CSRH—Ⅱ信号传输方案的选择

分析和比较了CSRH—Ⅱ（中国频谱日像仪二期工程,即厘米波段日像仪）的几种可行光传输方案（包括全频段适时模拟光传输,分频段分时模拟光传输,数字光传输等）的技术难度及性价比。对优选的分频段分时模拟光传输作了原理性电路设计及计算。     

基于以太网的CSRH天线阵控制系统研究方案

中国频谱日像仪(Chinese Spectral Radioheliograph,CSRH)一期工程包括40面天线(400 MHz ～2 GHz)组成的天线阵,二期工程包括60面天线(2～15 GHz).天线统一控制包括天线指向调整、目标源跟踪、射电定标等.无论何种情况,所有的天线均需统一协调工作.对CSRH天线阵列整体控制进行了研究,提出了一种基于以太网的CSRH天线阵控制方案,并对可能遇到的关键问题进行分析.     

CSRH-I的天线选择

介绍了CSRH(中国太阳射电频谱日像仪)3个与科学目标相关的系统指标:空间分辨率、时间分辨率和频率分辨率(射电望远镜专有技术指标).然后介绍CSRH 3个接收设备的关键技术指标:灵敏度、动态范围和极化隔离度(接收机通用技术指标).重点阐述了CSRH天线的3项选择:天线个数、天线尺寸及天线主要技术指标(增益、噪声温度及轴比)与上述指标的关系.     

光纤时间传输及相位补偿

介绍了国外几种利用光纤进行时间频率传递的方法和经验.对无补偿光纤时间频率传递方法、双向时间频率传递方法、光学机械温度补偿方法及电子共轭相位补偿方法作了较详细的描述.光纤时延主要随温度而变化,在200 km以内,时延的日变化为几纳秒,月变化为十几纳秒.在50 km内利用光纤传输100 MHz频率信号时,在不补偿情况下频率稳定度为: 3×10-14/s,1×10-15/d;光学补偿后的频率稳定度可达到1.5×10-14/s,1×10-17/d.电子共轭相位补偿后,温度变化20℃引起的相位变化降低了45倍.光纤传输对短期频率稳定度影响较小,对日及更长期的频率稳定度影响较大.     

CSRH阵列设计研究

介绍中国频谱日像仪(Chinese Spectral Radioheliograph,CSRH)天线阵排列的研究工作.根据CSRH观测目标,给出了在UV平面优化设计的性能指标.最后通过对螺旋阵参数的优化,根据洁化处理的图像质量决定了中国频谱日像仪天线阵列的设计方案.     

光纤时间频率传输数字相位补偿方法

为提高光纤时间频率传输的精度,提出了数字移相补偿方法。该方法采用单片机量化发送端和接收端射频信号的相位差,然后再控制数字移相器调整发送端射频信号相位,使二者相位趋于一致,实现传输光纤引起相位变化的前置补偿,从而提高时间频率传输精度。实验表明,该系统可将发射端信号和接收端信号的相位差减少到5似内。     

CSRH-Ⅱ信号传输方案的选择

分析和比较了CSRH-Ⅱ(中国频谱日像仪二期工程,即厘米波段日像仪)的几种可行光传输方案(包括全频段适时模拟光传输,分频段分时模拟光传输,数字光传输等)的技术难度及性价比。对优选的分频段分时模拟光传输作了原理性电路设计及计算。     

中国频谱射电日像仪FITS-IDI文件格式研究

我国新一代中国频谱射电日像仪（Chinese Spectral Radio Heliograph,CSRH）原始观测数据采用自定义格式,在进行后续处理与共享使用时必须转换相应的格式.在分析FITS-IDI（FITS Interferometry Data Interchange）格式的基础上,结合CSRH的实际观测模式与数据产出方式,定义与设计了符合项目情况的FITS-IDI格式及字段,并对FITS-IDI文件中若干字段的值如何获取、计算进行了深入讨论.根据定义生成的FITS-IDI文件已成功导入CASA软件,并可以进行后续处理.经过对CASA测量集文件的核实,证明了数据生成的正确性.本研究有效地推进了CSRH的建设工作,也对其他射电干涉阵数据存储有一定的参考价值.     

