Hugues CAPDEVILLE (CLS, FRANCE); Jean-Pierre CHAUVEAU (CLS, FRANCE)

To achieve optimal performance, the DIODE navigation software implemented in the DORIS receiver, and the ground processing for POD and Station Position Estimation, require precise knowledge of a set of on-board characteristics. This information is synthesized in a "DORIS Calibration Plan" document prepared for each mission/satellite. These parameters are then configured and uploaded to a dedicated memory area in the receiver. Among these, one of particular importance—due to its direct impact on the radial position—is the Phase Centre Offset (PCO) defined in the satellite reference frame.
The PCO is characterized at the antenna level by the manufacturer and referenced to the Antenna Reference Plane (as specified in the Mechanical Interface Control Document). Subsequently, the satellite manufacturer provides the position of the antenna reference frame within the satellite reference frame, derived from CAD models rather than physical measurements.
Recently, upon receiving updated information for Sentinel-3D, we discovered a significant discrepancy with Sentinel-3C. We suspected a misunderstanding regarding the antenna reference frame definition. An analysis was therefore conducted to assess the impact of this few-millimeters difference on orbital accuracy and scale factor.
We will present an overview of current PCO measurement methodologies, with particular attention to the analysis performed on the Sentinel-3 satellites. These considerations are also being prepared for the Genesis mission, which demands higher positioning accuracy.

Keywords: DORIS, antenna, center of phase, PCO
Participation: In person