Field performance of an all-semiconductor laser coherent Doppler lidar

We implement and test what, to our knowledge, is the first deployable coherent Doppler lidar (CDL) system based on a compact, inexpensive all-semiconductor laser (SL). To demonstrate the field performance of our SL-CDL remote sensor, we compare a 36 h time series of averaged radial wind speeds measured by our instrument at an 80 m distance to those simultaneously obtained from an industry-standard sonic anemometer (SA). An excellent degree of correlation (R2=0.994 and slope=0.996) is achieved from a linear regression analysis of the CDL versus SA wind speed data. The lidar system is capable of providing high data availability, ranging from 85% to 100% even under varying outdoor (temperature and humidity) conditions during the test period. We also show the use of our SL-CDL for monitoring the dependence of aerosol backscatter on relative humidity. This work points to the feasibility of a more general class of low-cost, portable remote sensors based on all-SL emitters for applications that require demanding laser stability and coherence.     

非对称空间外差干涉仪相位探测和漂移校正

针对多普勒非对称空间外差干涉技术,提出一种目标信号相位自校正的方法.首先通过连续采样单色光的干涉图跟踪绝对相位漂移;然后分段线性拟合不同风速下的干涉相位,通过计算两条拟合曲线距离去除相位漂移.搭建风速模拟实验平台,获得采样干涉图,并对相位误差进行校正.结果表明,在60.37 m/s的模拟风速下,相位漂移误差达到30.78 m/s,通过相位校正风速反演误差降低至3.51 m/s,风速精度得到较大改善.最终通过几组不同风速下的反演值得到了平均2.97 m/s的风速测量精度.     

不同风速下侧向散射激光雷达的回波信号分析

对不同风速条件下,CCD侧向散射激光雷达的回波信号进行了分析.根据Mie散射原理及侧向散射激光雷达工作原理,确定了大气气溶胶浓度与激光雷达侧向散射光强的相关性;进一步考虑气溶胶浓度与风速的关联,利用实验装置获取了激光雷达侧向散射光强与风速的关系,分析了不同风速条件下侧向散射激光雷达的回波信号.在轴流风机以及自然风两种条件下进行对比实验发现,当风速范围在1~4.5 m/s时,侧向散射光强随风速的增加而增加;当风速范围在4.5~6.0 m/s时,光强随风速的增加较少.对实验结果归一化处理,得到风速范围在1~4.5 m/s时,风速每增加1 m/s,侧向散射光强在轴流风机及自然风的实验条件下分别增加了3.7%和3.9%;风速范围在4.5~6.0 m/s时,风速每增加1 m/s,侧向散射光强分别减少了3.1%和3.8%,在自然风况的各个风向上都基本符合这一变化趋势.     

Application of fiber interferometer in coherent Doppler lidar

A novel coherent Doppler lidar (CDL) system based on single-mode fiber (SMF) components and instruments is presented to measure the speed of target. A fiber interferometer used in CDL system is reported.This fiber mixer is employed as a coherent receiver to resolve the shifts of signal-to-noise ratio (SNR) and mixing efficiency induced by backscattered field's wavefront error. For a certain wavelength, the maximum coupling efficiency between signal and SMF is determined by the ratio of pupil diameter to focal length of the coupling lens. The legible interference patterns and spectrum signals show that fiber interferometer is suitable to compensate for amplitude and phase vibrations. This robust coherent receiver can achieve improved CDL system performance with less transmitter power.     

