高光谱图像全局异常检测RFS-SVDD算法

针对SVDD用于高光谱图像全局异常检测时存在虚警率高的问题,提出RFS-SVDD算 法。RFS-SVDD将空间相邻且光谱相似的像元分为同一区域,根据区域大小将图像在空间上分 成潜在异常区域与背景区域,用背景区域中所有子区域的平均光谱RFS作为SVDD训练样本求 取支持向量。RFS是每个子区域中像元光谱的统计结果且不包含奇异像元,可以避免奇异像 元光谱和图像随机噪声对背景建模的影响。对HYMAP和AVIRIS图像数据的仿真结果表明：RFS -SVDD算法能抑制异常目标像元光谱和图像随机噪声对背景建模的干扰,降低SVDD用于高光 谱图像全局异常检测的虚警率。
     

基于BiGRU-SVDD的ADS-B异常数据检测模型

广播式自动相关监视（ADS-B）作为新一代空管监视技术,由于采用明文方式广播发送数据,因而存在易遭受网络攻击的安全问题。为了准确检测ADS-B数据攻击行为,在充分考虑时间相关性的基础上,提出了针对ADS-B数据的异常数据检测模型。首先利用双向门控循环单元（BiGRU）神经网络预测ADS-B数据,得到了ADS-B数据预测值。再将预测值和实际值作差,将差值放入支持向量数据描述（SVDD）训练,得到了能检测ADS-B异常数据的超球体分类器。并且,选择了合适的滑动窗口,在保证异常检测准确率的同时,缩短BiGRU神经网络的训练时长。实验结果表明,BiGRU-SVDD模型能检测出随机位置偏移攻击、高度偏差攻击、重放攻击、拒绝服务（DOS）等攻击下的ADS-B异常数据。并且,与其他机器学习和深度学习方法相比,BiGRU-SVDD异常检测模型的准确率更佳,适应性更优。     

TEC variability near northern EIA crest and comparison with IRI model

Monthly median values of hourly total electron content (TEC) is obtained with GPS at a station near northern anomaly crest, Rajkot (geog. 22.29°N, 70.74°E; geomag. 14.21°N, 144.9°E) to study the variability of low latitude ionospheric behavior during low solar activity period (April 2005 to March 2006). The TEC exhibit characteristic features like day-to-day variability, semiannual anomaly and noon bite out. The observed TEC is compared with latest International Reference Ionosphere (IRI) – 2007 model using options of topside electron density, NeQuick, IRI01-corr and IRI-2001 by using both URSI and CCIR coefficients. A good agreement of observed and predicted TEC is found during the daytime with underestimation at other times. The predicted TEC by NeQuick and IRI01-corr is closer to the observed TEC during the daytime whereas during nighttime and morning hours, IRI-2001 shows lesser discrepancy in all seasons by both URSI and CCIR coefficients.     

重力测量卫星三轴稳定模型预测控制方法

基于卫星重力测量姿态控制任务需求,提出了一种基于模型预测控制的三轴姿态稳定控制方法.给出了将控制力矩和扰动力矩分别作为控制变量和测量扰动的线性化方程,并将推力大小及其变化量作为约束条件.基于离散化状态方程,提出了满足多种约束条件的预测控制方法.通过数学仿真表明了模型预测方法对内编队卫星三轴稳定控制的有效性和可行性.     

基于线性重力差模型的拦截弹中制导技术

针对机载动能拦截弹的中制导段气动力作用可忽略且存在无法实时精确计算重力偏差等特点,提出了一种基于线性重力差模型的预测制导方法。通过线性模型逼近中制导过程中拦截弹与目标之间的重力偏差,以此为依据调整拦截弹的推力矢量并将重力偏差值消除。在此基础上采用延迟点火的策略使得拦截弹的拦截器助推级更好地修正预测模型与实际情况的偏差,经过仿真验证可以将整个中制导段的脱靶量限制在一个较小数值,从而为末制导段提供良好的初始条件。     

