Satellite Observations by Radio Telescopes for Superior Reference Frame Interconnections (SORTS)

射电望远镜的卫星观测有可能极大地改善甚长基线干涉测量观测实现的国际天体参考框架（ICRF）与河外射电源和动态实现天体框架的卫星轨道之间的框架联系。与此同时，国际地球参考框架（ITRF）作为VLBI和卫星大地测量观测的多技术解决方案的一致性将大大受益，否则它只依赖于在同一地点的地面观测站点的当地联系测量。精确的框架连接是空间精确导航的基础，也是观测海平面上升和其他全球地球动力学过程的先决条件。在SORTS项目中，我们涵盖了实现和分析专用于此类空间连接项目的卫星的VLBI观测所需的所有技术方面。现在是这一项目的最佳时间框架，因为关于携带VLBI转发器、激光反射器和GRASP或MicroGEM等全球导航卫星系统接收器的卫星的建议已接近被接受。在SORTS项目中，我们将研究噪声与调制信号在信噪比和群延迟和相位延迟的预测精度方面的应用。接下来，我们将建立一个完全现实的调度工具，考虑到所有特定于站点和源的限制，如回转率和集成时间，我们将缩小从调度到使用射电望远镜实际观测卫星的所有差距，从而实现自动化程序。将特别强调与类星体和卫星交替观测的联合时间表。为了从射电望远镜的观测结果中产生低地球轨道卫星的群延迟和相位延迟，我们将在相关软件中调整所有模型。最后，我们将扩展现有的大地测量分析软件，以便最佳地结合类星体和卫星观测。有了这个软件，我们将使用逼真的模拟观测，以确定轨道弧从各种类型的射电望远镜观测，我们将运行一系列的蒙特-卡罗模拟，以提供反馈给处理链中的早期步骤，如调度，并评估对帧关系的影响。SORTS项目是维也纳理工大学和波恩大学的一项联合奋进，两个组织的优势互补。此外，通过与位于德国韦策尔和瑞典翁萨拉的VLBI观测站的合作伙伴密切合作，我们将能够在很早的阶段就通过真实的观测，例如通过对全球导航卫星系统卫星的VLBI观测，验证我们的发展。

Satellite observations by radio telescopes have the potential to dramatically improve the frame ties between the International Celestial Reference Frame (ICRF) realized with Very Long Baseline Interferometry (VLBI) observations to extragalactic radio sources and satellite orbits realizing celestial frames dynamically. At the same time, the consistency of the International Terrestrial Reference Frame (ITRF) as a multi-technique solution from VLBI and satellite geodesy observations will benefit substantially, which otherwise solely relies on local tie measurements at co-located terrestrial observing sites. Accurate frame ties are fundamental for precise navigation in space and are a prerequisite for the observation of sea level rise and other global geodynamic processes.In project SORTS, we cover all technical aspects which are necessary for the realization and analysis of VLBI-like observations to satellites dedicated to such space-tie projects. Now is the optimal time frame for such a project because proposals for satellites which carry a VLBI transponder, laser reflectors and a GNSS (Global Navigation Satellite Systems) receiver like GRASP or MicroGEM are close to acceptance. In project SORTS, we will investigate the application of noise versus modulated signals in terms of signal-to-noise ratio and projected precision of group and phase delays. Next, we will set up a fully realistic scheduling tool taking into account all station- and source-specific restrictions like slewing rates and integration times and we will close all gaps from scheduling to the actual observations of satellites with radio telescopes allowing for automated procedures. Particular emphasis will be put on joint schedules with alternate observations to quasars and satellites. To generate group and phase delays from the observations by radio telescopes to satellites at low Earth orbits, we will adapt all models in the correlation software. Finally, we will expand existing geodetic analysis software for the purpose of optimally combining quasar and satellite observations. With this software, we will use realistically simulated observations to determine orbital arcs from various types of radio telescope observations and we will run series of Monte-Carlo simulations to provide feedback to earlier steps in the processing chain like the scheduling and to assess the impact on the frames ties. Project SORTS is a joint endeavor of the Vienna University of Technology and the University of Bonn with the strengths of both groups greatly complementing each other. Furthermore, in close co-operation with partners at the VLBI stations at Wettzell in Germany and Onsala in Sweden, we will be able to validate our developments with real observations already at a very early stage, for example with VLBI observations to GNSS satellites.