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911.
Sinha A. Kirubarajan T. Bar-Shalom Y. 《IEEE transactions on aerospace and electronic systems》2002,38(1):183-203
In a scenario of closely spaced targets special attention has to be paid to radar signal processing. We present an advanced processing technique, which uses the maximum likelihood (ML) criterion to extract from a monopulse radar separate angle measurements for unresolved targets. This processing results in a significant improvement, in terms of measurement error standard deviations, over angle estimators using the monopulse ratio. Algorithms are developed for Swerling I as well as Swerling III models of radar cross section (RCS) fluctuations. The accuracy of the results is compared with the Cramer Rao lower bound (CRLB) and also to the monopulse ratio technique. A novel technique to detect the presence of two unresolved targets is also discussed. The performance of the ML estimator was evaluated in a benchmark scenario of closely spaced targets - closer than half power beamwidth of a monopulse radar. The interacting multiple model probabilistic data association (IMMPDA) track estimator was used in conjunction with the ML angle extractor 相似文献
912.
G. S. Zaslavskiy V. A. Stepan’yants A. G. Tuchin A. V. Pogodin E. N. Filippova A. I. Sheikhet 《Cosmic Research》2014,52(5):353-364
The results of refining the parameters of the Spektr-R spacecraft (RadioAstron project) motion after it was launched into the orbit of the Earth’s artificial satellite in July 2011 showed that, at the beginning of 2013, the condition of staying in the Earth’s shadow was violated. The duration of shading of the spacecraft exceeds the acceptable value (about 2 h). At the end of 2013 to the beginning of 2014, the ballistic lifetime of the spacecraft completed. Therefore, the question arose of how to correct the trajectory of the motion of the Spektr-R satellite using its onboard propulsion system. In this paper, the ballistic parameters that define the operation of onboard propulsion system when implementing the correction, and the ballistic characteristics of the orbital spacecraft motion before and after correction are presented. 相似文献
913.
The fix error, for long-distance XIF navigation systems in which the distances to two or three ground-based stations are determined, is a function of the \"angles of cut\" of the lines of position, the standard deviation of the errors in determination of the distances (ranges) to the stations, and the degree of correlation of these distance determinations. An analysis is made of the errors which occur in a range determination. n. Estimates, applicable when comparing constant-error contours (isograms), are given. The equations for the constant-error contours are derived (based on a spherical earth) as a function of baseline length (and orientation where three stations are used) and the angles of cut of the lines of position. n. Various error isograms were computed and plotted through the use of a digital computer. A number of examples are presented. A method for determining the area covered acceptably by two stations is given and three-station coverage characteristics are discussed. 相似文献
914.
Based on the archive OMNI data for the period 1976–2000 an analysis has been made of 798 geomagnetic storms with D st < −50 nT and their interplanetary sources-large-scale types of the solar wind: CIR (145 magnetic storms), Sheath (96), magnetic clouds MC (62), and Ejecta (161). The remaining 334 magnetic storms have no well-defined sources. For the analysis, we applied the double method of superposed epoch analysis in which the instants of the magnetic storm beginning and minimum of D st index are taken as reference times. The well-known fact that, independent of the interplanetary source type, the magnetic storm begins in 1–2 h after a southward turn of the IMF (B z < 0) and both the end of the main phase of a storm and the beginning of its recovery phase are observed in 1–2 h after disappearance of the southward component of the IMF is confirmed. Also confirmed is the result obtained previously that the most efficient generation of magnetic storms is observed for Sheath before MC. On the average parameters B z and E y slightly vary between the beginning and end of the main phase of storms (minimum of D st and D st * indices), while D st and D st * indices decrease monotonically proportionally to integral of B z and E y over time. Such a behavior of the indices indicates that the used double method of superposed epoch analysis can be successfully applied in order to study dynamics of the parameters on the main phase of magnetic storms having different duration. 相似文献
915.
L.S. Novikov V.N. MileevK.K. Krupnikov A.A. MakletsovB.V. Marjin M.O. RjazantsevaV.V. Sinolits N.A. Vlasova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
The results of magnetospheric plasma fluxes measurement in geosynchronous orbit are presented. The measurements were done onboard the geosynchronous Russian “Electro” spacecraft (SC) in 1995–1997 years. The diurnal variations of the plasma density and temperature were observed at various levels of geomagnetic activity. 相似文献
916.
B. N. Korchuganov G. G. Dol'nikov M. V. Gerasimov O. F. Prilutskii R. Rider G. Waenke T. Economou 《Cosmic Research》2004,42(1):19-22
A theoretical and experimental feasibility study of possible determination of the hydrogen and deuterium concentrations in the surface layers of planetary bodies is presented. The method under study is the recoil proton and deuteron spectrometry of forward scattering in the course of elastic interaction of alpha particles with the nuclei of hydrogen isotopes. The spectra of recoil protons and deuterons were recorded using a prototype model of a hydrogen spectrometer, and these spectra were used to determine the hydrogen concentrations in the samples of different compositions. 相似文献
917.
Chien-Chung Yeh Hong Y.J. Ucci D.R. 《IEEE transactions on aerospace and electronic systems》1987,(6):809-813
A conjecture is made that a tapped delay line adaptive array of K elements can be used to suppress more than K - 1 noncoincidentcenter frequency interferers when the interferers operate within afraction of the signal bandwidth. This is possible because of theavailability in the increased number of degrees of freedom. Asimulation study is made verifying this conjecture for the case of atwo-element array and two interferers. Three and five tap sectionsare used in the simulation. The study indicates that the performanceimproves with increasing number of taps. 相似文献
918.
An efficient and systematic numerical technique is presented for predicting availability of an RF link between a ground station and a communication satellite. This new methodology takes into account the effects of weather and time-varying link geometry caused by satellite motion as well as the customary ground/satellite link parameters. The availability computed under the worst link geometry (5 deg elevation) has been compared with the average availability computed with the new methodology. The results indicate that the traditional worst-case design approach is too pessimistic to provide a realistic design criterion where links operate at K band or above. 相似文献
919.
920.
Abramovich Y.I. Spencer N.K. Gorokhov A.Y. 《IEEE transactions on aerospace and electronic systems》2007,43(3):1017-1051