Unit panel node detection by CNN on FAST reflector

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) has an active reflector.During observations, the reflector will be deformed into a paraboloid 300 meters in diameter. To improve its surface accuracy, we propose a scheme for photogrammetry to measure the positions of 2226 nodes on the reflector. The way to detect the nodes in the photos is the key problem in this application of photogrammetry. This paper applies a convolutional neural network(CNN) with candidate regions to detect the nodes in the photos. Experimental results show a high recognition rate of 91.5%, which is much higher than the recognition rate for traditional edge detection.     

射电天线口面温度定标

介绍一种天线口面温度定标的方法．当用这个方法对目标源进行温度定标时,由于定标源讯号和目标源讯号均由天线口面同路输入,因此波导和微波器件的传输损耗在定标的过程中被自动消除,因而这种温度定标方法能大大地提高观测资料的精度．目前无线口面温度定标方法除了在射电天文和微波天线测量中应用外,还广泛应用于雷达和无线电技术测量及微波遥感控制等．     

The control system of the active main reflector for FAST

The main reflector of FAST consists of about 1800 elementary units. Each unit has three adjustable supports to fix its position, and its position is adjusted by mean of mechanical actuators. According to the radio source position at any given time, all the actuators are continuously adjusted to form a proper paraboloid in real time during the course of the observation. The basic requirements of such a control system are discussed. A field bus control system based on LonWorks technology is suggested to control all 1800actuators. The main advantages of this distributed control system are its reliability, flexibility, efficiency and economics. This revised version was published online in July 2006 with corrections to the Cover Date.     

Φ1650mm口径反射镜的坦克链支撑研究

Phi 1650mm口径反射镜是某套大口径精密光学元件检测装置中的定标校正模块, 用于对检测光路中的缩焦透镜等光学部件进行定标. 反射镜口径越大, 由于自身重力引起的变形问题越严重, 面型精度受到的影响也越大. 对于Phi 1650mm口径反射镜, 系统要求的技术指标是面型误差的均方根(Root Mean Square, RMS)小于1/70波长(波长为\lk 632.8nm). 针对这块光轴始终处于水平状态的大口径反射镜, 提出了坦克链支撑方案, 并与传统的钢带支撑做对比. 对坦克链支撑方案进行有限元分析, 逐步确定了坦克链节数和中心距, 根据标准选取了型号C2162H的双节距大滚子坦克链. 基于赫兹接触理论, 对坦克链滚子与反射镜的边缘非线性接触进行了模型简化. 经过Zernike多项式拟合后, RMS为2.58nm, 满足设计要求. 坦克链支撑结构简单、成像质量好, 同时降低了反射镜的倾覆风险, 可靠性高.     

The Influence of Panel Gaps on the System NoiseTemperature of the FAST

1 INTRODUCTIONThe FAST is an ArecibChtype telescope with a number of innovations, which is to be built inthe unique karst area of Southwest China (Nan Rendong et al. 1996). Some basic parametersof the FAST have been tentatively suggested such as, curvature radius R = 300m, openingangle 0 = 120', and frequency range from 300MHz to 5 GHz. Baized on the fact that thecelltral part of a spherical surface deyiates little from a paraboloid as a proper focal length ischosen, a novel design…     

Intercomparisons of earth gravity models by means of lumped coefficients: Terms for eccentricity and longitude

The comparisons of the Earth gravity field models by the order of their harmonic coefficients, performed with the basic lumped coefficients (Planet. Space Sci.29, 653, 1981, Paper I) are here extended to cover all harmonic coefficients (both odd and even degree). The lumped coefficients (the “e-terms” and “longitudinal” terms), corresponding to 18 Earth models, are compared mutually (Figs. 2–15). The large differences, observed for various models and orders, are of particular interest: they are gathered into Table 1. The result of Paper I was a little pessimistic. The same is true here: various inhomogeneities, sometimes very large, in the accuracy of the harmonic coefficients must exist—even for low orders. Most of our comments and objections, however, relate to the older Earth models, which have only a historical value now. Our comparisons are only relative ones; an actual test of the accuracy of the models (their calibration) is possible via data with independent status (Kloko?ník, 1982, 1983).     

