星载激光雷达探测海面风速昼夜差异研究

采用夜间数据反演海面风速已经取得较好的研究成果。由于受到太阳直射光和天空背景辐射等因素的影响,星载激光雷达信号在白天的信噪比较差。基于已有的反演关系模型,采用CALIPSO星载激光雷达532 nm通道2007年1月、4月、7月和10月的单脉冲昼夜数据,将AOD数据用来做大气双程透过率校正,以准同步的AMSR-E v7版本的海面风速为真值,进行反演海面风速的昼夜对比研究。研究结果表明,采用白天数据反演海面风速是可行的。通过采用恰当的关系模型来反演白天风速可以提高探测精度。     

Ka-band scintillations: measurements and model predictions

New propagation data from a 30/20-GHz propagation experiment at several US sites, including Fairbanks, AK, and Norman, OK, are presented to examine existing models for scintillations. Beacon measurements were collected at one sample per second continuously and at 20 samples per second for selected intervals. The widely separated measurement frequencies and the wide range of measurement elevation angles of about 8-52° provide a solid set of measurements to test existing models and formulate new ones. It is found that current scintillation prediction models overestimate the magnitude of scintillation. The Karasawa model was modified to fit the Fairbanks data, with this modification valid for the climate zone containing Fairbanks. The model of the radiocommunication sector of the International Telecommunication Union was examined for several sites, and an elevation angle modification was attempted to bring it into agreement with the data sets. Measurements indicate a frequency dependence of f^7/12     

Comparison of WindSat brightness temperatures with two-scale model predictions

Predictions of the polarized microwave brightness temperatures over the ocean are made using a two-scale surface bidirectional reflectance model combined with an atmospheric radiative transfer model. The reflected atmospheric radiation is found to contribute significantly to the magnitude and directional dependence of the brightness temperatures. The predicted brightness temperatures are also sensitive to the form of the shortwave spectrum. Calculations are made using a new physically based model for the wave spectrum, and preliminary comparisons are made with WindSat observations at 10.7, 18.7, and 37 GHz, for wind speeds ranging from 0-20 m/s and for vertically integrated atmospheric water vapor concentrations from 0-70 mm. Predictions of the mean (azimuthally averaged) brightness temperatures for vertical and horizontal polarization agree quite well with WindSat observations over this range of wind speeds and water vapor concentrations. The predicted azimuthal variations of the third and fourth Stokes parameters also agree fairly well with the observations, except for the fourth Stokes parameter at 37 GHz. Further adjustments of the wave spectrum are expected to improve the agreement.     

Retrieving ocean surface wind speed from the TRMM Precipitation Radar measurements

Spaceborne scatterometery has been used for many years now to retrieve the ocean surface wind field from normalized radar cross-section measurements of the ocean surface. Though designed specifically for the measurement of precipitation profiles in the atmosphere, the Precipitation Radar (PR) of the Tropical Rainfall Measuring Mission (TRMM) also acquires surface backscattering measurements of the global oceans. As such, this instrument provides an interesting opportunity to explore the benefits and pitfalls of alternative radar configurations in the satellite remote sensing of ocean winds. In this paper, a technique was developed for retrieving ocean surface winds using surface backscattering measurements from the TRMM PR. The wind retrieval algorithm developed for TRMM PR makes use of a maximum-likelihood estimation technique to compensate for the low backscattering associated with the PR configuration. The high vertical resolution of the PR serves to filter-out rain-contaminated cells normally integrated into Ku-band scatterometer measurements. The algorithm was validated through comparisons of ocean surface wind speeds derived from PR with remotely measured winds from TMI and QuikSCAT, as well as in situ observations from oceanographic buoys, revealing good agreements in wind speed estimations.     

ERS-1 scatterometer measurements. I. The relationship between radarcross section and buoy wind in two oceanic regions

Extensive European Remote Sensing Satellite (ERS-1) spacecraft scatterometer measurements were collocated within ±25 km of buoy measurements at midlatitudes and in the equatorial Pacific during 1992-1994. Two different directional functional forms for the geophysical model were fit to these measurements described by cross section maxima aligned and offset, with respect to the mean wind direction. The two models exhibit fits with similar residuals for each of three years in the equatorial region. Thus, neither of these two model functions can convincingly be identified as more accurate than the other unless additional factors are considered. Nevertheless, the offset model results in an average directional offset near 10° for each season during the three-year period; whereas, no such offset was inferred at midlatitudes. The cross section dependence on wind direction also exhibits another unexpected average property: a larger downwind compared to upwind cross section, A₁₀≈-0.25 dB in the equatorial Pacific. This characteristic could be caused by a concentration of the short Bragg waves on the backside of the long wave crests. Both of these unexpected characteristics are likely related to a dominant systematic swell traveling nearly perpendicular to the prevailing easterly winds across the equatorial Pacific Ocean. The possible cross section dependence on wind stress and wind speed is due to long waves when adjusting the buoy measurements to a common height are discussed     

Comparison of a diffraction based radiowave propagation model with measurements

A comparison between a theoretical diffraction based radio propagation model and measured path loss data for flat terrain in New Zealand in terms of variation in path length, frequency and environment is described. Results of measured town planning data for the model are also given.<>     

