Stability of DUT and UT/CSR Orbits for ERS-1

Remko Scharroo
Delft Institute for Earth-Oriented Space Research

The radial precision of the ERS-1 orbits has come down to about 5 cm. In this respect both the orbits procuced by DUT and UT/CSR are better than any. Since these orbits are generated fully independently (i.e., using different software, procedures, data weighting, data screening, arc lengths, gravity models, tide models, SLR station coordinates) it is likely that the differences between the orbits are representative for the error in any of these orbits. To say that the rms error will be sqrt(2) of the differences is probably too far fetched, but at the least a qualitative assessment can be obtained.

For long-term studies such as climate change, the stability of the orbits is of most importance. As in most short-term studies the absolute (or systematic) error is of lesser relevance, but any drift in these errors may lead to erroneous estimations of sea level or ice level trends. Similarly, seasonal cycles may be affecting climate studies.

We have analysed in two different ways the stability of the orbits:

by cross-comparing the ERS-1 orbits computed at UT/CSR and DUT/DEOS.
by studying the dual altimeter crossover height difference between ERS-1 and TOPEX and POSEIDON using either orbit solution as a reference.
by studying the altimetric derived sea level variations we can say something about the impact of the orbit selection on ocean studies and about the impact of the annual cycle in the orbit differences in particular.
by isolating the geographically anti-correlated orbit error we can see the impact of the time invariant contributions of the gravity model.

Questions or comments:

Remko Scharroo, remko.scharroo@lr.tudelft.nl.

10 March 1997.

Stability of DUT and UT/CSR Orbits for ERS-1

Remko ScharrooDelft Institute for Earth-Oriented Space Research

Remko Scharroo
Delft Institute for Earth-Oriented Space Research