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基础，也是解决地球系统（包括固体地球、水圈、大气层和冰冻圈）内全球变形和质量输运问题的基础。该观测系统的稳定性和分辨率对于各种应用都至关重要，从监测全球变化到导航中的微妙任务。甚长基线干涉测量（VLBI）、卫星激光测距（SLR）和全球导航卫星系统（GNSS）测量方法中的系统误差给出了实现全球参考框架的最终精度极限。它们通过由Wettzell大地测量观测站（GOW）等基础站建立的局部几何关系连接起来。这些联系假设基于几何的仪器参考点（例如，机械可达天线参考点）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测量可达的硬件延迟）重合。然而，可能会出现未考虑的传播延迟，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来生成并通过空中传输GNSS的外部时间参考信号。这一技术将为可变传播延迟建立一个参考，最终将从全球导航卫星系统测量过程中消除。该研究单位建立在GOW最近开发和运行的现有光学计时系统的基础上，包括VLBI望远镜。该工作计划分为四个主要的工作包，这是专注于本地伪卫星系统的发展。在该系统的帮助下，我们将消除GNSS测量过程中的可变偏差，并将GNSS接收机时钟与光学定时系统对准。通过这种方式，我们减少了GNSS和VLBI测量之间的不确定性。前三项任务是开发伽利略伪卫星系统，该系统从台站校准目标发射类似于伽利略E1BC的信号。该信号必须与表示时间标记的光脉冲串同步。其原因是，定时系统最宝贵的无漂移输出是光脉冲串。虽然最终目标是从接收系统中消除可变延迟，但这种同步必须发生在皮秒系统不确定性上。第四个工作包将利用当地全球导航卫星系统网络，以基于闭合的测量概念验证所开发的校准概念。此外，由于目标是统一GNSS和VLBI之间的时钟参数，我们建议做一个额外的实验，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.