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.

Comparison and Verification of Coherent Doppler Wind Lidar and Radiosonde Data in the Beijing Urban Area

As a new type of wind field detection equipment, coherent Doppler wind lidar(CDWL) still needs more relevant observation experiments to compare and verify whether it can achieve the accuracy and precision of traditional observation equipment in urban areas. In this experiment, a self-developed CDWL provided four months of observations in the southern Beijing area. After the data acquisition time and height match, the wind profile data obtained based on a Doppler beam swinging(DBS) five-beam inversion algorithm were compared with radiosonde data released from the same location. The standard deviation(SD) of wind speed is 0.8 m s^(–1), and the coefficient of determination R~2 is 0.95. The SD of the wind direction is 17.7° with an R~2 of 0.96. Below the height of the roughness sublayer(about 400 m), the error in wind speed and wind direction is significantly greater than the error above the height of the boundary layer(about 1500 m). For the case of wind speeds less than 4 m s^(–1), the error of wind direction is more significant and is affected by the distribution of surrounding buildings. Averaging at different height levels using suitable time windows can effectively reduce the effects of turbulence and thus reduce the error caused by the different measurement methods of the two devices.

Observation of nocturnal low-level wind shear and particulate matter in urban Beijing using a Doppler wind lidar

A field experiment of nocturnal mountain wind and corresponding particulate matter （PM） evolution under weak synoptic forcing at five sites within urban Beijing was conducted using a moving Doppler wind lidar and a fixed tower. Clear wind shear and zero-horizontal-wind zones at 40-320 m above the ground with a delay of 1.5 h were found at two sites between 20 km from north to south urban Beijing. The wind speed and height of the low-level jet at the north urban Beijing site were greater than those at the east urban Beijing site. The average horizontal distribution of low-level PM at 240 m was similar to the ground-level PM at night. The PM2.s （aerodynamic diameter ≤2.5 μm） accumulation center showed no abrupt changes with a shift in wind direction until the northerly wind jet arrived.

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.

Development and Potential of Space-Borne Doppler Wind Lidar

The advantage of lidar over other wind sensors is presented in this paper. With more than 20 years research, the development of the space-borne wind lidar is reviewed. Longer-term investigation has made many technologies suitable for the wind lidar measurement from an orbital platform become mature. However, there are still some problems to be solved. In order to obtain the optimal performance in wind detection, great importance is being attached to the simulation of a virtual space-borne wind lidar system on computer as developed by NASA and ESA.

基于LiDAR与可见光融合的自动风电叶片巡检方法

传统风机叶片使用人工吊篮、望远镜、手动操控无人机的方式进行巡检,存在巡检难度大、巡检效率低、拍摄数据规范性差等问题。为此,提出了一种在无人机平台上基于LiDAR与可见光融合的风机叶片自动化巡检的方法。通过融合可见光相机、激光雷达采集的多源数据自动规划风机状态的智能感知和无人机航线,可实现拍摄风机叶片的不同部位(前缘、后缘、迎风面、背风面)并选择最佳角度、最佳距离,在保证巡检安全的前提下极大地提升了叶片巡检的质量,同时降低了风机巡检人员的作业难度,提升了风机叶片的巡检效率。

Rlationship between the aerosol scattering ratio and temperature of atmosphere and the sensitivity of a Doppler wind lidar with iodine filter

The sensitivity of Doppler wind lidar is an important parameter which affects the performance of Doppler wind lidar. Aerosol scattering ratio, atmospheric temperature, and wind speed obviously affect the measurement of Doppler wind lidar with iodine filter. We discuss about the relationship between the measurement sensitivity and the above atmospheric parameters. The numerical relationship between them is given through the theoretical simulation and calculation.

Observation of Wind Shear during Evening Transition and an Estimation of Submicron Aerosol Concentrations in Beijing Using a Doppler Wind Lidar

The wind speed and direction measured over six months by a Doppler wind lidar（Windcube-8）were compared with wind cup anemometers mounted on the 325-m Beijing meteorological tower（BMT）.Five mountain–plain wind cases characterized by wind direction shear were selected based on the high-frequency（1.1 s）wind profile of the Windcube-8 and analyzed with 1-h mesoscale surface weather charts.Also analyzed was the relationship between insitu PM_1（aerodynamic diameter≤1μm）concentrations measured at 260 m on BMT and the carrier-to-noise ratio（CNR）of the co-located Windcube-8.The results showed that the 10-min averaged wind speed and direction were highly correlated（R=0.96–0.99）at three matched levels（80,140,and 200 m）.The evening transition duration was1–3 h,with an average wind speed of 1 m s^（–1） at 80 m above the ground.In addition,there was a zero horizontalwind-speed zone along the wind direction shear line,and in one case,the wind speed was characterized by a Kelvin–Helmholtz gravity wave.The variability of the PM_1 concentrations was captured by the CNR of the Windcube-8 in a fair weather period without the long-range transport of dust.

