Doppler properties of radars in circular orbits

Abstract

Expressions are presented for Doppler frequency shift, Doppler bandwidth, zero Doppler offset angle in spacecraft yaw and, in the SAR mode, the rate of Doppler frequency modulation, azimuth time-bandwidth product, resolution, available integration time and the location of principal azimuth ambiguities. The equations are simply expressed with virtually no approximations based on angles referenced to the satellite. Earth rotation is included, as is the geosynchronous case. (These results differ from expressions to be found elsewhere in the literature, most of which have been derived using flat-Earth approximations.).     

短波信道探测中多普勒频移的计算

为准确获取短波信道探测信号的多普勒频移,把被Zadoff-Chu序列调制的信号作为探测信号,以简化的Watterson模型作为短波信道,采用脉冲压缩技术,对多普勒频移的计算进行了理论推导,得出了一种多普勒频移的计算公式,对两条路径时公式的计算结果进行了仿真。结果表明,在两条路径的多普勒频移相差小于±0.3 Hz时,计算结果较为准确。在此基础上,仿真分析了多普勒频移对Zadoff-Chu序列的脉冲压缩的影响。分析表明,小于10 Hz的多普勒频移对Zadoff-Chu序列的脉冲压缩的影响可以忽略不计,将该序列应用在短波信道探测中比较合适。     

The ocean waveheight nondirectional spectrum from inversion of the HF sea-echo Doppler spectrum

The measured HF sea-echo Doppler spectrum consists of prominent first-order peaks, around which exist second-order sidebands of a continuous nature. Theoretical models developed elsewhere are interpreted here and shown to satisfactorily account for these first and second-order measured spectral features. Employing these theoretical models, this paper derives a simple inversion technique for obtaining the waveheight nondirectional spectrum. The result is a closed-form expression, independent of the wave directionality factor, the radar look direction, or the stage of development of the waveheight spectrum. Approximations required in the derivation are stated along the way, and are shown to become increasingly valid in the limit of high seas and/or radar frequencies. The technique is tested by attempting to recover several input waveheight nondirectional spectra for various radar look directions. Comparisons show that the technique produces acceptable results for $\text{k}{}_{\mathrm{o}}\text{h > 0.2}$, where $\text{k}{}_{\mathrm{o}}$ is the radar wavenumber and $\text{h}$ is the rms waveheight. Application of the inversion technique to measured data is straightforward. One employs one of the stronger second-order Doppler sidebands (vs. Doppler frequency with respect to the first-order Doppler-peak frequency) and divides it by a parameterless, dimensionless weighting function derived in this paper. He then divides this result by the adjacent first-order spectral energy. The latter normalization (i) serves to remove any unknown radar path loss or system gain factors, and (ii) also eliminates the need for any a priori knowledge of the wave or radar directionality and/or the assumption of a model for these latter quantities.     

基于软件无线电的高频多普勒接收机设计

利用软件无线电技术设计了一种新型高频多普勒接收机.该接收机采用高稳定度频率源、滤波放大器、数字下变频器等,系统具有参数设置灵活,同时进行多通道信号多普勒频移分析的能力,较好地克服了传统高频多普勒接收机存在的问题.实验和观测表明,新型软件式高频多普勒接收机可实时分析多个通道电离层信号回波的多普勒频移大小、强度以及随时间的变化,是观测电离层扰动的一种有效手段.     

高频多普勒与到达角探测系统中数据采集单元的设计

针对高频多普勒和到达角探测系统中的数据采集问题，提出了8253控制下的DMA方式的A／D工作模式，重点阐述大量数据采集的关键技术，实现了采样间隔的准确定时和数据的高速传输，在实践中取得了满意的效果。     

Performance analysis of ordered CFAR detectors for MIMO radars

Ordered statistics is one of the proposed solutions to improve the detection in a multiple target environment. Some variants of this technique have been proposed for the SISO (Single Input Single Output) radars such as the OS-CFAR (Ordered Statistics CFAR), the GOSCA-CFAR (Generalized Ordered Statistics, Cell Averaging CFAR), the OSGO-CFAR (Ordered Statistics Greatest Of CFAR) and the OSSO-CFAR (Ordered Statistics Smallest Of CFAR) to deal with multiple target situations. In this paper, we generalize these CFAR detectors for the MIMO (Multi Input Multi Output) radars with three different schemes. We derive closed-form expressions of the probability of false alarm (Pfa) and the probability of detection (Pd) in a homogeneous environment for two schemes. The performance of these detectors for a non-homogeneous clutter environment (presence of interfering targets and clutter edge) has been assessed and compared. The results obtained showed that the best performance is obtained by the OSSO-CFAR.     

