共查询到20条相似文献，搜索用时 78 毫秒
1.
在被动型氢原子钟数字伺服电路中,使用FPGA对误差信号进行数字信号处理。设计了一种简单的低通滤波器,与传统的FIR滤波器相比,节省了FPGA的使用资源,并且性能优于传统滤波器,能够很好地应用于被动型氢钟。 相似文献
2.
Computer control of a tunable 1/8 Å filter is described. The filter is installed in the 30-cm chromospheric telescope of the CSIRO Solar Observatory, Culgoora. 相似文献
3.
对于确定参数的滤波器,快速的相位捕捉能力和高的噪声抑制能力是相互矛盾的。利用数字滤波器参数容易改变的特点,主要研究二阶锁相环环路中变带宽数字滤波器的设计,从而使锁相环路在初始阶段具备快速的捕捉能力和在锁定状态具备高的噪声抑制能力。对数字锁相环系统及滤波器在原理上进行了细致分析,之后给出软件实现该滤波器的算法,并用Matlab对系统进行仿真。 相似文献
4.
Yu. D. Zhugzhda 《Astronomy Letters》2007,33(9):622-643
We show that no eigenmodes of sunspot oscillations with periods of ～ 3 min or shorter exist. A complex spectrum of the 3-min oscillations arises, because the sunspot atmosphere is a multiband filter for slow MHD waves. To ascertain why the filter transmission bands appear, we have investigated the propagation of waves through a sunspot atmosphere using both multilayered isothermal model atmospheres and various empirical model atmospheres. It turns out that there are several different mechanisms responsible for the appearance of transmission bands in the atmospheric filter for slow waves. The filter lowest-frequency transmission band arises from the effect of a Fabry-Perot interference filter at the resonance frequency of the temperature plateau. The frequency of this band is always lower than the cutoff frequency of the temperature minimum. The next (in frequency) transmission band appears at the cutoff frequency. The higher-frequency transmission bands result from the antireflection of the atmosphere, an effect well-known in optics and acoustics. The nonlinearity of the 3-min oscillations observed in the upper chromosphere and transition region has only an indirect effect on the properties of the filter, increasing its transmission in most bands due to a decrease in the amplitude of the wave reflected from the upper atmosphere caused by nonlinear wave absorption. Knowledge of the formation mechanisms for the 3-min oscillation spectrum has allowed us to suggest a technique for estimating the parameters of sunspot atmospheres from the 3-min oscillation spectrum, i.e., to lay the foundations for the seismology of sunspot atmospheres. 相似文献
5.
Chris Flynn 《Astrophysics and Space Science》2002,280(1-2):185-189
We summarise the case for ground based testing of the GAIA filter system. Two scenarios are evaluated; firstly, that ground
based testing be part of the (ongoing) filter design effort, and secondly that the filters be tested on real stars from the
ground after they have been finalised. We conclude that the filter design effort would benefit more efficiently and directly
from good flux calibrated spectra for representative stars of many types, rather than an immediate and concerted ground based
photometric effort. Ground based observations after the filter design has been frozen is highly recommended. We review an
initial study of the tolerances needed on the filter central wavelengths and bandwidths in manufacture, assuming millimagnitude
photometry. Further work is needed in this area.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
分布逼近的卡尔曼滤波及其在星载GPS卫星定轨中的应用 总被引：6，自引：0，他引：6
探讨了利用推广卡尔曼滤波估计非线性系统状态时存在的问题，进而简要介绍了目前自动控制领域广泛使用的分布逼近的卡尔曼滤波UKF(Unscented Kalman Filter)，考虑到卫星定轨中系统的动态方程和量测方程存在严重非线性的情形，提出了将UKF用于星载GPS卫星定轨．实例计算结果表明，UKF的性能要优于推广卡尔曼滤波． 相似文献
7.
Stephen A. Schoolman 《Solar physics》1973,30(1):255-261
Calculations were made to determine the effects which contrast elements of various thicknesses have in Lyot filters. A filter which is significantly narrower than the line at which it is looking produces the best results. Therefore, if the filter is broad the addition of as thick an element as possible is desired. However, if the filter is already narrow, a contrast element whose thickness equals that of the second Lyot element will produce the best performance. 相似文献
8.
We study the properties of power maps of solar acoustic waves filtered with direction filters and phase-velocity filters.
