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： 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.
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