MIMO雷达最大似然参数估计

多输入多输出(MIMO)雷达使用多个天线同时发射多个独立探测信号,并使用多个天线接收目标回波信号.本文考虑了发射空域分集、相干接收MIMO雷达模型及其最大似然(ML)参数估计方法.基于最大似然准则,本文推导了两种渐近最大似然算法.仿真实验的结果表明,在均匀噪声模型中,其中一种渐近算法与基于延迟求和波束形成的最大似然算法性能接近,而另一种渐近算法性能略差,但具有较低的计算复杂度.而在非均匀噪声模型中,本文所提出的两种渐近最大似然算法的性能均优于基于延迟求和波束形成的最大似然算法.     

基于AR模型估计的抗冲击干扰算法

高频雷达探测目标时,随机出现的冲击干扰会遮盖目标谱线,从而导致目标丢失.由于时域海面回波一般情况下绝对占优,因此基于时域的抗干扰算法不能有效地解决该问题.本文提出的算法利用海杂波距离谱分布结构上的特点,通过AR模型参数估计,重构并对消海杂波,反变换到时域的信号中突发冲击干扰能够占优,进而利用野值判别与剔除方法将幅度较突出的冲击干扰予以剔除,达到抑制突发冲击干扰的目的,使雷达在突发干扰情况下也能有效地发现和跟踪目标.     

利用数据平滑抑制无线电高度表的多普勒效应误差

针对多普勒效应对频率测量造成的误差使无线电高度表的测高精度受到影响的问题,提出使用加权平均算法、N次平均算法来抑制多普勒效应误差对测量的影响,并对它们的优缺点进行了分析,给出了各自适用的场合。这些算法分别在国内的三种无线电高度表上使用的效果证明了它们的可行性和可靠性。     

An empirical investigation of the relationship of IS strategy with firm performance

Given the important impact that an IS strategy has on the potential value IS brings to an organization, we develop and test a model of IS Strategy and Firm Performance. Our survey-based study provides strong evidence that firms with defined IS strategies (either IS Innovator or IS Conservative) perform better than those without defined IS strategies. Organizations without a clearly defined IS strategy actually experienced a negative relationship with firm performance. These organizations should realize the potentially negative outcomes of such a lack of strategy and work to extricate themselves before a consistent pattern of investing in IS without clear organizational benefit develops. Furthermore, the study suggests that the IS Innovator strategy is, in particular, associated with more superior firm performance than the IS Conservative strategy under conditions of environmental dynamism. Organizational leaders need to consider the external environments under which their organizations are operating and evaluate the influence those environments may have on their IS strategy’s ability to impact performance. Post hoc analysis results also reveal a fourth potential IS strategy, one that strives for ambidexterity. Ambidextrous firms were found to be associated with the most superior performance, leading to a potential extension of the existing IS strategy typology and a call for future research.     

An empirical investigation of the relationship between spectra differences and regression faults

Many software maintenance and testing tasks involve comparing the behaviours of program versions. Program spectra have recently been proposed as a heuristic for use in performing such comparisons. To assess the potential usefulness of spectra in this context an experiment was conducted, examining the relationship between differences in program spectra and the exposure of regression faults (faults existing in a modified version of a program that were not present prior to modifications, or not revealed in previous testing), and empirically comparing several types of spectra. The results reveal that certain types of spectra differences correlate with high frequency—at least in one direction—with the exposure of regression faults. That is, when regression faults are revealed by particular inputs, spectra differences are likely also to be revealed by those inputs, though the reverse is not true. The results also suggest that several types of spectra that appear, analytically, to offer greater precision in predicting the presence of regression faults than other, cheaper, spectra may provide no greater precision in practice. These results have ramifications for future research on, and for the practical uses of, program spectra. Copyright © 2000 John Wiley & Sons, Ltd.     

高频双基地雷达海杂波数值仿真

海杂波是高频雷达海态信息的重要载体,也是影响高频雷达海面低速目标检测的重要因素,针对高频双基地雷达在定位精度精确性和反隐身问题上起重要作用.为了准确检测海杂波海态参数信息,利用数值仿真方法对双基地海杂波的特性进行研究.在分析双基地一阶和二阶海杂波形成机理的基础上,利用海杂波雷达散射截面方程,对高频双基地海杂波进行仿真.针对复杂的二阶谱仿真,采用固定波数下二阶子谱叠加方法,避免了求解非线性方程,并在仿真中采用角频率离散化方法,提高运算速度.仿真结果表明双基地海杂波不仅与雷达海态和雷达工作频率有关,还与双基地角密切相关.结果证明方法有效,为目标检测提供科学依据.     

