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1.
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. 相似文献
2.
500 m口径球面射电望远镜(Five-hundred-meter Aperture Spherical Radio Telescope,FAST)是一个超大口径的可动望远镜,有三项技术创新,一是选址,二是轻型馈源索支撑,三是主动反射面。在主动反射面上,单元面板的面型和面板的出厂加工精度对电磁波在反射面的汇聚有很大影响。FAST主反射面由4 600块三角形反射面板拼接而成,每块面板为边长11 m三角形,这对FAST反射面面板的测量技术提出了更高的要求。摄影测量直接在影像上进行量测,无需接触物体本身;所摄影像信息丰富,可以从中获得所研究物体的大量几何信息和物理信息;适用于大范围、多目标测量,效率高。目前世界上最大的射电望远镜,如GBT和ARECIBO都是采用摄影测量技术进行反射面面形检测。在对现有的面型检测技术调研并试验后,提出基于数字近景摄影测量的方法,对FAST反射面11 m单元面板的面型进行检测,数分钟完成反射面板面型的一次检测,测量精度达到2.5 mm,经过调整后的单元面板的面型精度达到了3.0 mm,结果表明摄影测量应用于FAST反射面单元面板面型检测是可行的。 相似文献
3.
《天文和天体物理学研究(英文版)》2020,(8)
The reflector system of Five-hundred-meter Aperture Spherical radio Telescope(FAST) is designed as 4450 rigid panels supported by a flexible cable-net structure. We use 10 total stations to measure2225 nodes of the cable-net and then control the shape of the reflectors. Every time, it takes at least 35 minutes to finish the calibration of the whole cable-net once. It is indeed far too inefficient. Thus, we developed a set of highly efficient instrument CRRS(CCD Rotation Ranging System). It is based on photogrammetry and can finish the measurement in 1 minute. However, the target we used in CRRS is active target, and it has serious electromagnetic interference problems to affect the use of FAST. Take the above reasons into consideration, we plan to identify the nodes by taking the gap between the reflector panels as the feature condition. The new method can take the place of active targets to finish the measuring task. The present work focuses on the following aspects. First, combined with the characteristics of FAST reflector images,the representative algorithms of image edge detection are discussed. Second, the process of node extraction is introduced in detail so that we know that it works. In addition, experimental results are given to draw a conclusion so that Canny algorithm was used for continuous research of reflector edge detection. 相似文献
4.
《天文和天体物理学研究(英文版)》2020,(1)
FAST, the largest single-dish radio telescope in the world, has a 500-meter diameter main reflector and a 300-meter diameter illuminated area. It has a main reflector that can vary its shape, which continuously changes the shape of the illuminated area in reflector into a paraboloid. In this article, we propose a quasiCassegrain system for FAST. The detailed design results are provided. Such a quasi-Cassegrain system only needs to add a 14.6-meter diameter secondary reflector, which is close to the size of the feed cabin. The distance from the secondary reflector to the focus is only 5.08 m, and it has excellent image quality. In this quasi-Cassegrain system, the shape of the illuminated area in the main reflector continuously changes into an optimized hyperboloid. Using this quasi-Cassegrain system from frequency 0.5 GHz to 8 GHz, the multi-beam system can include 7 to 217 feeds. If this system is used in combination with Phased Array Feed(PAF) technology, more multi-beam feeds or a higher working frequency can be used. 相似文献
5.
500 m口径球面射电望远镜(Five-hundred-meter Aperture Spherical radio Telescope,FAST),整体结构处于复杂的喀斯特地貌上,反射面承受风载荷作用,需要进行抗风设计。建立了FAST反射面及其周边山地地形的计算流体动力学(Computational Fluid Dynamics,CFD)计算模型,计算域范围为40 km×10 km×5.5 km。确定了入口风速剖面的基准高度为海拔810 m。计算了不同风向下反射面风压系数分布特征,得出了不利风向。对挡风墙的研究结果表明,挡风墙高度选择的效果优于位置选择。该研究结果可为FAST工程提供抗风设计的初步参考。 相似文献
6.