基于星载激光雷达的AOD与海面风速关系研究

海面上空气溶胶的产生和传输在一定程度上和风有关,研究气溶胶和风速间的关系,对增加大气模式的预测精度有重要意义。文中使用CALIPSO卫星CALIOP激光雷达L2（V3.01）气溶胶层与云层数据,与准同步AQUA卫星的AMSR-E海面风速数据,采用2007年和2008年的1月、4月、7月、10月共8个月的观测数据,研究波长为532 nm的气溶胶光学厚度（AOD）与海面风速间的关系及其随季节、年份的变化。结果显示,无云条件下,全球海洋上空AOD与风速存在关系：当风速在0-12 m/s时,AOD随风速增大而增加,当风速在4-12 m/s时,AOD与风速近似线性关系,当风速>14 m/s时,AOD趋于平稳。     

Ocean surface wind speed measurements of the Special SensorMicrowave/Imager (SSM/I)

An operational wind speed algorithm was developed. This algorithm is based on the D-matrix approach, which seeks a linear relationship between measured SSM/I brightness temperatures and environmental parameters. D-matrix performance in the low-to-medium wind speed range was validated by comparing algorithm-derived wind speeds with near-simultaneous and colocated measurements made by the anemometers of offshore ocean buoys. Results indicate that for approximately 85% of the time, the D-matrix-retrieved winds will have an accuracy better than the Defense Meteorological Space Program goal of ±2 m/s. For the remaining 15% of the time, the scene will be rain-flagged and retrieval accuracies will be worse than ±2 m/s     

Comparison of GTD propagation model wide-band path loss simulationwith measurements

The geometrical theory of diffraction (GTD) wedge diffraction has been used successfully in the GTD propagation model to predict narrowband continuous-wave (CW) radiowave propagation characteristics. The GTD propagation model uses a two-dimensional terrain profile approximated as piecewise-linear and computes reflection and diffraction effects with model output representing a complex approximation to the narrowband channel transfer function. Using the narrowband GTD model as a starting point, a wideband terrain-sensitive model has been developed which is capable of predicting wide-bandwidth propagation characteristics. The complex wideband channel transfer function calculated by the GTD model is transformed to the time domain by a fast Fourier transform (FFT). The results are then used to predict time-domain radio transmission loss in the form of a bandlimited approximation to the channel impulse response. Important channel parameters such as delay spread, and wideband received signal level can then be calculated. The GTD predicted results are put in a suitable format and compared with measurements obtained by SRI International     

Building corner diffraction measurements and predictions using UTD

Measurements of the electric field in the vicinity of the corner of a stone building are presented. The experimental results are compared to theoretical predictions using the uniform theory of diffraction (UTD) for dielectric wedges and simple specular ground reflections. The comparison of the two results show close agreement indicating that UTD is a viable approach for predicting the diffracted field around building corners in applications such as propagation modeling for communications systems operating in urban environments     

Model-based estimation of wind fields over the ocean from windscatterometer measurements. I. Development of the wind field model

For pt.II see ibid., vol.28, no.3, p.361-373 (1990). A parametric model for near-surface mesoscale wind fields suitable for use in a model-based approach to estimate the wind field over a large region of the scatterometer measurement swath from measurements of the radar backscatter of the ocean's surface is discussed. The assumptions made in developing the model are described, and the accuracy of the resulting model is evaluated. The model is based only on scatterometer data and is computationally tractable, consisting of a linear equation relating the near-surface wind field to a vector of model parameters which is estimated from the scatterometer measurements. Tradeoffs in the accuracy of the model and the number of unknown parameters are considered     

小型风机最大功率点快速跟踪策略的仿真研究

风力发电系统的输出功率受外界因数和风速的影响。为了提高小型风机发电机组的转换效率,文中采用一种最大功率优化跟踪算法。以变步长来跟踪风速变化,当功率变化小于一个阈值时停止搜索,来实现最大功率收索的快速性和稳定性。以带齿轮箱6 kW的鼠笼异步式风力发电并网为基础,通过Matlab/Simulink软件仿真结果证实此种方法与定步长爬山法相比,能够达到快速跟踪最大功率点和避免达到最大功率点附近的时候频繁波动。     

A novel FBG velocimeter with wind speed and temperature synchronous measurement

Based on frequency demodulation method, a novel fiber Bragg grating (FBG) velocimeter which can achieve wind speed and temperature synchronous measurement is proposed in this paper. The wind speed and temperature synchronous measurement is realized by cup anemometer (CA) signal modulation and Hilbert-Huang transformation (HHT) signal processing. The working principle of the novel FBG velocimeter is demonstrated and its theory calculation model is also set up by using basic mechanical knowledge and blade element momentum (BEM). Further, calibration experiment is carried out on one prototype of the FBG velocimeter to obtain its measurement performance. HHT is introduced to deal with calibration experiment data. After data analyses, the results show that the novel FBG velocimter can achieve high-precision wind speed measurement of 0.012 m/s with minimum detection limit of 0.41 m/s, and its temperature detection precision is 10.6 pm/°C.     

