A correction model of dispersive troposphere delays for the ACES microwave link

[1] The Atomic Clock Ensemble in Space (ACES) will be a future ESA experiment which utilizes ultra-stable clocks on-board the International Space Station (ISS). This mission is expected to perform tests of fundamental physics (relativity, possible drift of fundamental constants with time) and at the same time allows to compare the ACES time reference with respect to ground stations by using a novel microwave link concept. However, uncorrected dispersive troposphere delays pose the risk of degrading the performance of this microwave link over longer integration periods. Thus, a semi-empirical correction model has been developed which is only based on input from meteorologic sensors at the ground stations. The proposed model has been tested with simulated ISS overflights at different potential ACES ground station sites, and it could be demonstrated that this model is capable to remove biases and elevation dependent features caused by the dispersive troposphere delay difference between the uplink and downlink. The model performs well at all sites by reducing the impact on all reasonable averaging time scales by at least 1 order of magnitude. Similar studies like this might be of importance for other time and frequency transfer instruments or future space geodetic instruments.

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