VLBI2010技术的时间比对应用研究

Next generation frequency standards are expected to outperform the current atomic clocks by several orders of magnitude and provide a more stable time scale. In order to compare such advanced frequency standards it is necessary to develop new and improved methods for time and frequency (T&F) transfer that can carry the unprecedented precision over distances of several thousand kilometers. The three major goals of VLBI2010 are 1 mm station position on global scales, continuous measurements, and turnaround time to initial geodetic results of less than 24 h. It is seen that a great potential in this new technology for the comparison of next generation frequency standards over intercontinental distances without the need to pay for satellite transponder fees as in the case of TWSTFT. Moreover, as VLBI does not rely on orbital information like the GNSS, the long-term frequency transfer stability can be improved gradually with time. This project will assess and explore the possibilities of VLBI and VLBI2010 for time and frequency transfer. We will use the Vienna VLBI Software (VieVS) with the classical least-squares solution as well as a Kalman filter solution for the routine provision of those parameters. A Kalman filter is particularly well suited for describing clock variations, and it allows that clock information from external sources like GNSS can be added to the filter, specifically for stabilization at short time scales. This also include studies with twin telescopes because having more telescopes connected to one clock improves the estimation of clock parameters considerably. Nowadays, this solution has never been involved in related fields both at home and abroad, so more detailed research of the technique is of great significance.

高稳定度频标的发展需要与之相匹配的高精度、高稳定度的时间比对技术。基于VLBI2010技术的新一代甚长基线干涉测量系统将实现全球基线测量达到１毫米精度、连续观测以及24小时之内发布数据产品。VLBI2010技术能够在国际甚至洲际距离上实现原子钟的比对，长期稳定性可以随着时间的推移逐渐提高，并且不需要像使用卫星双向法去支付高额的卫星转发费用，也不需要像GNSS技术依赖轨道信息。本项目着眼于未来VLBI2010的全球全面实现并考虑当前VLBI的技术特点，研究VLBI技术在时间比对领域的应用，分析最小二乘解算方法和Kalman滤波方法的解算差异，评估钟差比对精度和各项误差因素，通过使用双天线系统提高时钟参数的估计，考虑多技术融合手段提供最佳的短期和长期的频率稳定，可为VLBI2010技术在时间比对应用的全面开展提供技术支撑。

为满足高精度频标发展所要求的与之相匹配的高精度时间比对需求，本项目开展了VLBI技术在时间比对领域的应用研究。具体而言，项目的研究可以概括为以下几个方面：.（1）项目以目前国内外VLBI大地测量技术的现状为基础，并考虑VLBI2010的发展，研究时间比对模型和解算方法，评估钟差比对的精度。.（2）利用国际VLBI测天测地组织（IVS）的VLBI大地测量实测数据，通过数据处理和解算分析，估计测站钟差，验证了VLBI技术用于时间比对的可行性。.（3）分别考虑全球分布的VLBI2010测站网和国内VLBI2010测站网，进行Monte Carlo仿真研究，通过仿真评估了VLBI2010用于时频传递的技术特征和精度水平，验证时间比对算法的精度和效能。.以上研究验证和评估了VLBI技术在时间比对领域的应用价值，为未来VLBI技术在时间比对的工程应用提供支撑。