Subjects: Astronomy >> Astrophysical processes submitted time 2023-12-06 Cooperative journals: 《天文研究与技术》
Abstract： Solar eruptions are important manifestations of solar activity, including solar flares and coronal mass ejections (CMEs). They can potentially impact satellite communications and navigation systems, ground power grid systems, and the human living environment. Monitoring and studying solar radio bursts not only enable the prediction of space weather but also serve as a research tool in solar physics. This article introduces a dual-channel high-speed solar radio frequency spectrum observation system designed and developed based on the LabVIEW platform. It aims to monitor solar radio bursts, which are characterized by their randomness, short duration, and rapid changes. The system utilizes a high-speed signal acquisition card with a sampling rate of 1.5GS/s, providing a time resolution of up to 4ms and a frequency resolution of 45.7764 kHz. The acquired signals are processed through FFT power spectrum analysis and displayed as frequency spectra and waterfall plots. The system extracts information such as the frequency, intensity, and duration of solar radio bursts. The observed data is uploaded to a server using the FTP file transfer protocol, optimizing storage resources and facilitating data sharing. This integrated system is specifically applied to analyze signals in the frequency range from 70 MHz to 700 MHz output by the 11-meter solar radio telescope at Chengjiang Fuxian Lake Observatory.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-11-24 Cooperative journals: 《天文研究与技术》
Abstract： VHF (Very High Frequency) band is one of important observation bands in Radio astronomy field. In this band, we usually use the array to form phased array telescope. In another hand, sparse array has more space resolution and lower side lobe level comparing with the regular array. Furthermore, based on array integrated optimization algorithms, we can effectively form the main beam and reject the Maximum side lobe levels and far side lobe levels. In this paper, at first, we review the development and research status of VHF sparse array in radio astronomy filed and analyze difficulties. The second, we promote a pipeline for sparse array building. The first step is constructing the optical elements configuration based on some optimization algorithms. And then, we promote a signal processing structure based on high performance computing severs and FPGA (Field Programmable Gate Array) SOPC (System On Programmable Chip) platform. In this platform, taking advantage of strong computing capability, in the GPU embedded in severs can compute the weighting parameters of different elements and different frequency channels. And then, transmitting these parameters through the high-speed bus and delivery them to each element in FPGA SOPC. We also analyze the data rate with multi-beams that can transmit the weighting parameters in real-time. This work can provide a technical base for future large-scale VHF array building.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-11-24 Cooperative journals: 《天文研究与技术》
Abstract： The GCRF (Gaia Celestial Reference Frame) based on Gaia astrometric data has systematic differences from the ICRF (International Celestial Reference Frame) based on VLBI (Very Long Baseline Interferometry). An external independent evaluation of the data from Gaia is required to link optical and radio reference frame. Celestial bodies with both optical and radio radiation are generally used to link the two frames, quasars are used at the dark end (magnitude G≥15), and radio stars are used at the bright end (G≤13). It is very difficult to apply for the ordinary VLBI observations, so we try to focus on some geodesic observations that can use phase reference mode to observe radio stars in geodesic observations. In order to test the feasibility of this kind of observation, we use piggy-back phase referencing mode in geodetic observation of IVS (The International VLBI Service for Geodesy and Astrometry) and LBA (Large Baseline Array), and select Del Lib and HR 1099 as the targets. Our observations have obtained the VLBI images, flux densities and single￣epoch coordinates of these two radio stars, and the coordinate accuracy is higher than that of the previous work; at the same time, we also combine the data of the previous work to fit parallax and proper motion of the two radio stars. Our results are consistent with the results of the previous VLBI work and Gaia′s, and some of the accuracy is higher. Our work verify the feasibility of observing radio stars with piggy-back phase referencing mode in geodetic observation, and lay a certain foundation for the subsequent enrichment of VLBI astrometric samples of radio stars and linking of optical and radio reference frames.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-11-17 Cooperative journals: 《天文研究与技术》
Abstract： In order to complete the monitor of ultra-broadband spectrum for solar radio burst，Yunnan Observatories have designed and developed 4 solar radio spectrometers with the frequency range of 15-80 MHz，100-750 MHz，600-4 200 MHz and 4-15 GHz，which are called decametric, metric, decimetric and resolution centimetric solar radio spectrometer, respectively. For the decametric solar radio spectrometer, the spectral resolution and temporal resolution have reached 7. 6 kHz and 1 ms, respectively. For metric and decametric, the spectral resolution and temporal resolution have reached 9. 5 kHz and 10 ms, respectively. For the centimetric spectrometer, the spectral and temporal resolution have reached 76 kHz and 10 ms, respectively. Each spectrometer includes antenna system, receiver and digital spectrometer. In order to obtain a spectrum with ultra-high spectral resolution, the maximum word length of FFT is 262 144, which cannot be achieved by one-time FFT in FPGA, the parallel FFT algorithm is need. For the large word length of FFT, the data need to be transformed into a FFT with two small word length by doing a row decomposition and then parallel processing. In this paper, the algorithm is studied and simulated by using Matlab, then is applied to digital spectrometer. The test results of the digital spectrometer are good consistency with the simulation, indicating the successful application of the algorithm on the digital spectrometer. This paper introduces the composition of solar radio spectrometer and the method of implementing ultra-high resolution based on FPGA.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-10-23 Cooperative journals: 《天文研究与技术》
