Target acquisition performance in the presence of JPEG image compression

This paper presents an investigation on the effect of JPEG compression on the similarity between the target image and the background,where the similarity is further used to determine the degree of clutter in the image.Four new clutter metrics based on image quality assessment are introduced,among which the Haar wavelet-based perceptual similarity index,known as HaarPSI,provides the best target acquisition prediction results.It is shown that the similarity between the target and the background at the boundary between visually lossless and visually lossy compression does not change significantly compared to the case when an uncompressed image is used.In future work,through subjective tests,it is necessary to check whether this presence of compression at the threshold of just noticeable differences will affect the human target acquisition performance.Similarity values are compared with the results of subjective tests of the well-known target Search_2 database,where the degree of agreement between objective and subjective scores,measured through linear correlation,reached a value of 90%.

Torpedo's Search Trajectory Design Based on Acquisition and Hit Probability Calculation

Taking aim at light torpedo search trajectory characteristic of warship, by analyzing common used torpedo search trajectory, a better torpedo search trajectory is designed, a mathematic model is built up, and the simulation calculation taking MK46 torpedo for example is carried out. The calculation results testify that this method can increase acquisition probability and hit probability by about 10%-30% at some situations and becomes feasible for the torpedo trajectory design. The research is of great reference value for the acoustic homing torpedo trajectory design and the torpedo combat efficiency research.

DCT domain filtering method for multi-antenna code acquisition

For global navigation satellite system （GNSS） signals in Gaussian and Rayleigh fading channel, a novel signal detection algorithm is proposed. Under the low frequency uncertainty case, after performing discrete cosine transform （DCT） to the outputs of the partial matched filter （PMF） for every antenna, the high order com- ponents in the transforming domain will be filtered, then the equalgain （EG） combination for the inverse discrete cosine transform （IDCT） reconstructed signal would be done subsequently. Thus, due to the different frequency distribution characteristics between the noise and signals, after EG combination, the energy of signals has almost no loss and the noise energy is greatly reduced. The theoretical analysis and simulation results show that the detection algorithm can effectively improve the signal-to-noise ratio of the captured signal and increase the probability of detection under the same false alarm probability. In addition, it should be pointed out that this method can also be applied to Rayleigh fading channels with moving antenna.

New acquisition decision algorithm for multiple access interference suppression in DSSS system

For decreasing the multiple access interference of weaker signal acquisition in direct sequence spread spectrum（DSSS） systems,a new single decision algorithm is presented.The maximum value of correlation results is conventionally detected.However,there may be not only one strong peak among correlation results when the cross-correlation noise is strong enough to affect the correlation results.The proposed algorithm decreases the false alarm probability through the decision of the ratio of the maximum value and the second maximum value of the correlation results.Theoretical analysis and simulation results indicate that the proposed algorithm effectively suppresses the acquisition problem of multiple access interference in DSSS system.

New Acquisition Algorithm for Direct Sequence Spread Spectrum Signals

Aiming at improving acquisition performance for direct sequence spread spectrum （DSSS） signals, a new acquisition algorithm based on fast Fourier transform （FFT） is proposed. The code phases are parallel searched throughout the Doppler frequency domain. Since the influence of Doppler frequency errors on peak-to- average ratios of correlation power shows a pattern similar to the sinc function, it is our belief that by judging on peak-to-average ratios for different Doppler frequency errors false alarm probabilities should be lowered. Analyses have supported the underlying principle of this new algorithm. Simulation results have also indicated that the new algorithm can effectively improve the acquisition performance for DSSS signals.

Dual-channel Method for Fast Long PN-code Acquisition

Long PN-code acquisition is a difficult and time-consuming task due to long code period.To accelerate acquisition,folding methods like XFAST are widely used.In highdynamic environment however,the application of those methods are largely restricted due to nonnegligible residual frequency.This paper proposes a new dual-channel method for fast acquisition of long PN-code.In the proposed method,both non-overlapping local PNcode blocks are employed to correlate with input sample block;the detection process is eased through finding the maximum value among correlation results and verification is made with all the full and partial peaks taken into account.False alarm probabilities from analysis of the verification process are derived.Both theoretical and Monte Carlo simulations reveal that,with respect to acquisition probability and mean acquisition time under the same false alarm rate,dual-channel method has advantage over zero-padding and XFAST based folding methods under certain false alarm probabilities.

