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Improved kHz-SLR Tracking Techniques and Orbit Quality Analysis for LEO-Missions

Walter Hausleitner(1), Georg Kirchner(2), Roland Pail(3) and Helmut Goiginger(3)

(1) Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
(2) Austrian Academy of Sciences, Lustbühelstrasse 46, 8042 Graz, Austria
(3) Graz University of Technology, Steyrergasse 30, 8010 Graz, Austria


The Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) is a low Earth orbiting (LEO) satellite dedicated to sensing the Earth’s gravity field with a very high spatial resolution. Much effort will have to be spent on the precise determination of the complex orbit in order to gain maximum accuracy for the data products. The precise orbit information of low Earth orbiting gravity field missions currently in orbit is mainly provided by GPS/SST, which is operated in high-low (CHAMP) or in a low-low (GRACE) configuration. All these spacecraft have in common, that they carry laser retro-reflectors on board. This points out the importance of Satellite Laser Ranging (SLR) as an independent external tracking instrument.

SLR is a method to measure distances between the SLR ground station and the satellite by means of very short laser pulses. The SLR technique can very efficiently be used for the calibration and validation of low Earth gravity mission products, i.e. to assess the quality of GPS orbits and gravity field solutions, respectively. Since October 2003 the Space Research Institute of the Austrian Academy of Sciences (AAS/SG) runs a new kHz-SLR system at the observatory Graz/Lustbuehel. This system is capable of performing ranging measurements at a 2 kHz rate compared to the commonly used 5-10 Hz rate. However, it is assumed that hardly any SLR station will be able to provide ranging observations to very low orbiting spacecraft such as GOCE. For the purpose of raising the laser tracking efficiency a project applied by AAS/SG and TUG/INAS was approved and will be funded by a national organisation. The project aims on the one hand to the implementation of optimized kHz-SLR tracking techniques in order to improve the tracking efficiency of LEO satellites, and on the other hand to the establishment of quality assessment tools for LEO orbits and derived gravity field solutions.

The activities focus on a number of hardware upgrades and methodical improvements in order to achieve a faster target acquisition. This increases the number of observations per pass and further improves the normal point accuracy as well as the overall system stability. The quality assessment process considers two aspects: GPS/SST derived orbits will be evaluated using orbital arcs generated from the global set of SLR data in a kinematic and a dynamic mode. Quick-look gravity field solutions (QL-GFA) from SST and SGG data will be provided by TUG/INAS in the frame of the operational GOCE data processing. The quality of these can be assessed by analyzing the residuals resulting from orbit adjustments using the corresponding coefficients.


Workshop poster

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry