Study Of The UT1 Measurement With The 13m Broadband VLBI Network

Universal Time(UT1)is a time scale defined by the rotation of the earth,which is an important element of National Standard Time UTC(NTSC).The UT1 service is of cirtical in the fields of satellite navigation,deep space exploration and astronautic missions.Due to the irregularity of the Earth's rotation,UT1 cannot be accurately modeled thus needs to be maintained by space geodetic techniques such as VLBI/GNSS.Presently,the United States and Russia have realized daily UT1 measurements product services,however,the UT1 service used in China is mainly depends on the products provided by International Earth Rotation and Reference System Services(IERS).In order to establish high-precision UT1 measurement and product service,the National Time Service Center has developed a 3×13m wide-band VLBI system(NTSC-VLBI).In this thesis,we focus on the methodology of using such system to measure UT1 and refine the accuracy of UT1.The main achievements and innovations are as follows:1)Based on the NTSC-VLBI system,systematically carried out the research on UT1 measurement,established UT1 data processing flow,and carried out the UT1 experiments.Participated in the development of 13 m astrometry and geodesic VLBI system of NTSC,which is based on the VLBI2010 specification with the characteristics of small aperture,fast source switching,feed cooling and broadband observation.A pratical schedule and observation strategy is proposed and optimized by taking into account of the site environment and antenna characteristics,the data processing flow is designed,and experiments are carried out.Statistically,our measurements shows a 14.5 ?s systematical deviation with respect to IERS C04 series,the standard deviation based on hundreds of msesurements is 58.8 ?s.2)Carried out the error analysis of UT1 measurement,the methods used for station coordinates corrections and instrumental electrical delay calibrations are proposed,effectively improves the UT1 measurement accuracy.Station coordinates,atomospheric and ionospheric residuals and clock errors,the main error sources,are studied,it is found that the coordinate change of Kashi station and Jilin station will reduce the UT1 measurement accuracy,then the coordinates of the two stations are refined.In data processing,the residual delay of strong source is used to correct residual delay of other radio sources,at the same time,strong quasar scans are designed half an hour before and after the UT1 block.These data are used to monitor clock behaviors and correct the unmodeld residual delay.3)To meet the requirement of UT1 service,data acquisition scheme is proposed,which can effectively reduce the amount of original data without affecting the UT1 measurement accuracy.The data acquisition scheme is optimized to reduce the amount of observation data with the bandwidth synthesis,and an 8-channel 256 MHz acquisition method is proposed to balance the measurement accuracy and network consumptions used for data transfer.The results show that the 8-channel UT1 measurement accuracy is close to that of 16-channel 512 MHz measurement,meanwhile,the amount of data is reduced by 50%.4)A integration scheme based on NTSC-VLBI and i GMAS is proposed to obtain continuous and high-precision UT1 products.NTSC-VLBI system can measure UT1 with high accuracy,but it is difficult to ensure the continuity.international GNSS Monitoring and Assesment System(iGMAS)can provide continuous data of LOD.Combining the advantages of the two techniques,a integration scheme is proposed.Based on the observation data of 2018,the actual test is carried out.The results show that after fusion,a-7.8 ?s systematical deviation with respect to IERS C04 series,the standard deviation is 33.4 ?s.5)A preliminary UT1 product service is realized,it's products has been used in Chinese deep space exploration missions,as a backup UT1/ERP products.A preliminary UT1 keeping scheme is established,including generation of observation outline,automatic return of observation data,data correlation processing,post-processing,UT1 estimation and prediction,also the prediction of EOP is also studied,which is at the same level as the international prediction results.The UT1 product is now as a backup for Chinese deep space exploration missions.