An Approximation for the Doppler Broadening Function and Interference Term Using Fourier Series

The calculation of the Doppler broadening function and of the interference term are important in the generation of nuclear data. In a recent paper, Goncalves and Martinez proposed an analytical approximation for the calculation of both functions based in sine and cosine Fourier transforms. This paper presents new approximations for these functions, and , using expansions in Fourier series, generating expressions that are simple, fast and precise. Numerical tests applied to the calculation of scattering average cross section provided satisfactory accu- racy.

Dependence of interferogram phase on incident wavenumber and phase stability of Doppler asymmetric spatial heterodyne spectroscopy

Instrument drifts introduce additional phase errors into atmospheric wind measurement of Doppler asymmetric spatial heterodyne spectroscopy (DASH). Aiming at the phase sensitivity of DASH to instrument drifts, in this paper we calculate the optical path difference (OPD) and present an accurate formula of DASH interferogram. By controlling variables in computational ray-tracing simulations and laboratory experiments, it is indicated that initial phase is directly determined by incident wavenumber, OPD offset and field of view (FOV). Accordingly, it is indicated that retrieved phase of DASH is sensitive to slight structural change caused by instrument drift, which provides the proof of necessary-to-track and -correct phase errors from instrument drifts.

The Downlink Adjacent Interference for Low Earth Orbiting (LEO) Search and Rescue Satellites

NOAA (National Oceanic and Atmospheric Administration) - LEO environmental satellites provide continuous coverage of Earth, supplying high-resolution global meteorological, oceanic and space observation data. In addition, these satellites are part of the international COSPAS – SARSAT program, which aides search and rescue teams worldwide. The USA segment, referred to as SARSAT (Search and Rescue Satellite Aided Tracking) system, is designed to provide distress alert and location data to assist on search and rescue operations. SARSAT locates distress beacons (406MHz) activated at distress locations. The system calculates a location of the distress event using Doppler processing techniques. Processed data is continuously retransmitted through the SARSAT downlink to Local User Terminals (LUT) when satellites are in view. The downlink adjacent interference is expected when two satellites operate in close proximity and share the same frequency. The downlinks of all SARSAT LEO satellites use the same 1544.5 MHz frequency. In cases where the satellites are within the main lobe of the local user terminal antenna, transmissions from adjacent satellites act as interference to one-another, effectively decreasing the signal-to-noise ratio of the desired downlink. This can result in missed distress beacon bursts or no stored solutions received at the LUT, consequently no data is provided about a distress location. Analysis on interference prediction, impacts on system operation and recommendations for mitigating interference periods where the duration may be significant, are presented in this paper.

INTERFERENCE CANCELLATION FOR MOBILE DISPERSIVE CHANNELS

A robust interference canceller for Multi-Carrier Code Division Multiple Access(MC-CDMA) using Orthogonal Frequency Division Multiplexing (OFDM) in Rayleigh fading isproposed. This interference canceller is robust in the sense that it cancels Inter-Carriers Inter-ference (ICI) and is suitable for use in dispersive channels. To come up the effects of the signaldispersion, Doppler shifts and delay spreads on the performance of MC-CDMA systems over mo-bile fading channels, this interference canceller exploits the merit of the orthogonal signaling andpilot signals to evaluate the channel parameters. This interface canceller is well suited to work initerative turbo interference cancellation.

DS/FH信号跟踪的频率相位修正技术

直序/跳频(direct sequence/frequency hopping,DS/FH)扩频信号的跟踪受到多普勒效应和电离层效应的严重影响,使其难以应用于卫星导航的抗干扰领域。为了解决该问题,提出将递归最小二乘滤波修正的方法应用在DS/FH信号跟踪上。将处于不同通道中心频率的多普勒频率估计转化到DS/FH信号的整体中心频率进行并滤波,在频率捷变时对载波数控振荡器进行修正。根据对频率跳变前后载波相位和码相位突变的观察,实时估计电离层的电子密度,在频率捷变时修正载波相位和码相位。仿真实验证明,所提方法能够有效地消除DS/FH信号跟踪中的频率相位不连续问题,其跟踪精度与直序扩频信号度基本是相同量级。

