Overview
Near-real time validation
Principally during the validation phase but also extended to the whole Jason-1 mission, we intend to estimate the quality of the operational precise orbit. This estimation will be mainly based on orbit errors determination using a laser-based short-arc technique. In the framework of TOPEX/Poseidon such a technique has proved to be able to evaluate not only the precision but also the accuracy of dynamic orbits. However, it can only be done in specific area where a dense SLR data coverage is available, namely US and Europe. We will then also compare results with other independent methods such GPS-based reduced dynamic technique.
Web sites on Orbit Validation using Short-arc Technique:
- TOPEX/Poseidon Precice Orbits from CNES and GSFC
- TOPEX/Poseidon and Jason-1 from CNES POE
- TOPEX/Poseidon and Jason-1 from CNES DORIS/MOE
- Jason-1 and Jason-2 from CNES DORIS/MOE (daily updated: results available within 1-2 days)
Long term stability
The validation process describes previously will be able to evaluate the « short-period » orbit errors (over a repeat cycle). However it is important to estimate the long-period stability of the orbit determination process in order to prevent any very low-frequency orbit errors which can induce not realistic sea level signals. This will be done using an orbit filtering technique and a semi-analytical theory of the mean orbital motion applied over long time period.
Error Analysis
Error analyses, as scientific objective in space geodesy, are going to play an increasing role in space geodetic projects like altimetry. The improvement of the precise orbit determination and the estimation of its error budget in time and space have been undoubtedly great priorities in this field. However, taking into account the new requirements of Jason, at the level of one centimeter, our objectives are to enlarge the study of the error propagation above the orbit determination. From a global point of view, by analyzing the laser and DORIS tracking measurements (precision and biases) associated to a given terrestrial reference frame and their « true » capability to control the orbit determination. From a regional and local point of view, by establishing and monitoring a dedicated geodetic network including laser, DORIS and GPS positioning and tide gauges measurements in order to be able to re-iterate at several occasions an absolute calibration campaign.