Abstract： The 1 m New Vacuum Solar Telescope (NVST) is capable of high-resolution imaging observations better than 0.2″, but cannot yet routinely observe high-resolution magnetic fields. Many magnetic structures and solar activity exist at small scales, requiring high-resolution magnetic field observations. NVST offers excellent seeing, and if the magnetometer has fast modulation capabilities and is coupled with statistical reconstruction techniques, it is expected to achieve high-resolution solar magnetic field measurements. The main problems faced by NVST in measuring magnetic fields include time-varying polarisation due to bending-axis optical paths, optical axis shifts due to telescope attitude changes and wind loading, and the effects of turbulence. In this paper, we analyze in detail the requirements for high-resolution observation of the solar magnetic field and the solar magnetic field measurement problems faced by NVST, formulate the basic parameters of the magnetometer, propose the requirements for the polarisation analyzer, and design a high-resolution observation scheme for the photospheric magnetic field. Finally, the optical path for the magnetometer is designed using ZEMAX optical design software, and the results show that the optical design can meet the requirements of high-resolution imaging.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-10-23 Cooperative journals: 《天文研究与技术》
Abstract： Film thickness uniformity is an important indicator for the preparation of high-performance optical films. In order to further improve the uniformity of the film thickness of the 2.4 m primary mirror reflective film, an optimization scheme for the film thickness uniformity of the large-aperture telescope coating is designed. Based on the cosine distribution law followed by vacuum thermal evaporation, combined with the geometry of ZZ3200 vacuum coater and the actual needs of telescope coating, a film thickness calculation program is written to simulate the theoretical distribution of film thickness. The film thickness optimization design method and optimization results are given. Method 1: Add a correction mask at a suitable position inside the evaporation source, the results show that the radius of curvature of the mask is installed within 3 mm, and the Peak to Valley value of film thickness inhomogeneity decreases from 15% to 4% without mask, this method has certain universality, but the installation position of the mask should be accurately controlled; Method 2: Combined with the circular hole structure in the middle of the reflection primary mirror, the double ring evaporation source is designed, and the results show that when the center distance between the inner and outer ring evaporation sources is 10 cm and 130 cm, respectively, and the number of evaporation sources in the outer ring is 12 times that of the inner ring, the PV value of film thickness uniformity is 1.85%, which is designed for the mirror with a round hole in the center, and is suitable for most reflective astronomical telescope coatings.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-10-23 Cooperative journals: 《天文研究与技术》
Abstract： The magnetic imager of ground-based solar telescope will be affected by atmospheric turbulence during polarimetry, resulting in inaccurate measurement results. By synchronously detecting the wavefront aberration, and to use deconvolution reconstruction of the sun′s narrow band polarization image, the poor photons problem caused by the narrow band filter can be overcome. The high-resolution image reconstruction algorithm is applied to the reconstruction of the sun′s polarized image. During the reconstruction process, inaccurate wavefront sensing result can lead to I crosstalk between the reconstructed polarization image and the real polarization signal, resulting in certain difference. To study the impact of wavefront sensing accuracy on polarization image reconstruction accuracy during the reduction, a simulation model is established in this paper to study the I crosstalk of polarimetry results under different seeing and wavefront sensing accuracy. The results indicate that the reconstruction quality of polarized images is positively correlated with the accuracy of wavefront sensing. Under certain conditions, increasing the number of frames used for image reconstruction and reducing image resolution can also reduce the I→QUV crosstalk.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-10-20 Cooperative journals: 《天文研究与技术》
Abstract： Radio astronomical telescope is a key system in astronomical observation, deep space exploration and other researches. It is of great significance to improve its sensitivity and reduce the system noise temperature. However, because the frequency band allocated to radio astronomy research is limited and often shared with other businesses, radio astronomy telescopes are vulnerable to strong radio frequency interference. After these interferences enter the RF receiver, intermodulation interference, amplifier saturation and other problems will occur in the low-temperature amplifier, raising its noise background and reducing the detection sensitivity of the radio telescope to weak signals. The filtering metasurface technology can effectively suppress radio astronomy radio frequency interference, but the additional introduced noise needs to be controlled. In this paper, we propose a method to reduce the noise temperature of filtering metasurface in radio astronomical telescope. We study the relationship between the dissipative loss and reflection loss of filtering metasurface and its noise temperature, and minimize the noise temperature by restricting the direction of mismatched reflections. Using the method proposed in this paper, the system noise temperature can be reduced by 35.4%. If the filtering metasurface is set in the cooling chamber, an additional noise temperature of only 0.11K can be achieved.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-03-13 Cooperative journals: 《天文研究与技术》
