基于Mark5B＋GPU脉冲星观测系统

云南天文台40m射电望远镜进行的脉冲星观测数据量巨大,必须实现数据的实时处理,否则将会产生海量的数据积压.为实现这一目标,采用图形处理器架构,对Mark5B数据进行解码、消色散、折叠等处理.实验结果表明,对以1s8MB的实时采样,可以在0.51s内处理完成,从而实现了实时处理的要求.首先介绍这一观测系统各部分的图形处理器实现,然后相对于传统中央处理器构架,对各部分的运算速度进行了详细的对比.针对时间开销最大的消色散部分,分析了单次傅里叶变换的数据量大小对执行效率的影响.从系统最终的输出轮廓和柱状图上可以看到实时处理的结果符合要求.最后对存在的问题和未来的工作进行了讨论.     

大口径射电望远镜电磁兼容评估技术研究

电磁兼容性是设备或系统的重要性能指标, 也是保障系统的工作效能和提高系统可靠性的重要因素. 大口径射电望远镜运行阶段, 台址周围无线电业务及内部潜在的电磁干扰会降低观测系统灵敏度、影响天文观测的质量. 本论文针对拟建的新疆110 m全向可动射电望远镜(Qi Tai raido Telescope, QTT)开展了系统电磁兼容评估技术及控制方法研究, 具有重要的工程应用价值. 首先, 依据现有电波环境测量方法的不足, 深入分析了仪器设备的关键参数配置方法及测量时间计算方法, 采用Y因子法校准测量数据, 提出一种准实时电波环境测量方法. 面向高重复性宽带频谱, 分析了宽带频谱信号和噪声特征, 结合标准差理论, 提出一种基于邻值比较的信噪分离方法, 并采用邻值统计方法优化关键参数, 提高信噪分离精度. 针对QTT台址, 开发了自动化电波环境监测系统, 该系统6 GHz以下频段系统增益大于40 dB, 系统噪声系数小于2 dB, 测量不确定度小于1.49 dB, 具有极高的系统灵敏度和测量精度; 分析了频谱监测数据流, 设计了基于HDF5 (Hierarchical Data Format version 5)的数据存储格式, 开发了自动化电波环境测量和监控软件及数据处理软件. 依据QTT台址长期监测数据, 评估分析了台址电磁环境、主要干扰源特征及其影响. 其次, 提出大口径射电望远镜馈源口面干扰电平限值量化方法, 建立了基于台址地形的电波传播模型, 分析了现有电波传播模型的优缺点及适应性, 结合QTT台址实际地形及地质特征, 采用Longley-Rice和Two-Ray电波传播模型, 预测分析了QTT台址潜在干扰区域电磁干扰达到射电望远镜的电波路径衰减, 结合大口径射电望远镜天线增益量化方法, 提出设备所在位置干扰电平限值量化方法, 运用该方法对QTT台址潜在干扰区域的干扰电平限值进行量化. 依据设备所在位置干扰电平限值, 调研分析了国内外军用、民用电磁兼容测量标准, 结合电磁干扰对射电天文观测的影响, 提出一种大口径射电望远镜电磁兼容控制方法, 解决了现有电波暗室测量系统无法直接测量评估电子设备电磁兼容的问题, 该电磁兼容控制方法计划应用于QTT建设及运行阶段, 确保系统拥有良好的电磁兼容性. 最后, 依据QTT台址潜在干扰区域干扰电平限值, 结合典型电子设备电磁辐射频谱, 分析了QTT电磁兼容设计需求, 提出电磁兼容设计初步方案. 另外, 针对台址建筑设施内的中低电磁辐射干扰源, 提出一种低成本建筑屏蔽方法, 应用于QTT台址现有建筑.     

A real-time software backend for the GMRT

The new era of software signal processing has a large impact on radio astronomy instrumentation. Our design and implementation of a 32 antennae, 33 MHz, dual polarization, fully real-time software backend for the GMRT, using only off-the-shelf components, is an example of this. We have built a correlator and a beamformer, using PCI-based ADC cards and a Linux cluster of 48 nodes with dual gigabit inter-node connectivity for real-time data transfer requirements. The highly optimized compute pipeline uses cache efficient, multi-threaded parallel code, with the aid of vectorized processing. This backend allows flexibility in final time and frequency resolutions, and the ability to implement algorithms for radio frequency interference rejection. Our approach has allowed relatively rapid development of a fairly sophisticated and flexible backend receiver system for the GMRT, which will greatly enhance the productivity of the telescope. In this paper we describe some of the first lights using this software processing pipeline. We believe this is the first instance of such a real-time observatory backend for an intermediate sized array like the GMRT.     

