Impact of the South-Atlantic Anomaly radiations on DORIS Ultra-Stable Oscillator: resulting effects on DORIS measurements and orbit determination for Sentinel-3A and Sentinel-6A
Théo Gravalon (CELAD/CLS, France)
Event: 2024 IDS Workshop
Session: Precise Orbit Determination
Presentation type: Oral
DOI: 10.24400/312072/i03-2024.3915
Abstract
Most of altimetry missions rely on both DORIS and GNSS for orbit determination purpose. For both techniques, the knowledge of a frequency reference is crucial.
For the DORIS system, this reference comes from an onboard Ultra-Stable Oscillator (USO). The behaviour of this USO is affected by irradiation rates, especially in the vicinity of the South-Atlantic Anomaly (SAA) where the radiations are important. Throughout DORIS processing, the rapid variations of the USO due to radiations are not accounted, as the behaviour of the latter is only modelled by a polynomial. Consequently, high irradiations rates such as in the SAA result in higher DORIS residuals. This effect is strongly visible for stations located in the SAA region.
The configuration of Sentinel-3A and Sentinel-6A where both GPS and DORIS receiver are coupled to the USO allows to mitigate this issue. Indeed, the GNSS clock is determined during the orbit determination processing. This clock can be used in state and place of the third order polynomial.
This integration of the GPS clock as the modelled DORIS USO is hereby presented. The impact of this modification in the orbit determination is discussed regarding DORIS residuals at first. Notable differences are observable, especially for the DORIS stations located in the SAA.
The resulting orbits are compared with the new POE-G standard orbits in order to characterize the impact of such a correction on the DORIS processing for both Sentinel-3A and Sentinel-6A.
Contribution: IDS24_s3_Gravalon_SAAeffectsForS3A_S6A.pdf (pdf, 5444 ko)
Corresponding author:
Théo Gravalon
CELAD/CLS
France