Abstract： Continuously rotating waveplates as the polarization modulator is an important candidate polarimeter configuration for many solar telescopes to measure the solar magnetic field. It is widely adopted in many ground-based or space-based solar telescopes for the solar magnetic field measurement. In this paper, we present the derivation and formula of the Fourier demodulation in the context of continuously rotating waveplates. We further testify the formula correctness by using the synthetic FeI Stokes profiles, which are produced by the RH radiative transfer code with a given atmosphere model. In addition, we calculate the effect of the home-position errors, the positioning errors of the waveplate rotation and the time difference between the waveplate slot time and the detector frame time on the demodulated results, by using two kinds of demodulation methods, i.e., the demodulation matrix and the Fourier analysis. The main findings are: (1) The new Fourier analysis can provide more accurate results than the simple one adopted by the step-wise modulation. Similar results are obtained when we do the relative error estimation using these two demodulation methods. (2) Considering the relative errors due to the home-position angle error, we find the demodulated linear polarization are almost the same using these two methods. However, in the case of circular polarization, the demodulation based on the demodulation matrix is more reliable. Whatever which method is applied, it is shown that the home-position angle error has the same effect on both the circular and linear polarization. The relative error of 10-3 requires the home-position angle accuracy within ten arc seconds. (3) Calculating the relative error caused by the position error of the waveplate rotation, we find the demodulation results are almost equal using these two methods. Both of them show that the position error has more influence on the linear polarization. Furthermore, the requirements of the position accuracy are much higher (ten of arc seconds) than that in the case of step-wise modulation (0.1 degree) in order to achieve the relative error of 10-3. (4) It is crucial to precisely match the detector frame time and the waveplate rotation slot time. We investigate the relative error due to the difference between them and find that the time difference (∆) can cause cross-talk between the linear polarization signals. It has more prominent effect on the linear polarization than on the circular polarization. The time difference as a percent of the waveplate slot time (∆/T) is required to be smaller than 1% if the relative error is smaller than 10-3 for the linear polarization.
Subjects: Astronomy >> Astrophysical processes submitted time 2023-01-17 Cooperative journals: 《天文研究与技术》
Abstract： Radio astronomy uses antenna array for observation in the HF-VHF frequency band. According to the requirements of SKA (square kilometer array), the gain, structure consistency, stability, impedance change trend, polarization purity and other aspects of each array element antenna need to reach high indicators to meet the requirements of Sun, Jupiter, Epoch of reionization and other measurements in polarization measurement, antenna tracking stability and receiver broadband matching and other aspects. According to the performance requirements proposed in SKA requirement 2165: polarization purity 2135-38 and sensitivity per polarization 2814-15. And after summarizing the experience of the original design, this study designed a new type of inverted "V" grid dipole antenna suitable for HF-VHF for the 10-90MHz frequency band, which has the advantages of light weight and small wind resistance. The structure has the advantages of slow impedance change and good polarization purity in the ultra-wide frequency band of 10-90MHz. Among them, in terms of impedance change: the real part of the impedance of the antenna changes from about 0.8Ω to 631.132Ω, which is better than the low-frequency array antenna of the low-frequency radio array, reducing the difficulty of receiver matching and noise; in terms of polarization purity: the overall axial ratio of the antenna is less than 0.41dB, with good polarization isolation for strong polarization signals such as solar radio bursts.
Subjects: Astronomy >> Astrophysical processes submitted time 2022-08-31 Cooperative journals: 《天文研究与技术》
Abstract： W-Projection and W-Stacking are classical wide field imaging methods in radio interferometry. In this paper, the parallel computing implementation of these two imaging methods is carried out. First, the basic principle of the two imaging methods is analyzed, based on which the key factors for the parallel computing implementation of the imaging methods are discussed. The parallel computing experiments are carried out based on RASCIL for these imaging methods using calibrated radio interferometry observation data. The performances of the two imaging methods parallel computing are obtained by analyzing the parallel computation time, as well as the parallel efficiency and parallel resource configuration. The results show that both imaging methods are suitable for the parallel computing configuration of Strong Scaling, while the parallel computing of W-Stacking based on RASCIL has a great potential for performance improvement.