On the architecture for the X part of a very large FX correlator using two-accumulator CMACs

This paper presents an improved input-buffer architecture for the X part of a very large FX correlator that optimizes memory use to both increase performance and reduce the overall power consumption. The architecture uses an array of two-accumulator CMACs that are reused for different pairs of correlated signals. Using two accumulators in every CMAC allows the processing array to alternately correlate two sets of signal pairs selected in such a way so that they share some or all of the processed data samples. This leads to increased processing bandwidth and a significant reduction of the memory read rate due to not having to update some or all of the processing buffers in every second processing cycle. The overall memory access rate is at most 75 % of that of the single-accumulator CMAC array. This architecture is intended for correlators of very large multi-element radio telescopes such as the Square Kilometre Array (SKA), and is suitable for an ASIC implementation.     

Antenna data storage concept for phased array radio astronomical instruments

Low frequency Radio Astronomy instruments like LOFAR and SKA-LOW use arrays of dipole antennas for the collection of radio signals from the sky. Due to the large number of antennas involved, the total data rate produced by all the antennas is enormous. Storage of the antenna data is both economically and technologically infeasible using the current state of the art storage technology. Therefore, real-time processing of the antenna voltage data using beam forming and correlation is applied to achieve a data reduction throughout the signal chain. However, most science could equally well be performed using an archive of raw antenna voltage data coming straight from the A/D converters instead of capturing and processing the antenna data in real time over and over again. Trends on storage and computing technology make such an approach feasible on a time scale of approximately 10 years. The benefits of such a system approach are more science output and a higher flexibility with respect to the science operations. In this paper we present a radically new system concept for a radio telescope based on storage of raw antenna data. LOFAR is used as an example for such a future instrument.     

New design of large fully-steerable radio telescope reflector based on homogenized mesh structure

The self-weight of a large fully-steerable radio telescope is one of the important factors affecting its performance. In the existing reflector system scheme, the problem of surface accuracy caused by its large and heavy structure has seriously restricted the application and implementation of large radio telescopes.Therefore, a new mesh structure scheme for a large fully-steerable radio telescope reflector is proposed in this paper. This scheme is based on a homogenized mesh back-up structure in the form of a quasi-geodesic grid and regular quasi-tri-prism or tetrahedron, which can significantly reduce the structural complexity and self-weight of the reflector under the condition that the reflector can meet the desired performance requirements. Finally, the feasibility and rationality of the scheme are evaluated by numerical simulation analysis, which has significant advantages and provides a new design for the reflector of a large fullysteerable radio telescope.     

Scalable desktop visualisation of very large radio astronomy data cubes

Observation data from radio telescopes is typically stored in three (or higher) dimensional data cubes, the resolution, coverage and size of which continues to grow as ever larger radio telescopes come online. The Square Kilometre Array, tabled to be the largest radio telescope in the world, will generate multi-terabyte data cubes – several orders of magnitude larger than the current norm. Despite this imminent data deluge, scalable approaches to file access in Astronomical visualisation software are rare: most current software packages cannot read astronomical data cubes that do not fit into computer system memory, or else provide access only at a serious performance cost. In addition, there is little support for interactive exploration of 3D data.We describe a scalable, hierarchical approach to 3D visualisation of very large spectral data cubes to enable rapid visualisation of large data files on standard desktop hardware. Our hierarchical approach, embodied in the AstroVis prototype, aims to provide a means of viewing large datasets that do not fit into system memory. The focus is on rapid initial response: our system initially rapidly presents a reduced, coarse-grained 3D view of the data cube selected, which is gradually refined. The user may select sub-regions of the cube to be explored in more detail, or extracted for use in applications that do not support large files. We thus shift the focus from data analysis informed by narrow slices of detailed information, to analysis informed by overview information, with details on demand. Our hierarchical solution to the rendering of large data cubes reduces the overall time to complete file reading, provides user feedback during file processing and is memory efficient. This solution does not require high performance computing hardware and can be implemented on any platform supporting the OpenGL rendering library.     

The Dynamic Spectrum of Interplanetary Scintillation: First Solar Wind Observations on LOFAR

The LOw Frequency ARray (LOFAR) is a next-generation radio telescope which uses thousands of stationary dipoles to observe celestial phenomena. These dipoles are grouped in various ‘stations’ which are centred on the Netherlands with additional ‘stations’ across Europe. The telescope is designed to operate at frequencies from 10 to 240 MHz with very large fractional bandwidths (25?–?100 %). Several ‘beam-formed’ observing modes are now operational and the system is designed to output data with high time and frequency resolution, which are highly configurable. This makes LOFAR eminently suited for dynamic spectrum measurements with applications in solar and planetary physics. In this paper we describe progress in developing automated data analysis routines to compute dynamic spectra from LOFAR time–frequency data, including correction for the antenna response across the radio frequency pass-band and mitigation of terrestrial radio-frequency interference (RFI). We apply these data routines to observations of interplanetary scintillation (IPS), commonly used to infer solar wind velocity and density information, and present initial science results.     