Code acquisition method based on wavelet transform filtering

In order to improve the acquisition probability of satellite navigation signals, this paper proposes a novel code acquisition method based on wavelet transform filtering. Firstly, the signal vector based on the signal passing through a set of partial matched filters （PMFs） is built. Then, wavelet domain filtering is performed on the signal vector value. Since the correlation signal is low in frequency and narrow in bandwidth, the noise out-of-band can be filtered out and the most of the useful signal energy is retained. Thus this process greatly improves the signal to noise ratio （SNR）. Finally, the detection variable when the filtered signal goes through the combination process is constructed and the detection based on signal energy is made. Moreover, for the better retaining useful signal energy, the rule of selection of wavelet function has been made. Simulation results show the proposed method has a better detection performance than the normal code acquisition methods under the same false alarm probability.

面向复杂介质的地震散射波采集技术

地震勘探是一项以地震采集技术为基础的系统工程。变革地震采集技术既是采集装备升级、波场理论创新的发力点,也是解决地震处理、解释技术问题的源头。地震勘探发展历程体现了采集装备能力提升、地质需求驱动、波场理论拉动的作用,其中,地震采集技术既充满活力,也面临着深刻的挑战。面对小尺度、非层状、非均匀介质成像问题,以及大数据与人工智能高速发展的时代背景,以共中心点叠加为特征,采用稀疏、规则、单一观测系统的反射波地震采集技术越来越显示出不适应性,为适应小尺度、非层状、隐蔽性目标成像要求,以共中心点离散化为特征,采用随机、遍历性、多观测系统的散射波地震采集技术势在必行。作为散射波地震采集技术的理论基础,随机理论及概率波的研究逐渐得到重视。

Acquisition probability differences in cloud coverage of the available Landsat observations over mainland Southeast Asia from 1986 to 2015

Landsat data are the longest available records that consistently document global change.However,the extent and degree of cloud coverage typically determine its usability,especially in the tropics.In this study,scene-based metadata from the U.S.Geological Survey Landsat inventories,ten-day,monthly,seasonal,and annual acquisition probabilities(AP)of targeted images at various cloud coverage thresholds(10%to 100%)were statistically analyzed using available Landsat TM,ETM+,and OLI observations over mainland Southeast Asia(MSEA)from 1986 to 2015.Four significant results were found.First,the cumulative average acquisition probability of available Landsat observations over MSEA at the 30%cloud cover(CC)threshold was approximately 41.05%.Second,monthly and ten-day level probability statistics for the 30%CC threshold coincide with the temporal distribution of the dry and rainy seasons.This demonstrates that Landsat images acquired during the dry season satisfy the requirements needed for land cover monitoring.Third,differences in acquisition probabilities at the 30%CC threshold are different between the western and eastern regions of MSEA.Finally,the ability of TM,ETM+,and OLI to acquire high-quality imagery has gradually enhanced over time,especially during the dry season,along with consequently larger probabilities at lower CC thresholds.

指向统计素养培育的中学数学教学策略——以线性回归模型的建立为例

统计素养是中学生数学核心素养的有机组成部分。针对培养学生统计素养的关键环节,以案例形式设计了对应的教学策略。首先,建立统计观念环节,涵盖了古典概率和非古典概率模型;其次,收集统计数据环节,涵盖普查获取数据和抽样获取数据;最后,分析统计数据环节,涵盖线性回归和非线性回归。

对潜快速防御反击模型构建及鱼雷捕获概率分析

针对潜艇快速防御反击中的鱼雷攻击问题,基于线导导引方法和模型,构建水面舰艇鱼雷快速防御反击模型。对鱼雷捕获潜艇概率进行了仿真计算,结果表明该方法中鱼雷直航段捕获目标概率极低,因此不建议水面舰艇在无较精准鱼雷射距时采取以打击敌潜艇为目的的防御反击,研究方法和结果可为演训效果评估等提供参考,亦可为对潜防御时的作战决策提供支撑。

无线节点状态数据与地震数据关系的探讨

采用HyperQ质控技术可监控节点的工作状态,但在面对大排列、长偏移距和复杂工作环境等挑战时,发现并及时处理任何指标不合格的节点变得异常困难,特别是在复杂区域,会显著增加经济成本和操作难度。本文通过数据统计的方法,研究了节点状态数据与地震数据之间的关系,明确了能够指示地震数据质量的主要指标,当这些指标出现异常时,地震数据极有可能存在异常。在施工中,可以集中有限的资源,及时处理主要指标异常的节点,从而在经济成本可承受的前提下提高地震采集资料的质量。将本文方法应用于海外某项目中,在经济成本基本不增加的情况下,将单炮中异常道比例低于3%的单炮比例从83.75%提高到了95.74%。

