摘要
GRACE类重力卫星通过监测全球月时变重力场变化,为研究地球质量变化以及全球气候变化提供了重要的地球物理基础数据.测量星间距离变化的星间测距系统是重力卫星的关键载荷,GRACE/GRACE-FO(GRACE Follow-On)和中国首对重力卫星均搭载了微米级测量精度的星间微波测距系统(KBR).该系统基于超稳晶振(USO)进行授时授频,并借助GPS精密定轨后处理精确计算本地时钟(USO时钟)与GPS时钟之间的钟差,完成双星之间的时间同步以及对USO频率的精密测量.因此,USO/GPS时钟精度直接影响KBR的测距精度.本文基于GRACE-FO数据,深入研究了不同时钟精度以及USO时钟低频特征的影响因素对KBR测距的具体影响.首先评估了USO时钟和GPS时钟的精度,及其对KBR有偏距离和载波频率变化改正(FV改正)的影响;之后进一步分析了USO时钟低频精度的影响因素,包括相对论效应和载荷处理单元(IPU)的温度场变化.研究结果表明:(1)与USO时钟相比,GPS时钟可将KBR测距的低频(<1 mHz)精度提高1~2个量级,满足有偏距离的计算需求,但GPS时钟的高频(1~6 mHz)噪声会在FV改正中引入高于KBR设计噪声水平的噪声;(2)在影响USO时钟低频精度的因素中,相对论效应是单星USO时钟与GPS时钟之间在1 cpr和2 cpr频率处钟差的主要成分,而该效应引起的相对钟差对有偏距离的测量影响可以忽略不计,但在FV改正的1 cpr和2 cpr频率处仍是主要影响因素.双星IPU的温度场相对变化与相对钟差之间的相关系数在70%的时间段内高于0.6,表明温度场变化是影响USO时钟低频精度的潜在因素.此外,USO频率漂移的年际变化与卫星IPU的温度变化高度相关,但相对钟差的误差与卫星IPU的温度变化并未表现出明显的相关性.本研究为评估KBR测距中的时钟噪声以及优化数据预处理算法提供了理论依据.
The GRACE-type gravity satellites provide essential baseline geophysical data for the study of changes in Earth's mass and global climate by monitoring the global monthly time-varying gravity field variation.The inter-satellite ranging system,which is used to measure the distance variations between two satellites,is a key payload on the gravity satellites.GRACE/GRACE-FO and China's first pair of gravity satellites are both equipped with a K-Band Ranging system(KBR)with micrometer accuracy.The KBR relies on an Ultra-Stable Oscillator(USO)to generate the on-board time tag and carrier frequencies,and then uses the clock offset between the local clock(USO clock)and the GPS clock which estimated in the GPS precision orbit determination to synchronize the local clocks of the two satellites and precisely measure the USO’s frequencies,so the accuracy of the USO/GPS clocks directly affects the ranging accuracy of the KBR.Based on GRACE-FO data,this paper deeply investigates the specific effects of different clock accuracies and the factors that influence the low-frequency characteristics of USO on the ranging accuracy of the KBR.Firstly,we evaluate the accuracy of the USO clock and the GPS clock and their effects on the calculation of the KBR biased range and the carrier Frequency Variation correction(FV correction),and then further analyze the influencing factors of the lowfrequency accuracy of the USO clock,including relativistic effects and the temperature variations of the Instrument Processing Unit(IPU).The results show that:(1)Compared with the USO clock,the GPS clock can improve the low-frequency(<1 mHz)accuracy of the KBR ranging by 1~2 orders of magnitude,which meets the requirements of the biased range calculation,but the high-frequency(1~6 mHz)noise of the GPS clock introduces noise higher than the KBR design noise level in the FV correction;(2)Among the influencing factors of the low-frequency accuracy of the USO clock,the relativistic effect is the main component of the clock error between the USO clock and the GPS clock at 1 cpr and 2 cpr for the case of single-satellite,while the relative clock error caused by the relativistic effect has a negligible influence on the measurement of the biased range,but it is still the main influencing factor on the FV correction at 1 cpr and 2 cpr.The correlation coefficients between the relative temperature variation of the two satellites and the relative clock error are higher than 0.6 for 70%of the period,indicating the temperature variation is a potential factor affecting the low-frequency accuracy of the USO clocks.In addition,the inter-annual variation of the USO frequency drift is highly correlated with the temperature variation of satellite IPU,but the error of the relative clock error does not exhibit a significant correlation with such temperature variations.This study provides a theoretical foundation for evaluating clock noise in KBR ranging and optimizing the data pre-processing algorithms.
作者
闫易浩
王长青
钟敏
尹恒
朱紫彤
穆庆禄
梁磊
YAN YiHao;WANG ChangQing;ZHONG Min;YIN Heng;ZHU ZiTong;MU QingLu;LIANG Lei(Max-Planck-Institut für Gravitationsphysik(Albert-Einstein-Institut)and Institut für Gravitationsphysik,Leibniz Universität Hannover,Hannover 30167,Germany;State Key Laboratory of Geodesy and Earth’s Dynamics,Innovation Academy for Precision Measurement Science and Technology,Chinese Academy of Sciences,Wuhan 430077,China;School of Geospatial Engineering and Science,Sun Yat-Sen University,Zhuhai Guangdong 519082,China;Ministry of Education Key Laboratory of TianQin Mission,TianQin Research Center for Gravitational Physics&School of Physics and Astronomy,Sun Yat-sen University,Frontiers Science Center for TianQin,Gravitational Wave Research Center of China National Space Administration,Zhuhai Guangdong 519082,China;School of Marine Technology and Geomatics,Jiangsu Ocean University,Lianyungang Jiangsu 222005,China;School of Geographic Information and Tourism,Chuzhou University,Chuzhou Anhui 239099,China)
出处
《地球物理学报》
北大核心
2026年第1期83-96,共14页
Chinese Journal of Geophysics
基金
国家自然科学基金项目(42174103)
国家自然科学基金(12261131504,42204091)
马克思普朗克研究所-中国科学院LEGACY项目(M.IF.A.QOP18098)
智慧地球重点实验室基金资助项目(KF2023YB02-04)资助。
