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在轨人造目标的地基观测光谱存在红化效应,影响对目标反射光谱的理解应用.目标在进入空间环境后外露材料表面粗糙度发生变化.本文结合材料的光谱散射特性、卫星轨道和观测条件,仿真分析了卫星表面材料粗糙度变化对红化效应的影响.基于文献中实验数据,设计不同粗糙度的卫星表面材料样本,模拟空间环境中材料表面粗糙度的变化.利用双向反射分布函数,建立不同粗糙度材料样本的光谱散射模型.理论模拟结果表明,材料表面粗糙度的变化会影响其光谱散射特性,散射光谱形态和散射分布取决于粗糙度及入射-反射几何关系.引入网格剖分和可见面片,利用材料双向反射分布函数,仿真计算卫星表面材料在不同粗糙度状态下,整个卫星在可见光波段的反射光谱信号.仿真结果表明,随着卫星表面材料粗糙度的增加,其反射光谱在600nm之后随波长增加而呈现上升趋势,这表明空间环境中外露材料表面粗糙度变化是卫星产生红化效应的原因之一. 相似文献
425.
颗粒增强金属基纳米复合材料脉冲电沉积制备研究 总被引:2,自引:1,他引:1
采用脉冲电沉积,在普通碳钢表面制备了Ni-W-P/CeO2-SiO2颗粒增强金属基纳米复合材料,研究了脉冲峰值电流密度和脉冲占空比对电沉积过程的影响,采用纳米颗粒的质量百分含量、沉积速率、显微硬度和表面形貌进行表征。结果表明:增加脉冲峰值电流密度或脉冲占空比,Ni—W—P基质金属晶粒细化,CeO2和SiO2纳米颗粒的质量百分含量提高。当脉冲频率为1000Hz,脉冲峰值电流密度和脉冲占空比分别为40A/dm^2和50%时,沉积速率最快(56.24μm/h),显微硬度最高(712Hv)。此时,Ni—W—P基质金属轮廓清晰,晶粒细小而均匀,CeO2和SiO2纳米颗粒以弥散态均匀分散在基质金属中。 相似文献
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Thiago Statella Pedro Pina Erivaldo Antônio da Silva 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
The paper presents and evaluates three methods for automatically estimating the main orientation of Martian dust devil tracks in MOC and HiRISE images. Inferring such information about dust devils from their tracks is important to better understand the near surface wind. The methods considered were based on gradient direction, directional openings and morphological granulometry. The accuracy of the methods was asserted by comparing the results to a set of directions estimated visually and assumed to be the ground truth. The higher accuracy was reached using directional openings. Besides, the directions inferred by this method were compared to those predicted by the GCM and the results agreed. 相似文献
428.
Stefaan Van wal Simon Tardivel 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(1):411-435
The impact of nonspherical bodies is complex, even at low velocities where contacting bodies are assumed to be rigid. Models of varying complexity (e.g. finite element methods) can be used to evaluate such impacts, but it is advantageous to use impulsive models such as that by Stronge, which are computationally inexpensive and governed by (fixed) material interaction coefficients. Stronge’s model parameterizes nonspherical rigid-body impacts with energetic restitution and Coulomb friction coefficients. This model was successfully used in large-scale simulations of ballistic lander deployment to asteroids and comets, whose trajectories involve dozens of chaotic bounces. To better understand the complex dynamics of these bouncing trajectories, this paper performs a dedicated study of idealized bouncing in two dimensions and on a flat plane, in order to limit the involved degrees of freedom. Using a numerical implementation of Stronge’s model, the motion of a bouncing square is simulated with different impact conditions: the square’s impact attitude, velocity, and mass distribution as well as the surface restitution and friction coefficients. The simulation results are used to investigate how these conditions affect the bouncing motion of the square, with a distinction between first impacts with zero angular velocity and successive impacts in which the square is spinning. This reveals how a single “macroscopic” bounce that separates two ballistic arcs may often consist of multiple micro-impacts that occur in quick succession. For the different impact conditions, we show how the number of micro-impacts per macro-bounce varies, as well as the normal, tangential, and total kinematic restitution coefficients. These are different from the energetic material restitution coefficient that parameterizes the impact. Finally, we examine how the settling time and distance of the bouncing trajectories change. These trends provide insight into the bouncing motion of ballistic lander spacecraft in small-body microgravity. 相似文献
429.
Xinggang Zhang Shuanggen Jin 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Global positioning system (GPS) observations can be used to estimate the geocenter motion, but are subjected to large uncertainties and effects due to uneven distribution of GPS stations and high-degree aliasing errors. In this paper, uncertainties and effects on geocenter motion estimates from global GPS observations are investigated and assessed with different truncated degrees and selected GPS network distributions based on different plate motion models, including NUVEL-1A, MORVEL56 and ITRF08. Results show that the selected GPS stations have no big effects on geocenter motion estimates based on different plate motion models, while large uncertainties are found at annual and semi-annual components when using different truncated degrees. Correlations of geocenter motion estimates from selected GPS networks with GRACE and SLR are better with truncated degree 3, and higher truncated degrees will degrade geocenter estimates. Smaller RMS also shows better results with the truncated degree 3 and the NUVEL1A has the worse results because more GPS sites are eliminated. For annual signal with truncated degree 3, four GPS strategies can reduce annual amplitudes by about 29.2% in X, 5.6% in Y, and 27.9% in Z with respect to truncated degree 1. Annual phases of all GPS solutions from MORVEL56 and ITRF08 are almost close to the GRACE solution with truncated degrees from 3 to 10, while the semi-annual signals are relatively weaker for all cases. 相似文献
430.
Yonglong Zhang Junfeng Li Xiangyuan Zeng 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(10):3328-3342
Asteroids are coming to be a popular topic in the areas of astrophysical studies and deep space exploration recently. However, surface dynamics of asteroids is still a difficult problem. This paper aims at the motion analysis of surface particles for different asteroids. The dynamical analysis method of particles’ movement is given for three parts: global motion trend, local motion trend and static analysis. A dimensionless parameter ζ is defined to distinguish the predominant term to determine the distribution of effective potential. Three kinds of common asteroids: spheroidal asteroid, spindle-shaped asteroid and dumbbell-shaped asteroid are all discussed for those three parts with different parameter ζ. The motion trend of particles on the surface of each kind of asteroid is given. The static analysis of surface particles for different asteroids is also illustrated. Based on them, some common rules for different shaped asteroids are revealed. This paper could not only provide a reference for asteroid exploration missions but also be meaningful for the research of morphologic evolution of asteroids. 相似文献