共查询到20条相似文献，搜索用时 62 毫秒
1.
利用计算机数值模拟的方法，对等功率谱滤波方法的图像恢复效果进行测定，原始清晰图像选用以（0，0）为圆心的台阶式灰度图，且台阶灰度值非常接近，这些清晰图像首先进行系统退化，然后加入噪声（本文选用白噪声）生成脏图，图像恢复采用等功率谱滤波器，并将信噪比简化为常数k，图像恢复效果的好坏，用恢复后图像的信噪经和台阶的陡度（台阶的下底宽减上底宽，单位为像素个数）来定量测量，并结合普通图像的恢复，进行定性的视觉观察，主要测量退化图像的信噪比对图像恢复效果的影响，结果是：当信噪比＞15：1，图像恢复效果较好，当信噪比小于该值时，图像恢复效果较差，当信噪比下降到5：1时，图像恢复效果极差，几乎无法辨认，其次是系统传递函H对图像恢复效果的影响，也进行了一些讨论，最后，通过对实际的天文图像进行恢复，验证了测量过程的合理性和结果的正确性，并列举了等功率谱波器的一个典型应用，即在同态滤波器中使用等功率谱滤波器的传递函数。 相似文献
2.
Seng-le Wen Zhi-min Peng Jun-hui Fan Guang-zhong Xie 《Chinese Astronomy and Astrophysics》2002,26(4):1428-403
The near-infrared data of the quasar 3C273 are collected from available literature and are used to analyze its variability properties. The largest amplitudes of variations are ΔJ = 1.0, ΔH = 0.9, and ΔK = 0.86. The color indices are J − H = 0.82, J − K = 1.96, and H − K = 1.13. Analysis with the discrete correlation function (DCF) method indicates that the variability between any two infrared bands is correlated without any time lag. The relation between the color index and brightness is also investigated and the result indicates that the spectrum steepens when the source first dims, while it flattens after the source has dimmed to a some extent, suggesting that the emission of 3C 273 at near-IR consists of at least two components. Some discussions are presented. 相似文献
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A theoretical model is proposed for interpreting the coherent emissionmechanism of solar radio moving type IV bursts. Energetic electrons produced in flares captured by an expanding and rising magnetic flux tube exhibit a beam-like distribution of velocities on the top of the flux tube. These excite beaming plasma instability and directly amplifies O-mode electromagnetic waves. The instability growth rate sensitively depends on the coronal plasma parameter, ƒpe/ƒce and the beam-temperature Tb. This can qualitatively explain the high brightness temperature and high degree of polarization as well as the broad spectrum observed in this type of solar radio bursts. 相似文献
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Using a complete non-local convection theory, we carried out the theoretical calculations of 7Li depletion of the solar convective envelope models with different convective parameters c1 and c2, and got a model of the solar convection zone consistent with the observed 7Li abundance and the depth of the solar convection zone determined by helioseismic techniques. The overshooting distance of effective non-local convective mixing of 7Li is very extensive, which is about 1.07HP or 0.09R. However, the super-radiative temperature zone is much narrower, and it is only 0.20HP or 0.016R. 相似文献
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太阳图像中存在各种不同尺度、亮度和结构的物理活动现象,由于太阳日冕高动态活动和传感器设备等因素的影响,太阳图像成像质量不佳。根据太阳动力学天文台(Solar Dynamic Observatory,SDO)的大气成像仪(Atmospheric Imaging Assenbly,AIA)拍摄不同波段数据结构的动态范围大、噪声大、结构相对模糊等特点,提出一种基于盲退卷积的图像增强方法。首先对图像进行去噪和降低动态范围的处理,基于图像功率谱的分布假设,从原图中估计点扩散函数(Point Spread Function,PSF)的功率谱;然后使用相位提取算法恢复点扩散函数的相位,再退卷积得出较高质量的目标图像;最后通过轮廓切片分析、功率谱分析以及点扩散函数分析对增强结果进行定量和定性评价。实验结果表明,相比现有的图像增强方法,该方法在有效增强太阳日冕图像细节结构的同时,能够复原原图中因模糊无法识别的结构。 相似文献
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Zhao-yu Yang Li-ming Song Rong-feng Shen Zhuo Li Yu-sheng Lu 《Chinese Astronomy and Astrophysics》2005,29(4):361-369
This work presents a possible luminosity estimator for long γ-ray bursts (GRBs) based on their light curves. We use the method of variability analysis in the time domain to calculate the power density spectrum (PDS) for each of the 12 GRBs with known redshifts observed by CGRO/BATSE. The peak of the power density spectrum P is a measure of the intensity of variability of the given light curve and a strong correlation is found between P and the isotropic peak luminosity L of the GRB. It is a successor to the lag-luminosity relation of Norris et al. (2000) and the variability-luminosity relation of Reichart et al. (2001). 相似文献
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Zhi-gen Yang Wen-yao Zhu C. K. Shum Feng-chun Shu 《Chinese Astronomy and Astrophysics》2002,26(4):303-502
The vertical deformation rates (VDRs) and horizontal deformation rates (HDRs) of Shanghai VLBI station in China and Kashima and Kashima34 VLBI stations in Japan were re-analysed using the baseline length change rates from Shanghai to 13 global VLBI stations, and from Kashima to 27 stations and from Kashima34 to 12 stations, based on the NASA VLBI global solution glb1123 (Ma, 1999). The velocity vectors of the global VLBI stations were referred to the ITRF97 reference frame, and the Eulerian vectors of different models of plate motion were used for comparative solutions. The VDR of Shanghai station is estimated to be −1.91±0.56 mm/yr, and those of Kashima and Kashima34 stations, −3.72±0.74mm/yr and −8.81±0.84mm/yr, respectively. The difference between the last two was verified by further analysis. Similar estimates were also made for the Kokee, Kauai and MK_VLBA VLBI stations in mid-Pacific. 相似文献
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We investigate the properties of the Whittaker-Vondrak method of data smoothing as a numerical filter. We obtain the theoreticlal expression relating the mixing parameter , the period P and the frequency response A, thus verifying an empirical result found by Vondrak, and generalize the expression to other definitions of “smoothness”. Using the noise spectra before and after the filter, we give the formulae for estimating the mean error per unit weight, the mean error of a filtered value, and the autocorrelation in the filtered series. 相似文献