Performance results of HESP physical model

As a continuation to the published work on model based calibration technique with HESP(Hanle Echelle Spectrograph) as a case study, in this paper we present the performance results of the technique. We also describe how the open parameters were chosen in the model for optimization, the glass data accuracy and handling the discrepancies. It is observed through simulations that the discrepancies in glass data can be identified but not quantifiable. So having an accurate glass data is important which is possible to obtain from the glass manufacturers. The model’s performance in various aspects is presented using the ThAr calibration frames from HESP during its pre-shipment tests. Accuracy of model predictions and its wave length calibration comparison with conventional empirical fitting, the behaviour of open parameters in optimization, model’s ability to track instrumental drifts in the spectrum and the double fibres performance were discussed. It is observed that the optimized model is able to predict to a high accuracy the drifts in the spectrum from environmental fluctuations. It is also observed that the pattern in the spectral drifts across the 2D spectrum which vary from image to image is predictable with the optimized model. We will also discuss the possible science cases where the model can contribute.     

The Herschel-PACS photometer calibration

This paper provides an overview of the PACS photometer flux calibration concept, in particular for the principal observation mode, the scan map. The absolute flux calibration is tied to the photospheric models of five fiducial stellar standards (α Boo, α Cet, α Tau, β And, γ Dra). The data processing steps to arrive at a consistent and homogeneous calibration are outlined. In the current state the relative photometric accuracy is ～2 % in all bands. Starting from the present calibration status, the characterization and correction for instrumental effects affecting the relative calibration accuracy is described and an outlook for the final achievable calibration numbers is given. After including all the correction for the instrumental effects, the relative photometric calibration accuracy (repeatability) will be as good as 0.5 % in the blue and green band and 2 % in the red band. This excellent calibration starts to reveal possible inconsistencies between the models of the K-type and the M-type stellar calibrators. The absolute calibration accuracy is therefore mainly limited by the 5 % uncertainty of the celestial standard models in all three bands. The PACS bolometer response was extremely stable over the entire Herschel mission and a single, time-independent response calibration file is sufficient for the processing and calibration of the science observations. The dedicated measurements of the internal calibration sources were needed only to characterize secondary effects. No aging effects of the bolometer or the filters have been found. Also, we found no signs of filter leaks. The PACS photometric system is very well characterized with a constant energy spectrum νF _ν = λF _λ = const as a reference. Colour corrections for a wide range of sources SEDs are determined and tabulated.     

Wavelength calibration by combining arc and night sky lines for LAMOST

A novel method is presented for the wavelength calibration of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). The proposed method combines the arc lines and night sky lines, and can achieve high performance. Firstly, the initial wavelength calibration is performed by employing arc lines. Afterwards, the centroids of sky lines are calculated by the initial calibration results and adjusted by the gravity method iteratively. Finally, the ultimate wavelength calibration is obtained by fitting the centroids of arc lines and sky lines with their corresponding wavelengths. Experiments are performed on the data observed by LAMOST, and the results of the proposed method are more accurate than that of the calibration only by arc lines or sky lines. The calibration sky lines are dense in the red channel (5,700–9,000 Å) of LAMOST, but only a few ones are in the blue channel (3,700–5,900 Å). The new method achieves excellent results in the red channel as the substantial sky lines are employed, and the calibration accuracy of the blue channel is also enhanced in some degree by the scare sky lines.     

Understanding the behaviour of X-shooter via the application of a physical model

We show how traditional instrument quality control trending can be augmented by the use of a physical instrument model. The ESO VLT archive contains a detailed record of instrument diagnostics and calibration parameters while ESO quality control monitors changes in critical parameters. The physical model allows changes in positions, orientations and other physical properties of a spectrograph to be determined from standard wavelength calibration exposures via an optimisation process that seeks the physical model parameters that best reproduce the calibration features in the data. We introduce physical model parameters to the quality control monitoring. When applying this technique to archived calibration exposures, we find that the results are sensitive to the combination of parameters open to the optimisation process. Therefore we determine the most favourable set of physical parameters to optimise for each arm. We then show correlations between several physical parameters and instrument temperature sensor readings and epoch. In addition we find clear discontinuities in some physical parameter values that correspond to known maintenance events.     

The Gaia Data Release 1 parallaxes and the distance scale of Galactic planetary nebulae

In this paper we gauge the potentiality of Gaia in the distance scale calibration of planetary nebulae (PNe) by assessing the impact of DR1 parallaxes of central stars of Galactic PNe (CSPNe) against known physical relations. For selected PNe targets with state-of-the-art data on angular sizes and fluxes, we derive the distance-dependent parameters of the classical distance scales, i.e., physical radii and ionized masses, from DR1 parallaxes; we propagate the uncertainties in the estimated quantities and evaluate their statistical properties in the presence of large relative parallax errors; we populate the statistical distance scale diagrams with this sample and discuss its significance in light of existing data and current calibrations. We glean from DR1 parallaxes 8 CSPNe with S/N> 1. We show that this set of potential calibrators doubles the number of extant trigonometric parallaxes (from HST and ground-based), and increases by two orders of magnitude the domain of physical parameters probed previously. We then use the combined sample of suitable trigonometric parallaxes to fit the physical-radius-to-surface-brightness relation. This distance scale calibration, although preliminary, appears solid on statistical grounds, and suggestive of new PNe physics. With the tenfold improvement in PNe number statistics and astrometric accuracy expected from future Gaia releases the new distance scale, already very intriguing, will be definitively constrained.     

