| 其他摘要 | Almost all celestial bodies’ radiation is polarized. The polarization information of electromagnetic radiation is very important for us to understand the celestial body’s magnetic field, dynamics parameters, thermodynamic parameters, polarization radiation transfer mechanism, and the physical information of the medium in the radiation process. The new generation of solar telescopes, for example, the 4m solar telescope Daniel K. Inouye Solar Telescope (DIKST) in the USA, the European space solar magnetic field measurement project Solar magnetism eXplorer (SolmeX), China Giant Solar Telescope (CGST), and the Coronal Magnetism and Plasma Assembled Scopes (COMPASS) and their polarimetric accuracy needs to be 10−4Ic. For such high polarimetric accuracy requirements, the influence of optical components' installation and adjustment accuracy, the polarization modulation scheme, the demodulation method, and errors introduced by data processing will directly affect the polarimetric accuracy. How to achieve stable, efficient, and reliable high-precision polarimetry of 10−4Ic is a major technical problem encountered by the current astronomical technology discipline. The purpose of this thesis is to systematically analyze and demonstrate the key technologies and methods of the solar polarimetry from the influence of the installation and adjustment accuracy of optical components, the polarization modulation scheme and demodulation method, and the error introduced by the data processing for the target of the deviation measurement accuracy of the order of 10−4Ic. The main content and innovations of the thesis are:1. The influence of the installation and adjustment accuracy of optical components. Taking the polarization analyzer of the rotating waveplate as an example, the errors that affect the accuracy of polarimetry are divided into three types from the geometric dimensions: axial, altitude, and azimuth. Modeling simulation analyzes the error sources that can introduce axial error, altitude error, and azimuth error. Then the sensitivity of various errors and the transmission of geometric errors to deviation measurement errors are discussed in combination with actual working conditions. On this basis, the correction methods of the above three types of errors are given. Besides, tolerance analysis and precision design are carried out for the instrument design of the next-generation instrument with a polarimetric accuracy of the order of 10−4Ic.2. The demodulation method of dual-beam integral field spectrum polarimetry system. We systematically analyzed and demonstrated the traditional dual-beam polarization demodulation method, the polarization optical switch demodulation method based on beam switching, and the reduced polarization optical switch demodulation method from the mathematical principle. The following conclusions are given: in the traditional two-beam demodulation method, the main source of polarimetric error is the gain deviation of the two beams; in the polarization optical switch demodulation method based on beam switching: the main source of the demodulation error is originated from ignoring Stokes parameters of the second-order error of the signal; in the reduced polarization optical switch demodulation method: the main source of the demodulation error is by omitting the high-order error, i.e. ignores the product of the solar Stokes Q/I and the reference sample data. Based on theoretical analysis, the FASOT-1B telescope of the Yunnan Observatory of the Chinese Academy of Sciences was used to observe the solar active area NOAA 12738. The demodulation results show that in either it is polarization sensitivity or polarimetric accuracy, the reduced polarization optical switch demodulation method is better than the polarization optical switch demodulation method, and the polarization optical switch demodulation method is better than the traditional dual-beam demodulation method.3. The accurate registration method of corona polarized image. A high-precision registration method for corona low-signal-to-noise ratio images is proposed. The red line polarization data observed in the total solar eclipse in the United States in 2017 was used for image registration and imaging polarimetry. The results show that the traditional Cross-Correlation (CC) algorithm cannot achieve high-precision image registration, and the registration result of the coronal red line image is not satisfactory. We proposed the method of image enhancement based on Blind Deconvolution (BD) plus Noise Adaptive Fuzzy Equalization method (NAFE), and then cross-correlation registration of the enhanced corona image can achieve better registration results. 4. Key technologies of integral field spectrum polarimetry system. Principal component analysis for low signal-to-noise ratio spectral noise reduction, spectrum extraction of the integrated field spectrum (IFS), flat field of IFS, and instrument profile correction in the direction of dispersion of the IFS are discussed. The IFS data observed during the 2017 total solar eclipse in the United States, the total solar eclipse in Chile in 2019, and the FASOT-1B telescope of the Yunnan Astronomical Observatory of the Chinese Academy of Sciences are used for the experiments. The results show that the principal component analysis method has an obvious denoising effect on low signal-to-noise ratio IFS. Specific research ideas are put forward for the extraction of the IFS, the flat field of IFS, and the correction of the instrument profile in the direction of dispersion. These three problems form relatively complex system problems and need to be further studied in the follow-up work. |
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