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231.
G. Cremonese M. T. Capria V. Achilli F. Angrilli P. Baggio C. Barbieri J. Baumgardner N. Bistacchi F. Capaccioni A. Caporali I. Casanova S. De Bei G. Forlani S. Fornasier D. Hunten W. H. Ip M. Lazzarin I. Longhi L. Marinangeli F. Marzari M. Massironi P. Masson M. Mendillo B. Pain G. Preti R. Ragazzoni J. Raitala G. Salemi M. Sgavetti A. Sprague E. Suetta M. Tordi S. Verani J. K. Wilson L. Wilson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,33(12):2182-2188
MEMORIS (MErcury Moderate Resolution Imaging System) is a wide angle camera (WAC) concept for the ESA mission BepiColombo. The main scientific objectives consist of observing the whole surface of Mercury in the spectral range of 400–1000 nm, with a spatial resolution of 50 m per pixel at peri-Herm (400 km) and 190 m at apo-Herm (1500 km). It will obtain a map of Mercury in stereo mode allowing the determination of a digital elevation model with a panchromatic filter through two different channels. The camera will also perform multispectral imaging of the surface with a set of 8–12 different broad band filters. A third channel dedicated to limb observations will provide images of the atmosphere. MEMORIS will thus monitor the surface and the atmosphere during the entire mission, providing a unique opportunity to study the relationship between surface regions and the atmosphere, as suggested by ground-based observations and theory. 相似文献
232.
B. Paul B.K. De A. Guha 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(3):1227-1233
Following Tanna et al. (2013), we computed the percentage of occurrence of S4 index for the period of 2012–2015 using the data of the dual frequency GPS receiver at the Tripura University, Agartala station (23.76°N, 91.26°E) situated at the northern crest of the equatorial ionization anomaly (EIA) region of the Indian Subcontinent. We have observed discrepancy in the results contradicting the actual scintillation occurrence. The distinctly noticeable discrepancy is that the maximum occurrence month is shifted to April 2013 instead of March 2014. The problem arises due to the denominator term used in the percentage of occurrence ratio i.e. the total number of days of observed scintillation activity during the complete period under consideration. But the conventional percentage of occurrence methodology uses the number of days of observation (the total number of days for which data is available) during each month in the denominator. It correctly assigns the maximum occurrence to March 2014 instead of April 2013 and the obtained monthly statistics follow the solar activity during this period. 相似文献
233.
234.
Design Principles of MIMO Radar Detectors 总被引:4,自引:0,他引:4
This paper considers the problem of multiple-input multiple-output (MIMO) radars employing space-time coding (STC) to achieve diversity. To this end, after briefly outlining the model of the received echo, a suitable detection structure is derived, and its performance is expressed in closed form as a function of the clutter statistical properties and of the space-time code matrix. Interestingly, this receiver requires prior knowledge of the clutter covariance, but the detection threshold is functionally independent thereof. At the transmitter design stage, we give two criteria for code construction: the first is based on the classical Chernoff bound, the second is an information-theoretic criterion. Interestingly, the two criteria lead to the same condition for code optimality, which in turn specializes, under the assumption of uncorrelated clutter and square code matrix, in some well-known full-rate space-time codes. A thorough performance assessment is also given, so as to establish the optimum achievable performance for MIMO radar systems. 相似文献
235.
Johan De Keyser 《Space Science Reviews》2005,121(1-4):225-235
The Earth’s magnetosphere is an accessible region for improving our knowledge of the dynamics of collisionless plasmas. We
focus here on the magnetopause a typical plasma discontinuity. We discuss recent developments in describing the structure
of the magnetopause by means of reconstruction techniques, which translate in situ data into spatial information. We review short- and long-duration reconstruction methods and discuss the ideas behind them.
The emphasis is on long-duration reconstruction methods in a multi-spacecraft context. 相似文献
236.
Antonini M. De Luise A. Ruggieri M. Teotino D. 《Aerospace and Electronic Systems Magazine, IEEE》2005,20(9):25-29
A possible classification of satellites can be related to their capability to provide or not provide real-time services. Nonreal-time systems store the information, and forward it to destination later, usually by means of low Earth orbit (LEO) satellites. Nowadays the main application of these systems is small data exchange to/from remote sites where no other communication infrastructure is available, hence, covering a niche market. Low on-board memory storage capability and, moreover, low bit rate due to little bandwidth allocated for these systems do not allow us to collect and forward a considerable volume of data in the short visibility window of the satellite passage. New applications and services can be conceived through the deployment of new systems able to overcome the above-described limitations, while existing applications can be provided more cost-effectively. These aspects are addressed together with an experimental interactive system which allows huge data collection in W-band and for forwarding to the Internet. 相似文献
237.
