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1.
大倾角地球同步轨道(GEO)卫星相对地面并非完全静止,其星下点做南北方向的"8"字周期运动,倾角越大运动范围越大.这会降低地面望远镜对其进行凝视观测时的有效曝光时间,无法获得较高的信噪比.对地球同步轨道的监测中,在硬件条件不变的前提下,提出亚像素图像平移叠加方法.根据目标的运动速度和相邻帧图像的时间间隔,在亚像素尺度平移并对齐多幅图像,使GEO目标星象在图像序列中的位置重合,通过叠加多幅序列图像来提高目标信噪比,从而达到提升整个系统探测能力的目的.实测图像叠加结果表明,该方法可以显著提高该类目标的信噪比.叠加5幅图像时,整数像素叠加图像的信噪比约为原图像的1.7倍,而亚像素叠加图像的信噪比是原图像的2倍左右. 相似文献
2.
In order to improve the ability to find the faint and small celestial bodies in the solar system, a method of shifting and stacking images which improves the detection efficiency of faint moving objects is applied to process the sequential optical images. This method determines the existence of moving objects by using the method of false position to pre-estimate the apparent velocities of moving objects, then determines iteratively the accurate positions of moving objects based on the SNR (Signal-to-Noise Ratio) and elongation of stellar image. Using the sequential images of the China Near Earth Object Survey Telescope (CNEOST), we carry out an experiment and succeed in detecting asteroids fainter than 21 magnitude which are invisible on a single image. Thus, the feasibility of this method is verified. 相似文献
3.
使用快速鲁棒性主成分分析(Fast Robust Principal Component Analysis,Fast RPCA)方法对日冕序列图像中的日冕喷流活动进行检测。检测的基本思路是利用快速鲁棒性主成分分析方法中低秩和稀疏分解的思想与日冕序列图像中有着变化尺度稍小且占比较大的随机变化背景成分、变化尺度较大且占比较小的日冕喷流的特点相结合,实现随机复杂多变的动态背景和稀疏运动目标之间的分离,从而检出作为前景变化的日冕喷流。采用太阳动力学天文台(Solar Dynamics Observatory,SDO)卫星的大气成像仪(Atmospheric Imaging Assembly,AIA)两组不同时间段、不同波段、不同观测位置的日冕序列图像作为研究对象。研究内容主要包括日冕序列图像的预处理、日冕喷流检测、快速鲁棒性主成分分析方法与帧间差分法的检测结果对比分析。实验结果表明,与帧间差分法相比,快速鲁棒性主成分分析方法能够检出强度较弱的日冕喷流,且提高了日冕喷流检测的准确度。 相似文献
4.
由于地球电离层的阻挡以及其他干扰,在地面难以进行有效的甚低频天文观测,而使用搭载于绕地或绕月轨道卫星上的甚低频天线进行干涉观测会大大提高观测灵敏度和角分辨率.卫星定位精度会影响观测数据的处理结果,进而影响成图质量,并且会大幅影响飞行项目的复杂度和总成本.首先分析卫星姿态控制精度和星间基线测量精度对绕地轨道甚低频干涉观测的影响,之后对干涉观测中信号延时误差进行仿真,研究延时误差与数据相关处理中条纹搜索范围之间的关系,并对数据计算速度需求进行估算.分析和仿真结果可以辅助相关空间甚低频观测项目总体方案的制定和工程指标的优化. 相似文献
5.
Perturbation theory based on Lie transforms is used to obtain a second-order long period solution for inclination and right ascension of ascending node, of near-equatorial circular satellite orbits. The solution includes the average effects of the Earth's oblateness and the luni-solar perturbations. Three algorithms, useful in mission analysis, are then given. The first algorithm finds the initial node location that results in a decrease of inclination to zero and it also finds the corresponding time to arrive at this zero inclination. The second algorithm determines the initial nodal band that maintains the orbital inclination below a specified value for a given time interval. The third algorithm obtains the initial node location that maximizes the time in which the satellite can be maintained within a given inclination tolerance without the use of any active control and it also obtains the corresponding maximum time. The results of the first and the third algorithms are given for 24-h near-equatorial circular satellite orbits and are cast in simple closed forms. 相似文献
6.