A mobile incoherent Mie-Rayleigh Doppler wind lidar with a single frequency and tunable operation of an injection Nd︰YAG laser

A mobile incoherent Doppler lidar system has been experimentally demonstrated to be able to transmit reliable single frequency operation laser pulse, even after truck transit and in very high vibration environments. The linewidth of the injection-seeded pulse Nd:YAG laser can be measured by means of an I2 molecular filter. And, lidar validation experiments demonstrated the feasibility and capability of measuring wind field by the Mie-Rayleigh Doppler wind lidar. The un-certainty of measured wind speed is 0.985m/s in the altitude range from 2 to 4 km.

Wind vector retrieval algorithm from spaceborne lidar data

The principal purpose of this paper is to extract entire sea surface wind＇s information from spaceborne lidar, and particularly to utilize a appropriate algorithm for removing the interference information due to white caps and subsurface water. Wind speeds are obtained through empirical relationship with sea surface mean square slopes. Wind directions are derived from relationship between wind speeds and wind directions im plied in CMOD5n geophysical models function （GMF）. Whitecaps backscattering signals were distinguished with the help of lidar depolarization ratio measurements and rectified by whitecaps coverage equation. Subsurface water backscattering signals were corrected by means of inverse distance weighted （IDW） from neighborhood non-singular data with optimal subsurface water backscattering calibration parameters. To verify the algorithm reliably, it selected NDBC＇s TAO buoy-laying area as survey region in camparison with buoys＇ wind field data and METOP satellite ASCAT of 25 km single orbit wind field data after temporal-spa tial matching. Validation results showed that the retrieval algorithm works well in terms of root mean square error （RMSE） less than 2m/s and wind direction＇s RMSE less than 21 degree.

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.

Wind Motions around the Tropical Cirrus Using Simultaneous Radar and Lidar Observations over Gadanki (13.45°N, 79.18°E), India

The present study describes variation of peak linear depolarization ratio (LDR) with wind around the cloud altitude using simultaneous observation of winds and cirrus cloud for the first time using Indian MST radar and polarization lidar co-located over a low latitude station Gadanki (13.7°N and 79.2°E). Three different cases of passage of the cirrus at different altitudes are noticed, one during a North-East monsoon day and other two during South-West monsoon days. The zonal wind below the cloud height has shown similar variation with LDR during 02 November 2006 and the meridional wind within the cloud height during 25 July 2007 and 08 June 2006 has shown opposite variation with LDR. Even though there is a significant increase in zonal wind due to the existence of tropical easterly jet (TEJ) above cloud height during 25 July 2007 and 08 June 2006, also, the vertical wind is found to be continuously varying during 25 July 2007 and it is upward dominant in the initial stage and is mostly downward in the later stage of observation on 08 June 2006, there is a slight descent in cloud altitude only during 25 July 2007. Thus, the wind above the cloud height alone may not affect the ascent/descent of the cloud top altitude. The potential temperature gradient is high within the cloud heights when the cirrus present near the cold point tropopause indicates the maximum air-mass mixing near the tropopause.

中国典型复杂地形风能资源特性及其形成机制

为提高对复杂地形风资源特性及其形成机制的认识,改进复杂地形风场数值模拟方法,分别选取代表极大起伏山地与宽谷地形的藏南谷地、代表极大起伏山地与深谷地形的横断山区以及代表中、小起伏丘陵山地的山西高原开展风资源特性观测实验,分析不同典型复杂地形条件下天气背景风场、局地大气环流、地形动力强迫、地表摩擦与热力作用对风资源特性形成的贡献,结果表明:山西高原局地大气环流的作用较小;藏南谷地和横断山区的山谷风环流对其风能资源特性的形成起主要作用,尤其是横断山区还存在多尺度的局地大气环流,传统的风电场风资源CFD数值模拟不足以描述如此复杂的风场。因此,在局地大气环流作用明显的复杂地形地区,需要采用中尺度与CFD结合的风电场选址风资源数值模拟方法。

