Long-term regional stability of the orbit time series for climate-driven sea level rise applications

To meet future climate science question needs (e.g., closure of the sea-level budget, estimating the Earth energy imbalance), sea level must be determined with an uncertainty of a few tenths of a millimeter per year for decadal trends at the regional scale (Meyssignac et al., 2023). In satellite altimetry, the radial component of the orbit is of primary interest, since the sea level measurement is related directly to this component. For this reason, various issues related to the assessment of radial orbit error trends are discussed in this study. In particular, projections of orbit errors on the global oceans will be used to reveal significant drifts in the geographically correlated errors (GCE), that are aliased directly into any calculation of regional mean sea level (MSL) rate.

Precision Orbit Determination (POD) is achieved owing to the combination of tracking techniques such as Doppler Orbitography by Radiopositioning Integrated on Satellite (DORIS), Global Navigation Satellite System (GNSS) or Satellite Laser Ranging (SLR). Besides these measurement systems, various geophysical models are used to complement reduced dynamic orbit solutions. The idea here is to quantify the uncertainty in orbit determination when changing from one technique or geophysical model to another and assess the possibility of achieving a sub-mm/y radial orbit stability. The focus of this study is on the long-term (seasonal to decadal time scales) stability of the Jason-3 and Sentinel-3A orbit error on a regional scale (> 1,000 km) for deriving independent error budgets on two different legacy satellite altimetry orbits.

First, this study reviews orbit errors dependent on the tracking technique, with an aim to monitoring the long-term stability of all available tracking systems operating on Jason-3 and Sentinel-3A (GPS, DORIS, SLR). As the temporal variations of the geopotential remain one of the primary limitations in the POD modeling, the overall accuracy of the latest Jason-3 and Sentinel-3A CNES solutions is evaluated through comparison with test orbits based on different time-variable gravity and geocenter motion models. Finally, the terrestrial reference frame accuracy (ITRF2014 versus ITRF2020) and its effect on Jason-3/Sentinel-3A orbits will be discussed.