considering the effects of atmospheric temperature, pressure, and Mie contamination must be performed for wind retrieval from a Rayleigh Doppler lidar（RDL）, since the so-called Rayleigh response is directly related to the convolution of the optical transmission of the frequency discriminator and the Rayleigh–Brillouin spectrum of the molecular backscattering. Thus, real-time and on-site profiles of atmospheric pressure, temperature, and aerosols should be provided as inputs to the wind retrieval. Firstly, temperature profiles under 35 km and above the altitude are retrieved, respectively,from a high spectral resolution lidar（HSRL） and a Rayleigh integration lidar（RIL） incorporating to the RDL. Secondly,the pressure profile is taken from the European Center for Medium range Weather Forecast（ECMWF） analysis, while radiosonde data are not available. Thirdly, the Klett–Fernald algorithms are adopted to estimate the Mie and Rayleigh components in the atmospheric backscattering. After that, the backscattering ratio is finally determined in a nonlinear fitting of the transmission of the atmospheric backscattering through the Fabry–Perot interferometer（FPI） to a proposed model.In the validation experiments, wind profiles from the lidar show good agreement with the radiosonde in the overlapping altitude. Finally, a continuous wind observation shows the stability of the correction scheme.

Observation of Stable Marine Boundary Layer by Shipborne Coherent Doppler Lidar and Radiosonde over Yellow Sea

Shipborne observations obtained with the coherent Doppler lidar(CDL)and radiosonde during 2014 campaign were used to study the structure of marine boundary layer in the Yellow Sea.Vertical wind profiles corrected for ship motion was used to derive higher-order statistics,showing that motion correction is required and significant for turbulence analysis.During a day with weak mesoscale activity,a complexed three-layer structure system was observed.The lowest layer showed a typical stable boundary layer structure feature.An aerosol layer with abrupt variation in wind speed and relative humidity always appeared at the middle layer,the formation of which may be due to Kelvin-Helmholz instability.The top layer encountered a dramatic change in wind direction,which may result from the warm advection from the Eurasian continent on the basis of backward trajectory analysis.Furthermore,the MABL height in stable regime was derived from potential temperature,CDL signal-to-noise ratio(SNR)and CDL vertical velocity variance,respectively.The stable boundary layer(SBL)height in SBL can be derived from the inversion layer of potential temperature profile,and the mixing height in SBL can be retrieved from the vertical velocity variance gradient method.Neither the SBL height nor the mixing height is in agreement with the height retrieved from CDL SNR gradient method because of different definition and criterion.One of the limitations of SNR gradient method for MABL retrieval is that it is easier to be affected by the lofted decoupled aerosol layer,where the retrieved result is less suitable.Finally,the higher-order vertical velocity statistics within the marine stable boundary layer were investigated and compared with the previous studies,and different turbulence mechanisms have an important effect on the statistics deviation.

Decoupling of temporal/spatial broadening effects in Doppler wind LiDAR by 2D spectral analysis

Pulse echo accumulation is commonly employed in coherent Doppler wind LiDAR(light detection and ranging)under the assumption of steady wind.Here,the measured spectral data are analyzed in the time dimension and frequency dimension to cope with the temporal wind shear and achieve the optimal accumulation time.A hardware-efficient algorithm combining the interpolation and cross-correlation is used to enhance the wind retrieval accuracy by reducing the frequency sampling interval and then reduce the spectral width calculation error.Moreover,the temporal broadening effect and spatial broadening effect are decoupled according to the strategy we developed.

Noise reduction in LOS wind velocity of Doppler lidar using discrete wavelet analysis

The line of sight (LOS) wind velocity can be determined from the incoherent Doppler lidar backscattering signals. Noise and interference in the measurement greatly degrade the inversion accuracy. In this paper, we apply the discrete wavelet denoising method by using biorthogonal wavelets and adopt a distance-dependent thresholds algorithm to improve the accuracy of wind velocity measurement by incoherent Doppler lidar. The noisy simulation data are processed and compared with the true LOS wind velocity. The results are compared by the evaluation of both the standard deviation and correlation coefficient. The results suggest that wavelet denoising with distance-dependent thresholds can considerably reduce the noise and interfering turbulence for wind lidar measurement.