坐标转换在雷达组网中的应用

雷达组网需要进行坐标转换的计算,其前提需要知道各个雷达之间的相互位置,所以首先要测量雷达之间的相对坐标。本文介绍了在雷达组网中可采用的测量雷达间相对坐标的几种方法,并分析了这些测量方法适应的条件,测量精度。根据测量的简易程度、适应范围以及测量精度讨论了各自的优缺点。     

蒸发波导对雷达探测距离的影响

电磁波在大气环境中传播受到各种因素的影响,引起电磁波出现异常传播现象,尤其在陷获折射条件下,形成大气波导传播。本文在介绍大气波导的分类基础上,重点论述了蒸发波导对雷达探测距离的影响。     

Beam pointing errors of phased arrays for digital switched beam acoustic radars

Phased array antennas and corresponding driving electronics units have been introduced in Atmospheric Acoustic probing. Using modern microprocessor systems in conjunction with suitable digital electronics, it is possible to implement an acoustic probing system, with full beam switching capabilities.

The radiation pattern of a planar M × N phased array acoustic radar equipped with digital phase shifting circuits for the beam switching, is examined and all the necessary formulas are presented. For a given accuracy of phase quantization, the set of beam pointing directions which can be achieved without deterioration, due to this quantization, is computed and diagrams showing the mapping of the available beam pointing directions throughout space are presented. The relation between the cardinal number of this set of directions and the accuracy of the phase quantization is also presented.

The beam pointing errors, due to the accuracy of the phase quantization and the dissimilarities among the array's elements are analysed using simulation techniques     

Real-time digital signal processing of phased array radars

With the advance of hardware and software technology, modern phased array radars are now built with commercial-off-the-shelf (COTS) components, and it opens up a new era in real-time resource scheduling of digital signal processing. This paper targets the essential issues in building a component-oriented signal processor (SP), which is one of the two major modules in modern phased array radars. We propose a simple but effective task allocation policy and a real-time scheduling algorithm to address the design objectives of SPs. We are able to bound the number of processing units needed for a component-oriented SP in the design time, while everything was done empirically in the past. A series of experiments was done to demonstrate the strength of our methodology.     

一种基于优先级调度的相控阵机动目标跟踪方法

在相控阵雷达跟踪加搜索（ＴＡＳ）工作方式下,为跟踪较大的机动目标,提出一种目标机动检测器设计方法,得到归一化的目标机动系数．基于该方法,给出了一种动态计算优先级的调度算法,较好地解决了机动多目标跟踪的资源调度问题．与几种常用机动检测器相比较,结果表明了这种机动检测器具有更高的检测概率．最后在多目标环境下进行机动目标跟踪的蒙特卡罗仿真,仿真结果显示了多目标机动检测器和资源调度算法的有效性．     

Stereoelectronic explanations for the mechanistic details of transimination and HF elimination reactions

The β-fluoroamines are commonly used as substrate analogs to determine the mechanistic details of enzymatic reactions. Presence of fluorine atom gives rise to the alterations in the electronic profile and the pK_a of molecules which results in mechanistic deviations. The fluorine-substituted mechanism-based substrate analogs are widely used in the inactivation of pyridoxal 5′-phosphate (PLP)-dependent enzymes. The presence of fluorine atom also alters the sequence of reactions taking place in PLP-dependent enzymes where the HF elimination reaction appears in between the transimination and inactivation reactions. Despite the amount of the works on β-fluoroamines, the effect of stereoelectronic differences on the transimination and HF elimination reactions taking place in PLP-dependent enzymes has not been investigated yet. A density functional theory study is conducted to elucidate mechanistic details of the reactions occurring in PLP-dependent enzymes. In order to understand the mechanistic insights of different isomers and the effect of the fluorine atom, 4-amino-3-fluorobutanoic acid (3-F-GABA) enantiomers are chosen to be investigated besides 4-aminobutanoic acid (GABA), which is the natural substrate for γ-aminobutyric acid aminotransferase (GABA-AT). The investigated β-fluoroamines are the experimentally proposed potential inhibitors of PLP-dependent enzyme GABA-AT.     

A target recognition method for maritime surveillance radars based on hybrid ensemble selection

In order to improve the generalisation ability of the maritime surveillance radar, a novel ensemble selection technique, termed Optimisation and Dynamic Selection (ODS), is proposed. During the optimisation phase, the non-dominated sorting genetic algorithm II for multi-objective optimisation is used to find the Pareto front, i.e. a set of ensembles of classifiers representing different tradeoffs between the classification error and diversity. During the dynamic selection phase, the meta-learning method is used to predict whether a candidate ensemble is competent enough to classify a query instance based on three different aspects, namely, feature space, decision space and the extent of consensus. The classification performance and time complexity of ODS are compared against nine other ensemble methods using a self-built full polarimetric high resolution range profile data-set. The experimental results clearly show the effectiveness of ODS. In addition, the influence of the selection of diversity measures is studied concurrently.