Subjects: Astronomy >> Astrophysical processes submitted time 2022-01-14 Cooperative journals: 《天文研究与技术》
Abstract：远程天文台具有观测效率高、运行成本低等优点，因此远程观测应用越来越广泛。5G网络技术的发展为利用手机等移动终端实现远程观测提供了可能，物联网和社交网络技术的进步也为其提供了数据传输、数据共享以及人性化操作的新途径。为实现云南天文台14英寸望远镜的远程观测和验证基于物联网和社交网络的远程天文台技术，自行设计研发了一套远程天文台控制软件，以微信聊天模式收发控制命令，以微信图片格式传输观测图像，以微信群组方式控制用户权限，实现了手机等移动终端基于微信的远程观测功能，为远程天文台控制软件设计及社交网络在天文观测中的应用提供了可借鉴的经验和方法。
Subjects: Astronomy >> Astrophysical processes submitted time 2021-07-06 Cooperative journals: 《天文研究与技术》
Abstract：月球物理天平动是对月球运动在空间摆动的描述。确定月球物理天平动,可以推测物理天平动的激发与耗散机制,比如陨击、月震和核幔粘滞摩擦等,故测定月球物理天平动对认识太阳系中天体的起源、演化及结构等,都具有十分重要的意义。本文利用最新的INPOP19a历表的数据，完成了对历表提取的欧拉角到月球物理天平动的转换，得到的物理天平动数值分别与该系列历表INPOP17a以及被广泛使用的DE430对比，发现不同历表的物理天平动之差存在着稳定周期。对比历表欧拉角的差别，计算出地心到月面反射器A15的距离最大有30厘米的差别，此结果对月球激光测距的预报精度有较大的影响，为后续的高精度测月研究打下基础。研究结果表明，INPOP19a最为稳定，故在月球物理天平动研究中推荐使用INPOP19a。
Subjects: Astronomy >> Astrophysical processes submitted time 2021-06-18 Cooperative journals: 《天文研究与技术》
Abstract：本文提出，用深度神经网络代替快速傅里叶变换法，求解无碰撞引力N体数值模拟方法PM-Tree中的势能，以提升PM-Tree方法的效率，验证深度学习方法加速无碰撞引力N体数值模拟的可行性。无碰撞引力N体数值模拟对研究星系、暗物质晕以及宇宙大尺度结构的形成和演化都有重要意义。而无碰撞引力N体数值模拟的传统方法在大规模问题上的模拟计算非常耗时，其中常用的PM-Tree方法的主要耗时部分是求解势能（解Poisson方程）。本文提出使用深度神经网络代替传统方法加速求解Poisson方程，多次调整并训练和测试深度神经网络模型结构，最终选用了辅以残差网络局部结构的Encoder-Decoder整体结构。验证了深度神经网络解Poisson方程的计算时间复杂度为；同样数据下进行测试，速度快于快速傅里叶变换方法求解和有限差分法求解；在同等采样率的情况下，精度优于快速傅里叶变换方法求解；并且具有可扩展性。故无碰撞引力N体数值模拟中，用深度神经网络可以提升PM-Tree方法中求解势能的速度，从而有效提升整体模拟速度。
Subjects: Astronomy >> Astrophysical processes submitted time 2021-06-18 Cooperative journals: 《天文研究与技术》
Abstract： 卫星激光测距中，为满足不同距离目标的测距要求，需要调整激光光束发散角。通常利用离焦式扩束系统改变两透镜间距离调整发散角会产生离焦像差，影响激光光束质量和系统测距能力。因此，研究离焦像差对激光光束质量和系统测距能力的影响具有重要意义。首先，分析扩束系统对基模高斯光束的变换作用，得到发散角和离焦量的关系。其次，基于基模高斯光束的传播理论，得到离焦像差对光束能量密度空间分布的影响。最后，对于不同距离的卫星，计算存在离焦像差和无离焦像差时激光测距系统接收的回波光子数。仿真结果表明：发散角和离焦量近似服从线性关系，离焦量变化，发散角变化；离焦像差影响光束的能量密度分布，使光斑弥散；对于不同距离的卫星，在不同角放大率下无离焦像差时测距系统接收到的回波光子数约为存在离焦像差时的2倍，可有效提高系统的测距能力。
Subjects: Astronomy >> Astrophysical processes submitted time 2021-05-27 Cooperative journals: 《天文研究与技术》
