同波束VLBI差分时延率研究

A Study of Difference Delay Rates Derived from Processing of Same-Beam VLBI Data

通过分析SELENE的两颗小卫星Rstar和Vstar的同波束VLBI数据,发现两卫星间差分时延率中由中性大气和电离层引起的长周期变化已被去除,且在小角距时,短周期变化也能绝大部分被去除。但角距离越大,去除部分越小。通过将2008年一年中8个台站组成的所有基线的相关相位拟合残差数据分别平滑积分30 s与60 s后,再通过5点直线拟合求得时延率,得出单卫星时延率随机误差分别约为0.32 ps/s RMS与0.20 ps/s RMS,而差分时延率随机误差分别为0.19 ps/s^0.32 ps/s RMS与0.09 ps/s^0.17 ps/s RMS。单卫星的时延率随机误差在秋季最大,春季最小,而差分时延率的随机误差在全年基本稳定。

As shown by our analyses difference delay rates from SELENE same-beam VLBI data are almost not influenced by long-term effects on radio signals from the ionosphere and neutral atmosphere. The short-term effects on radio signals from the atmosphere can be mostly eliminated if the separation angle between two satellites is small （ 〈 0. 1 o） , but becomes more appreciable and more difficult to be eliminated as the separation angle increases. We further integrate the residuals of correlation phases for a set of data after fits to their systematic trends are subtracted. The data were observed with all baselines of 8 VLBI stations through 2008. Some integrations are over time intervals of 60s or 30s, and each integration generates a data point for detailed analyses. We apply linear fits to every 5 data points to find delay rates and difference delay rates. Statistics of these show that rms values of random errors of delay rates of two satellites are about 0. 20ps/s and 0. 32ps/s, respectively. Our statistics also show that rms values of random errors of difference delay rates of two satellites are 0. 09ps/s to 0. 17ps/s and 0. 19ps/s to 0.32ps/s, respectively. Random errors of delay rates are statistically small in the spring and larger in the autumn, but those of difference delay rates are stable throughout the year.