An open-loop control algorithm is put forward for continuous paraboloid deformation of the active reflector system of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).The method is based on a calibration database and interpolation in 2D spatial domain and temperature domain,respectively.It is completely independent of real-time measurement of cable nodes so that it has advantage of working all-weather and no additional electro-magnetic interference(EMI).Furthermore,its control accuracy can be effectively improved via reasonable layout of the calibrated paraboloids and increasing calibration accuracy.Meanwhile deformation safety is considered via calibration as well.Finally its control accuracy is also confirmed via site measurements of paraboloid deformations. 相似文献
7.
Hai-Yan Zhang Ming-Chang Wu You-Ling Yue Heng-Qian Gan Hao Hu Shi-Jie Huang 《天文和天体物理学研究(英文版)》2018,(4)
An active reflector is one of the three main innovations incorporated in the Five-hundredmeter Aperture Spherical radio Telescope(FAST).The deformation of such a huge spherically shaped reflector into different transient parabolic shapes is achieved by using 2225 hydraulic actuators which change the position of the 2225 nodes through the connected down tied cables.For each different tracking process of the telescope,more than 1/3 of these 2225 actuators must be in operation to tune the parabolic aperture accurately and meet the surface error restriction.This means that some of these actuators are inevitably located within the main beam of the receiver,and Electromagnetic Interference(EMI)from the actuators must be mitigated to ensure the scientific output of the telescope.Based on the threshold level of interference detrimental to radio astronomy described in ITU-R Recommendation RA.769 and EMI measurements,the shielding efficiency(SE)requirement for each actuator is set to be 80 d B in the frequency range from 70 MHz to 3 GHz.Therefore,Electromagnetic Compatibility(EMC)was taken into account in the actuator design by measures such as power line filters,optical fibers,shielding enclosures and other structural measures.In 2015,all the actuators had been installed at the FAST site.Till now,no apparent EMI from the actuators has been detected by the receiver,which demonstrates the effectiveness of these EMC measures. 相似文献
8.
射电天文中焦面阵或多波束馈源的应用 总被引：4，自引：1，他引：3
焦面阵技术或者多波束馈源系统已经日益广泛地应用于现代射电望远镜，因为它可以充分地利用同一射电望远镜反射面所能提供的信息，在观测比射电望远镜方向瓣大得多的展源时数倍乃至数十倍地提高观测的速度；当存在大气层或电离层的起伏或不均匀影响观测成像质量时，可消除这种影响，提高观测质量；利用焦面阵各单个馈源接收到的信息的互相关，则可以实时监控射电望远镜的反射面、二次反射面、指向精度，从而降低地面上大射电望远镜或空间射电望远镜的精度要求和造价。目前焦面阵已经愈来愈广泛地配置在毫米波射电望远镜和大型射电望远镜的主要波段。对此作了一个较新和全面的评述，对焦面阵应用中的限制，包括相位误差的限制和性能价格比的考虑和可能的前景作了简要的介绍。还分析了在计划中的大型主动球反射面射电望远镜（即FAST）上，配置焦面阵的相应限制、问题和难点，提出了初步的建议，并给出经中英双方讨论后初步拟定的FAST频段、波束及低噪声放大器的配置。 相似文献
9.
YanSu Guo－DingLi 《中国天文和天体物理学报》2001,1(2):190-194
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… 相似文献
10.
FAST在深空探测中的应用前景 总被引：4，自引：0，他引：4
FAST（Five hundred meters Aperture Spherical Telescope)拟利用贵州省的喀斯特洼地，建立世界上最大的500米口径的球面射电望远镜。主动反射面新概念的提出，实现了望远镜的宽频带和全偏振能力；馈源及支撑系统简化的方案，使FAST对天体和航天器的跟踪范围得到很大的补充。分析预研中的FAST的测控功能，并论证其在未来深空网（DSN）中的重要作用和地位及开展国际合作的可能性。 相似文献
11.