高频雷达中射频干扰的RD图表现机理与建模仿真

射频干扰对于高频超视距雷达是一大威胁。本文研究射频干扰的距离-多普勒图表现机理和建模方法,分析了射频干扰频域特性与距离-多普勒图表现的关系,讨论了雷达信号处理中的射频干扰信号频谱变化。根据高斯白噪声通过线性滤波器的特性,设计滤波器响应函数来产生不同频谱和距离-多普勒图形态的射频干扰。基于以上研究,本文将射频干扰分为单频、窄带和宽带3类,归纳出射频干扰的距离-多普勒图表现机理,并提出了基于卷积的射频干扰新型建模方法。实测数据和仿真表明:本文对射频干扰距离-多普勒图表现机理分析合理,建模方法能很好地模拟多数实测干扰距离-多普勒图形态。

基于地基雷达的月球成像综述

基于地基雷达的月球成像有利于研究地月系统及太阳系演化等科学问题,可以为登陆任务中的着陆区选址提供有力的科学依据,也有助于验证用于深空探测的地基雷达设备的可行性。地基雷达具有穿透性强、全天候、全天时和低成本等优势,国内外已开展一系列基于地基雷达对月球成像的工作,成像方法主要包括时延多普勒方法及干涉成像方法。在不同阶段,采用不同的地基雷达设备和参数,获得了一系列不同分辨率的月球正面图。梳理了国内外地基雷达设备及其参数、成像方法及探测结果等,展望了基于地基雷达设备对月球进行成像的发展趋势。

连续波Doppler引信扫频波辐照效应

为研究扫频波对连续波Doppler引信的效应规律及作用机理,开展了典型引信扫频波辐照效应试验,结合现有文献研究结论,提出了普适的扫频波辐照下连续波Doppler引信效应规律及作用机理。试验结果表明:扫频波辐照下引信会意外发火,引信临界干扰电场强度与扫频频段有关;扫频步长、频点驻留时间与引信是否意外发火密切相关,受试引信意外发火时要求扫频步长≥7 k Hz,频点驻留时间≤483 ms;扫频参数不会影响受试引信临界干扰电场强度。扫频波辐照下连续波Doppler引信意外发火原因为:扫频波频率变化导致引信自差机振荡状态发生跳变,引起高频电路输出电压波动,从而推动执行级误动作。

基于自适应多普勒滤波的雷达欺骗干扰抑制

为了应对现代干扰机密集相干假目标的威胁,以线性调频雷达抗灵巧噪声和C&I干扰为背景进行研究。首先,提出基于YOLOv5的复合干扰距离-多普勒域分布特征提取和干扰识别的干扰参数初步估计方法;然后,综合特征区域搜索和频谱内插等方法对多普勒参数进行精确估计,利用提取到的精确参数设计多普勒滤波器组对干扰进行抑制;最后,利用抑制后的信号构建检验统计量,利用方差检验判断是否需要更新多普勒滤波器权重,进行自适应调节。仿真结果表明,所提方法可以在低信噪比和多欺骗干扰的环境下对干扰进行有效抑制,对密集假目标干扰的抑制具有参考意义。

多普勒雷达高速数据传输的迭代合并均衡算法

为解决多普勒雷达高速数据在传输过程中存在的码间串扰、拥塞风险高等问题,本文设计了一种迭代合并均衡算法。通过模拟多普勒雷达数据的高速传输过程,确定传输信道具有衰落与时变特性,存在误码、拥塞等现象。然后,装设数据传输迭代合并均衡器,根据传输信道的迭代估计结果,确定均衡器的启动条件。在合并并重新分配传输信道资源后,通过滤波实现码间干扰的补偿,再通过多次迭代完成数据传输的均衡处理任务。测试结果表明:与传统均衡算法相比,在应用本文算法后,多普勒雷达高速数据传输的衰落量降低了0.7 GB,信道间接收功率均衡度提高了0.9,传输拥塞概率的数值由2.05%下降至0.10%。

The Light Timing Calculations of the Interferometer in the Quest to Detect Light Speed Anisotropy and a Case Study of the Michelson-Morley and Miller Mt Wilson Experiments

This paper formulates the light timing calculations for each interferometer arm;one that is parallel to the direction of motion of the interferometer through space and the other that is perpendicular. The calculations are done for a vacuum-mode interferometer and then for a gas-mode interferometer. The calculations show that no light timing difference is detectable in a vacuum-mode interferometer, but once an optical medium is present in the light path down the arms of the interferometer, this is no longer the case and a timing difference is detectable. Further to this, the timing equations obtained from the analysis are used to model the historical experiments of Michelson-Morley and Miller (Mt Wilson) and predictions are made by the model that accurately match the actual recorded results from those experiments. Thus, this timing analysis confirms that there is a light speed anisotropy in a reference frame that is moving through space, indicating the presence of a preferred Aether reference frame through which the Earth is moving.