It is shown that the merger times of a satellite galaxy moving on the periphery of the primary galaxy obtained under the impulsive and adiabatic approximations reduce to the decay time predicted by Chandrasekhar's formula for dynamical friction if the satellite galaxy is regarded as a mass point. 相似文献
7.
We investigate the significance of long time stabilty predictions in the light of Nekhoroshev's theory by studying the orbits
of artificial satellites. As a simplified model problem we consider the so-called J2problem for an earth's satellite, neglecting luni-solar perturbations and nonconservative effects. We consider a wide range
of orbits, excluding those which are too close to the critical inclination. Most of the orbits turn out to be stable for times
larger than the estimated age of the solar system, thus proving that, as far as dissipation can be neglected, stability in
Nekhoroshev's sense may be effective for physically realistic systems.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Solar telescopes will never be able to resolve the smallest events at their intrinsic physical scales. Pixel signals recorded
by SOHO/(CDS, EIT, SUMER), STEREO/SECCHI/ EUVI, TRACE, SDO/AIA, and even by the future Solar Orbiter EUI/HRI contain an inherent “spatial noise” since they represent an average of the solar signal present at subpixel scales.
In this paper, we aim at investigating this spatial noise, and hopefully at extracting information from subpixel scales. Two
paths are explored. We first combine a regularity analysis of a sequence of EIT images with an estimation of the relationship
between mean and standard deviation, and we formulate a scenario for the evolution of the local signal-to-noise ratio (SNR)
as the pixel size becomes smaller. Second, we use an elementary forward modeling to examine the relationship between nanoflare
characteristics (such as area, duration, and intensity) and the global mean and standard deviation. We use theoretical distributions
of nanoflare parameters as input to the forward model. A fine-grid image is generated as a random superposition of those pseudo-nanoflares.
Coarser resolution images (simulating images acquired by a telescope) are obtained by rebinning and are used to compute the
mean and standard deviation to be analyzed. Our results show that the local SNR decays more slowly in regions exhibiting irregularities
than in smooth regions. 相似文献
9.
研究了在高空电离层中运动的带电荷的卫星受电感应阻力后对轨道根数产生的摄动影响。研究结果表明 ,电感应阻力对带电卫星的轨道半长轴、轨道偏心率、近地点赤经、历元平赤经均有周期摄动影响 ,但除对半长轴有长期摄动效应外对其它轨道根数均无长期摄动。轨道倾角和升交点赤经不受摄动影响。文中以飞行在高度 1 50 0km的电离层中的导体卫星作为算例。计算结果显示 :带电导体卫星在高空电离层中带有一定电量时电感应阻力对轨道半长轴的缩短产生显著效应 相似文献
10.
暗弱天然卫星与主带小行星相比,具有亮度低、速度变化快的特点.在观测这类天体时,不能简单地延长曝光时间来提高其信噪比.尝试观测多幅短曝光的CCD (chargecoupled device)图像,采用移位堆叠(shift-and-add)方法,希望提高目标成像的信噪比,获得暗弱天然卫星的精确测量结果.使用2018年4月9—12日夜间,中国科学院云南天文台1 m望远镜(1 m望远镜)拍摄的木星5颗暗卫星的229幅CCD图像,实施了移位堆叠试验.为了验证结果的正确性,与相近日期中国科学院云南天文台2.4 m望远镜(2.4 m望远镜)观测的相同木卫图像的测量结果进行了比较和分析.位置归算采用了JPL (Jet Propulsion Laboratory)历表.结果表明,对CCD图像使用移位堆叠方法,通过叠加约10幅曝光时间100 s的图像, 1 m望远镜能观测暗至19等星的不规则天然卫星,而且测量的准确度与2.4 m望远镜的测量结果有良好的一致性. 相似文献
11.