Abstract： 对中国科学院云南天文台现有的光纤式IFU集成化检测系统进行改进，实现了该系统的可视化和自动化检测功能。根据检测流程，通过一键式操作完成光学元件自动切换、成像系统连续离焦控制、自动化数据采集及数据处理等，可一次性检测出光纤阵列排布精度、微透镜阵列排布精度、光纤焦比退化、光纤透过率等基本参数，增加了计算赝狭缝端每根光纤沿光轴方向排布精度的功能，并在实验室验证了自动化系统的性能。该系统实现全自动化后，可将原来需要数周的检测时间缩短至一天之内，极大地提高了工作效率，有利于促进国内光纤积分视场单元制作和测试工艺的发展。
Subjects: Astronomy >> Astrophysical processes submitted time 2021-04-14 Cooperative journals: 《天文研究与技术》
Abstract：本文使用快速鲁棒性主成分分析(Fast RPCA，Fast Robust Principal Component Analysis)方法对日冕序列图像中的日冕喷流活动进行检测。检测的基本思路是利用Fast RPCA方法中低秩和稀疏分解的思想与日冕序列图像中有着变化尺度稍小且占比较大的随机变化背景成分、变化尺度较大且占比较小的日冕喷流的特点相结合，以此来实现随机复杂多变的动态背景和稀疏运动目标之间的分离，从而检测出作为前景变化的日冕喷流。采用太阳动力学天文台(Solar Dynamics Observatory，SDO)卫星上大气成像组件(Atmospheric Imaging Assembly，AIA) 观测设备的两组不同时间段、不同波段、不同观测位置的日冕序列图像作为研究对象。研究内容主要包括日冕序列图像的预处理、日冕喷流检测、Fast RPCA方法与帧间差分法的检测结果对比分析。实验结果表明，与帧间差分法相比，Fast RPCA方法能够检测出强度较弱的日冕喷流且提高了日冕喷流检测的准确度。
Subjects: Astronomy >> Astrophysical processes submitted time 2020-08-14 Cooperative journals: 《天文研究与技术》
Abstract：随着天文技术的不断发展，远程观测和自主观测逐渐成为天文观测的主流趋势，自动调焦技术也越来越受到重视。电动调焦器是天文望远镜不可或缺的附属设备，是实现自动调焦的关键设备。为实现云南天文台丽江天文观测站10英寸米德望远镜的自动调焦，自行研发了一套天文电动调焦器，设计相关控制电路，制定串口通信协议，并编写了一套开源ASCOM驱动程序SS Focuser。本文详细介绍了该电动调焦器的结构原理和实现方法，实测结果表明具有很好的稳定性，完全满足设计要求，为天文电动调焦器设计提供了可借鉴的经验和方法。
Subjects: Astronomy >> Astrophysical processes submitted time 2020-04-20 Cooperative journals: 《天文研究与技术》
Abstract：分子谱线可以在射电频谱上显现，但是采用离散数字功率谱分析算法会引入离散误差，难以获得分子谱线准确的频谱信息。针对射电频谱上离散数字功率谱分析中带来的频率偏移问题进行比值校正法研究和处理。该方法是频谱矫正方法的一种，特点在于算法简单，方便快捷。利用射频信号相同、分辨率不同和不同射频信号、不同分辨率情况下，归一化频率偏移量的变化确定该方法的校正效果，最终实现了射频为80.0MHz，141.8MHz和270.8MHz的频谱校正，提高了相应的频谱分辨率可达7.5Hz/channel。通过实验结果对比，确定了测试系统的最佳频率分辨率为50Hz/Channel或200Hz/channel。
Subjects: Astronomy >> Astrophysical processes submitted time 2019-07-30 Cooperative journals: 《天文研究与技术》
Abstract：经过十余年的不断建设和发展，中国虚拟天文台（China-VO）已成为支撑天文学观测、研究、教学的重要技术和资源平台。随着多信使天文学和时域天文学时代的到来，虚拟天文台也需要升级自身的核心能力，以给天文工作者提供更精准的服务和技术支撑。为此，中国虚拟天文台团队结合天文学的发展方向和信息技术发展趋势梳理了一份核心技术需求清单，并以问卷的形式针对领域内专家和用户开展了调研。通过对调研结果的统计和分析，中国虚拟天文台明确了未来一段时期的主要努力方向和目标，计划采用平台化的开发模式，并开放第三方开发接口，以吸引更多感兴趣的开发者基于虚拟天文台资源做出实用的工具，更好地实现资源与技术向服务的快速转换。
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