Macroscopic effects in electromagnetically-induced transparency in a Doppler-broadened system

We study the electromagnetically-induced transparency（EIT） in a Doppler-broadened cascaded three-level system.We decompose the susceptibility responsible for the EIT resonance into a linear and a nonlinear part, and the EIT resonance reflects mainly the characteristics of the nonlinear susceptibility. It is found that the macroscopic polarization interference effect plays a crucial role in determining the EIT resonance spectrum. To obtain a Doppler-free spectrum there must be polarization interference between atoms of different velocities. A dressed-state model, which analyzes the velocities at which the atoms are in resonance with the dressed states through Doppler frequency shifting, is employed to explain the results.

基于轻量化网络的干扰信号智能识别算法

针对干扰信号识别时卷积神经网络模型体积大、训练周期长、对硬件存储和计算要求高等问题,本文提出了一种基于改进轻量级网络模型SqueezeNet的干扰信号智能识别算法。该方法首先利用距离多普勒(Range⁃Doppler,RD)处理获得目标及干扰信号的RD图像,接着采用滑窗变换、归一化等技术对RD图像进行重塑;然后采用基于RD信息尺寸的隐层和通道剪枝措施对SqueezeNet网络进行改进,缩小了模型尺寸和存储空间;最后利用不同参数的测试样本拓展网络模型的泛化性能。仿真实验表明,在参数量减少到原网络1/30的情况下,改进的SqueezeNet网络对每种干扰的识别正确率可达到95%以上,且训练时间大大减少。

多普勒超声诊断装备的新技术应用及常见故障维修

基于多普勒超声诊断装备的新技术应用和工作原理,探讨设备常见故障的维修路径。在临床诊疗需求不断提升和医学技术不断发展的背景下,从多普勒超声诊断装备新技术的临床应用和技术原理角度分析设备发展趋势,总结多普勒超声诊断的临床应用优势。当设备运行中出现故障时,依据故障现象进行原因分析,制定故障排查思路,并逐一进行设备部件的检查,从而提高故障维修的时效性,降低设备管理成本和难度,为设备更好地服务临床诊疗活动提供保障。

调频多普勒引信静动态干扰信号响应差异性研究

在无线电引信抗干扰静动态等效试验方法的研究中,需要在内场构造干扰场景模拟出真实的动态场景,为了明晰抗干扰试验中引信对干扰信号响应的静动态等效关系,进行引信静动态干扰信号响应差异性研究。理论推导了调频引信静动态干扰信号响应差异性,建立了典型场景下的调频多普勒引信和干扰信号模型,结合三维天线方向图拟合出了引信动态条件下对干扰信号响应曲线,得到了引信静动态干扰信号响应的检波信号包络对比结果。理论及仿真结果表明,弹道运动和天线特性会在距离、速度和方向系数三个方面产生较为显著的影响,通过合理地信号调制即可在内场构造干扰场景模拟出真实的动态场景,为引信抗干扰静动态等效试验方法的建立提供技术支撑。

海上风电机雷达回波及其微多普勒特征

精确模拟海上风电机雷达回波并提取其微多普勒特征,是解决海上风电场对邻近雷达台站无源干扰的关键问题。由于现有算法将风电机所处的海面背景直接以平面良导体等效而过于简单,且传统的等间距散射点模型无法表征风电机叶片的三维异形曲面特征。为此,在回波求解时引入粗糙海面前向复反射系数,同时结合风电机的三维散射点等效模型,提出了基于时域回波电场的海上风电机雷达回波数值模拟算法。根据矩量法中RWG函数离散电场方程的思想,建立风电机三维散射点等效模型。考虑到电磁波作用在海面时的畸变效应,利用粗糙海面前向复反射系数推导出了时域回波电场求解公式,并获取了海上风电机雷达回波的模拟结果。最后,将风电机海面背景下的回波微多普勒特征与自由空间下的进行对比,证明海面背景不可忽略。进一步采用控制单一变量的方法分析了微多普勒频移的海况响应特性,即浪高的均方根与多普勒频移呈负相关。这也为后续海上风电机回波的识别与滤除提供理论参考。