The Herschel PACS photometer calibration

We present a flux calibration scheme for the PACS chopped point-source photometry observing mode based on the photometry of five stellar standard sources. This mode was used for science observations only early in the mission. Later, it was only used for pointing and flux calibration measurements. Its calibration turns this type of observation into fully validated data products in the Herschel Science Archive. Systematic differences in calibration with regard to the principal photometer observation mode, the scan map, are derived and amount to 5 ? 6 %. An empirical method to calibrate out an apparent response drift during the first 300 Operational Days is presented. The relative photometric calibration accuracy (repeatability) is as good as 1 % in the blue and green band and up to 5 % in the red band. Like for the scan map mode, inconsistencies among the stellar calibration models become visible and amount to 2 % for the five standard stars used. The absolute calibration accuracy is therefore mainly limited by the model uncertainty, which is 5 % for all three bands.     

Correction Method of Antenna Pointing Error Caused by the Main Reflector Deformation

The pointing accuracy of a radio telescope is usually less than one-tenth of its antenna beam width. For large-aperture antennas at the short-centimeter band or millimeter-wave band, the pointing accuracy must be as high as several arc seconds. Therefore, for large-diameter and high-frequency reflector antennas, the pointing problem has become an important focal point to realize the antenna performance. Among many structural subsystem factors that affect the antenna pointing accuracy, there has been only less study on the factor of main reflector deformation. Based on the structural characteristics of the antenna, a reflector space coordinate system is established in this paper. And based on the space coordinates of the main reflector surface points after deformation, a non-linear least squares fitting method with 3 degrees of freedom is proposed to accurately predict the antenna pointing. Finally, the space geometric relationship is used to strictly derive the precise adjustments on the elevation and azimuth in order for correcting the antenna pointing error, and the indirect relationship between the main reflector deformation and the pointing error is constructed. This has certain guiding significance for improving the pointing accuracy of large radio antennas.     

薄施密特校正板的加工方法研究

针对薄板玻璃的刚度差，在研磨中容易产生变形这一特点，提出了一种新的加工方法。以加工薄施密特校正板（厚径比小于1／40）为例，用传统的上盘粘接固定工件进行加工，工件在下盘前的面形精度较好，但下盘后产生的变形使其面形精度下降，不能满足要求。采用真空模具法，吸附工件从而使工件固定产生预期的变形，面形精度易于控制，使加工非球面转变为加工平面，降低了加工难度，消除了工件在粘接过程中温度所引起的变形，降低了加工时的不均匀压应力，从而减少了变形，使得加工后的面形与加工过程中的面形接近，最终保证了工件的面形精度。     

一种偏振定标单元方位角误差的约束非线性最小化优化定标方法

偏振定标单元(Polarization Calibration Unit, PCU)对于定标由偏振系统和天文望远镜产生的仪器偏振至关重要, 然而偏振定标单元 中偏振元件光轴的方位角误差是限制定标精度的主要因素之一. 为解决该问题, 提出了一种基于约束非线性最 小化优化的方位角误差定标方法, 该方法具有定标精度高、定标速度快的优点. 首先将偏振定标单元中的线性 偏振片和四分之一波片的光轴方位角误差设置为两个待优化的自由变量, 然后利用产生和测量的Stokes参数 以及偏振定标获得的响应矩阵定义优化目标函数, 最终使用约束非线性最小化优化方法来确定 两个偏振元件的方位角误差. 分别从理论模拟和实际测量两个方面对优化方法进行了验证, 实验结果表明, 该 优化方法能够成功获得上述两个方位角误差, 精度分别优于2.79$''$和2.72$''$. 此外, 从理论上 计算分析了不同方位角误差对各Stokes分量的影响情况. 该优化方法有望应用到我国太阳望远镜中偏振定标 装置的误差定标及研制之中.     