A direction filter is used to isolate acoustic waves propagating in a narrow range of directions. The acoustic-power map of
the waves filtered with a direction filter shows extended reduced-power features behind magnetic regions with respect to the
wave direction. A phase-velocity filter is further applied to isolate waves with similar wave paths. In the power maps of
the waves filtered with both a direction filter and a phase-velocity filter, a reduced-power image of a sunspot appears behind
the sunspot with respect to the wave direction. The distance between the sunspot and the secondary image is consistent with
the one-skip travel distance of the wave packet associated with the phase-velocity filter. The waves filtered with direction
and phase-velocity filters at the location of the secondary image could be used to probe the sunspot. In the quiet Sun, spatial
fluctuations exist in any acoustic-power map. These fluctuations are mainly caused by interference among modes with the same
frequency. The fluctuations are random with two properties: They change rapidly with time, and their magnitude decreases with
the square root of the number of frames used in computing the acoustic-power map. 相似文献
9.
Transmission curves and theoretical calculi of the magneto-optical filter, designed and built by the authors, are shown together with some observed transmission spectra. At present the filter has a total halfwidth of ≈80mÅ; and the maximum transmission is 25%. From the analysis of the theoretical curves and from the observed spectra, we deduced the possibility of making up a filter with a very narrow passband (less than 30mÅ) and a very high transmission (up to nearly 100% apart from losses arising from the glass cell, lenses and polarizers). The article concludes with a selection and discussion of photographs obtained with the filter. 相似文献
10.
11.
The effectiveness of equal power spectrum filtering in image restoration is analyzed via digital simulation. We start with a gray-scale map of concentric rings with different grey values. To obtain a dirty image, the original image is first transformed via a linear space-invariant system. Then, white noise is mixed into the image. The equal power spectrum filter is then used for the image restoration. The signal to noise ratio (SNR) and a defined steepness of the steps, together with the visual impression, are accepted to characterize the performance of the image restoration. It is concluded that a satisfactory restoration can be realized when the SNR > 15. When SNR < 5, the image is completely un-restorable. The effect of system's transfer function on image restoration is also discussed. The effectiveness of the presented model of equal power spectrum filter is confirmed by applying it to the restoration of an actual astronomical image. Finally, a typical application of the equal power spectrum filter is given. 相似文献
12.
本文概述了高质量消色差波片(水晶+MgF_2)的设计原理,晶体材料的光学质量检查,延迟量的误差控制以及波片胶合等方面的问题. 相似文献
13.
14.
Ling Bai Ping Quo Zhan-Yi Hu Department of Computer Science Beijing Normal University Beijing National Laboratory of Pattern Recognition Institute of Automation Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2005,5(2):203-210
An automated classification technique for large size stellar surveys is proposed. It uses the extended Kalman filter as a feature selector and pre-classifier of the data, and the radial basis function neural networks for the classification. Experiments with real data have shown that the correct classification rate can reach as high as 93%, which is quite satisfactory. When different system models are selected for the extended Kalman filter, the classification results are relatively stable. It is shown that for this particular case the result using extended Kalman filter is better than using principal component analysis. 相似文献
15.
We present an image processing technique, the improved OMC filter (also called Madmax), which selects maxima of convexities of intensity modulations of an image. The filter computes second derivatives of the image in multiple directions around each pixel. It is shown to be efficient for pattern recognition, and bright hair-like or small anisotropic features can be enhanced. The filter is tested on artificially generated images, and the effect of a different number of directions in which the second derivatives are calculated is evaluated. Ca ii H line images of spicules and prominences obtained with Hinode/SOT are also used to illustrate its efficiency on real data. It is shown how to make the choice of the sensitive parameters to be used in improving the image visibility. 相似文献
16.
Y. D. Zhugzhda 《Solar physics》2008,251(1-2):501-514
Two competing theories of sunspot oscillations are discussed. It is pointed out that the normal mode (eigenoscillations) theory is in contradiction with a number of observations. The reasons for this are discussed. The revised filter theory of the three-minute sunspot oscillations is outlined. It is shown that the reason for the occurrence of the multipassband filter for the slow waves is the interference that appears from the multilayer structure of the sunspot atmosphere. In contrast with Zhugzhda and Locans (Sov. Astron. Lett. 7, 25?–?27, 1981) it is shown that along with the Fabry?–?Perot chromospheric passband the cutoff frequency passband and a number of the high-frequency passbands occur. The effect of the nonlinearity of the sunspot oscillations in the upper chromosphere and the transition region is taken into account. The spectra of the distinct empirical models of the sunspot atmosphere are explored. An example of the interpretation of the sunspot oscillations based on the revised filter theory is presented. Only the filter theory can explain the complicated behavior of the oscillations across the sunspot. The observations provide evidence of the nonuniformity of the sunspot atmosphere. 相似文献
17.
