遥测数据压缩算法的设计与实现

介绍遥测数据在数据存贮过程中的特点 ,分析对遥测数据进行压缩的必要性 ,特别地还分析了数字信号处理方法在遥测数据压缩中的应用。设计了自适应的遥测数据压缩算法。系统中使用多种压缩算法 ,包括预测编码、Huffman编码、游程编码、1- 9编码等 ,通过使用快速傅里叶变换、离散余弦变换、小波理论 ,将遥测数据信号转换到频域 ,再通过一般压缩算法进行压缩 ,在符合数据处理精度要求的前提下 ,引进有损压缩算法 ,达到最高压缩比。实践证明 ,使用多种压缩算法相结合 ,能使数据压缩率提高十多倍 ,远远高于压缩软件的压缩比。     

基于小波神经网络的双足步行机器人步态规划控制器

对于传统的神经网络中神经元模型在结构和信息存储能力上存在的不足，本文提出了一种基于广义小波其函数网络的神经元集聚模型，这种小波神经网络不仅收敛速度快，非线性逼近能力更好，而且具有内部结构变尺度、自适应调整和广义信息存储等智能化特点，更符合生物原型的实际情况。静态学习和准动态学习仿真实验证明这种神经网络结构的有效性。     

A study on possible solar and geomagnetic effects on the precipitation over northwestern Argentina

The precipitation over Tucuman (26.8°S; 65.2°W), which is representative of the Northwestern region of Argentina, is analyzed in search of an association with solar and geomagnetic activity, with the purpose of contributing to the controversial issue on the connection between climate variation and anthropogenic vs. natural forcing. Monthly time series of precipitation, sunspot number (Rz), and aa index were used for the period 1884–2010. A wavelet analysis was performed first which, due to the time series length, shows significant results only for periodicities lower than 32 years. Due to the transient character and non-constant phase of the results, any sustained wavelet coherence between precipitation and either sunspots or aa could be noticed. Moving averages and correlations were also assessed. The 11 and 22-year running mean of precipitation is positively correlated to Rz and aa when the whole period of analysis is considered. However, a shift in the long-term behavior of precipitation is noticed around 1940, which implies different correlation values with Rz and aa when the period before or after this year are considered. The solar cycle length is also considered for this statistical study and partly confirms the results obtained with Rz and aa. We propose plausible physical explanations based on geomagnetic activity and total solar irradiance effects over atmospheric circulation that could support the statistical result. A deeper analysis and broader geographical coverage is needed in order to detect a connection between precipitation and solar variability discernible from greenhouse gases effects. We emphasize the idea of the importance of recognizing and quantifying the different forcing acting on precipitation (or any other climate parameter), which sometimes can be barely evident from a solely statistical analysis.     

Accuracy analysis of GNSS-IR snow depth inversion algorithms

In recent years, with the continuous development of Global Navigation Satellite System (GNSS), it has been applied not only to navigation and positioning, but also to Earth surface environment monitoring. At present, when performing GNSS-IR (GNSS Interferometric Reflectometry) snow depth inversion, Lomb-Scargle Periodogram (LSP) spectrum analysis is mainly used to calculate the vertical height from the antenna phase center to the reflection surface. However, it has the problem of low identification of power spectrum analysis, which may lead to frequency leakage. Therefore, Fast Fourier Transform (FFT) spectrum analysis and Nonlinear Least Square Fitting (NLSF) are introduced to calculate the vertical height in this paper. The GNSS-IR snow depth inversion experiment is carried out by using the observation data of P351 station in PBO (Plate Boundary Observatory) network of the United States from 2013 to 2016. Three algorithms are used to invert the snow depth and compared with the actual snow depth provided by the station 490 in the SNOTEL network. The observations data of L1 and L2 bands are respectively used to find the optimal combination between different algorithms further to improve the accuracy of GNSS-IR snow depth inversion. For L1 band, different snow depths correspond to different optimal algorithms. When the snow depth is less than 0.8 m, the inversion accuracy of NLSF algorithm is the highest. When the snow depth is greater than 0.8 m, the inversion accuracy of FFT algorithm is higher. Therefore, according to the different snow depth, a combined algorithm of NLSF + FFT is proposed for GNSS-IR snow depth inversion. Compared with the traditional LSP algorithm, the inversion accuracy of the combined algorithm is improved by 10%. For L2 band data, the results show that the accuracy of snow depth inversion of various algorithms do not change with the variations of snow depth. Among the three single algorithms, the inversion accuracy of FFT algorithm is better than that of LSP and NLSF algorithms.     