连续模式相干测风激光雷达性能优化分析及实验研究

基于风场探测的需求,采用1 550 nm波长连续激光种子源搭建了一套全光纤结构多普勒相干测风雷达系统。从雷达方程出发,对连续激光相干雷达载噪比方程和不同雷达收发望远镜聚焦位置下风速合成权重进行了分析。针对测风雷达要求设计了5~200 m的变焦激光收发望远镜模块。扩束系统采用伽利略折射式结构,发射光束准直下扩束比为23,光学质量接近衍射极限。标定测试通过对旋转电机圆盘转速测量完成。转盘转速范围为-3 000 r/min到+3 000 r/min,转盘直径为26 cm。在视向速度多普勒频移分别为正向和负向时,雷达系统速度测量结果与通过圆盘转速计算值的相关系数为0.998与0.993,标准差为0.151 m/s和0.229 m/s。使用该测风激光雷达开展室外大气风速探测实验,取得了良好效果。     

Estimation and interpolation of underwater low frequency ambient noise spectrum using artificial neural networks

In this work, estimation of ambient noise spectrum influenced by wind speed and wave height carried out for the frequency range of 500 Hz to 5 kHz using Feed forward Neural Network (FNN) is presented. Ocean ambient noise measurements were made in the shallow waters of Bay of Bengal using a portable data acquisition system with a high sensitivity hydrophone at a depth of 5 m from the surface.100 sets of data covering a rage of wind speeds from 2.5 m/s to 8.5 m/s with approximately 15 sets of data falling within 1 m/s over the range of wind speed were used for training the FNN. The parameter wave height which contributes to the noise producing mechanism is also used for training along with wind speed. The results revealed that the proposed method is useful in the estimation and interpolation of underwater noise spectrum level and hence in simulation for the considered frequency range. These were confirmed by calculating the Mean Squared Error (MSE) between the experimental data and the simulation. As the measurements of the underwater ambient noise level are very difficult in remote oceanic regions, where conditions are often inhospitable, these studies seem to be relevant.     

Wind measurements with incoherent Doppler lidar based on iodine filters at night and day

An incoherent Doppler wind lidar based on the iodine filter at 532 nm is presented for day and night wind measurements, which was developed by the Key Laboratory of Ocean Remote Sensing of Ministry of Education of China, Ocean University of China. The system operates with a fiber and a narrow-band interference filter to reject daylight. A photon counter is used to improve the detection range. Two iodine filters are used to lock the transmitting laser frequency and to discriminate the Doppler frequency shift, respectively. The method to retrieve the wind profile is described. The detection range of wind profiles (with a 136 m vertical resolution) extends from 100 m to 15 km at night and to 12 km during daytime. The detection range covers the troposphere in the middle and high latitude areas. The comparison experiments between the lidar and radiosonde were performed both during the night and during the day. The standard deviation of the wind direction and speed were 15.5° and 3.1 m/s at night and 15.7° and of 3.2 m/s during the day. This system also has the capability to measure the aerosol backscattering ratio. PACS 42.68.Wt; 92.60.Gn; 92.60.Mt     

Wind dependence of ambient noise in shallow water of Bay of Bengal

This work reports on investigations into the wind dependence of ambient noise in the Bay of Bengal. Ambient noise measurements were made in the shallow water of Bay of Bengal using a portable broadband, high frequency data acquisition system together with a sensitive hydrophone suspended from the measuring platform at a depth of 5 m from the surface where the ocean depth was 25 m. Periodic measurements were carried out for one year corresponding to a wind speed range between 2 m/s and 9 m/s during summer, monsoon and winter seasons. The proportionality of the noise level with wind speed for frequencies ranging from 500 Hz to 6 kHz for each season was studied. The analysis reveals that the correlation between the wind speed and the ambient noise spectrum level was higher at lower frequencies. The results of empirical fitting based on analysis were used for noise level prediction and the model predictions compare well with the measured noise level. Further it was observed that the wind generated noise level measured during summer was approximately 8 dB less than that in other seasons. On the other hand the proportionality between the noise level and the wind speed was less during winter.     