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Hang Heng-rong Chen Ya-feng Zang Zhi-yun
Huang Lin
Guo Zi-he Hao Jin-xin 《Chinese Astronomy and Astrophysics》1994,18(4):403-410In 1990 and 1992, using the 60 cm reflector of Beijing Observatory, we carried out photoelectric UBV observations of the Be star EM Cep and obtained 277 data sets. After combining the published minimum times over the years we made the O — C analysis and found an improved period of 0.806184 d or a single wave period of 0.403092d. Our analysis also showed a quickening tendency of the period at a rate dP/dt = −8.8514 × 10−10. The light curve is characterized by sharp minima and broad maxima. We found a detectable variation of the U — B colour index with the phase. 相似文献
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G. Efstathiou 《Monthly notices of the Royal Astronomical Society》2005,356(4):1549-1558
Destriping methods for constructing maps of the cosmic microwave background (CMB) anisotropies have been investigated extensively in the literature. However, their error properties have been studied in less detail. Here we present an analysis of the effects of destriping errors on CMB power spectrum estimates for Planck -like scanning strategies. Analytic formulae are derived for certain simple scanning geometries that can be rescaled to account for different detector noise. Assuming Planck -like low-frequency noise, the noise power spectrum is accurately white at high multipoles (ℓ≳ 50) . Destriping errors, though dominant at lower multipoles, are small in comparison to the cosmic variance. These results show that simple destriping map-making methods should be perfectly adequate for the analysis of Planck data and support the arguments given in an earlier paper in favour of applying a fast hybrid power spectrum estimator to CMB data with realistic '1/ f ' noise. 相似文献
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G. Kovács 《Solar physics》1983,82(1-2):123-128
The accuracy of frequency determination by a least squares technique for an autoregressive spectral estimator is studied and compared with the Fourier method. Using numerical tests the probability distribution function of the peak location is calculated. The autoregressive filter order is optimized in the sense of minimum variance of the peak location. Simple sinusoidal signals with additive Gaussian noise are considered and the effect of other components is only indicated. Generally, a filter order between 1/3 and 1/2 of the total data number and a not very dense data sampling, gives the most stable spectrum. The results are numerical. 相似文献
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Using extensive N-body simulations we estimate redshift space power spectra of clusters of galaxies for different cosmological models (SCDM, TCDM, CHDM, ΛCDM, OCDM, BSI, τCDM) and compare the results with observational data for Abell–ACO clusters. Our mock samples of galaxy clusters have the same geometry and selection functions as the observational sample which contains 417 clusters of galaxies in a double cone of galactic latitude |b|>30° up to a depth of 240 h−1 Mpc. The power spectrum has been estimated for wave numbers k in the range 0.03k0.2 h Mpc−1. For k>kmax0.05 h Mpc−1 the power spectrum of the Abell–ACO clusters has a power-law shape, P(k)∝kn, with n≈−1.9, while it changes sharply to a positive slope at k<kmax. By comparison with the mock catalogues SCDM, TCDM (n=0.9), and also OCDM with Ω0=0.35 are rejected. Better agreement with observation can be found for the ΛCDM model with Ω0=0.35 and h=0.7 and the CHDM model with two degenerate neutrinos and ΩHDM=0.2 as well as for a CDM model with broken scale invariance (BSI) and the τCDM model. As for the peak in the Abell–ACO cluster power spectrum, we find that it does not represent a very unusual finding within the set of mock samples extracted from our simulations. 相似文献
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D. Sutton B. R. Johnson M. L. Brown P. Cabella P. G. Ferreira K. M. Smith 《Monthly notices of the Royal Astronomical Society》2009,393(3):894-910
Map making presents a significant computational challenge to the next generation of kilopixel cosmic microwave background polarization experiments. Years worth of time ordered data (TOD) from thousands of detectors will need to be compressed into maps of the T , Q and U Stokes parameters. Fundamental to the science goal of these experiments, the observation of B modes, is the ability to control noise and systematics. In this paper, we consider an alternative to the maximum likelihood method, called destriping , where the noise is modelled as a set of discrete offset functions and then subtracted from the time stream. We compare our destriping code (Descart: the DEStriping CARTographer) to a full maximum likelihood mapmaker, applying them to 200 Monte Carlo simulations of TOD from a ground-based, partial-sky polarization modulation experiment. In these simulations, the noise is dominated by either detector or atmospheric 1/ f noise. Using prior information of the power spectrum of this noise, we produce destriped maps of T , Q and U which are negligibly different from optimal. The method does not filter the signal or bias the E- or B-mode power spectra. Depending on the length of the destriping baseline, the method delivers between five and 22 times improvement in computation time over the maximum likelihood algorithm. We find that, for the specific case of single detector maps, it is essential to destripe the atmospheric 1/ f in order to detect B modes, even though the Q and U signals are modulated by a half-wave plate spinning at 5 Hz. 相似文献
17.