Sodium fluorescence Doppler lidar to measure atmospheric temperature in the mesopause region

A sodium fluorescence Doppler lidar system has been developed to measure environmental parameters of the middle and upper atmosphere. The lidar system mainly comprises a transmitter system,receiver system,data acquisition and control system and data analysis system. A narrowband 589 nm laser is used to excite sodium atoms in the mesopause region. Excitation of the sodium atoms results in resonance fluorescence,which is collected by the receiver. The temperatures in the mesopause region(about 75-105 km) can be derived by analyzing the Doppler-broadened width of the sodium fluorescence. Observations were made with the lidar system,and the number density of sodium atoms and atmospheric temperature profiles were extracted from the observation data. Comparisons of the lidar temperatures and TIMED/SABER temperatures show good agreement,illustrating the reliability of the sodium fluorescence Doppler lidar measurements.

Incoherent pulse Doppler lidar as the velocimeter system

This note reports a new type of incoherent pulse laser Doppler lidar velocimeter with iodine molecular filter as a frequency discriminator. Its transmitter subsystem applies a Nd:YAG pulse laser which is injected with a single longitudinal-mode diode pumped continuous seeder laser. The field experiment proved that this velocimeter measurement results are consistent with those measured by photoelectric velocimeter. Measurements of eight different velocities show that the standard deviation is 0.56m/s, the range resolution is 3.75m.

Theoretical description of improving measurement accuracy for incoherence Mie Doppler wind lidar

For the nonlinearity of Fabry-Perot interferometer（FPI） transmission spectrum,the measurement uncertainty of incoherent Mie Doppler wind lidar based on it increases evidently with the increase of backscattering signal Doppler shift.A method of repeating the use of the approximate linear part of FPI transmission spectra for reducing the high uncertainty of a big Doppler shift is proposed.One of the ways of realizing this method is discussed in detail,in which the characteristics of FPI transmission spectrum changing with thickness and incident angle are utilized simultaneously.Under different atmosphere conditions,it has been proved theoretically that the range of measurement uncertainty drops to one-sixth while its minimum has no serious change.This method can be used not only to guide the new system design,but also as a new working way for the fabricated system.

Robust Solution for Boundary Layer Height Detections with Coherent Doppler Wind Lidar

Although coherent Doppler wind lidar(CDWL)is promising in detecting boundary layer height(BLH),differences between BLH results are observed when different CDWL measurements are used as tracers.Here,a robust solution for BLH detections with CDWL is proposed and demonstrated:mixed layer height(MLH)is retrieved best from turbulent kinetic energy dissipation rate(TKEDR),while stable boundary layer height(SBLH)and residual layer height(RLH)can be retrieved from carrier-to-noise ratio(CNR).To study the cause of the BLH differences,an intercomparison experiment is designed with two identical CDWLs,where only one is equipped with a stability control subsystem.During the experiment,it is found that the CNR could be distorted by instrument instability because the coupling efficiency from free-space to the polarization-maintaining fiber of the telescope is sensitive to the surrounding environment.In the ML,a bias up to 2.13 km of the MLH from CNR is found,which is caused by the CNR deviation.In contrast,the MLH from TKEDR is robust as long as the accuracy of wind is guaranteed.In the SBL(RL),the CNR is found capable to retrieve SBLH and RLH simultaneously and robustly.This solution is tested during an observation period over one month.Statistical analysis shows that the root-mean-square errors(RMSE)in the MLH,SBLH,and RLH are 0.28 km,0.23 km,and 0.24 km,respectively.

一种基于多普勒原理的相干测风激光雷达及其外场应用

精确观测大气风场在气象、军事、航空航天等领域具有十分重要的意义。相干测风激光雷达能够实时有效地进行大气矢量风场探测。为此研制出一款基于多普勒原理的相干测风激光雷达,并进行外场观测验证了其性能。该系统可探测垂直上空45~3000m的水平风场以及垂直气流,最大可探测风速为60m/s。分析比对了该雷达于2021年10月16日08:00―20日00:00在广州市黄埔区气象局观测的数据与同时段同地点微波风廓线雷达的观测数据,结果表明二者具有良好的一致性。重点分析了2021年10月18日10:00―20日00:00的典型观测数据,进一步验证了该相干测风激光雷达所测数据的准确性。该雷达在风场探测上的应用将为气象参数监测和预报精度的提高以及极端灾害性天气的预警提供实时数据支撑。