射电望远镜控制系统中的数据传输序列化分析

控制系统能衔接、集成和管理射电望远镜的软硬件系统。控制系统的序列化工具可以将射电望远镜的不同设备、操作系统、编程语言和网络之间传输的信息进行编码和解码,增强系统之间数据的传输效率。分析和比较了3款二进制序列化工具Msgpack,Protobuf和Flatbuffers的编码原理及特性,并通过一个实例测试了它们的序列化数据大小、序列化时间和中央处理器利用率。结果表明,Msgpack的综合性能优于Protobuf和Flatbuffers,适用于周期长、需求易变的射电望远镜系统之间传输信息的编码和解码。     

基于FS系统对乌鲁木齐VLBI射电望远镜进行天线测量

在天文观测中射电望远镜性能参数的好坏直接影响到观测数据质量,为了保证观测质量,提高观测效率,需要对天线性能进行测量.当前进行天线测量的方法有场地测量法和射电天文法,不同的方法应用范围和效果不同.对于大型天线而言采用射电天文法进行天线测量高效快捷.针对VLBI射电望远镜,介绍了使用终端FS系统对天线参数进行测量（基于射电天文法）的方法和过程,以乌鲁木齐南山25 m天线增益和指向精度测量作为范例,重点叙述了测量的方法和步骤,并对该方法进行了讨论.     

Polarization Observation Experiments for Radio Flares of Stars at the 6 cm Band

We have performed radio polarization observation experiments of the stars V772 Her and β Per with the Urumqi 25 m radio telescope at the 6 cm waveband, and obtained light curves of the stars after data processing and calibration. A radio ?are from the star V772 Her was detected on 2011 April 13. The degree of linear polarization of this ?are is about 30%, and the polarization angle is about 4°. We have detected also the slowly-varying component of the radio radiation from β Per, as well as a short ?are superposed on it, which has a very weak linear polarization.     

乌站25m射电望远镜天线效率自动测量的软件实现

经常测量天线参数对于改进天线性能以及联测和单天线观测的数据处理都是至关重要的。以前的记录仪手工测量方式,非常繁琐和低效率,不利于对测量结果进行有效的统一管理和深入分析。根据天线效率的测量为例,在PC和Windows2000/XP软硬件平台下统一编程,集成实现天线参数测量的自动化、操作的人性化以及数据分析和曲线拟合的可视化。这将大大降低人工,提高测量效率,更好地保证天线的可靠、高精度的运行以及观测数据的处理。     

The Lofar Central Processing Facility Architecture

Reconfiguration is a key feature characteristic of the LOFAR telescope. Software platforms are utilised to program out the required data transformations in the generation of scientific end-products. Reconfigurable resources nowadays often replace the hard-wired processing systems from the past. This paper describes how this paradigm is implemented in a purely general-purpose telescope back-end. Experiences from high performance computing, stream processing and software engineering have been combined, leading to a state-of-the-art processing platform. The processing platform offers a total processing power of 35 TFlops, which is used to process a sustained input data- stream of 320 Gbps. The architecture of this platform is optimised for streaming data processing and offers appropriate processing resources for each step in the data processing chains. Typical data processing chains include Fourier transformations and correlation tasks along with controlling tasks such as fringe rotation correction. These tasks are defined in a high level programming language and mapped onto the available resources at run time. A scheduling system is used to control a collection of concurrently executing observations, providing each associated application with the appropriate resources to meet its timing constraint and give the integrated system the correct on-line and off-line look and feel.     

1-Gbps VLBI, The First Detection of Fringes

We report on the detection of VLBI fringes from quasars by a new VLBI system operating at 1 Gbps (1024 Mbits-per-second). Newly developed 1024 Msps (mega sample-per-second) AD samplers and 1024 Mbps recorders were used for the observations. A correlator with external buffers was used for the 1024 Mbps correlation processing of the tapes data.Our new VLBI system enabled 1024 Mbps VLBI, and this allowed the sampling of a 512 MHz bandwidth from a radio telescope receiver. This is the highest sampling speed ever used for VLBI, and the widest bandwidth used for VLBI observation. Initial sensitivity as evaluated by SNR comparison with earlier VLBI systems produced results to matched the expanded bandwidth. In our first observations, simultaneous optical fibre linked real-time VLBI observations were made to check the validity of data and precisely detemine the clock offsets among the radio telescopes.     

e-VLBI observations of GRB 080409 afterglow with an Australasian radio telescope network

Transcontinental e-VLBI observations were conducted in June 2008 with telescopes in Australia,China and Japan. Detections were made of the radio-loud quasar PKS B0727-115, which shows superluminal motion, and the intra-day variable quasar PKS B0524+034. The latter source was used as a phase reference calibrator for observations at the position of the gamma-ray burst GRB 080409, for which an upper limit to the radio emission is set. Australia Telescope Compact Array data were also used to derive a limit on the radio flux density of the GRB afterglow. These observations demonstrate the capability to form a large Australasian radio telescope network for e-VLBI, with data transported and processed in realtime over high capacity networks. This campaign represents the first step towards more regular e-VLBI observations in this region.     

