Abstract
In the last decade, we have been witnessing a rapid development of the constellations of Global and Regional Navigation Satellite Systems (GNSS/RNSS). Besides the well-known GPS and GLONASS, newly developed systems such as Galileo, BeiDou, QZSS and NAVIC have become increasingly important. All satellites of new GNSS are equipped with laser retroreflector arrays (LRA) dedicated to Satellite Laser Ranging (SLR). SLR allows, e.g., an independent validation of microwave-based orbit products. Therefore, a fully operational online service called the multi-GNSS Orbit Validation Visualizer Using SLR (GOVUS) has been developed allowing for near real-time analysis of the quality of multi-GNSS orbits. The mean offsets of SLR residuals for Center for Orbit Determination in Europe (CODE) orbits in 2016 are at the level of −8, −38, −14, and −107 mm, for BeiDou, Galileo, GLONASS, and QZSS, respectively, with the standard deviations of 66, 36, 29, and 100 mm. Moreover, GOVUS can be used as a database containing information on equipment used at SLR stations and multi-GNSS satellite parameters. This paper includes a comprehensive description of the functionality and the structure of the developed service with exemplary analyses. The paper points out the most critical issues, limitations and challenges of multi-GNSS and SLR tracking network in the context of the SLR orbit validation. The goal of the paper and GOVUS itself is to determine: (1) what is the current quality of multi-GNSS orbits validated using SLR results; (2) what kinds of systematic errors can affect GNSS orbits and SLR observations; and (3) how to provide the online analysis tools to the broadest possible multi-GNSS community. The service has been officially operating since March 2017 as the Associate Analysis Center of the International Laser Ranging Service (ILRS ACC).
Highlights
The multi-Global Navigation Satellite Systems (GNSS) Pilot Project (MGEX) [1] was initiated in 2013 with the major motivation to increase the effort to prepare full integration of new constellations, e.g. Galileo, BeiDou, and QZSS, into the International GNSS Service (IGS) [2] processing routine, which is currently focused on GPS and GLONASS only solutions
A new Associated Analysis Center of the International Laser Ranging Service [7] at the Wroclaw University of Environmental and Life Sciences (IGG ILRS Analysis Centers (AAC)) has been established providing a service called as multi-GNSS Orbit Validation Using Satellite Laser Ranging (SLR) (GOVUS) as its main component
With this functionality we are able to divide the biases which originate from the stations’ characteristics, e.g., range biases, detector-related biases, from general problems of models used for the multi-GNSS orbit determination, e.g., mismodeling of the solar radiation pressure, antenna thrust, albedo or mismodeling of the satellite attitude, as well as an anomalistic behavior of particular satellites in the constellation. All of these capabilities would crosslink the extensive knowledge about the station-satellite dependencies and multi-GNSS orbit quality. Both IGS and ILRS provide today observations originating from the multi-GNSS constellation and put a lot of effort on a continuous and comprehensive improvement of multi-GNSS products
Summary
The multi-GNSS Pilot Project (MGEX) [1] was initiated in 2013 with the major motivation to increase the effort to prepare full integration of new constellations, e.g. Galileo, BeiDou, and QZSS, into the International GNSS Service (IGS) [2] processing routine, which is currently focused on GPS and GLONASS only solutions. Several IGS Analysis Centers (AC) prepare separately combined multi-GNSS solutions consisting of homogeneous and aggregated processing of all systems, i.e., GPS, GLONASS, Galileo, BeiDou, and QZSS. There is a limited number of dedicated tools that would guarantee a constant and near real-time information about the quality of the products provided by particular ACs based on an autonomous SLR validation process. A new Associated Analysis Center of the International Laser Ranging Service [7] at the Wroclaw University of Environmental and Life Sciences (IGG ILRS AAC) has been established providing a service called as multi-GNSS Orbit Validation Using SLR (GOVUS) as its main component
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