Finding Desirable Orbit Options for the “Extension of Life” Phase of Jason-1

Abstract

The ageing of Jason-1, the risk of losing control of the satellite, and the collision risk with TOPEX/Poseidon (still in orbit and no longer maneuverable) initiated a reflection on a so-called “extension of life phase” (EoL) phase that would involve moving Jason-1 to a new orbit to mitigate collision risks while optimizing its science return. This paper describes three practical consequences of any such EoL phase: 1) the ability to build an unprecedented low inclination and high precision geodetic dataset, 2) the loss of coordination with Jason-2 and the associated mesoscale (and sea state) sampling degradation, and 3) the increased topography height error budget stemming from the use of a gridded mean sea surface in place of the classical repeat track analysis that operational systems have been using and improving for almost two decades.

More than 17,000 potential orbits were analyzed to identify desirable altitude ranges that could host a Jason-1 EoL phase. The objective was to minimize the sampling degradation of ocean observations (primary objective of Jason-1) while securing a good geodetic EoL dataset (secondary objective of Jason-1). After a first automated screening and scoring process, the final orbit candidates are analyzed through an end-to-end Observing System Simulation Experiment (OSSE) protocol, assessing the multimission observational capability of the EoL phase in a DUACS/AVISO-like system.

All EoL orbits are shown to be largely inferior to the interleaved orbit as far as oceanography is concerned. Yet some EoL options are shown to be more desirable than others because their sampling patterns blend well with Jason-2. Good geodetic orbit options could provide a unique bathymetry-oriented dataset and help improve gridded mean sea surfaces (MSS), while repetitive options with a short cycle could cancel some additional EoL errors if a conservative repeat track strategy is preferred.

Keywords:

• Jason-1
• satellite altimetry
• mesoscale
• geodesy
• orbit parameters
• mean sea surface
• sea surface height

Acknowledgements

Most analyses synthesized in this article were supported by CNES (SALP project and SLOOP initiative). This work was stimulated by discussions among a small subset of the Ocean Surface Topography Science Team tasked with evaluating the scientific merits of a Jason-1 EoL phase. The discussions from the EoL group were exceedingly helpful to improve, and to complement the original work. The authors would like to acknowledge the contribution of Gregg Jacobs for his help in evaluating operational oceanographic applications, as well as David Sandwell and Walter Smith for highlighting the potential scientific benefit of a geodetic orbit, Remko Scharroo for performing complementary analyses, Ole Anderson for providing the DTU10 Mean Sea Surface, and Mercator-Océan for providing SSH model outputs used in sampling simulations. The author would like to thank both anonymous reviewers for their in-depth feedback and their help in improving the manuscript.