机器人动态受力感知及零重力运动模拟技术

针对航天器在轨服务任务的地面零重力模拟需求,研究基于工业机器人的零重力运动模拟技术。建立基于BP神经网络的受力感知预测模型,该模型采用机器人末端姿态、加速度、角速度和角加速度作为输入层参数,采用机器人末端六维力传感器数据作为输出层参数,实现了对机器人末端负载的高精度动态受力感知。设计正交试验方法确定机器人的运动路径点进行样本数据采集,实现了受力感知预测模型对机器人全工作空间的覆盖。进一步,基于对机器人末端负载的受力感知数据,应用动力学理论计算负载在失重状态下的运动速度,并控制机器人执行相应的运动,实现了对机器人末端负载的零重力运动模拟。     

太阳系边际探测飞行任务规划

针对太阳系边际探测任务,开展了星际多目标飞越的任务规划,采用小推力混合优化设计方法完成了基于借力飞行及电推进技术的行星际转移轨道联合优化设计,对比研究了面向日球层鼻尖和尾部探测的星际多目标探测飞行方案.研究表明,探测器在2024-2025年发射,可飞抵日球层鼻尖区域,在2027-2030年发射可飞抵日球层尾部区域,并可...     

Uncertainties in gravity wave parameters,momentum fluxes,and flux divergences estimated from multi-layer measurements of mesospheric nightglow layers

Measurements of dynamic parameters of atmospheric gravity waves, mainly the vertical wavelength, the momentum flux and the momentum flux divergence, are affected by large uncertainties crudely documented in the scientific literature. By using methods of error analysis, we have quantified these uncertainties for frequently observed temporal and spatial wave scales. The results show uncertainties of ～10%, ～35%, and ～65%, at least, in the vertical wavelength, momentum flux, and flux divergence, respectively. The large uncertainties in the momentum flux and flux divergence are dominated by uncertainties in the Brunt-Väisälä frequency and in spatial separation of the nightglow layers, respectively. The measured uncertainties in fundamental wave parameters such as the wave amplitude, intrinsic period, horizontal wavelength, and wave orientation are ～10% or less and estimated directly from our nightglow image data set. Other key environmental quantities such as the scale height and the Brunt-Väisälä frequency, frequently considered as constants in gravity wave parameter estimations schemes, are actually quite variable, presenting uncertainties of ～4% and ～9%, respectively, according to the several solar activity and seasonal atmosphere scenarios from the NRLMSISE-00 model simulated here.     

The flyby anomaly: A case for strong gravitomagnetism?

In the last two decades an anomalous variation in the asymptotic velocity of spacecraft performing a flyby manoeuvre around Earth has been discovered through careful Doppler tracking and orbital analysis. No viable hypothesis for a conventional explanation of this effect has been proposed and its origin remains unexplained. In this paper we discuss a strong transversal component of the gravitomagnetic field as a possible source of the flyby anomaly. We show that the perturbations induced by such a field could fit the anomalies both in sign and order of magnitude. But, although the secular contributions to the Gravity Probe B experimental results and the Lense–Thirring effect in geodynamics satellites can be made null, the detailed orbital evolution is easily in conflict with such an enhanced gravitomagnetic effect.     

On the performance of IRI-2016 to predict the North-South asymmetry of the equatorial ionization anomaly around 73°E longitude

The ionospheric total electron content (TEC) in both northern and southern Equatorial anomaly regions are examined by using the Global Positioning System (GPS) based TEC measurements around 73°E Longitude in the Asian sector. The TEC contour charts obtained at SURAT (21.16°N; 72.78°E; 12.9°N Geomagnetic Lat.) and DGAR (7.27°S; 72.37°E; 15.3°S Geomagnetic Lat.) over 73°E longitude during a very low solar activity phase (2009) and a moderate solar activity (2012) phase are used in this study. The results show the existence of hemispheric asymmetry and the effects of solar activity on the EIA crest in occurrence time, location and strength. The results are also compared with the TEC derived by IRI-2016 Model and it is found that the North-South asymmetry at the EIA region is clearly depicted by IRI-2016 with some discrepancies (up to 20% in the northern hemisphere at SURAT and up to 40% in the southern hemisphere at DGAR station for June Solstice and up to 10% both for SURAT and DGAR for December Solstice). This discrepancy in the IRI-2016 model is found larger during the year 2012 than that during the solar minimum year 2009 at both the hemispheres. Further, an asymmetry index, (A_i) is determined to illustrate the North-South asymmetry observed in TEC at EIA crest. The seasonal, annual and solar flux dependence of this index are investigated during both solstices and compared with the TEC derived by IRI.