Aspects of time as it relates to space geodesy

Abstract

High accuracy space geodesy relies on accurate and stable frequency standards, time interval counters, event timers and measured time offsets relative to UTC. These requirements are becoming more stringent as the global networks of space geodesy stations strive towards higher accuracy. This invariably leads to continual instrumentation upgrades and instrumental developments. In addition to the station frequency standard high stability and accuracy requirements, several relativistic considerations are required during data processing to reach optimal measurement accuracy. These aspects of time are discussed and quantified for each of the techniques of VLBI, GPS, SLR and LLR. It is proposed that fundamental space geodesy stations be equipped with the new generation of frequency standards that will allow chronometric geodesy. This will allow time determination within a stable and defined terrestrial reference frame, linked to the celestial reference frame via the Earth orientation parameters, and will also provide a link between the relativistic and classical geoid at these stations.