排序方式: 共有74条查询结果,搜索用时 15 毫秒
51.
52.
Jianguo Yan Fei Li Jingsong Ping James M. Dohm Yuji Harada Zhen Zhong 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
An improvement to the Martian gravity field may be achieved by means of future orbiting spacecraft with small eccentricity and low altitude exemplified through a newly proposed mission design that may be tested in upcoming reconnaissance of Mars. Here, the near equatorial orbital character (with an inclination approximating 10°, eccentricity as 0.01 and semi-major axis as 4000 km) is considered, and its contribution to Martian gravity field solution is analyzed by comparing it with a hypothetical polar circular orbiter. The solution models are evaluated in terms of the following viewpoints: power spectra of gravity field coefficients, correlations of low degree zonal coefficients, precise orbit determination, and error distribution of both Mars free air gravity anomaly and areoid. At the same time, the contributions of the near equatorial orbiters in low degree zonal coefficients time variations are also considered. The present results show that the near equatorial orbiter allows us to improve the accuracy of the Martian gravity field solution, decrease correlation of low degree zonal coefficients, retrieve much better time variable information of low degree zonal coefficients, improve precise orbit determination, and provide more accurate Mars free air gravity anomaly and areoid around the equatorial region. 相似文献
53.
54.
55.
为应对海上作战平台的威胁,有效防御和打击这类目标,设计了5种天基海洋监视体系方案,通过利用模糊理论量化和聚合评价指标,利用层次分析法确定各层指标权重,对其进行了综合评价和优劣排序。所采用的模糊综合评价方法能够比较有效地处理定性、定量指标的量化与聚合问题,评价结果能够合理区分各方案的优劣情况。 相似文献
56.
依据经典的浮标应召搜潜方法,结合实际搜潜过程,以某型反潜巡逻机为背景,建立了反潜巡逻机布放圆形阵、方形阵和三角形阵搜潜航路规划的数学模型。对3种阵形的搜潜效能进行分析,仿真了初始距离、潜艇初始位置散布、潜艇经济航速和海洋环境噪声级对浮标阵搜潜效能的影响。仿真结果分析表明:相同条件下,方形阵的搜潜效能要略高于圆形阵和三角形阵的搜潜效能;3种包围阵的搜潜效能均随初始距离、初始位置散布、潜艇经济航速和海洋环境噪声级的增大而降低。 相似文献
57.
The interaction of the solar wind with the Martian exosphere and ionosphere leads to significant loss of atmosphere from the
planet. Spacecraft data confirm that this is the case. However, the issue is how much is actually lost. Given that spacecraft
coverage is sparse, simulation is one of the few ways for these estimates to be made. In this paper the evolution of our attempts
to place bounds on this loss rate will be addressed. Using a hybrid particle code the loss rate with respect to solar EUV
flux is addressed as well as a variety of numerical and chemical issues. The progress made has been of an evolutionary nature,
with one approach tried and tested followed by another as the simulations are improved and better estimates are produced.
The results to be reported suggest that the ion loss rates are high enough to explain the loss of water from Mars during earlier
solar epochs. 相似文献
58.
Deepak Dhingra 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Floors of similar sized craters, representing material from similar depth horizons, have been studied to explore their suitability as mineralogy indicators at various depths within the lunar crust. Clementine UV–vis multispectral data was used to generate mineral abundance maps of crater floors and surroundings using a modified version of algorithm given by Pieters et al. (2001) [Pieters, C.M., Head, J.W., Gaddis, L., Jolliff, B. and Duke, M. Rock types of the south pole aitken basin and extent of basaltic volcanism, JGR (106) E11, 28001–28022, 2001.]. Substantial processing of the crater floor material due to variety of geological processes is evident in the generated maps, making straight forward interpretations difficult. However, systematic compositional trends in fresh craters on the floors of target craters seem to indicate the feasibility of such an effort. 相似文献
59.
G. Salamunićcar 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The Mathematical Statistics Theory (MST) and the Mathematical Theory of Stochastic Processes (MTSP) are different branches of the more general Mathematical Probability Theory (MPT) that can be used to investigate physical processes through mathematics. Each model of a stochastic process, according to MTSP, can provide one or more interpretations in the MST domain. A large body of work on impact crater statistics according to MST exists, showing cumulative crater frequency (N km−2) as a function of age (years) for some particular crater diameter. However, this is only one possible representation in the MST domain of the bombardment of the planetary surface modeled as a stochastic process according to MTSP. The idea that other representations are possible in the MST domain of the same stochastic process from MTSP has been recently presented. The importance of the approach is that each such mathematical-based interpretation can provide a large amount of new information. Coupled with MOLA data, Topography-Profile Diagrams (TPD) are one of the many examples that can provide a large amount of new information regarding the history of Mars. TPD consists of: (1) Topography-Profile Curve (TPC), which is a representation of the planet’s topography, (2) Density-of-Craters Curve (DCC), which represents density of craters, (3) Filtered-DCC (FDCC), which represents DCC filtered by a low-pass filter, included with the purpose of reducing the noise, and (4) Level-of-Substance-Over-Time Curve (LSOTC), which represents interpretation of the influence on the distribution of craters shown by FDCC. TPC uniquely corresponds to the computation of TPD, whereas DCC depends on algorithms for computing the elevation of each crater according to the topography, center coordinates, and radius of impact crater, and FDCC relies on the architecture of the custom designed low-pass filter for filtering DCC. However, all variations of DCC and FDCC, which includes the various impact crater data sets, showed a correlation among the density of craters and elevation over 70–80% of the planet surface. Additionally, if we assume that the ocean primarily caused the noted correlation, LSOTC offers a mathematical approach for estimating topographic change of the ocean’s extent over time. Accordingly, TPD is the first new practical application of MTSP to lunar and planetary sciences, showing correlation of topography to a physical process. 相似文献
全球导航卫星系统反射(GNSS-R)技术应用中需GNSS-R信号模拟器来测试反射信号接收机,以降低成本。为此,提出了一种基于双基雷达原理的全球导航卫星系统(GNSS)海面反射信号建模方法。首先,分析了GNSS-R双基雷达遥感原理,根据延迟和多普勒频率在海面的分布特点,选择海面的反射点,并计算相应反射单元的面积;然后,对散射系数进行了计算;最后,对多条反射信号的合路信号进行相关的仿真验证。验证结果表明:模拟的海面反射信号的相关功率曲线与ZV模型理论曲线的相关系数优于0.92,能够有效地用于GNSS海面反射信号的生成。 相似文献