Polarization diversity detection in compound-Gaussian clutter 总被引:1,自引:0,他引:1
De Maio A. Alfano G. Conte E. 《IEEE transactions on aerospace and electronic systems》2004,40(1):114-131
We present the problem of polarization diversity detection in compound-Gaussian clutter with unknown covariance matrix. To this end we assume that a set of secondary data, free of signal components and with the same covariance structure of the cell under test, is available. Due to the lack of a uniformly most powerful (UMP) detector we resort to a design procedure based upon the Rao and the Wald tests. Specifically we first derive the Rao and the Wald tests assuming that the covariance matrix is known, and then we substitute into the derived decision rules a suitable estimate of the clutter covariance. Interestingly, the newly proposed detectors share the constant false alarm rate (CFAR) property with respect to the texture statistical characterization. Moreover simulation results have shown that the Wald test based detector ensures a performance level higher than the Rao test. We have also conducted a further performance analysis, in the presence of real clutter data and in comparison with the previously proposed generalized likelihood ratio test (GLRT) based receivers, which highlights that, in general, the Wald test receiver outperforms its counterparts. Finally, since the newly proposed decision rules as well as the previously designed GLRTs do not ensure the CFAR property with respect to the clutter covariance matrix, we have developed a sensitivity analysis on the probability of false alarm (P/sub fa/), based on simulated clutter with covariance matrix estimated from real radar data. The results have shown that (P/sub fa/) is only slightly affected by variations in the clutter correlation properties and hence the CFARness is substantially achieved. 相似文献
238.
贫困大学生信息的档案化管理与"绿色通道"的建立 总被引:1,自引:0,他引:1
近年来,贫困大学生人数日益增加,他们的心理问题也愈益突出,引起社会的普遍关注.实现高校贫困大学生信息的档案化管理和建立相应的"绿色通道",可以有效地预防贫困大学生的心理问题,从而促进他们全面、健康地发展. 相似文献
239.
Conte E. De Maio A. Farina A. 《IEEE transactions on aerospace and electronic systems》2005,41(1):205-218
We design three statistical tests to ascertain whether radar data comply with the hypotheses of multivariate Gaussianity, spatial homogeneity, and covariance persymmetry, respectively. For the first issue we develop a statistical procedure based on quadratic distributional distances, which exploits the representation of Gaussian vectors in generalized spherical coordinates. As to the spatial homogeneity we propose a technique, based on the Kolmogorov-Smirnov (KS) test, relying on the properties of quadratic forms constructed from Gaussian vectors and Wishart distributed matrices. Finally, in order to analyze the persymmetry property of the disturbance covariance matrix, we design a testing procedure based on the generalized likelihood ratio test (GLRT). We thus apply the new tests to L-band experimentally measured clutter data, collected by the MIT Lincoln Laboratory Phase One radar, at the Katahdin Hill site. The results show that the multivariate Gaussian hypothesis for the considered data file is reasonable. On the contrary the assumption of spatial homogeneity can be done only within small clutter regions which, in general, exhibit also a persymmetric covariance matrix. 相似文献
240.
高超声速飞行器模型不确定性影响分析 总被引:2,自引:2,他引:0
吸气式高超声速飞行器具有严重的弹性机体和推进系统耦合的典型特征,其分析模型存在较大的不确定性,标称系统和真实系统之间存在偏差,因此研究不确定性对稳定性的影响对于控制器设计具有重要意义。针对典型的乘波体构型高超声速飞行器,建立了气动/结构/推进相互耦合的动力学模型,总结了建模中的不确定因素并将其以加性不确定模型的形式表示出来。以不确定性矩阵的最大奇异值为边界模型,以不确定性矩阵的H∞范数来表示不确定性因素对稳定性影响的大小,并通过不确定性矩阵的边界曲线分析不确定因素对模态特性的影响。结果表明,惯性因素的不确定性对稳定性的影响最大,而且其对飞行器的短周期模态和弹性模态均有较大的影响;同时,对于这一类飞行器的控制器设计必须考虑飞行器的弹性自由度。 相似文献