射电天文信号非常微弱,电磁环境对射电望远镜观测至关重要,通常可以利用地形、建立无线电宁静区、进行电磁屏蔽与防护等手段来减小电磁干扰.然而,仍有一些干扰难以屏蔽.故提出了一种基于自适应滤波的干扰消除方法,可用于复杂噪声环境中天文信号的提取.该方法借助自适应横向滤波器,采用最小均方(Least Mean Square, LMS)误差算法,以系统误差和收敛性为评判标准,通过改变步长与阶数对滤波效果进行优化,仿真结果显示该滤波器能在保证算法收敛的前提下有效提取信号.为了检验该算法的有效性,选取了新疆天文台南山26 m射电望远镜和Parkes 64 m射电望远镜记录的观测数据,采用设计的滤波器分别对不同的实测数据进行测试,验证了该滤波器的有效性.理论分析与实验结果一致表明该方法能有效消除天文观测中的干扰信号,具有一定的实用性. 相似文献
18.
《Chinese Astronomy and Astrophysics》2006,30(2):203-214
Using the Kalman filter algorithm, we have processed on-board GPS data of Shenzhou 4. The research focuses on three problems, namely, the selection criteria for the model error variance matrix of the Kalman filter, the effects of GPS signal interruption or runs of outliers on the recursive filtering, and the method to monitor the filter running status (normal or divergent). The aim is to evaluate the reliability of long-time stationary running of this algorithm used for on-board autonomous orbit determination 相似文献
19.
Wenda Cao Klaus Hartkorn Jun Ma Yan Xu Tom Spirock Haimin Wang Philip R. Goode 《Solar physics》2006,238(1):207-217
We discuss a near-infrared (NIR) narrow-band tunable birefringent filter system newly developed by the Big Bear Solar Observatory (BBSO). This is one of the first narrow-bandpass NIR filter systems working at 1.56 μm which is used for the observation of the deepest solar photosphere. Four stages of calcite were used to obtain a bandpass of 2.5 Å along with a free spectral range (FSR) of 40 Å. Some unique techniques were implemented in the design, including liquid crystal variable retarders (LCVRs) to tune the bandpass in a range of ±100 Å, a wide field configuration to provide up to 2° incident angle, and oil-free structure to make it more compact and handy. After performing calibration and characteristic evaluation at the Evans Facility of the National Solar Observatory at Sacramento Peak (NSO/SP), a series of high-resolution filtergrams and imaging polarimetry observations were carried out with the Dunn Solar Telescope of NSO/SP and the 65-cm telescope of BBSO, in conjunction with the high-order adaptive optics system and the Fabry–Pérot Interferometer (FPI). In this paper, we describe the optical design and discuss the calibration method. Preliminary observations show that it is capable of serving as either a stand-alone narrow-band filter for NIR filtergram observations or an order-sorting filter of a FPI applied to NIR two-dimensional imaging spectro-polarimetry. 相似文献
20.
Salvatore Alfano 《Celestial Mechanics and Dynamical Astronomy》2012,113(3):321-334
For satellite conjunction prediction containing many objects, timely processing can be a concern. Various filters are used to identify orbiting pairs that cannot come close enough over a prescribed time period to be considered hazardous. Such pairings can then be eliminated from further computation to quicken the overall processing time. One such filter is the orbit path filter (also known as the geometric pre-filter), designed to eliminate pairs of objects based on characteristics of orbital motion. The goal of this filter is to eliminate pairings where the distance (geometry) between their orbits remains above some user-defined threshold, irrespective of the actual locations of the satellites along their paths. Rather than using a single distance bound, this work presents a toroid approach, providing a measure of versatility by allowing the user to specify different in-plane and out-of-plane bounds for the path filter. The primary orbit is used to define a focus-centered elliptical ring torus with user-defined thresholds. An assessment is then made to determine if the secondary orbit can touch or penetrate this torus. The method detailed here can be used on coplanar, as well as non-coplanar, orbits. 相似文献