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排序方式: 共有264条查询结果,搜索用时 140 毫秒
1.
本文研究了入射波电场为任意线极化时,平直地面反射波中左旋圆极化分量和右旋圆极化分量的数学描述,引入了地面对这类波的等效反射系数的概念,并给予了物理解释,讨论了应用的有关问题。  相似文献   
2.
介绍几种航天雷达高度表,其中包括弹载雷达高度表、“土星”雷达高度表和“天空实验室”雷达高度表,最后介绍一种卫星雷达高度表的设计方法。  相似文献   
3.
讨论了测向定位中双站交会定位及定位误差分析、三站交会定位、多站交会定位若干问题,首次尝试将最小二乘法和递推最小二乘法用于多站测向定位,减少了大量的矩阵求逆,数据利用效率高,可以提高测向定位的精度和简化运算。特别是在存在多径效应的情况下,有利于发现和去除野值。在测向站组网数据的处理和应用上有较强的实用性和推广价值。  相似文献   
4.
张立东 《上海航天》2004,21(6):59-61
在单天线横截面方向图计算公式的基础上,计算了圆柱体导弹引信双天线、三天线和四天线布局的方向图。讨论了不同布局下引信载频、弹体直径及天线布局与作用盲点的关系。双天线布局的实际测试表明,测试值与计算结果较为吻合,所用的计算方法正确,可为引信天线布局与引信工作频率确定提供设计依据。  相似文献   
5.
The existence of a “dense” lunar ionosphere has been controversial for decades. Positive ions produced from the lunar surface and exosphere are inferred to have densities that are ?106107 m?3 near the surface and smaller at higher altitudes, yet electron densities derived from radio occultation measurements occasionally exceed these values by orders of magnitude. For example, about 4% of the single-spacecraft radio occultation measurements from Kaguya/SELENE were consistent with peak electron densities of ~3×108 m?3. Space plasmas should be neutral on macroscopic scales, so this represents a substantial discrepancy. Aditional observations of electron densities in the lunar ionosphere are critical to resolving this longstanding paradox. Here we theoretically assess whether radio occultation observations using two-way coherent S-band radio signals from the Lunar Reconnaissance Orbiter (LRO) spacecraft could provide useful measurements of electron densities in the lunar ionosphere. We predict the uncertainty in a single LRO radio occultation measurement of electron density to be ~3×108 m?3, comparable to occasional observations by Kaguya/SELENE of a dense lunar ionosphere. Thus an individual profile from LRO is unlikely to reliably detect the lunar ionosphere; however, averages of multiple (~10) LRO profiles acquired under similar geophysical and viewing conditions should be able to make reliable detections. An observing rate of six ingress occultations per day (~2000 per year) could be achieved with minimal impact on current LRO operations. This rate compares favorably with the 378 observations reported from the single-spacecraft experiment on Kaguya/SELENE between November 2007 and June 2009. The large number of observations possible for LRO would be sufficient to permit wide-ranging investigations of spatial and temporal variations in the poorly understood lunar ionosphere. These findings strengthen efforts to conduct such observations with LRO.  相似文献   
6.
Stellar flares     
Radio and X-ray observations of stellar flares provide the most direct probes of energy relaase particle acceleration, and energy transport on stars other than the Sun. In this review, the observational basis for our understanding of the flare phenomenon on other stars is briefly described and outstanding interpretive and theoretical issues are discussed. I shall confine my attention to objects which are solar-like, to the extent that they possess deep convective envelopes and display activity which is presumed to be magnetic in origin. These include pre-main sequence objects, classical flare stars, and close binaries. Future directions are briefly discussed.  相似文献   
7.
随着全球导航卫星系统(Global Navigation Satellite System,GNSS)掩星大气探测技术的兴起,GNSS遥感探测数据在气象数据资源中逐步占据重要地位,但是目前的掩星探测数量远不能满足数值天气预报等应用的需求,未来更需要充分利用GNSS信号资源,开展更大规模的GNSS掩星卫星星座探测.本文以世界气象组织发布的大气海洋数据需求为参考,提出新一代GNSS遥感探测星座任务需求与设计约束.在理想大气模型假设下,利用几何解析方法研究了探测卫星星座构型参数对探测性能的影响,并建立了新一代GNSS遥感探测卫星星座设计基本准则.以风云卫星为子星座,给出了星座规模同为40颗的三种GNSS遥感探测微纳卫星星座设计方案.研究结果表明,具备该规模的探测星座可满足数值天气预报等气象应用的最低数据需求,三种构型方案中,由高、中、低倾角三组Walker子星座与风云卫星子星座组建的GNSS遥感探测星座探测性能最优.  相似文献   
8.
Global observations of S4 amplitude scintillation index by the GPS Occultation Sounder (GNOS) on FengYun-3 C (FY3C) satellite reveal global dynamic patterns of a strong pre-midnight scintillations in F-region of the ionosphere during the St. Patrick’s Day geomagnetic super storm of 17–19 March 2015. The observed strong scintillations mainly occurred in the low latitudes, caused by equatorial plasma bubbles. During the main storm phase (March 17), the scintillations were first triggered in the New Zealand sector near 160°E longitudes, extending beyond 40°S dip latitude. They were also enhanced in the Indian sector, but significantly suppressed in East Asia near 120°E longitude and in Africa around 30°E longitude. During the initial recovery phase (March 18–19), the global scintillations were seldom observed in GNOS data. During the later recovery phase (after March 19), the scintillations recovered to the pre-storm level in Indian, African, and American sectors, but not in East Asian and any of Pacific sectors. These results closely correlate with observations of the density depletion structures by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite, and ground-based instruments. Such consistency indicates reliability of our scintillation sensing approach even in a case-by-case comparison study. The prompt penetration electric field and disturbance dynamo electric field are suggested as the main factors that control the enhancement and inhibition of the scintillations during the storm, respectively.  相似文献   
9.
In this paper, we compared the F2-Layer critical frequency (foF2) derived from FORMOSAT-3/COSMIC radio occultation (RO) and ionosondes at Chiang Mai, Chumphon and Kototabang during the years 2008–2015 to evaluate the performance of COSMIC RO over Southeast Asia region. The results show that the time development of foF2 values derived from COSMIC RO generally agrees well with those from ionosonde measurements. However, the differences between the foF2 derived from COSMIC RO and that derived from ionosonde observations display latitudinal dependence. COSMIC RO tends to underestimate foF2 at Chiang Mai and Kototabang, which is near to the north EIA crest and the south one, respectively, while a little overestimate foF2 at Chumphon, which is close to the geomagnetic equator. COSMIC RO agrees best with ionosonde at Chumphon and worst at Chiang Mai. At each ionosonde station, the quality of COSMIC RO data degrades with the increase of solar activity. In addition, at the station Chiang Mai and Kototabang, COSMIC RO performs better in summer than in equinox and winter. Furthermore, the differences in foF2 derived from COSMIC RO and that from ionosonde measurements vary with local time, i.e., the differences in foF2 are generally smaller at night and larger in noontime when equatorial ionization anomaly (EIA) is well developed.  相似文献   
10.
射频识别(RFID)技术现已广泛用于物流、金融、零售等各个行业.航空领域的RFID应用起步较晚,通过对RFID技术在飞机制造商、原始设备生产厂家(OEM)、航空公司的一些典型的应用案例的分析,提出RFID技术应用于航空领域所面临的挑战及必要性,为其未来航空业自动识别技术的发展指明了方向.  相似文献   
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