A cross bow-tie dipole feed with cavity and symmetrical E and H plane pattern is presented for the Five hundred-meter Aperture Spherical radio Telescope(FAST).In this paper we describe the design,optimization and simulation results of a wide-band cross dipole feed with cavity covering the frequency range from 300 MHz to 600 MHz for FAST.The main goals of our design are to ensure that,(1)we cover the octave bandwidth,(2)the feed has symmetrical E and H plane pattern,and(3)the physical dimension is suitable for mounting it in the reserved position of the FAST feed cabin.The initial results indicate that we have met most of our design goals.This kind of feed had been equipped with the multi-beam receiver to carry out observation on the platform of FAST cabin. 相似文献
12.
The surface accuracy of a large parabolic antenna is an important indicator to evaluate the quality of the antenna.It not only directly affects the antenna’s aperture efficiency,thereby determining the shortest wavelength that the antenna can work,but also affects the main lobe width and side lobe structure of the antenna pattern.Microwave holography is an important method for parabolic antenna profile detection.In this article we adopt a new algorithm to adjust the panels for the large radio telescope with an active main reflector through the TM65 m antenna’s aperture phase profile.The panels of the TM65 m radio telescope is in a radial pattern with 14 rings.Each corner of the panel is fixed on the screw of the actuator to move up and down,and the adjacent corners of the four panels share an actuator.We use the method of plane fitting to calculate the adjustment value of every panel’s corner.But one actuator,which simultaneously controls the common corner of the adjacent panels,will have different adjustment values according to the different plane fitting equation based on adjacent panels.In this paper,the adjustment value of the adjacent panels’crosspoints are constrained to be equal to the constraint condition to calculate each actuator’s adjustment value of the TM65 m radio telescope.Through multiple adjustments and application of the new algorithms,the accuracy of the TM65 m antenna reflector profile has been improved from the original 0.28 mm to the current 0.19 mm. 相似文献
13.
《天文和天体物理学研究(英文版)》2020,(1)
This paper proposes an active sub-reflector suitable for large radio telescopes, which can compensate both of the deformation of the main reflector and sub-reflector position offsets. The mathematical formula of the main reflector deformation compensated by the sub-reflector is deduced based on Cassegrain and Gregory antenna structures. The position of the sub-reflector is adjustable to compensate for defocusing errors on high and low elevations, which are mainly caused by the deformation of the sub-reflector supporting legs. In this paper, the method of obtaining the optimum position of the sub-reflector from the aperture phase by the interferometric method is introduced. The actual measurement is verified on the Tianma 65 m radio telescope, which provides a new way to diagnose the position error of the sub-reflector. 相似文献
14.
The reflector of the Five-hundred-meter Aperture Spherical radio Telescope(FAST)consists of 4450 reflector units.Installation of the reflector faces the challenges of large span,complex terrain,serious interference,complex processes,high position and inability to use conventional equipment.The installation technology for the flexible reflector with a large span was specially studied and designed.Two half-span arc-moving cable cranes and two transfer trucks were jointly operated along a path that follows a circular beam.After installation of the reflector was completed,two half-span cable cranes were merged into a set of full-span cable cranes for maintenance of the reflector.Installation of the reflector combines features of unit and site topography of FAST.The installation technology follows scientific and reasonable practices,and is highly efficient and convenient.It represents a breakthrough in many key technologies in construction and maintenance techniques.It has promoted related technical progress in the construction and maintenance of complex projects.It has also provided an important reference for the construction and maintenance of similar projects,and has strong significance and applicability. 相似文献
15.