基于单Fabry-Perot标准具的双频率多普勒激光雷达数据反演技术

本文导出了大气后向散射信号光入射到Fabry-Perot (F-P)标准具的有效透过率表达式. 在基于单F-P 标准具的双频率多普勒激光雷达系统中, 采用平均值法定量分析了瑞利后向散射信号对风场测量准确度的影响. 提出了同时反演风速和后向散射比的非线性迭代方法, 并通过仿真试验验证了该方法的有效性. 同时, 导出了径向风速和后向散射比测量误差的具体表达式, 并据此进行了仿真. 仿真结果表明: 若假定望远镜接收到的总后向散射光子数为50000, 径向风速测量误差随后向散射比的增大迅速减小, 在±25 m/s的风速测量动态范围内, 当R_β > 1.2时, 误差小于3 m/s; 后向散射比测量误差随后向散射比的增大而增大, 与径向风速大小几乎无关, 当R_β<10时, 相对误差小于13%. 关键词： 多普勒激光雷达 Fabry-Perot标准具 边缘技术 双频率     

C波段机载合成孔径雷达海面风场反演新方法

针对基于散射计地球物理模型函数的机载合成孔径雷达(SAR)海面风场反演中存在的风向获取依赖于图像风条纹或数值预报、 散射计数据和浮标等背景场资料, 风向与SAR图像时空分辨率不匹配, 进而影响机载SAR海面风场反演精度等问题, 本文根据机载SAR对海探测特点, 研究一种适用于C波段机载SAR的海面风场反演新方法. 利用SAR图像距离向不同入射角的后向散射系数, 依据地球物理模型构造最小代价函数, 通过代价函数的求解直接从机载SAR数据同时反演出海面风速和风向. 利用论文提出的海面风场反演方法分别对仿真SAR数据和实测C波段机载SAR数据进行风向、 风速的反演误差分析及试验验证.研究结果表明, 该方法适用于机载SAR海面风场反演, 可不依赖背景风向直接反演出精度较高的风速和风向; 雷达后向散射系数误差是决定海面风速、风向反演精度的关键因素, 辐射定标精度越高则反演误差越小; 海面风速反演误差随着风速的提高而增大, 当海面风速大于18 m/s时, 风速反演误差显著增加, 而海面风向的反演误差与风速无明显关系. 关键词： 机载合成孔径雷达 海面风场 多入射角     

基于菲佐干涉仪与多通道光电倍增管阵列的多普勒频移检测技术

提出了基于菲佐干涉仪和多通道光电倍增管(PMT)阵列探测器组合的多普勒频移检测的方案,适用于风速测量的直接探测多普勒激光雷达。首先介绍了工作原理,再根据菲佐干涉仪光谱特征对频移检测用干涉仪进行了优化设计,优化设计的菲佐干涉仪腔长150mm、平板反射率0．755。对提出的菲佐干涉仪和多通道光电倍增管阵列探测器组合的方案进行了数值模拟,以分子散射作为背景噪声,计算了该方法的风速测量误差。模拟结果表明,设计的基于菲佐干涉仪的直接探测多普勒测风激光雷达,在30 s的积分时间内、探测高度5 km以下,风速测量误差可以达到0．56 m/s。     

基于FPGA的高速电光选通系统设计

介绍了一种获取高速调制电信号的新方法－基于FPGA的高速电光选通系统.此系统分为选通脉冲和高压调控两个模块.选通脉冲模块由高速信号放大、FPGA延时、可控延迟传输线三个部分组成.利用FPGA高密度、高可靠性、可反复擦写和可以现场编程、灵活调制的特点,将整个系统的主要控制部分集成在FPGA中,并将延时分为数字延时和模拟延时两部分.然后利用FPGA实现数字延时,可控延时线实现模拟延时.经试验检测,高压部分可以产生重复频率1 Hz~1 kHz,步进1 Hz,延时范围为0~1 μs,步进为1 ns,幅度为8 000 V,前沿和后沿小于10 ns,抖动小于1 ns的高压矩形电脉冲,从而满足各种电光调制系统中的需要.     

