Navigation Accuracy Category-Position Models and Estimate Position Uncertainty Calculations for TIS-B System

Navigation accuracy category-position (NACp) is an important parameter for system accuracy of traffic information service-broadcast (TIS-B), which is determined by estimate position uncertainty (EPU). Centered about the problems that the existing EPU calculation based on noise measurement is low in accuracy and unfit for describing uncorrected biases in target reports, this article analyses the traditional NACp model, and uses the least square estimation (LSE) in EPU calculation. Furthermore, it proposes an extended NACp model, which considers both noise and biases and acquires EPU estimation with the help of approximate multiplex Taylor expression. Analysis and simulation show that the proposed method not only leads to significant improvement of the accuracy of EPU calculation, but is fit for EPU calculation with tracking biases in TIS-B system as well. As such it can find application in practice to depict different kinds of error models in TIS-B system.     

基于话音／数据综合通信网络的空中交通管制中心之间的广域联接

话音／数据综合通信网络是民航中南地区传输雷达信号、话音移交信号、 Ａ Ｆ Ｔ Ｎ 信号、 Ｖ Ｈ Ｆ 信号等的广域网络。网络采用了目前先进的交换机、民航卫星网络、邮电 Ｄ Ｄ Ｎ 网络，把位于中南六省区的话音和数据信号进行集成传输，适应了空管业务的快速增长，提高了信号传输的可靠性，减少信号的延迟，节省了运行成本。     

数传接收机自动检测设备的设计

介绍了某型数传接收机自动检测设备的设计，该检测设备采用硬件平台、软件平台的模式，具有自动化程度高、通用性和扩展性强等优点，重点介绍了专用测试资源双脉冲信号源的设计和设备故障诊断方法。应用该设备可以完成对数传接收机的出厂调试和修理厂定检维修等功能。     

ALGORITHMS FOR TRACKING MANEUVERING TARGET WITH PHASED ARRAY RADAR

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Experimental investigations on the power extraction of a turbine driven by a pulse detonation combustor

In order to grasp the interaction mechanism between the pulse detonation combustor（PDC）and the turbine,the experimental work in this paper investigates the key factors on the power extraction of a turbocharger turbine driven by a PDC.A PDC consisting of an unvalved tube is integrated with a turbocharger turbine which has a nominal mass flow rate of 0.6 kg/s and50000 r/min.The PDC-turbine hybrid engine is operated on gasoline-air mixtures and runs for6＋min to achieve a thermal steady state,and then the engine performance is evaluated under different operating conditions.Results show that the momentum difference per unit area between the turbine inlet and outlet plays an important role in the power extraction,while the pressure peak of the detonation has little effect.The equivalence ratio of fuel and air mixture and the transition structure between PDC and turbine are also important to the power extraction of the turbine.The present work is promising as it suggests that the performance beneft of a PDC-turbine hybrid engine can be realized by increasing the momentum difference per unit area through the optimal design of transition section between the PDC and turbine.     

Meteor radar temperatures over Collm (51.3°N, 13°E)

The method of obtaining absolute temperature estimates by measuring the ambipolar diffusion coefficient with meteor radars in the mesopause region is basically well known. However, there is still a need to refine and adjust the background temperature gradient model which is necessary to calculate the temperature values. Therefore, a detailed comparison with independent temperature measurements is necessary to evaluate the performance of the method and to obtain more information about the temperature gradient. Recent studies provide some evidence that the impact of the gradient model on temperature estimates affects the absolute temperatures, but that it is of minor importance for wave analysis. This paper focuses on a detailed evaluation of the meteor radar temperatures by comparing them with SABER satellite and OH-emission mesopause region temperatures. The seasonal variation of the observed temperatures is well reproduced by the COMMA general circulation model.     

隐身卫星的现状及其在空间攻防中的应用

空间攻防是空间技术的一个主要研究内容。隐身卫星正以独特的优势在空间对抗领域中发挥重要作用。首先论述了卫星隐身的主要手段,其次分析了国内外隐身卫星的发展现状,最后详细介绍了隐身卫星在未来空间攻防中的应用前景。     

Detection of regolith buried water stream channels on Mars with the help of synthetic aperture radar

A major theme in the study of Mars is the search for evidence that water was present in the past or is present today, either at or below the surface. Biological life is connected to water. Hence much research is focused on the detection of water stream channels, which in the past flowed on Mars. In these areas, the petrified remains of the former life on Mars may be found. These channels may be under the regolith layer; however, the radio wave penetrating ability allows for the detection of these channels under the regolith.     

NOVEL RADAR SIGNAL SORTING METHOD BASED ON GEOMETRIC COVERING

With the increase of complexity of electromagnetic environment and continuous appearance of advanced system radars, signals received by radar reconnaissance receivers become even more intensive and complex. There- fore, traditional radar sorting methods based on neural network algorithms and support vector machine （SVM） cannot process them effectively. Aiming at solving this problem, a novel radar signal sorting method based on the cloud model theory and the geometric covering algorithm is proposed. By applying the geometric covering algo- rithm to divide input signals into different covering domains based on their distribution characteristics, the method can overcome a typical problem that it is easy for traditional sorting algorithms to fall into the local extrema due to the use of complex nonlinear equation to describe input signals. The method uses the cloud model to describe the membership degree between signals to be sorted and their covering domains, thus it avoids the disadvantage that traditional sorting methods based on hard clustering cannot deinterleave the signal samples with overlapped param- eters. Experimental results show that the presented method can effectively sort advanced system radar signals with overlapped parameters in complex electromagnetic environment.     

An overview of radar soundings of the martian ionosphere from the Mars Express spacecraft

The Mars Express spacecraft carries a low-frequency radar called MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) that is designed to study the subsurface and ionosphere of Mars. In this paper, we give an overview of the ionospheric sounding results after approximately one year of operation in orbit around Mars. Several types of ionospheric echoes are commonly observed. These include vertical echoes caused by specular reflection from the horizontally stratified ionosphere; echoes from a second layer in the topside ionosphere, possibly associated with O⁺ ions; oblique echoes from upward bulges in the ionosphere; and a variety of other echoes that are poorly understood. The vertical echoes provide electron density profiles that are in reasonable agreement with the Chapman photo-equilibrium model of planetary ionospheres. On the dayside of Mars the maximum electron density is approximately 2 × 10⁵ cm⁻³. On the nightside the echoes are often very diffuse and highly irregular, with maximum electron densities less than 10⁴ cm⁻³. Surface reflections are sometimes observed in the same frequency range as the diffuse echoes, suggesting that small isolated holes exist in the nightside ionosphere, possibly similar to those that occur on the nightside of Venus. The oblique echoes arise from upward bulges in the ionosphere in regions where the crustal magnetic field of Mars is strong and nearly vertical. The bulges tend to be elongated in the horizontal direction and located in regions between oppositely directed arch-like structures in the crustal magnetic field. The nearly vertical magnetic field lines in the region between the arches are thought to connect into the solar wind, thereby allowing solar wind electrons to heat the lower levels of the ionosphere, with an attendant increase in the scale height and electron density.