CoAuthors

Daniel Arnold (AIUB, Switzerland); Adrian Jäggi (AIUB, Switzerland)

Analysis of attitude dependent deficiencies in precise orbit solutions of Jason-3

C.Kobel, D.Arnold, A.Jäggi

The Jason-3 satellites’ mission is to supply data for scientific, commercial, and practical applications
to sea level rise, sea surface temperature, ocean temperature circulation, and climate change. The
surface height is determined by radar altimetry measurements. To interpret these measurements, a
precise orbit determination (POD) is required. The goal of this study is to identify (and remove)
existing deficits in the Jason-3 POD process to further improve the high accuracy of the resulting orbit
solutions. One of the characteristics of Jason-3 is that the satellite regularly changes its attitude,
depending on the elevation of the Sun above the orbital plane. The LEO is either in a yaw-steering or
in a fixed-yaw attitude mode, with the x-axis of the satellite-body-fixed frame pointing in the flight or
anti-flight direction. Previous analyses have shown that different systematic errors in the resulting
orbits are present, depending on the attitude mode in which the satellite is operating. These
systematics are further analyzed in this study.
We use two different satellite geodesy techniques: the Global Positioning System (GPS) as one of the
most important techniques for POD, and Satellite Laser Ranging (SLR) for LEO orbit validation by
highly precise distance measurements from ground stations to the LEO retroreflector arrays. On the
one hand, GPS observations are used for the POD of Jason-3, on the other hand, to derive potential
corrections for the phase center offsets (PCO) of the LEO receiver antenna used in the POD process.
The different attitude modes allow the estimation of corrections in all three components of the
antenna frame, which is not possible for many LEOs which are operated in a fixed-yaw attitude
mode. First results show that in the radial direction, which is of central importance for altimetry
satellites, different corrections will be estimated when comparing the two fixed-yaw attitude modes.
Using SLR, as an independent technique, allows for estimation of offsets in the orbit frame as well as
in the satellite-body-fixed frame. Validity and sensitivity tests of the SLR analysis will be performed,
e.g., by introducing artificial offsets and checking the capability of recovering them from the SLR
analysis. By comparing the offset estimations from the two different techniques (GPS and SLR), it
may be possible to get a better understanding of the presence and magnitude of systematics
orbit errors for the different attitude modes.