Andrea Maier

Reprocessing campaign in the framework of the EGSIEM project at AIUB

In the framework of the European Gravity Service for Improved Emergency Management (EGSIEM) project, monthly gravity field solutions derived from the Gravity Recovery and Climate Experiment (GRACE) mission will be combined. Since an improved reference frame is a prerequisite for precise orbit and gravity field determination, a reprocessing campaign (Repro15) was initiated at the Astronomical Institute of the University of Bern (AIUB), with more than 250 globally distributed tracking stations of the International GNSS Service (IGS), homogeneously processed for the interval between 2003 to the end of 2014. Since the Low Earth Orbiting satellites (LEOs) are tracking with a higher sampling than the usual 30 s of the IGS tracking stations, we included the 1 Hz dataset provided by the IGS real-time pilot project/service. The procedures established by the Center for Orbit Determination in Europe (CODE, hosted at AIUB), have been applied for the reprocessing. The new Empirical CODE Orbit Model (extended ECOM) has been applied to model the GNSS orbits. The procedure to densify the satellite clock corrections down to 5 s is applied to the GLONASS satellites for the first time.

Evaluation of ITRF2014 Solutions

For the most recent International Terrestrial Reference Frame (ITRF) realization three candidates have been provided, namely an ITRF2014 solution by IGN, DTRF2014 by DGFI-TUM, and JTRF2014 by JPL. There are significant differences in the way how these solutions have been generated, which parametrization has been applied, and how the solutions from the different space-geodetic techniques are combined.

Sensitivity of Simulated LRO Tracking Data to the Lunar Gravity Field

The Lunar Reconnaissance Orbiter (LRO) is the first spacecraft in interplanetary space routinely tracked with 1-way optical laser ranges. Therefore, the mission is a suitable testbed to investigate the potential of laser ranging for precise orbit determination and lunar gravity field recovery compared to radiometric observations. As a first step, we simulated laser ranges and range-rates from various ground stations to LRO. The synthetic data were used to retrieve the satellite orbit. Further, we estimated three sets of spherical harmonic coefficients representing the lunar gravity field: one set based on laser ranges, one set based on range-rates, and one set based on laser ranges and range-rates. We found laser ranging to be capable of recovering the coefficients up to degree and order ≈ 12 without applying regularization. From a joint inversion we conclude that laser ranges only slightly improve the findings obtained from range-rates. Preliminary real data results based on twelve days of laser ranging observations show a range residual root mean square (RMS) value of 2.3 m. The RMS value in total position between our solution and a published LRO orbit derived from radiometric data and altimetric crossovers is about 550 m.