《New Astronomy》2022
Radio frequency interference (RFI) identification is a key step in radio data processing. In order to efficiently process huge volumes of data produced by modern large radio telescopes, such as the Five-hundred-meter Aperture Spherical radio Telescope (FAST), exceptional balance between accuracy and performance (throughput) is required for RFI flagging algorithms. RFI-Net is a single-process RFI identification package based on deep learning technique, and has achieved a higher flagging accuracy than the classical SumThreshold method. In this paper, we present a scalable RFI flagging toolkit, which can drive parallel workflows on multi-CPU and multi-GPU clusters, with RFI-Net as its core detector. It can automatically schedule the workload and aggregate itself after errors according to the running environment. Moreover, its main components are all pluggable, and can be easily customized according to requirements. The experiments with real data of FAST showed that using eight parallel workflows, the toolkit can process sky survey data at a speed of 66.79 GB/h, which means quasi-real-time RFI flagging can be achieved considering the data rate of FAST extragalactic spectral line observations. 相似文献
16.
MEI Geng-jun XIANG Bin-bin WANG Na WANG Zhao-jun 《Chinese Astronomy and Astrophysics》2021,45(2):236-251
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. 相似文献
17.
Hai-Yan Zhang Ming-Chang Wu You-Ling Yue Heng-Qian Gan Hao Hu Shi-Jie Huang Xin-Xin Zhang Jin-Hai Sun Bo Peng Ren-Dong Nan FAST Collaboration 《天文和天体物理学研究(英文版)》2020,(5):171-174
Radio Frequency Interference(RFI)mitigation is essential for supporting the science output of Five-hundred-meter Aperture Spherical radio Telescope(FAST)due to its high sensitivity.In order to protect FAST from RFI,an Electromagnetic Compatibility(EMC)study has been carried out and the operation of a Radio Quiet Zone(RQZ)is ongoing.RFI measurements of the telescope instruments and monitoring of the active radio services outside the site have revealed the radiation properties of the RFI sources.Based on the measurement results and theoretical analysis,various EMC methods have been implemented for the telescope to decrease the RFIs.Meanwhile,the main RFI sources in the FAST RQZ,such as mobile stations,broadcast stations and navigation instruments,have been identified,and the technical measures have been adopted to protect the quiet radio environment around the site.The early science outputs of FAST have demonstrated the efficiency of RFI mitigation methods. 相似文献
18.
随着毫米波天文学和空间通信的重要性日益提高, 对天线性能提出了越来越高的要求, 而天线性能往往受到其反射器表面精度的限制. 微波全息技术是一种快速有效的检测反射面天线表面轮廓的测量技术. 通过微波全息测量得到天线口径场, 计算天马65m射电望远镜反射面与理想抛物面的偏差. 天马65m射电望远镜的主反射面板是放射状的, 有14圈. 面板的每个角都固定在面板下方促动器的螺栓上进行上下移动, 且相邻面板交点处的拐角共用一个促动器. 采用平面拟合的方法可以计算各块面板拐角处的调整值, 但是同一个促动器会得到4个不同的调整量. 通过平面拟合, 同时以天线照明函数为权重的平差计算方法得到相邻面板拐角的一个平差值, 即天马65m射电望远镜1104个促动器的最佳调整值. 通过多次调整和新算法的应用, 天马65m射电望远镜反射面的面形精度逐渐提高到了0.24mm. 相似文献
19.
Using the generic hydrodynamic model of gamma-ray burst(GRB) afterglows, we calculate the radio afterglow light curves of low luminosity, high luminosity,failed and standard GRBs in different observational bands of FAST’s energy window.The GRBs are assumed to be located at different distances from us. Our results rank the detectability of GRBs in descending order as high luminosity, standard, failed and low luminosity GRBs. We predict that almost all types of radio afterglows except those of low luminosity GRBs could be observed by a large radio telescope as long as the domains of time and frequency are appropriate. It is important to note that FAST can detect relatively weak radio afterglows at a higher frequency of 2.5 GHz for very high redshift up to z = 15 or even more. Radio afterglows of low luminosity GRBs can only be detected after the completion of the second phase of FAST. FAST is expected to significantly expand the sample of GRB radio afterglows in the near future. 相似文献
20.
The control system of the active main reflector for FAST 总被引：1，自引：0，他引：1
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. 相似文献