Coherent Doppler lidar wind retrieval for a typhoon based on the genetic simulated annealing algorithm

A method of spectrum estimation based on the genetic simulated annealing(GSA)algorithm is proposed,which is applied to retrieve the three-dimensional wind field of typhoon Nangka observed by our research group.Compared to the genetic algorithm(GA),the GSA algorithm not only extends the detection range and guarantees the accuracy of retrieval results but also demonstrates a faster retrieval speed.Experimental results indicate that both the GA and GSA algorithms can enhance the detection range by 35%more than the least squares method.However,the convergence speed of the GSA algorithm is 17 times faster than that of the GA,which is more beneficial for real-time data processing.

基于激光雷达观测的呼伦贝尔一次沙尘过程分析

基于测风激光雷达和地面常规观测资料,借助机器学习算法以及HYSPLIT(Hybrid Single-Particle LagrangianIntegrated Trajectory)模型分析了发生在呼伦贝尔的一次典型的沙尘天气过程。研究表明,本次沙尘起始时南风突增,风向转西南偏南风后风速降低,传输减弱,当风向转西风时,沙尘传输增强,在西风降低后沙尘传输结束。沙尘传输期间,湍流运动偏弱,混合层高度抬升受限。借助机器学习分粒径计算发现,沙尘前期传输以粗颗粒为主,后期粗、细颗粒物均有明显增长。不同传输时期粒径的不同,暗示沙尘的源可能发生变化,后向轨迹揭示沙尘传输前期来自蒙古国西北部,经过我国锡林郭勒后北上到达呼伦贝尔;而后期沙尘是从俄罗斯南部直接进入呼伦贝尔。最后研究发现,沙尘前至起始时刻,总传输通量对沙尘的响应早于地面颗粒物浓度变化,且沙尘期间总传输通量值显著高于沙尘前和沙尘后。因此,总传输通量变化以及阈值设定可为沙尘预警的新参考指标。

测风激光雷达与风廓线雷达的探测性能评估及数据融合

测风激光雷达和风廓线雷达作为L波段探空测风的有效补充,均可以提供高时空分辨率的大气风场信息,然而由于工作原理和适用条件存在明显差异,在探测性能上各有优缺点,单一设备的探测数据已不能满足精细化预报的要求。本研究使用2020年1—5月北京南郊观象台的L波段探空资料对同址观测的测风激光雷达和风廓线雷达进行了数据质量评估,结果表明测风激光雷达与探空的一致性较高,U、V分量的相关系数分别为0.97和0.98,均方根误差分别为1.1和0.95 m·s^(-1),然而在2 km以上数据获取率较低且偏差较大;风廓线雷达与探空相比,U、V分量的相关系数分别为0.94和0.93,均方根误差分别为2.94和2.91 m·s^(-1),风廓线雷达的探测距离虽然更远,但在0.5 km以下和6 km以上的测量偏差较大。考虑到两种测风雷达在不同探测高度上的性能优缺点,提出分段曲面拟合法对两者的水平风资料进行融合处理,并选取个例对融合效果进行验证,结果表明,融合后的风廓线与融合前相比,风向和风速的一致性均得到明显提升。

铁共振荧光多普勒激光雷达光源的频率稳定性研究

种子注入的372 nm稳频Nd:YAG激光器作为铁共振荧光多普勒激光雷达的激光光源,其性能将直接影响大气温度和径向风速的测量精度,属于研制难度较大但极其重要的关键技术。文中对激光光源的频率稳定性进行了仿真分析和实验研究。利用蒙特卡洛方法,仿真了振荡级输出1116 nm脉冲光的频率稳定性(均方根)应小于1 MHz;对改进型Ramp-Fire种子注入技术进行了详细介绍,并在振荡级光路中采用了该技术;通过激光拍频实验,测量得出1116 nm脉冲光在10 min内的频率稳定性的均方根为543.24 kHz,其结果满足指标要求,可将频率抖动和频率漂移引起的系统误差减少至0.51 K和0.61 m/s。文中所做工作为铁共振荧光多普勒激光雷达实现大气温度和径向风速的高精度测量提供了必要保障。

