Galileo pseudolite calibration target used to consolidate time between space geodetic techniques

全球大地测量观测系统（GGOS）是所有全球变化研究的计量基础，也是处理地球系统（包括固体地球、水圈、大气和冰冻圈）内全球变形和质量输送的基本问题的计量基础。该观测系统的稳定性和分辨率对于各种应用至关重要，从监测全球变化到导航中的微妙任务。超长基线干涉测量（VLBI）、卫星激光测距（SLR）和全球卫星导航系统（GNSS）测量方法的系统误差是实现全局参照系的最终精度限制。它们由Wettzell大地观测站（GOW）等基础站点建立的局部几何联系连接起来。这些联系假设基于几何的仪器参考点（例如，机械可访问的天线参考点）与技术上有效的参考点（例如，天线相位中心加上通过GNSS或VLBI测量可访问的硬件延迟）一致。然而，可能会出现无法解释的传播延迟，并导致两点之间的系统变量偏移。应利用时间作为探测信号来研究这些可变延迟。特别是，我们将使用来自有源延迟补偿光纤线路的时钟信号，为空中GNSS生成和传输外部时间参考信号。该技术将为可变传播延迟建立一个参考，最终将从GNSS测量过程中消除。该研究单元建立在GOW最近开发和运行的现有光学定时系统的基础上，包括VLBI望远镜。工作计划分为四个主要工作包，重点是本地伪卫星系统的开发。在此系统的帮助下，我们将消除GNSS测量过程中的可变偏置，并将GNSS接收机时钟对准光学定时系统。通过这种方式，我们减少了GNSS和VLBI测量之间的不确定性。前三个任务是开发伽利略伪卫星系统，该系统从站校准目标传输类似于伽利略E1BC的信号。该信号必须与代表时间标记的光脉冲序列同步。其原因是定时系统最宝贵的无漂移输出是光脉冲串。虽然最终目标是消除接收系统的可变延迟，但这种同步必须在皮秒级的系统不确定性下进行。第四个工作包通过利用本地GNSS网络的基于封闭的测量概念验证了开发的校准概念。此外，为了统一GNSS和VLBI之间的时钟参数，我们提出了一个额外的实验，包括GNSS和VLBI网络。

The Global Geodetic Observing System (GGOS) is the metrological basis for all global change research and for essential questions dealing with global deformation and mass transport within the System Earth consisting of the solid Earth, hydrosphere, atmosphere, and cryosphere. The stability and resolution of this observing system are of paramount importance for all sorts of applications, reaching from monitoring of global change to delicate tasks in navigation. The ultimate accuracy limit in realizing a global reference frame is given by the systematic errors in Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), and Global Navigation Satellite System (GNSS) measurement methods. They are connected by local geometric ties established by fundamental stations like the Geodetic Observatory Wettzell (GOW). These ties assume that the geometrically based instrumental reference point (e.g. a mechanically accessible antenna reference point) coincides with the technically effective reference point (e.g. the antenna phase center plus hardware delays accessible via the GNSS or VLBI measurements). However, unaccounted propagation delays may appear and cause systematic variable offsets between both points. These variable delays shall be investigated by utilizing time as a probe signal. In particular, we will use the clock signal from an active delay-compensated optical fiber line to generate and transmit an external time reference signal for GNSS over the air. This technique will establish a reference for the variable propagation delays, which will eventually be removed from the GNSS measurement process. The research unit builds on the existing optical timing system recently developed and operated at GOW, including VLBI telescopes. The work program is structured into four major work packages, which are focused on the development of the local pseudolite system. With the help of this system, we will remove the variable bias from the GNSS measurement process and align the GNSS receiver clock to the optical timing system. In this way, we reduce the uncertainty between GNSS and VLBI measurements. The first three tasks are developing the Galileo pseudolite system, which transmits a signal similar to Galileo E1BC from the station calibration target. This signal must be synchronized to the optical pulse train, representing time markers. The reason for this is that the most precious drift-free output of the timing system is the optical pulse train. While the ultimate goal is to remove the variable delays from the receiving system, this synchronization must occur on picosecond systematic uncertainty. The fourth work package verifies the developed calibration concept with a closure-based measurement concept utilizing a local GNSS network. Furthermore, as the goal is to unify the clock parameter between GNSS and VLBI, we proposed to do an additional experiment that includes GNSS and VLBI networks.