Combination of GNSS and SLR measurements : contribution to the realization of the terrestrial reference frame

Abstract

The accurate and precise implementation of the International Terrestrial Reference Frame (ITRF) is a fundamental requirement for the development of Earth System Sciences. The actual realization of the reference frame, in fact, directly impacts a number of different tasks ranging from precise satellite orbit determination to altimeter calibration, satellite antenna offset assessment for Global Navigation Satellite System (GNSS) and validation of center of mass corrections for spacecrafts carrying on board retro-reflectors for Satellite Laser Ranging (SLR). As a consequence, all the studies investigating motions of the Earth’s surface, including oceans and ice-sheets, strictly depend on the availability of a reliable TRF that is fundamental for geo-referencing the relevant measurements. ITRF realizations must then be periodically updated, in order to account for newly acquired observations and for upgrades in data analysis procedures and/or combination methods. Any innovative computation strategy should ameliorate the realization of the frame physical parameters, namely the origin and the scale, upon which a number of scientific applications critically rely. This work addresses the potential of combining GNSS and SLR observations via their co-location on board GPS/GLONASS satellites. GNSS vehicles equipped with retro-reflector arrays can be tracked by SLR ground stations, which allows determining the spacecraft orbits by means of both optical and microwave signals. In principle, the inter-technique connection so achieved could be exploited for the computation of the ITRF in place of terrestrial ties. These lasts are known to be currently a limiting factor of the frame accuracy because of their inhomogeneous distribution and of their discrepancies with space geodesy estimates due to technique systematic errors. In this study, the strength of the alternative link in orbit has been thoroughly investigated in order to evaluate the performances of the selected space tie approach under the available operational conditions. The analysis focuses on the characterization of the precision, the accuracy and the pertinence of the combined frame parameters.