基于雷达探测数据的尾涡危险区评估

针对尾涡危险区域的研究可以有效避免后机尾涡危险遭遇事件的发生,提出了一种基于激光雷达探测数据的尾涡危险区计算方法。根据雷达实测数据反演飞机尾涡的演化轨迹和速度环量;基于后机遭遇前机尾涡的空气动力学响应构建滚转力矩系数模型;考虑尾涡在实际场景下的演化情况,结合反演得到的尾涡特征参数,计算飞机遭遇尾涡时的滚转力矩并计算尾涡危险区。结果表明:基于激光雷达探测数据反演尾涡特征参数,左涡和右涡的位置、环量并不一致,据此结合滚转力矩系数模型计算得到的整体危险区域也具有不对称性,当单涡更稳定时,对应的危险区域也更大。以B738为后机,选取某一尾涡探测片段验证,对于涡心坐标位置为左涡(390 m,8.61°),右涡(435 m,8.85°)的尾涡,左涡、右涡的环量分别为256.83 m^(2)/s和223.35 m^(2)/s,左涡相对右涡实际划设的危险区覆盖范围更大,因此后机与前机左右尾涡的安全阈值区域不同,可据此对横向间隔做出不同调整,因此所提方法有利于为分析后机遭遇安全性、缩短尾流间隔提出重要参考。

利用双通道激光雷达验证低信噪比反演算法

针对相干测风激光雷达(LiDAR)在低信噪比(SNR)下反演算法的可靠性和精度难以验证的问题,搭建了一种双通道的脉冲相干测风LiDAR系统,可以同时获取高、低SNR的2组数据,并使用高SNR通道的结果作为真值,比较利用不同的算法在低SNR通道进行矢量风速估计的结果。该系统避免了使用其他观测设备作为真值时难以配准或观测目标不统一的问题。本文研究利用雷达获取的观测结果验证了各个算法的有效性,并在各个算法间进行了横向对比。最终,依据各个算法的性能表现和计算复杂度,指明了各个算法具有优势的使用场景。该结果对于充分利用现有系统、使用新算法提高低SNR下的数据获取效率,或在指定探测指标的前提下降低激光能量等硬件要求、实现系统小型化有一定意义。

新型多普勒测风激光雷达Windcube的风参数观测与验证

2007年12月11～14日,中国科学院大气物理研究所与法国Leosphere公司在该研究所位于北京市北三环和北四环之间的325m气象塔试验场内联合开展了一次测风激光雷达Windcube的外场演示试验。Wind-cube观测数据随后与325m气象塔上的风杯风速仪测得的风速资料进行了对比,结果是:由两种手段获得的所有6层匹配高度(63m、80m、100m、120m、160m和200m)上的10min风速平均值一致性很好,相关系数都达到或超过0.98。使用矢量法对6层高度上的风向资料进行平均,得到风向的10min平均值,两者的相关系数均达到0.99。与国产测量低层大气风廓线的高精度多普勒激光雷达相比,Windcube的风速测量精度稍优,风向表现相当。验证结果表明,该型多普勒测风激光雷达是一款观测结果可靠、机动性能良好的低层大气风廓线测量仪器。

大气稳定度对边界层垂直风切变的影响

大气边界层垂直风切变是高层建筑、航空和风能利用等领域影响安全的重要因素,对大气垂直分布的研究具有重要实际价值。选用位于河北张家口地区的激光雷达测试场地的140 m测风塔数据,通过测风塔和激光雷达的同期外场测量,验证激光雷达与测风塔对垂直风切变的测量精度,研究大气稳定度对于垂直风切变的影响。结果表明:1)大气稳定度对风切变影响显著,风速切变、风向切变与大气稳定度的相关系数分别为0.48和0.54;2)风速切变随位温梯度的增加而增加,当位温梯度达到0.08 K·m^(-1)后,风速切变保持在0.35~0.40;3)位温梯度大于0时,风向随高度增加顺时偏转;位温梯度小于0时,风向随高度增加逆时针偏转;中性大气风向的垂直分布较为一致。通过测风塔和激光雷达的垂直观测建立了风速切变、风向切变与大气稳定度的关系模型,对风场垂直分布相关的研究与应用具有较好的参考价值。

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。