Yang Xu-hai Hu Yong-hui Li Zhi-gang Li Xiao-hua Zheng Xing-wu 《Chinese Astronomy and Astrophysics》2003,27(4):470-480
Near real-time transfer of GPS common-view data is no longer a problem, but near real-time data processing of the data still calls for study, because it is not yet achieved by the usual smoothing and filtering techniques. Based on the characteristics of the GPS common-view data, a Kalman filtering algorithm is designed for estimating the time difference between two sites, while greatly reducing the observational noise. The algorithm is applied to the time difference between the National Time Service Center (NTSC) of China and the Communications Research Laboratory (CRL) of Japan (Over 2000 km apart), and to that between the CRL and the Korean Research Institute of Standards and Sciences (KRIS) (over 1000 km apart). The root mean square errors of the results obtained by the Kalman filter relative to those obtained from the Circular T of BIPM are less than 2.9 ns and 2.6 ns, in the two cases. Further, it is pointed out that, when multi-site data within a common-view network are available we can further improve the accuracy of the time comparisons by indirect observation adjustment. This statement was justified by application to the data from all three stations, i.e. NTSC, CRL, and KRIS. 相似文献
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The remarkable improvement in the estimates of different cosmological parameters in recent years has been largely spearheaded by accurate measurements of the angular power spectrum of cosmic microwave background (CMB) radiation. This has required removal of foreground contamination as well as detector noise bias with reliability and precision. Recently, a novel model-independent method for the estimation of CMB angular power spectrum from multi-frequency observations has been proposed and implemented on the first year WMAP (WMAP-1) data by Saha et al. [Saha, R., Jain, P., Souradeep, T., 2006. ApJL, 645, L89]. We review the results from WMAP-1 and also present the new angular power spectrum based on three years of the WMAP data (WMAP-3). Previous estimates have depended on foreground templates built using extraneous observational input to remove foreground contamination. This is the first demonstration that the CMB angular spectrum can be reliably estimated with precision from a self contained analysis of the WMAP data. The primary product of WMAP are the observations of CMB in 10 independent difference assemblies (DA) distributed over five frequency bands that have uncorrelated noise. Our method utilizes maximum information available within WMAP data by linearly combining DA maps from different frequencies to remove foregrounds and estimating the power spectrum from the 24 cross-power spectra of clean maps that have independent noise. An important merit of the method is that the expected residual power from unresolved point sources is significantly tempered to a constant offset at large multipoles (in contrast to the l2 contribution expected from a Poisson distribution) leading to a small correction at large multipoles. Hence, the power spectrum estimates are less susceptible to uncertainties in the model of point sources. 相似文献
19.
M. A. K. Glasmacher M. A. Catanese M. C. Chantell C. E. Covault J. W. Cronin B. E. Fick L. F. Fortson J. W. Fowler K. D Green D. B. Kieda J. Matthews B. J. Newport D. F. Nitz R. A. Ong S. Oser D. Sinclair J. C. van der Velde 《Astroparticle Physics》1999,10(4):183-302
The energy spectrum of cosmic rays with primary energies between 1014 eV and 1016 eV has been studied with the CASA-MIA air shower array. The measured differential energy spectrum is a power law (dj/dE ∝ E−y) with spectral indices γ of 2.66±0.02 below approximately 1015 eV and 3.00±0.05 above. A new method is used for measuring primary energy derived from ground-based data in a compositionally insensitive way. In contrast with some previous reports, the “knee” of the energy spectrum does not appear sharp, but rather a smooth transition over energies from 1015 eV to 3.0 × 1015 eV. 相似文献
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G. A. Chuntonov 《Astrophysical Bulletin》2013,68(4):461-464
We search for the variable component of themagnetic field in γ Equ by studying four Nd III lines with the Main Stellar Spectrograph of the 6-m BTA telescope of the Special Astrophysical Observatory via accumulation and cyclic transfer of the electronic image of the Zeeman spectrum on the CCD. The single exposure time was set equal to 1/8 of the spectral variability period. We detected no variable component in the magnetic field of γ Equ with a period of 12.1 min in the November 5/6, 2003 observations. 相似文献