CSRH选址地质勘探与无线电环境监测

主要介绍了近一年来CSRH项目的选址工作进展,其中包括无线电环境干扰测试、应选站址的多方面调研、站址的地质勘测等情况.     

CSRH的数字光传输

简述了日像仪高频部分的数字光传输的基本方案及其优点,对于日像仪高频部分(2 ～ 15 GHz)太阳信号,分时的变频选出32个5 MHz带宽的窄带所选信号.将此信号采样量化,通过数字光发射与接收设备完成3 km的数据传输功能.在数字光传输过程中,太阳信号经过码型变换、光调制、光纤传输、光解调,再完成码型反变换恢复出太阳信号本身.另外还对光纤数字传输的重要指标作了简要的阐述和计算,如误码率、抖动、漂移等.     

Radiative transfer in disc galaxies – II. The influence of scattering and geometry on the attenuation curve

We investigate the influence of scattering and geometry on the attenuation curve in disc galaxies. We investigate both qualitatively and quantitatively which errors are made by either neglecting or approximating scattering, and which uncertainties are introduced as a result of a simplification of the star–dust geometry. We find that the magnitude of these errors depends on the inclination of the galaxy and, in particular, that, for face-on galaxies, the errors due to improper treatment of scattering dominate those due to imprecise star–dust geometry. Therefore we argue that, in all methods aimed at determining the opacity of disc galaxies, scattering should be taken into account in a proper way.     

Integral methods in astronomical spectroscopy

We discuss the milestones of development of the integral methods used in the optical spectroscopy of astronomical objects. We analyze the reasons why some of these methods did not get wide practical application. We demonstrate that a combination of integral methods with multichannel detectors allow increasing the efficiency of the existing astronomical telescopes while pursuing the given spectroscopic programs. A technique of radial velocity measurements not susceptible to positional errors, typical of diffraction spectroscopy, is as well discussed.     

Roche tomography of cataclysmic variables – I. Artefacts and techniques

Roche tomography is a technique used for imaging the Roche-lobe-filling secondary stars in cataclysmic variables (CVs). In order to interpret Roche tomograms correctly, one must determine whether features in the reconstruction are real, or the result of statistical or systematic errors. We explore the effects of systematic errors using reconstructions of simulated data sets, and show that systematic errors result in characteristic distortions of the final reconstructions that can be identified and corrected. In addition, we present a new method of estimating statistical errors on tomographic reconstructions using a Monte Carlo bootstrapping algorithm, and show this method to be much more reliable than Monte Carlo methods which 'jiggle' the data points in accordance with the size of their error bars.     

Observations of photospheric pole-equator temperature differences

Using photoelectric methods we have repeated Plaskett's (1970) measurements of poleequator temperature differences. We average many limb-darkening scans to reduce statistical errors. We then analyze the differences between the average polar and equatorial scans. Plaskett's large poleequator temperature differences are not confirmed. Our data yield a pole-equator temperature difference of 1.5K±0.6K, although we cannot rule out systematic errors of 3–4 K.     

Minimum star tracker specifications required to achieve a given attitude accuracy

We describe the principles of the computation of minimum specifications of the optical system and array detector of the star attitude sensor to achieve the required attitude accuracy for the given exposure. The computations assume that the attitude error is influenced only by random noise of diverse origin, whereas all systematic errors have been eliminated. We report the specifications required for trackers meant for different purposes. We show that the errors of existing star trackers exceed the lowest achievable error by one order of magnitude because of unaccounted biases. We discuss the types of these biases and the methods that can be used to take them into account or eliminate them.     

A quantitative comparison of vector magnetic field measurement and analysis techniques

We make a quantitative comparison between spectral vs filter measurement and analysis techniques for extraction of solar vector magnetic fields from polarimetric data using as a basis the accurately calibrated, high angular resolution Stokes profile data from the Advanced Stokes Polarimeter. It is shown that filter-based measurements deliver qualitative images of the field alignment for sunspots that are visually similar to images derived from the more detailed analysis of the Stokes profiles. However, quantitative comparison with least-squares fits to the full Stokes profiles show that both the strength of the field predicted by the filter-based analysis and its orientation contain substantial errors. These errors are largest for plage regions outside of sunspots, where the field strengths are inferred to be only a fraction of their true values, and errors in the orientation of 40–50° are common. Within sunspots, errors of 20° are commonplace. The greatest source of these errors is the inability of the filter-based measurements to account for the small fill fraction of magnetic fields or, equivalently, scattered light in the instrument, which reduce the degree of polarization. The uncertainties of the full profile fitting methods are also discussed, along with the errors introduced by coarser wavelength sampling of the observed Stokes profiles. The least-squares fitting procedure operates best when the profiles are sampled at least as frequently as one Doppler width of the line.On leave from the Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Precision of the ephemerides of outer planetary satellites