星间光链路(OISLs)中捕获系统分析及仿真

星间光链路 (OISL s)是极具前景的星间通信手段 ,捕获是星间光链路建立的关键技术之一。本文对 OISLs中捕获系统的设计要点进行说明 ,重点对捕获系统的捕获概率、捕获时间以及捕获链路进行数学分析 。

一种大步进伪码快速捕获方法的研究

在无线电导航系统中,低信噪比的情况下长伪码序列的快速捕获和重捕成为系统必须解决的一个重要问题.针对该问题,提出了一种大步进伪码快速捕获方法,并给出了大步进伪码快速捕获的原理和实现方法,详细分析了该方法的检测概率、虚警概率和平均捕获时间.该方法易于采用大规模集成芯片和数字信号处理算法实现且已经应用到实际接收机系统中,仿真结果和实践证明该方法具有较快的捕获速度,捕获灵敏度高,能够在低信噪比下稳定工作.

一种实用的归一化互相关景象匹配算法

相关匹配算法是景象匹配定位系统的核心。本文提出一种用于景象匹配定位系统的相关匹配算法，称之为归一化互相关景象匹配算法，并进行了理论分析和用真实的景象数字地图进行了大量的计算机仿真试验。试验结果表明，该算法在信噪比不小于１并且实时图大小不小于１０×１０个网格的条件下，其正确匹配概率大于９７％，圆概率误差在一个景象数字地图的网格以内。

火箭助飞鱼雷捕获概率的解析模型

针对火箭助飞鱼雷作战方式及弹道形式与传统声自导鱼雷的不同,深入分析了搜索区域、落点散布和目标散布等影响火箭助飞鱼雷捕获概率的关键因素,得出了各要素的数学描述。进而综合考虑3个要素的相互关系,并根据不同射击方式下目标散布模型的本质区别,分别采用"误差综合"与"全概率"的思想,构建了前置点和现在点2种典型射击方式下火箭助飞鱼雷捕获概率的解析模型。且其计算值与仿真实验结果吻合良好。

机动平台与卫星间激光通信捕获系统仿真研究

假设初始指向在方位和俯仰方向的误差来源独立且同分布,CCD噪声电流服从标准的正态分布,CCD平均信号服从泊松分布,在此基础上创建捕获仿真系统。捕获系统采用光栅螺旋扫描和扫描/跳步的捕获方式,给出了最大捕获时间和捕获概率的计算公式。通过运行仿真程序,分析了两个终端的相对速度对捕获系统的影响情况,对捕获系统的各项参数进行了优化选取,并提出了带速度补偿的扫描捕获路径算法,提高了系统的捕获概率。

天基非合作目标探测中的捕获概率模型

针对空间目标瞄准捕获系统中的捕获概率问题,在设计空间卫星光电探测平台时,采用常用的捕获方式进行建模,分析了空间光电探测系统在不确定区域中对不同机动目标的捕获概率。首先提出了空间机动目标的时间相关运动模型,然后以空间螺旋扫描的捕获方式为例,建立了捕获-目标的捕获概率模型。并且针对实际应用,取捕获分辨角范围为0.6～0.8 mrad,则对应的扫描角度间隔Iθ范围为0.42～0.702 mrad,设计了扫描、捕获的Monte-Carlo计算机仿真实验模型。经过5 000次捕获验证,得到了在不同时刻进入视场的任意方向的非合作目标的捕获概率模型,与室内捕获实验结果相符。为空间卫星光电目标捕获跟踪系统的设计提供了一定的理论依据。

自适应基因遗传算法及其在知识获取中的应用

本文针对基因遗传算法中杂交率和变异率的难以选取问题,提出了一种自适应基因遗传算法.该方法利用降半Г分布函数对杂交率和变异率进行自适应调整,以保证群体的多样性和进化过程的稳定性,克服算法的未成熟收敛问题.最后以故障诊断知识获取为例,阐述该方法的有效性.

基于LPI的相控阵雷达辐射控制方法

相控阵雷达可通过合理配置工作参数优化其性能。针对雷达在电子对抗环境中需要具备低截获概率(low probability of intercept,LPI)的要求,从低截获原理出发,对两种辐射能量控制策略:最小功率策略和最小驻留策略的实现方法进行了理论推导。在此基础上,建立以检测概率为目标的探测性能优化模型,并给出了两种能量控制策略下的最优辐射控制方案。