基于拉曼散射的分布式光纤温度传感技术的研究

论述了基于拉曼散射的分布式光纤温度传感器的基本工作原理、结构、系统特点及信号处理方法。该结构及信号处理方法具有一定的空问分辨率，保证了系统的实用性。将分布式光纤传感器与传统的复用温度光纤传感器阵列进行了比较。通过使用分布式光纤温度传感器信号处理系统和信号处理软件相结合进行实验，得出结论。     

基于CCD的单缝衍射条纹光强测量与小波去噪技术研究

通过CCD的数据采集对单缝衍射条纹的光强进行测量试验,简要分析了试验中的噪声来源.提出使用小波技术对CCD的采集信号进行噪声滤除,详细讨论了小波的分解与重构以及在去除噪声中的应用.试验结果表明,小波技术能完全滤除噪声.     

Prediction of pilot workload in helicopter landing after one engine failure

This paper presents a method to predict the pilot workload in helicopter landing after one engine failure. The landing procedure is simulated numerically via applying nonlinear optimal control method in the form of performance index, path constraints and boundary conditions based on an augmented six-degree-of-freedom rigid-body flight dynamics model, solved by collocation and numerical optimization method. UH-60A helicopter is taken as the sample for the demonstration of landing after one engine failure. The numerical simulation was conducted to find the trajectory of helicopter and the controls from pilot for landing after one engine failure with different performance index considering the factor of pilot workload. The reasonable performance index and corresponding landing trajectory and controls are obtained by making a comparison with those from the flight test data. Furthermore, the pilot workload is evaluated based on wavelet transform analysis of the pilot control activities. The workloads of pilot control activities for collective control, longitudinal and lateral cyclic controls and pedal control during the helicopter landing after one engine failure are examined and compared with those of flight test. The results show that when the performance index considers the factor of pilot workload properly, the characteristics of amplitudes and constituent frequencies of pilot control inputs in the optimal solution are consistent with those of the pilot control inputs in the flight test. Therefore, the proposed method provides a tool of predicting the pilot workload in helicopter landing after one engine failure.     

基于最小熵准则的频偏估计算法研究

提出了一种基于SEM(Spectrum Entropy Minimization,频谱熵最小化)的频偏估计算法。研究发现,频偏越小,离散信号频谱的熵越小。根据这一性质建立了相关算法,通过一维搜索的方式得到使相位补偿后信号频谱熵最小的频偏估计。仿真结果表明:SEM算法的估计性能能够达到CR(Cramer-Rao,克拉美罗)下界,而且估计的稳定性和鲁棒性较好,具有一定的应用价值。     

一种基于小波变换的伪码跟踪环路多径抑制方法

多径效应是GPS等卫星导航系统的重要误差源之一,严重影响导航系统的性能。针对多径效应,在分析了多径信号模型和伪码自相关函数特征的基础上,提出了一种基于小波变换的多径抑制方法。该方法利用自相关函数曲线斜率突变点位置不受多径信号影响的特性,通过小波变换检测其斜率突变点位置,进而利用得到的鉴相误差调整码相位,达到多径抑制的目的。仿真结果表明,该方法不受多径条数的影响,鉴相结果更准确,多径抑制能力得到显著提高。
     

Near 13.5-day periodicity in Muon Detector data during late 2001 and early 2002

In this study we perform a continuous Morlet wavelet transform method in time series of secondary cosmic rays and 1 AU interplanetary medium parameters for the interval from October 2001 to October 2002. The near 13.5-day periodicity was obtained during late 2001, and it was remarkable for muon data. Even though some works have pointed out that the main activations of the 13.5 day recurrence in near-Earth solar wind are related, e.g., with the heliosheet crossings or to the occurrence at 1 AU of two high speed streams approximately 180° apart in solar longitude per solar rotation, we aim to show that the period of about half the solar rotation during the end months of 2001 present in muon time series was apparently due to the occurrence of non-recurrent interplanetary disturbances. The interconnections among successive Forbush decreases, recovery phases and gradual muon depressions (associated with corotating interaction regions) seem to play an important role in such 13.5-day periodicity.