PRECISE DOMESTIC VLBI IN 22GHz BAND FOR GEODESY

22 GHz频段VLBI具有带宽宽、传播延迟小、可改正对流层延迟、射电源体积小等优点，是一种强有力的大地测量技术。然而，在22 GHz频段大地测量中，VLBI的实现存在着观测源数量少、对频率标准和频率分配系统的稳定性要求高、射电源的流量密度小等困难。我们开发了所需的系统，并明确了VLBI系统具有测量精度在几厘米或更小的基线的潜力。本项目研究的内容包括：1)22 GHz相位稳定光纤链路VLBI系统的研制；2)22 GHz射电源的测量和观测射电源的选择；3)利用该系统进行国内VLBI观测；4)基线估计。VLBI观测是在水泽-鹿岛(通信研究实验室)和水泽-鹿儿岛两条基线上进行的。在水泽-鹿岛基线上测得的延迟，在积分时间为258s的情况下，误差为59ps(路径长度为1.8 cm)，而在S/X波段，误差为160s，误差为82ps。这一结果表明，22 GHz VLBI可用于精度在几厘米或更小的大地测量。

VLBI in 22GHz band is a powerful technique for geodesy because of wide bandwidth, small propagation delay, possibility of the correction for tropospheric delay and small size of a radio source. However, there are some dificulties to realize VLBI in 22GHz band for geodesy such as a small number of observed sources, requirement of a high stable frequency standard and frequency distribution system, small flux density of a radio source. We developed the system required for it, and make it clear that the VLBI system has the potential to measure a baseline with an accuracy of a few cm or less.The items studied in this project are as follows, 1) development of 22GHz VLBI system with phase-stabilized opical fiber link, 2) surveying radio sources at 22GHz and selection of the radio sources for the observation, 3) domestic VLBI observations with the system, 4)estimation of the baseline. The VLBI observations were carried out on two baselines of Mizusawa-Kashima (Communications Research Laboratory) and Mizusawa-Kagoshima. The error of the delay measured on the baseline of Mizusawa-Kashima was 59ps(1.8cm in path length) in the case of integration time of 258 sec, while the error was 82ps for 160 sec in S/X band. This result suggests that 22GHz VLBI is available for geodesy with an accuracy of a few cm or less.