Ephemerides of planetary satellites are needed to address many problems. These ephemerides are used for subsequent observations. A comparison of the available ephemerides with new observations allows the accuracy of the former to be assessed. However, the precision of the ephemerides must be known a priori when solving the tasks. In this paper we formulate and solve the problem of estimating the precision of the ephemerides of outer planetary satellites derived from observations when applied up to the future moments.The methods of assessing the precision of ephemerides involve producing a set of samples of the same ephemeris inferred from observations with different samples of Monte Carlo generated random errors (RO) superimposed onto it. The statistical parameters of simulated observational errors are based on the results of the reduction of real satellite observations. We compute the deviations of the samples of the ephemeris from the standard ephemeris inferred from real observations and adopt the root-mean-square deviation of the apparent coordinates as the precision of the ephemeris. We also use alternative methods: one based on the matrix of covariances of parameter errors (RP), and another one based on bootstrap samples of observations (BS).We use three methods (RO, RP, and BS) to estimate the precision of the ephemerides of all the 107 outer planetary satellites over the 2010-2020 time interval. The precision of the ephemerides of different satellites varies from 0.05 to 4.0 arcsec. For a number of satellites new observations are of vital importance for maintaining the precision of the ephemerides at a level that would allow identification of satellites during the reduction of observations. For some satellites the precision of their ephemerides is of the order of the sizes of their orbits and such satellites can be considered to have been lost. We show that the method of bootstrap samples (BS) can give doubtful results in the cases where there are few observations, which covered a time interval that is shorter than the orbital period of the satellite.Our results suggest obtaining more precise ephemeris making new observations at the times of maximum estimated errors of the ephemeris.All the inferred estimates of the precision of ephemerides are available from the MULTI-SAT ephemeris server: www.imcce.fr/sat (IMCCE), www.sai.msu.ru/neb/nss/index.htm (SAI).     

Observing gravitational radiation with QSO proper motions and the SKA

We discuss the ability of the SKA to observe QSO proper motions induced by long-wavelength gravitational radiation. We find that the SKA, configured for VLBI with multiple beams at high frequency (8 GHz), is sensitive to a dimensionless characteristic strain of roughly 10⁻¹³, comparable to (and with very different errors than) other methods in the 1/yr frequency band such as pulsar timing.     

A method of determining the kinematic properties of the primary mirror elements of the RATAN-600 radio telescope using modern laser measuring systems

We review the methods of determining the alignment errors of the primary mirror and flat reflector elements of the RATAN-600 radio telescope using a modern coordinate measuring system based on the Leica absolute tracker AT402. We computed the kinematic corrections for the elevation drives. The accuracy of the measurement method was estimated. The antenna readout with the introduced kinematic corrections was tested.     

A versatile birefringent filter

The theory of the olc birefringent filter is complicated and the general formulae describing its optical properties do not invite to any simple physical picture. Due to these formal difficulties, many of its inherent possibilities have not been fully appreciated. In this paper we point out some new possibilities for filters based on this general design.The detailed shape of the transmission profile is a function of the angles of the crystal plate optic axes. It is shown how unwanted transmission sidelobes can be suppressed to any desired level by altering the distribution of plate angles. By the same means, the transmission band can be split into two symmetrically placed replicas, and the distance between the two bands can be varied. In this way the filter can easily be tuned over half the free spectral range.Some of the error sources that are important to filter performance are discussed. An expression is given for the amount of parasitic light introduced by errors in the orientation of the plate optic axes and it is found that errors as large as 0°.5 can be tolerated. A laboratory experiment with 16 birefringent plates has shown that accuracies an order of magnitude better than this figure can easily be achieved. Manufacturing errors in the thickness of the plates can be compensated for by assembling the pile of plates in a particular way. The very strict tolerances usually quoted can therefore be considerably relaxed.