Research On Distance And Direction Measurement Technology Of Short-side And Its Application In FAST Datum Control Network

Five-hundred-meter Aperture Spherical radio Telescope(FAST)is located in a karst depression of Guizhou Province,whose high-precision datum reference control network is the basis of antenna operation and control.Aiming at key problem of high precision short side measurement in FAST project,the technology of distance and direction measurement and its application in measuring scheme's design and implementation are systematically is studied in this paper.The main completed work is listed as following:1)According to the measured data of the short-side triangulation,the influences of the external factors on the short-side azimuth observation and its characteristics are analyzed.On this basis,the alignment of the devices and target,telescope focusing error,vertical axis tilt error and horizontal refraction are analyzed respectively.In order to decrease the errors of devices and target panels,the method of rotating devices and target bases to another face in another half observations is raised.Moreover,a new type of hollow target panel the rotating observation tower is designed originally.The experiment fully validated the effectiveness of the method.2)The problem of systematic error and accidental error in electromagnetic wave ranging and its correction or mitigation measures are analyzed.In view of the problem of observation period selection,instrument and prism structure error and high inaccuracy of precision short edge ranging,Corresponding reduction of the impact of the measurement method.3)To meet the demand of FAST datum control network measurement,the measuring scheme combined with horizontal and vertical direction is presented.According to the survey results of FAST project and the existing measurement technology and capability,the design and implementation of the measurement scheme,and measurement of the short side,including distance and angle measurement are researched.The final test results can meet the precision requirement of the network.In accordance with the measurement results of plane coordinates,the problems were analyzed and summarized.4)According to requirement of repeated measurement of the network and stability monitoring in the later stage of FAST project,due to the difficulty in precise leveling measurement,it is proposed that the plane-elevation and three-dimensional measuring scheme are utilized in the inner and mid-outer circles of control network respectively,which can take place of leveling measurement,and decrease the influence of deflection of verticals(DoV)and height anomaly differences in the area of FAST.Thereby,the three dimensional geometric coordinates are obtained.Finally,feasibility of the scheme is verified by three-dimensional modeling and simulation experiments.