DORIS Alcatel ground antenna: Evaluation of the phase center variation models

Abstract

The DORIS ground antenna phase center variation (PCV) modeling is an important factor of the DORIS solution accuracy and affects also the DORIS solutions employed in the ITRF2020 realization. There are two different elevation dependent models available for the Alcatel antenna, called here 1.0 and 2.0. For the Starec antenna we have only one PCV model. We demonstrate the effect of the Alcatel PCV model selection, reaching a value around 15 mm in the estimated DORIS station height. The post-fit Doppler observation residual analysis proved a better performance of the residuals derived from the solution employing Alcatel PCV model 2.0, particularly in several specific elevation intervals over 50 degrees. The elevation dependent systematics in the residuals have been proven by the separation of the ascending and descending portions of the residuals. The residual mean calculated for the elevation intervals reached values with a mutually opposite sign for the ascending and descending observations. Moreover, we have compared the residuals of the Starec and Alcatel stations, whereas the Starec residual RMS was lower for elevations approximately under 50 degrees, the Alcatel residual RMS was lower for higher elevations. This result could relate to an eventual Starec PCV model imperfection at higher elevations.To check the compatibility of the Starec and Alcatel PCV models impact on the station height, we have performed the comparison of the measured vertical component of the DORIS-DORIS local ties to a value calculated from the DORIS observations. The pairs of the Alcatel-Starec stations were the object of interest. When repeating the experiment with both Alcatel models 1.0 and 2.0, we have found a similar level of agreement of the measured and observed/computed height difference, but with the opposite sign. The average difference reached 8.7 ± 2.5 mm for Alcatel PCV model 1.0 and −7.2 ± 2.4 mm for Alcatel PCV model 2.0.