Polarization Calibration of the <Emphasis Type="Italic">Chromospheric Lyman-Alpha SpectroPolarimeter</Emphasis> for a 0.1% Polarization Sensitivity in the VUV Range. Part II: In-Flight Calibration

The Chromospheric Lyman-Alpha SpectroPolarimeter is a sounding rocket instrument designed to measure for the first time the linear polarization of the hydrogen Lyman-\({\upalpha }\) line (121.6 nm). The instrument was successfully launched on 3 September 2015 and observations were conducted at the solar disc center and close to the limb during the five-minutes flight. In this article, the disc center observations are used to provide an in-flight calibration of the instrument spurious polarization. The derived in-flight spurious polarization is consistent with the spurious polarization levels determined during the pre-flight calibration and a statistical analysis of the polarization fluctuations from solar origin is conducted to ensure a 0.014% precision on the spurious polarization. The combination of the pre-flight and the in-flight polarization calibrations provides a complete picture of the instrument response matrix, and a proper error transfer method is used to confirm the achieved polarization accuracy. As a result, the unprecedented 0.1% polarization accuracy of the instrument in the vacuum ultraviolet is ensured by the polarization calibration.     

抛物面天线微波全息测量及结果分析

就上海佘山25 m抛物面天线上进行的相位相关法微波全息测量及其测量结果做了一定阐述。文章首先简要提到了微波全息测量技术在国内外的发展情况以及理论依据,其次介绍了我们所建立的测量系统的组成,重点讨论了基于窄带信号测量工作的有效性和准确性,采用自校准的数据处理手段,对测量误差做了估计和实际测试。当前我们已经取得了0.14 mm的测量精度(极限误差为0.2 mm),并分析了影响测量精度的各项因素。     

Methods of Laser,Non-Linear,and Fiber Optics in Studying Fundamental Problems of Astrophysics

Precise measurements of Doppler shifts of lines in stellar spectra allowing the radial velocity to be measured are an important field of astrophysical studies. A remarkable feature of the Doppler spectroscopy is the possibility to reliably measure quite small variations of the radial velocities (its acceleration, in fact) during long periods of time. Influence of a planet on a star is an example of such a variation. Under the influence of a planet rotating around a star, the latter demonstrates periodic motion manifested in the Doppler shift of the stellar spectrum. Precise measurements of this shift made it possible to indirectly discover planets outside the Solar system (exoplanets). Along with this, searching for Earth-type exoplanets within the habitable zone is an important challenge. For this purpose, accuracy of spectral measurements has to allow one to determine radial velocity variations at the level of centimeters per second during the timespans of about a year. Suchmeasurements on the periods of 10–15 years also would serve as a directmethod for determination of assumed acceleration of the Universe expansion. However, the required accuracy of spectroscopic measurements for this exceeds the possibilities of the traditional spectroscopy (an iodine cell, spectral lamps). Methods of radical improvement of possibilities of astronomical Doppler spectroscopy allowing one to attain the required measurement accuracy of Doppler shifts are considered. The issue of precise calibration can be solved through creating a system of a laser optical frequency generator of an exceptionally high accuracy and stability.     

Five-hundred-meter Aperture Spherical Telescope project

A Five hundred meter Aperture Spherical Telescope (FAST) is proposed to be built in the unique karst area of southwest China, and will act, in a sense, as a prototype for the Square Kilometer Array (SKA). It will be over twice as large as the Arecibo telescope coupled with much wider sky coverage. Some results from site surveys for such a SKA concept are briefly reported. Technically, FAST is not simply a copy of the existing Arecibo telescope but has rather a number of innovations. Firstly, the proposed main spherical reflector, by conforming to a paraboloid of revolution in real time through actuated active control, enables the realization of both wide bandwidth and full polarization capability while using standard feed design. Secondly, a feed support system which integrates optical, mechanical and electronic technologies will effectively reduce the cost of the support structure and control system. Pre-research on FAST has become a key project in the CAS. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inflight Calibration of the NEAR Multispectral Imager: II. Results from Eros Approach and Orbit

During the Near-Earth Asteroid Rendezvous (NEAR) spacecraft's investigation of asteroid 433 Eros, inflight calibration measurements from the multispectral imager (MSI) have provided refined knowledge of the camera's radiometric performance, pointing, and light-scattering characteristics. Measurements while at Eros corroborate most earlier calibration results, although there appears to be a small, gradual change in instrument dark current and flat field due to effects of aging in the space environment. The most pronounced change in instrument behavior, however, is a dramatic increase in scattered light due to contaminants accumulated on the optics during unscheduled fuel usage in December 1998. Procedures to accurately quantify and to remediate the scattered light are described in a companion paper (Li et al. 2002, Icarus155, 00-00). Acquisition of Eros measurements has clarified the relative, filter-to-filter, radiometric performance of the MSI. Absolute radiometric calibration appears very well constrained from flight measurements, with an accuracy of ∼5%. Pointing relative to the spacecraft coordinate system can be determined from the temperature of the spacecraft deck with an accuracy of ∼1 pixel.