Research Of Measuring Data Processing Method Of FAST Reflector Nodes

Five-hundred-meter Aperture Spherical Radio Telescope(FAST)is one of the Major National Science and Technology Projects.It is significant as a milestone for the development of radio astronomical observations,which will fundamentally improve the radio astronomical imaging capabilities.In astronomical observations,the spherical reflector at the karst site will change its shape to a 300-meter aperture instant paraboloid directing the celestial body by adjusting location of the nodes,while the feed will be moved to the focal point.It raises higher demands and tougher challenges for engineering technology,especially for large-scale measurement.In this paper,researches for the implementation of FAST reflector nodes measurement and data processing have been carried out.Main research results and innovations are listed as following.1.The celestial and terrestrial coordinate system involved in the construction and operation of FAST are studied.The conversion of celestial coordinate systems and the time systems are deduced,and the FAST spherical coordinate system and engineering coordinate system are defined here.Furthermore,the author participates in designation of the FAST reference control network,and an available optimized measuring scheme is proposed.The influences for results of astronomical observation derived from position and direction reference on are deduced.The corrections of results in astronomical observation are quantitatively analyzed.It is deduced that absolute and relative precision of the points' position can reach centimetric and millimetric level respectively.2.Motion trajectory and coverage area of the reflector surface in the tracking observation mode of FAST are quantitatively analyzed.The nodes' trajectory,which of the ideal condition and the status when feed is off the focus are studied.Thereby,it is proved that the motion of the nodes is a quasi-static process.Then,the location errors of the nodes are deduced and analyzed,while magnitudes of the errors are clarified,which provides the theoretical basis for the selection of the subsequent node measurement scheme.3.The author has participated in the developing work of total station measurement system for the nodes of FAST's reflector.Having conducted experiment for the arrangement of measuring devices.According to the valid angle between reflected light and normal of the cooperative target,the coverage of the devices mounted on different observation piers are calculated.Then,the influences of the meteorological factors are analyzed based on continuous observation data in the site.4.The conversion between the specific design coordinate system and the measuring coordinate system is deduced for the calculation of node measurement results in the instant paraboloid,and iterative computing methods of coordinate transformation parameters are studied.Moreover,the four-parameter model of total stations' backwards orientation is proposed here.The experiment shows that the simplified four-parameter conversion model can meet the precision requirements for total stations with precision leveling and automatic compensation device.5.The method of fitting parameters computation and accuracy evaluation for instant paraboloid of FAST antenna are studied.The importance of using half optical path difference(OPD)to measure the accuracy of the antenna surface is emphasized.By using the continuous interpolation points of the reflection surface,the integral form of the overall accuracy is deduced.Finally,the simulated and measured data are processed to fit and evaluate the antenna surface by using robust estimation,whose accuracy is improved by about two times.The position of the node is compensated according to offset in radial direction of spherical surface,whose precision is improved to a higher level,which is significant to improve performance of the antenna.