- Operational orbits generated with the JGM-2 gravity model, using SLR tracking data only. These orbits are included on the NOAA ERS-1 IGDRs.
- Off-line orbits based on the JGM-2 gravity model, and a combination of SLR and ERS-1/TOPEX dual-satellite crossovers as tracking data.

In this Section some results of the ERS-1 POD are presented. Especially the quality of three types of orbits will be discussed:

To assess the quality of the orbit solutions various techniques may be applied. Residuals between measured and computed quantities, such as SLR range residuals, altimeter height residuals, and crossover height differences, are important indicators to monitor the orbit accuracy. Of course, the most valuable and independent measure of the orbit accuracy comes from measurements which did not enter in the POD itself.

Also, comparisons between two partly overlapping arcs produced with the same gravity model but from different measurements, or between two completely overlapping arcs based on different gravity models and/or measurements, yield a quantitative impression of the orbit precision of either of the arcs.

In the following Sections these indicators will be used to discuss the quality of various types of orbits generated by DUT/SSR&T.

Thu 16 Feb 1995