基于回波模型仿真的ADCP实验室校准中波束间干扰研究

针对声学多普勒流速剖面仪(ADCP)水域环境校准效率低下的问题,提出了一种实验室水池环境下多个波束同时校准方案。通过建立一种精准的仿真回波模型,并进行湖试实验验证了模型的准确性,经由换能器对回波模型在实验室消声水池中进行回发,可以实现对ADCP多个波束同时校准,同时利用回波模型探究校准时波束间的干扰误差。在底跟踪校准模式中,波束间的干扰误差与底速度成正相关,在速度1.6 m/s以下,相对误差在0.5%以下,超过1.6 m/s时,误差超出实验ADCP的测量精度;水跟踪校准模式下波束间的干扰误差呈现高斯噪声的特性,其相对误差集中在0%附近。实验与仿真的结果证明了ADCP实验室多个波束同时校准方案的可行性,其误差经过有效屏蔽能控制在测量精度范围内。

基于原型与主动学习的天波雷达干扰检测方法

本文研究天波雷达基于距离⁃多普勒(Range⁃Doppler,RD)图像的干扰检测问题。在干扰检测过程中,错误检测可能是干扰的漏检与虚警问题,为此考虑采用主动学习方法,将算法模型难以判决的样本由专家标注,并将标注样本加入至训练集中以达到提升检测性能的目的。同时,也需要解决训练集样本的冗余问题,为此使用原型数据学习方法,建立有干扰和无干扰样本数据云,有效地降低训练集样本量。实测数据实验表明,原型方法将初始训练集样本数量降低至23.5%,主动学习方法取得的检测准确率为97.42%,而传统监督学习最近邻方法准确率为87.96%。因此,本文方法能够有效提升天波雷达干扰检测能力,为天波雷达是否需要进行干扰处理与换频检测等工作提供可靠依据。

PC-FFT:一种时频协同的差分水声OFDM信号ICI抑制方法

载波间干扰(Inter-Carrier Interference,ICI)是制约差分水声正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)信号检测性能的瓶颈性因素。本文提出了一种时频协同的新型ICI抑制方法,称为分段-单频率校正快速傅里叶变换(Partially-Single-Frequency-Corrected Fast Fourier Transform,PC-FFT)。具体而言,首先,PC-FFT在时域上以OFDM符号时长为单位,对接收信号做互不重叠的均匀划分,化快变信号为多段准静态信号;其次,在频域上对每段短信号分别在一个频点上做补偿;最后,线性加权每一段补偿短信号的傅里叶变换输出,输入差分检测器。为了确定权重和补偿频率,本文建立了以二者为变量,以最小化信号检测均方误差为目标的优化问题。在该问题中,权重与补偿频率高度耦合,致使其严重非凸。为了降低复杂度,本文设计了一种坐标轮换下降的算法,其基于特征值分解求解权重,基于梯度下降法求解补偿频率,二者交替执行直至收敛。仿真和实测水声信道的测试结果均表明,在大多普勒频偏下,相较现有的部分快速傅里叶变换(Partial Fast Fourier Transform,P-FFT)、分数快速傅里叶变换(Fractional Fast Fourier Transform,F-FFT)和分段频移快速傅里叶变换(Partially-Shifted Fast Fourier Transform,PS-FFT)等方法,PC-FFT具有更好的ICI抑制性能。具体地,当载波数为1024、多普勒因子达3.5×10^(-4)、信噪比在10~30 dB范围变化时,PC-FFT相较于PS-FFT可将均方误差降低55.08%~67.64%,而P-FFT和F-FFT几乎无法工作。

一种新型的多普勒调制技术

在传统的斩波器调制技术中,被测对象“被动”地接受外来调制光的照射,由于这种照射一般要经过一定的光学系统来完成,因此,调制照射发生在每一个光束经过的光学元件上,这些元件必定会存在某些加工缺陷,从而产生与调制照射同频率、固定位相差的杂散信号,只要这些信号在探测器的视场里,就会形成背景干扰,从而降低信噪比。利用MichelsonM-orley动态干涉技术,建立了一套基于Doppler频移原理的调制器。与传统的调制技术相比,多普勒调制技术是将被测目标自身运动产生的多普勒频移在干涉仪光路中造成的干涉场的交替变化作为调制频率来实现光的调制,可以有效地消除目标以外一切背景因光调制而产生的噪声影响,极大地改善微弱信号探测的信噪比。实验结果表明:调制信号频率稳定度(相对标准差)可达到±1%左右,能满足锁相放大器参考信号的需要。