Research On Ultra-high Precision Optical Distortion Calibration Method For Telescope System

Exoplanet exploration has always been an important issue of greatest concern to human society and the scientific community.At present,the most commonly methods used by exoplanet detection in the world are transiting star method and apparent velocity method.However,neither of them can effectively detect Earth-like planets in the habitable zone of sun-like stars.The apparent velocity method is limited by the detection accuracy,and the transit method is limited by the low detection probability.High-precision astrometry can well make up for the detection defects of the transit method and the apparent velocity method.When the measurement accuracy reaches the order of micro-arcseconds,it is possible to detect long-period planets around nearby stars and realize the search for terrestrial planets in the habitable zone.The realization of ultra-high precision astrometry requires observation by the telescope mounted on the outer space satellite platform.However,environmental factors such as satellite vibration and temperature changes will affect the distortion of the optical system of the telescope.Therefore,it is necessary to calibrate the optical distortion of the telescope with ultra-high precision,which can ensure the validity and accuracy of the measured data.Therefore,in order to realize the ultra-high precision calibration of distortion,a calibration method based on distortion gradient reconstruction is proposed in this paper.The main work is as follows:First of all,the cause of the distortion of the optical system is analyzed,and a mathematical model is established to provide a theoretical basis for the study of distortion calibration.The existing distortion calibration methods such as the fourconstant model method,the standard orthogonal basis calibration method and the diffraction pupil calibration method are introduced in detail.The accuracy of the star whose calibration accuracy is limited by the star catalog can not reach the order of micro arcseconds,the processing is difficult to achieve,and the strict application range of the observation target star is seriously limited.Therefore,in order to solve these problems,a new calibration method is proposed to achieve high precision calibration.Then,the calibration method based on distortion gradient reconstruction is introduced.The realization of high-precision distortion calibration in this method requires high-precision star spacing measurement,so the micro-pixel star spacing measurement technology is described in detail,and the current star spacing measurement accuracy can meet the requirements.Then the method proposed in this paper is analyzed in detail,and the algorithm flow of the calibration method is summarized.Finally,the experimental verification is carried out according to the proposed calibration method,and the simulation analysis and experimental experiments are carried out respectively.According to the requirements of the project,the optical system is designed,the theoretical value of optical system distortion is obtained,and the proposed method is used for data processing.The results show that when the wave aberration of the optical system is controlled within 0.0733λ and the measurement error of star angular spacing is 0.3 micro-arcseconds,the distortion calibration accuracy can reach 0.28 micro-arcseconds,which meets the distortion calibration requirements of the nearest neighbor habitable planet exploration.The calibration method based on distortion gradient reconstruction distortion proposed in this paper makes full use of the star spacing measurement technology of micro-arcseconds measurement accuracy,and is not limited by the accuracy of right ascension and declination of stars in the catalogue.The calibration accuracy of the optical distortion of the telescope can reach the order of micro-arcseconds,which meets the accuracy requirements of exoplanet detection.