VLBI (Very Long Baseline Interferometry)技术观测卫星需要对干涉测量数据进行相关和后处理,通过相关、时延校准、条纹搜索,最终得到卫星的基线几何时延.基于天文开源软件建立起一套卫星干涉测量数据处理系统.该系统可工作在实时和事后两种状态,实现相关、中性大气、电离层、钟模型以及仪器硬件的时延校准、条纹搜索、生成基线时延和时延率序列.使用该系统处理北斗GEO (Geosynchronous Earth Orbit)卫星的干涉测量试验数据,得到了精度在1–2 ns量级的卫星基线时延序列. 相似文献
12.
The orbit of Proton 4, 1968-103A, has been redetermined, in greater detail and with better accuracy, in order to clarify previously puzzling features in the variation of orbital inclination. Orbital parameters have been determined at 25 epochs between December 1968 and July 1969, using about 1600 optical and radar observations with the RAE orbit refinement program PROP 6.During January 1969 the orbit passed through 31:2 resonance—when the ground track over the Earth repeats every two days after 31 revolutions of the satellite. A simultaneous least-squares fitting of theoretical curves to the values of inclination and eccentricity between 14 December 1968 and 6 March 1969 has yielded values for two pairs of lumped 31st-order geopotential coefficients, appropriate to an inclination of 51.5°. This is the first specific evaluation of 31st-order coefficients.The 15 values of inclination after the resonance, from March to near decay in July 1969, have been used to determine mean, morning and afternoon-evening values for the rotation rate of the atmosphere at a height near 260 km; the values of rotation rate, namely 1.1, 0.9 and 1.3 rev/day respectively, confirm the trends already established from analysis of other satellite orbits. 相似文献
13.
14.
Giorgio E. O. Giacaglia 《Celestial Mechanics and Dynamical Astronomy》1974,9(2):239-267
Lunisolar perturbations of an artificial satellite for general terms of the disturbing function were derived by Kaula (1962). However, his formulas use equatorial elements for the Moon and do not give a definite algorithm for computational procedures. As Kozai (1966, 1973) noted, both inclination and node of the Moon's orbit with respect to the equator of the Earth are not simple functions of time, while the same elements with respect to the ecliptic are well approximated by a constant and a linear function of time, respectively. In the present work, we obtain the disturbing function for the Lunar perturbations using ecliptic elements for the Moon and equatorial elements for the satellite. Secular, long-period, and short-period perturbations are then computed, with the expressions kept in closed form in both inclination and eccentricity of the satellite. Alternative expressions for short-period perturbations of high satellites are also given, assuming small values of the eccentricity. The Moon's position is specified by the inclination, node, argument of perigee, true (or mean) longitude, and its radius vector from the center of the Earth. We can then apply the results to numerical integration by using coordinates of the Moon from ephemeris tapes or to analytical representation by using results from lunar theory, with the Moon's motion represented by a precessing and rotating elliptical orbit. 相似文献
15.
The Viking Orbiters have obtained several images of Phobos at large phase angles in which the portion of the satellite not directly illuminated by the Sun is faintly visible. A photometric analysis of one such image is presented to prove that the phenomenon is real and can be explained by Marsshine (i.e., the illumination of Phobos by sunlight reflected from Mars). Such images provide cross sections of Phobos and are useful in determining the true shape and size of the satellite. The cross section observed in Picture 111A03 agrees closely with that predicted by triaxial ellipsoid model of Phobos developed by Duxbury (1974). 相似文献
16.
F. Namouni 《Monthly notices of the Royal Astronomical Society》1998,300(3):915-930
We study the interaction of a satellite and a nearby ringlet on eccentric and inclined orbits. Secular torques originate from mean motion resonances and the secular interaction potential which represents the m = 1 global modes of the ring. The torques act on the relative eccentricity and inclination. The resonances damp the relative eccentricity. The inclination instability owing to the resonances is turned off by a finite differential eccentricity of the order of 0.27 for nearly coplanar systems. The secular potential torque damps the eccentricity and inclination and does not affect the relative semi-major axis; also, it suppresses the inclination instability that persists at small differential eccentricities. The damping of the relative eccentricity and inclination forces an initially circular and planar small mass ringlet to reach the eccentricity and inclination of the satellite. When the planet is oblate, the interaction of the satellite damps the proper precession of a small mass ringlet so that it precesses at the satellite's rate independently of their relative distance. The oblateness of the primary modifies the long-term eccentricity and inclination magnitudes and introduces a constant shift in the apsidal and nodal lines of the ringlet with respect to those of the satellite. These results are applied to Saturn's F-ring, which orbits between the moons Prometheus and Pandora. 相似文献
17.