多普勒测风激光雷达与 L 波段探空对比分析

利用北京国家基本气象站内多普勒测风激光雷达和 L 波段探空系统在 2020 年 1 月 1 日至 5 月 31 日期间进 行了同步观测试验, 在经过观测数据时间和空间匹配的基础上, 以后者测风数据为参照标准, 从探测风廓线的高度、 风向和风速三个方面的一致性分析了激光雷达的测风数据质量。结果显示: 在观测试验期间, 激光雷达 56.5% 的观测 时间里最大探测高度不低于 2000 m, 2.9% 的观测时间最大探测高度不足 1000 m; 激光雷达探测获取的水平风向、风 速与 L 波段探空系统具有较好的一致性, 针对匹配得到的 8491 组对比观测数据, 其风向和风速数据拟合总相关系数 分别为 0.965 和 0.986; 总体风向、风速的平均偏差和均方根误差分别为 −1.3◦ 和 16.1◦、0.21 m·s −1 和 1.06 m·s −1 ; 在 2000 m 以上高度, 由于激光雷达观测数据的信噪比偏弱, 获得可信的观测数据量减少, 会对风向、风速一致性比对造 成不利影响。     

Comparison of modeled backscatter from slightly rough curvedsurfaces with numerical predictions

The slightly rough facet model has often been used to describe radar scattering from two-scale rough surfaces. Moment method scattering calculations are used to investigate the validity of a theoretical method for determining the maximum allowable facet sizes. The method is shown to give accurate facet sizes for rough surfaces with large-scale curvatures comparable to that expected on the ocean surface at angles of incidence where the traditional two-scale scattering model has proved to be valid     

基于混合特征提取的判决预测模型

法律判决预测指的是在给定案情描述的情况下,对案件的罪名和刑期进行预测.当前罪名预测主要使用深度神经网络模型,刑期预测主要使用混合深度神经网络模型.现有研究只关注局部特征或全局特征,没有考虑到将二者结合.因此本文使用双向门控循环单元提取上下文特征,并结合注意力机制学习文本中词的重要性,使用胶囊网络克服卷积神经网络丢失空间信息的缺点,学习文本局部与全局之间的关系特征.同时由于刑期分类时分类粒度较大,导致辅助决策结果不够理想.为实现更加理想的分类效果,将刑期按年进行更加细粒度的分类,分为28类.实验结果表明,该混合模型比基线模型效果更好,在罪名预测和28类刑期预测准确率分别为98.88％和74.32％.     

基于有理函数模型的GNSS-R岸基海面风速反演算法

岸基条件下,海浪不能充分生长,海浪谱的理论模型不足以完全描述相关时间和风速的关系,已有研究一般使用幂函数形式的经验模型反演海面风速。文中提出一种新的有理函数形式的经验模型,取代传统幂函数形式的经验模型进行海面风速的反演。试验数据分析表明,新的有理函数形式的经验模型反演得到的风速与实际风速的相关系数为0.986 2,均方根误差为0.45 m/s,与传统的幂函数形式的经验模型反演结果相比,其相关系数提高了0.80%,均方根误差降低了20.19%。     

风力发电机转速控制系统的建模与仿真

针对风力发电机非线性、随机性、扰动大等特点,设计基于带动量项的粒子群优化的支持向量机的风力发电机转速控制建模的新方法。利用支持向量机对小样本、高维度、非线性特性的映射能力,将风电系统的采样数据映射到高维的特征空间进行建模。支持向量机惩罚因子C和核参数σ的选择对建模效果影响较大,经验试凑的方法难以获得较好的参数,引入粒子群算法进行参数寻优。为了克服传统粒子群算法易陷入局部最优且收敛速度慢的缺陷,提出带动量项的改进粒子群算法寻优。以采集的风速、风力发电机转矩、桨距角作为输入信号,发电机转速数据作为输出信号,在Matlab环境中进行建模。实验结果表明,与传统算法相比,采用该方法的模型在准确性和收敛速度方面得到较大改善。     

Comparison of software-reliability-growth predictions: neuralnetworks vs parametric-recalibration

This paper compares empirically the predictive performance of two different methods of software reliability prediction: `neural networks' and `recalibration for parametric models'. Both methods were claimed to predict as good or better than the conventional parametric models that have been used-with limited results so far. Each method applied its own predictability measure, impeding a direct comparison. To be able to compare, this study uses a common predictability measure and common data-sets. This study reveals that neural networks are not only much simpler to use than the recalibration method, but that they are equal or better trend (variable term) predictors. The neural network prediction is further improved by preparing the data with a running average, instead of the traditionally used averages of grouped data points. Neural network predictions do not depend on prior known models. Off-the-shelf neural network software tools make it easy to apply the method     

Far-field predictions from near-field measurements using an exactintegral equation solution

This paper presents a new approach to derive far-field data needed in antenna and EMI/EMC testing from near-field measurements. An exact integral equation solution to the wave propagation problem is used to transform the near-field data to the far field. The method requires near-field measurements on two closed surfaces enclosing all sources and inhomogeneities. The approach is validated with numerical simulation of measurements of fields radiated from a known antenna