Open Loop Tracking Mode for Altimetry Missions
DESJONQUERES, Jean-Damien; PICOT, Nicolas

A new altimeter tracking mode has been developed based on the use of real time estimation of the satellite position (provided by the Doris Diode and or the GNSS instrument) and of a dedicated on-board Digital Elevation Model (also called “Open Loop Table Command”) stored in the altimeter onboard memory. This mode has been first tested on JASON-2 mission and we have demonstrated that it provides higher data return in coastal areas and for inland water located in sloppy terrain. This mode is also of interest to track specific targets (like a transponder). In addition this modes slightly reduces the 20Hz measurement noise over ocean. It is also implemented on AltiKa, Sentinel-3 and JASON-3 mission and should be re-used in the future for JASON-CS. We will explain the basics of this mode and in particular the way it is generated on ground, implemented on Sentinel-3 and JASON-3 missions where both autonomous tracking mode and open loop tracking mode are considered as operational modes and will be used alternately depending of the over-flight surface. Results from JASON-2 and AltiKa/ SARAL missions will also be presented, focusing on all surface types and the observed noise reduction will be further assessed thanks to ground prototypes.