基于相干多普勒激光雷达的斜程湍流参数反演方法研究

大气湍流广泛存在于大气中,其中斜程湍流对航空航天、天文观测等会产生不可忽视的影响。一方面利用相干多普勒测风激光雷达获得的高时空分辨风场探测数据,另一方面基于Kolmogorov局地均匀各项同性理论,即在惯性子区内湍流的特征只与湍能耗散率ε有关,将速度结构函数法应用到飞机着陆阶段下滑道扫描模式中,通过实测数据的速度结构函数与模型速度结构函数最小二乘法拟合,从而估算激光雷达扫描范围内的大气湍流参数(径向风速方差、湍流积分尺度和ε等)。根据下滑道扫描区域数据的时空分布特征,给出大气湍流参数的斜程空间分布图,并与同步观测的飞机下滑道风切变强度数据进行了对比分析,发现两者具有较好的一致性,证实了斜程湍流参数反演方法的可靠性。

基于地基与星载激光雷达技术的武夷山山谷风环流研究分析

山谷风是一种热力驱动产生的局地环流,武夷山市三面环山,中部为丘陵地带,使得该地常年盛行山谷风。基于地面气象观测站、边界层测风激光雷达及激光雷达卫星Aeolus数据研究了武夷山山谷风环流特征。结果表明,夏季出现山谷风日天数最多,山谷风日出现时大气日变化特征显著,表现为山风出现的时间段,以偏北风为主,风速较小,低空激光雷达回波信号较强,气流运动以下沉为主,垂直方向上形成环流圈;谷风阶段,以偏南风为主,较山风阶段风速有所增强,低空激光雷达回波信号减弱,以上升气流为主;激光雷达数据融合的风廓线可见,武夷山非山谷风日常出现在对流层中低层盛行偏南风的天气形势下,偏南风将水汽输送至当地,使得当地低空被较厚云层覆盖或出现降水过程,从而削弱了山地与谷地的热力差异,局地环流被打破,山谷风环流无法形成。

基于线型预测频谱估计的相干激光雷达功率谱分析方法

基于多普勒效应的相干激光雷达广泛应用于测风等大气探测领域,实际应用于风场观测时,由于噪声杂波干扰、回波信号较弱和风场不均匀性等影响了多普勒频移估计的精度。为准确估计激光雷达弱回波信号中的多普勒频移,提升相干测风激光雷达的探测距离和探测精度,文中开展了基于激光雷达功率谱信号的多普勒频移估计算法以及探测性能提升的评估研究。在快速傅里叶变换的基础上,提出了一种结合线性预测频谱估计与导数增强方法的功率谱分析方法,通过与常用的最大似然离散谱峰值频移估计算法(ML DSP算法)进行比较,验证了文中方法在相干测风激光雷达微弱信号频移估计过程中的优势。风速数据的时间及空间相关性分析结果表明,功率谱分析方法具有更好的风速估计稳定性,有效风场探测距离相较ML DSP算法提升了73%。与超声风速计对比结果表明,文中提出的综合算法在弱信号情况下的风速测量精度高,风速结果与超声风速计的标准偏差相较ML DSP算法降低了0.23 m/s,偏离率BIAS降低了0.3 m/s,有效提高了低信噪比范围内多普勒频移估计的精度。

Aeolus星载测风激光雷达进展综述

大气风场是气象中十分关键的要素之一,星载多普勒测风激光雷达能够实现大范围、高精度、不间断的风场测量,对于数值天气预报精度提升、气候研究和环境保护都有重要的意义。星载测风激光雷达的研究自20世纪至今已经有近30余年,在这个过程中,Aeolus是目前唯一成功发射的星载测风卫星。文中从Aeolus计划的提出开始,回顾了Aeolus的有效载荷ALADIN原理样机的地面试验,机载原型研发和机载试验的过程;对卫星发射至今的主要数据验证活动以及结果进行了总结,阐述了Aeolus产品出现误差的原因;针对Aeolus数据产品的实际应用,总结了星载测风数据对于气象研究的重要性和必要性;结合Aeolus的方案进行优化和模拟仿真,展示了仿真的结果。最后分析了Aeolus的数据特点,结合我国星载测风研究进程和气象领域的测风需求,提出了几点可以参考的内容和需要提高的技术,同时分析了三种不同的星载测风体制,其中混合体制的星载测风激光雷达具有优势,可作为我国未来研制星载测风卫星的主要方向。