SVLBI-based Coverage Analysis Of Target Celestial Bodies In Joint Satellite-ground Observation

Space Very Long Baseline Interferometry(SVLBI)is an extension of the ground very long baseline interferometry technology in space,that is,the baseline of the interferometer is extended into space to break through the limitation of the earth's diameter on the length of the baseline vector.For SVLBI,the space observation point has good maneuverability,so it can effectively improve the observation efficiency of the target celestial body,expand the coverage of the celestial area,and at the same time can obtain a certain size in a short time.UV coverage increases the amount of sampling of the spatial frequency information of the radio source and effectively reduces the gaps in the UV coverage map.Therefore,whether it is from the observation efficiency of the target celestial body or the imaging effect of the target celestial body,SVLBI technology has More advantages than ground VLBI technology.From an observation point of view,the SVLBI system's coverage of target celestial bodies includes not only the space-time domain coverage,that is,the visible duration of the radio source and the observation range of the celestial region;it should also be extended to the spatial frequency characteristics of the target celestial body,namely the SVBI technology Sampling ability of radio frequency information of radio source;both are internal organic wholes,which together affect the observation ability of SVLBI technology,and also must be considered in SVLBI system design and later data processing.At present,there are few studies on space-time coverage and spatial frequency domain coverage of SVLBI system.This article will focus on the coverage of the target celestial body in the SVLBI system,from space-time coverage and UV coverage to carry out research,put forward the analysis method of space observation,and design several types of scenarios for simulation and verification.The second chapter aims at the geometric observation model of SVLBI technology,analyzes the influence of baseline error and time delay error on the measurement accuracy of radio source angular position measurement,studies the influence of antenna sensitivity and observation frequency band on the survey observation efficiency of SVLBI system,and compares it with the ground Compare the observed performance of the system.Chapter three analyzes the main factors affecting the visibility of radio sources,establishes a mathematical model of the visibility of the target celestial body,proposes a calculation method based on the space-based and ground-based radio telescope coverage of the target celestial body,and gives a solution Process.On this basis,25 radio sources were selected,and the visible periods of the radio sources for satellites in four different orbital planes and four observation stations on the ground were calculated respectively.It can be seen from the calculation results that the visibility time of the space satellite to the radio power source is obviously better than that of the ground station for the full-sky visibility,and the percentage of the occlusion time of the celestial bodies is less than 10%;The time is continuous and concentrated near the summer solstice and winter solstice.The coverage of sky-based and ground-based radio telescopes in the sky survey is analyzed,and the corresponding coverage results under different observation durations are given.Through calculation,it can be seen that the coverage results of the ground stations and space satellites in the sky area after the whole year of observation will appear to be an approximate diamond-shaped area that is not covered.The maximum horizontal span of the diamond-shaped area is 30 °,which is the The angle of the sun's shadow coincides.The fourth chapter aims at the problem of interference imaging of SVLBI technology,and gives the theoretical derivation process of interference imaging and the method of restoring the brightness distribution of radio signal.A solution method for non-instant UV coverage plan is proposed.The non-immediate UV coverage plan of SVLBI satellite in elliptical orbit orbit is calculated by simulation.On this basis,the evaluation method of the difference in UV coverage results is given.The results show that the SVLBI satellite can obtain better UV coverage when it is in an elliptical orbit,and the theoretical spatial angular resolution can reach 17.04 micro-angle seconds.In order to increase the observation time of the radio telescope on the southern hemisphere radio source,a set of satellite orbit parameters were designed,and the calculation results were consistent with the design purpose,which verified the correctness of the satellite orbit parameters designed in this paper.The joint satellite-ground observation based on the SVLBI technology proposed in this paper realizes the coverage of the space and frequency domain of the target celestial body,which can be used for the subsequent selection of the radio source,the determination of the observation time,the coverage of the radio frequency domain and the space observation point The establishment of the track provides important method support and data support.