A. Papageorgiou T. V. Cawthorne A. Stirling D. Gabuzda A. G. Polatidis 《Monthly notices of the Royal Astronomical Society》2006,373(2):449-456
A comparison between low-frequency space very long baseline interferometry (VLBI) and high-frequency ground-based VLBI images can, in principle, be used to detect small variations in rotation measure (RM) on fine angular scales inaccessible to ground arrays alone. This paper reports an attempt to perform such a comparison using the jet in the quasar 3C 380. Observations made with the VSOP antenna HALCA together with a ground array at wavelength 1.6 GHz provide total intensity and polarization images of comparable resolution to those from the ground array alone at 5 GHz. The results provide an image showing derotated magnetic vector position angle of somewhat higher resolution than that available earlier. The results show variations in an RM around component A of the order of 10 rad m−2 that could not have been detected with the ground array alone. It is concluded that satellite VLBI observations provide a promising means to study the distribution of matter and magnetic fields around parsec-scale jets.
The ground observations used here follow the steady outward drift of component A, which has approximately doubled its distance from the core since the first observations in 1982. They also reveal total intensity and polarization structure associated with a bright knot 0.7 arcsec from the core which is reminiscent of that expected for a conical shock wave. 相似文献
The ground observations used here follow the steady outward drift of component A, which has approximately doubled its distance from the core since the first observations in 1982. They also reveal total intensity and polarization structure associated with a bright knot 0.7 arcsec from the core which is reminiscent of that expected for a conical shock wave. 相似文献
18.
Repeat Ground Track Orbits of the Earth Tesseral Problem as Bifurcations of the Equatorial Family of Periodic Orbits 总被引：1，自引：0，他引：1
Martín Lara 《Celestial Mechanics and Dynamical Astronomy》2003,86(2):143-162
Orbits repeating their ground track on the surface of the earth are found to be members of periodic-orbit families (in a synodic frame) of the tesseral problem of the Earth artificial satellite. Families of repeat ground track orbits appear as vertical bifurcations of the equatorial family of periodic orbits, and they evolve from retrograde to direct motion throughout the 180 degrees of inclination. These bifurcations are always close to the resonances of the Earth's rotation rate and the mean motion of the orbiter. 相似文献
19.
本文介绍在怀柔６０ｃｍ多通道太阳望远镜上运用斑点干涉像复原方法所取得的一些初步结果,对用短暴光方法（暴光时间不大于１０毫秒）获得的一系列“冻结”大气后的目标像用斑点干涉像复原方法进行处理,即可获得消除了地球大气影响的目标复原像,斑点掩模法即为斑点干涉像复原方法的一种,我们用它对日面中心的宁静区米粒进行处理,复原出了分率不劣于０．〃５的白光米粒象。 相似文献
20.
Wavelet Analysis of Space Solar Telescope Images 总被引：1，自引：0，他引：1
Xi-An Zhu Sheng-Zhen Jin Jing-Yu Wang Shu-Nian NingNational Astronomical Observatories Chinese Academy of Science Beijing Department of Mechanical Electric Engineering China College of Mining Technology Beijing 《中国天文和天体物理学报》2003,3(6):587-596
The scientific satellite SST (Space Solar Telescope) is an important research project strongly supported by the Chinese Academy of Sciences. Every day, SST acquires 50 GB of data (after processing) but only 10GB can be transmitted to the ground because of limited time of satellite passage and limited channel volume. Therefore, the data must be compressed before transmission. Wavelets analysis is a new technique developed over the last 10 years, with great potential of application. We start with a brief introduction to the essential principles of wavelet analysis, and then describe the main idea of embedded zerotree wavelet coding, used for compressing the SST images. The results show that this coding is adequate for the job. 相似文献