Enhancing satellite orbit accuracy for sea level monitoring through Earth radiation pressure modeling

The accurate determination of sea surface height begins with the precise characterization of the orbit of altimetric satellites with respect to the Earth’s center of mass. To produce precise estimates of the orbital height of such altimetric satellites, Precision Orbit Determination (POD) combines satellite-tracking information with force models, including gravity, atmospheric drag, radiation, and others, which govern the motion of these satellites.
However, it’s important to note that uncertainties arising from the modeling of non-gravitational forces, stemming from the interaction between photons, molecules, atoms, and satellite surfaces, constitute a significant source of error.

With the goal of achieving radial orbit errors below 0.1 mm/year at regional and decadal time scales, an update in the modeling of non-gravitational forces, specifically addressing Earth radiation pressure, was performed. Indeed, the traditional model used in CNES' ZOOM orbit determination software was based on an average approach (Knocke et al., 1988) accounting for latitude and time dependent reflected/emitted radiations which did not consider the spatial and temporal complexity of reflection phenomena, such as cloud dynamics.

To address this issue, an approach involving the use of observations from Earth radiation fluxes, such as CERES (NASA) and ERA5 (ECMWF), was adopted and tested during the lifetime of the Sentinel-6A and CryoSat-2 satellites. These efforts led to substantial improvements in the dynamic modeling of satellite orbits. Comparisons were made between the resulting satellite orbits and those based on the legacy model, with the aim of assessing their impact on sea level measurements. Although a slight discrepancy was observed between the two derived orbits, this difference was attributed to the introduction of empirical forces, typically employed to correct dynamic modeling errors. Consequently, an analysis of these empirical forces confirmed their relevance and underscored the value of the new force model