高度计风速与辐射计风速的变分融合研究

为实现高度计风速与辐射计风速的融合, 采用Kriging插值方法将辐射计风速插值到高度计路径得到高度计风速观测算子, 建立高度计风速与辐射计风速融合的代价函数; 利用变分方法求解分析风速, 得出融合结果. 分别在仅高度计风速有误差、 仅辐射计风速有误差和两者都有误差的情况下开展了模拟试验, 结果表明变分融合结果更接近于理想风速, 尤其在高度计路径上更为明显. 选取Jason-1高度计第241周期风速资料和与其时空匹配的国防气象卫星计划 F17上所搭载的专用传感器微波成像仪辐射计风速资料开展了实例试验, 结果表明融合后的结果更加接近于浮标观测结果, 证实了变分融合方法的有效性. 经统计, 上述高度计和辐射计资料有60%时空匹配, 开展风速融合有重要的理论及应用价值. 该变分融合方法可应用于我国海洋二号卫星所载高度计与辐射计风速反演结果的融合. 关键词： 高度计 辐射计 风速 融合     

移动式多普勒激光雷达光束扫描及风场反演技术研究

移动式多普勒激光雷达在外场实验过程中,考虑到工作平台的随机性,测量坐标系很可能不再是地面参考坐标系,这为三维矢量风场的反演带来困难。提出采用三维空间坐标旋转变换的方法建立了测量坐标系与地面参考坐标系的一般关系式,并进一步导出了反演三维风场的普遍公式。此外,在光束扫描过程中,由于二维扫描仪加工精度等的限制,光束存在一定的定向误差。采用Monte-Carlo模拟方法定量研究了光束指向偏差引起的风场测量误差,结果表明,当水平风速为100m/s时,1°的光束定向误差引起的水平风速大小误差为0.712m/s,方向误差为0.704°,与理论计算结果一致。理论分析结果还表明:当水平风速为100m/s时,1°的光束最大定向偏差引起的水平风速大小的最大偏差为1.16m/s,方向最大偏差为1°。     

一种基于光纤阵列的高速电光开关系统

提出了一种基于光纤阵列的新型电光开关,设计了高速电光选通电路.经实验测得,高压选通电路可获得电压幅度6 000 V可调,前、后沿小于30 ns,触发晃动小于1 ns,脉冲宽度为100 ns可调的高压矩形脉冲.用小口径电光晶体实现了大的通光口径、快的开关速度的惯性约束核聚变驱动系统光开关.选出了在100 ns标称开关速度内所关心的光信息,满足了惯性约束核聚变驱动系统中大的通光口径和均匀性的要求.     

LOW COHERENCE PULSED DOPPLER LIDAR WITH AMPLIFIED REFERENCE BEAM STORAGE

In this paper, we have successfully developed a new low coherence pulsed Doppler lidar concept for wind speed measurements, in which a pulsed laser is used as the source for measurement and reference beam. A fraction of the transmitted pulse is stored in a fiber optic ring resonator with a path length longer than the pulse. The output of the resonator is a pulse train that is used as the reference beam and can be mixed with the Doppler shifted measurement signal. Because this reference has traveled a distance equivalent to the measurement beam’s path length, low coherence sources can be used. Inserting an erbium-doped fiber amplifier into the resonator ensures that the stored pulses do not decay in amplitude. Careful control of gain and amplified spontaneous emission is required to prevent laser oscillation while maintaining sufficient gain for the signal. Experiments prove that 16 reference pulses of sufficient amplitude and stability can be generated. Computer simulations suggest that 70 pulses should be achievable, which would be equivalent to a Doppler lidar measurement range of 2,550 m.     