一种基于元学习的大口径射电望远镜俯仰轴承故障辨识方法研究

在经过长期运行后大口径射电望远镜俯仰轴会出现微小扭曲, 滚动轴承作为承载俯仰轴的核心部件, 也会因长期承受交变载荷增加疲劳风险, 导致轴承寿命以及望远镜指向精度的下降, 极大影响望远镜的性能. 以俯仰轴承为研究对象, 开展故障辨识方法研究, 可为望远镜天线的高性能运行提供重要支撑. 为实现在有限数据和复杂工作条件下准确地辨识俯仰轴承故障, 提出了一种小样本条件下基于元学习的故障辨识方法(Few-shot Meta-learning Fault Identification, FMFI). 首先将不同工况下的原始信号转换为时频图像数据, 之后按照元学习协议将数据样本随机采样到不同的学习任务中. 在有限样本的条件下, FMFI可以通过训练任务中的样本信息获取通用的先验知识, 在未知的测试任务下实现准确快速的故障辨识. 选取了与望远镜俯仰轴承工况具有相似性的变负载轴承数据集进行实验, 实验结果表明, FMFI方法具有很高的准确性和可靠性, 为大口径射电望远镜俯仰轴承的主动运维和高质量服役提供了有力的技术支持.     

Research on Receiver Anti-RFI of Delingha 13.7 m Telescope

In astronomical observations, the radio frequency interference (RFI) will cause pseudo spectra and reduce the reliability and validity of observational data. The RFI mitigation, which includes many technical innovations of devices and the method studies of data processing, aims at reducing the influence of RFI on the radio astronomical observation. Various efforts were made to improve the anti-RFI capability of the multi-beam receiver (Superconducting Spectroscopic Array Receiver, SSAR) of the Delingha 13.7 m telescope. The interference transmission path was analyzed. The concepts of the device RFI direct coupling coefficient and the device RFI system coupling coefficient were proposed. The proportions of interference introduced in the receiver system by the different devices were quantified, and the interference-susceptible devices in the system were located. After the anti-RFI treatment of the interference-susceptible devices, the anti-RFI capability of the receiver system is improved by 30 dB in average, and the astronomical observation efficiency of the telescope is increased by more than 10%.     

PSD法测量大型射电望远镜副面位姿

指向精度是大型射电望远镜天线具有挑战性的关键技术指标.在望远镜运行中,方位俯仰角的变化、重力以及日照等对副面撑杆的综合影响会引起望远镜的副面位姿改变从而引起指向误差的增加和天线效率的降低.基于天马65 m射电望远镜,使用位置传感器装置(PSD)法构建了副面位置偏移量测定系统,可以实时采集副面的3维位移数据,构建重力模型,将测试结果与射电法构建的现有副面模型进行对比,有较好的一致性.此外,该系统可以分析日照(引起撑腿局部温度效应)引起的副面位移情况,也可以监视风载和瞬时启停对副面位姿的影响.     

Simulation Studies for Faraday Rotation Measure Observations

Limited by the spatial resolution of a radio telescope, multiple sources may be overlapped in the observing direction of the telescope. The Faraday rotation measure (RM) and polarization angle (PA) measurements of a target radio source will be affected by the other background radio sources located in the directional beam. The simulation study indicates that the influence of background radio sources on the polarization measurement of the target source depends on the RM values of interference sources. The RM value obtained by fitting the data of polarization observations at 2 or 3 wavelengths is not reliable. To obtain the accurate RM value of the target source needs to make fitting on the Stokes parameters Q and U observed at multiple wavebands.     

Active Adaptive Arrays: The ASTRON Approach to SKA

It has been argued, for a number of reasons, that the next generation radio telescope should be a multi-element interferometer with a collecting area of about 1 km². The remaining parameters of such an instrument – frequency range, angular resolution, instantaneous bandwidth, etc. – will be science driven. The requirements for propagation studies are briefly discussed, and it is pointed out how variable-source confusion may differ from the normal variety. Finally, the Dutch project to achieve a large collecting area using adaptive arrays of active antennas is described. A systematic approach has been adopted, with the construction of arrays of increasing complexity to test design features at each state. Recently, development of a low frequency array (LOFAR) has become an additional option. It would facilitate tests of some of the larger instrument's features, and provide real data on the influence of the ionosphere and interfering sources. This revised version was published online in July 2006 with corrections to the Cover Date.