Observing APOD with the AuScope VLBI Array.

Andreas Hellerschmied,Jamie Mccallum,Jianfeng Cao,Lucia Mccallum,Johannes Böhm,Jing Sun

doi:10.3390/s18051587

Abstract

The possibility to observe satellites with the geodetic Very Long Baseline Interferometry (VLBI) technique is vividly discussed in the geodetic community, particularly with regard to future co-location satellite missions. The Chinese APOD-A nano satellite can be considered as a first prototype—suitable for practical observation tests—combining the techniques Satellite Laser Ranging (SLR), Global Navigation Satellite Systems (GNSS) and VLBI on a single platform in a Low Earth Orbit (LEO). Unfortunately, it has hardly been observed by VLBI, so major studies towards actual frame ties could not be performed. The main reason for the lack of observations was that VLBI observations of satellites are non-standard, and suitable observing strategies were not in place for this mission. This work now presents the first serious attempt to observe the satellite with a VLBI network over multiple passes. We introduce a series of experiments with the AuScope geodetic VLBI array which were carried out in November 2016, and describe all steps integrated in the established process chain: the experiment design and observation planning, the antenna tracking and control scheme, correlation and derivation of baseline-delays, and the data analysis yielding delay residuals on the level of 10 ns. The developed procedure chain can now serve as reference for future experiments, hopefully enabling the global VLBI network to be prepared for the next co-location satellite mission.

Highlights

The Global Geodetic Observing System (GGOS) has been established by the InternationalAssociation of Geodesy (IAG) in order to satisfy the expected future requirements of science and society, which are facing increasing challenges on a changing planet
The Chinese APOD-A nano satellite can be considered as the first prototype of a co-location mission enabling Very Long Baseline Interferometry (VLBI) with Satellite Laser Ranging (SLR) and Global Navigation Satellite Systems (GNSS) on an Low Earth Orbit (LEO) satellite.it has hardly been observed by VLBI, so major studies towards the actual frame ties could not be performed
The main reason for the lack of observations was that VLBI observations of satellites are non-standard, and suitable observing strategies were not in place for this mission

Summary

Introduction

The Global Geodetic Observing System (GGOS) has been established by the InternationalAssociation of Geodesy (IAG) in order to satisfy the expected future requirements of science and society, which are facing increasing challenges on a changing planet. GGOS aims to establish a terrestrial reference frame with an accuracy on the level of 1 mm or better on a global scale [1] This can only be achieved by a rigorous combination and integration of the different ground and space geodetic techniques. The ITRF determination fundamentally relies on differential coordinates—called local ties—connecting the reference points of the geodetic instruments that are typically located within distances of a few hundred meters at co-location sites (for a definition of local ties, we refer to [3]) These local tie vectors are usually determined by classical terrestrial measurements

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Conclusion