1.06 μm相干激光雷达动目标多普勒信号探测

介绍了一套1.06 μm脉冲式相干激光雷达测速演示系统.采用单块非平面环形激光器作为种子,注入到单纵模运转的Q开关高重复频率Nd∶YAG激光器为发射源,实现稳定的单频输出.通过外差式相干探测的方法,利用转速0~60 Hz可调、直径为10 cm的转盘为运动目标,回波信号被带宽为3.5 GHz的高速光电探测器响应后,经采样率为2.5 GS/s的A/D采样,输送到基于LabVIEW信号处理系统中,从而测量不同转速下的多普勒频移,各测速点的多普勒频移测量结果相对误差在3%以内.针对测量中存在的误差从激光器输出线宽和测速系统准确度两方面进行了误差分析,并提出了改进措施.演示系统的良好重复性证实了这种相干激光雷达系统的可行性.     

基于跨平台红外高光谱观测的对流层三维风场测量

精确的风场数据对提高数值天气预报准确性具有重要意义,对流层风是改进天气预报的要素之一。虽然利用气象卫星成像仪对连续云图追踪特征目标进行导风是一种有效的风场观测方法,且在区域和全球尺度上改善了数值天气预报,但仍存在风场高度分配模糊问题而产生误差。星基红外高光谱探测仪具备大气温湿度廓线垂直探测能力,通过分析各个垂直分层内的大气参数运动得到三维风场,能够提升风场垂直高度的准确性,改进风场高度分配模糊问题。提出了利用跨平台极轨气象卫星FY-3D星红外高光谱大气探测仪HIRAS和NOAA-20星跨轨红外探测仪CrIS交叉观测对流层三维风场的创新方法,根据两仪器近重叠轨道星下点交叉观测辐射数据匹配水汽通道图像,通过稠密光流法分析目标运动变化并计算风场,对风矢量进行质量控制后同ERA-Interim再分析资料作定量化比较,分析风速均值绝对偏差、均方根误差和风向均值绝对偏差。分别对2019年2月20日UTC世界时00:00,06:00,12:00的HIRAS和CrIS交叉数据计算200,300,400,600,650和1 000 hPa六组垂直高度风场,结果表明,风速范围的变化趋势与再分析资料表现一致,风速范围随高度降低而减小,高层对20 m·s-1以上风速更敏感,地表附近测得风速集中在10 m·s-1以内。风速均值绝对偏差多数小于3 m·s-1,最大不超过4 m·s-1,风速均方根误差多数小于3.5 m·s-1,最大不超过4.5 m·s-1,风向均值绝对偏差多数小于30°,最大不超过40°。风场误差主要来自仪器自身设计参数不同引入辐射数据的观测偏差,以及因数据空间分辨率不同导致在图像重投影处理过程中引入的定位偏差。     

米散射多普勒激光雷达性能改进

介绍了自行研制的米散射多普勒激光雷达的系统结构。针对系统存在的问题,对接收机子系统、工作时序、扫描方式等方面作了改造。实验结果表明:改造后系统光学鉴频器的频谱稳定性提高了2.8倍;消除了系统近距离的探测盲区;在0~2.5 km的高度范围内,当垂直距离分辨力为21.2 m、脉冲累积数为9 000发时,改造后的米散射多普勒激光雷达系统连续30 min测量的水平风速大小和方向的标准偏差的最大值分别小于1 m/s和18.3°,平均值分别小于0.43 m/s和7.7°;与探空仪的风场对比测量结果吻合得很好;当每个径向脉冲累积数为1 000发时,采用四波束扫描获得的2 km以下东西方向径向风速的相关系数为0.99,偏差为-0.038 m/s,标准偏差为1.34 m/s。     

RESEARCH ON SYSTEM IDENTIFICATION OF WALL SURFACE HEAT TRANSFER PROCESSES

A new experimental procedure is proposed based on an instrumental variable method [1] for analyzing wall surface heat transfer processes and deducing wall surface heat transfer coefficients under actual conditions. Tests were carried out under a wide range of conditions, and the heat transfer coefficient was found to vary from 8 to 26 W/m 2 ” K while wind speed ranged from 0 to 7.5 m/s, and correlations were obtained in terms of wind speed. In addition, the experiments indicated that wind direction does not have a significant effect on the heat transfer coefficient of wall surfaces.