Effects of IGS Products on GNSS-based Precise Orbit Determination

Abstract

With the successful application in 1992 for the TOPEX altimetry satellite mission of Precise Orbit Determination (POD) techniques based on data from the Global Positioning System (GPS), the orbit accuracy has continually increased due to improvements in dynamical force and observation models, measurement accuracy, and data processing strategies. In addition, the larger and more recent Global Navigation Satellite System (GNSS) has also contributed significantly to this increased accuracy. The International Global Navigation Satellite System (GNSS) Service (IGS) provides not only combined products, but also individual products from different analysis centers. Most of the IGS users use the IGS combined products, as the quality and accuracy of all products are becoming more consistent with one another through ongoing development efforts. Given these trends, the contemporary questions are: Are significant differences still encountered when using different IGS products for GNSS-based POD? At this time, how well can satellite orbits be determined by fixing IGS orbits and clocks? To gain insights into possible answers to these questions, we established study objectives and set out to improve our models and data processing strategies (1) to investigate the effects of different IGS products on GNSS-based POD, (2) to describe the recent advances in GNSS-based POD, and (3) to present the levels of orbit accuracy that can be achieved based on the current models and methods. Moreover, we proceeded under the recognition that the effects of the IGS products vary for different IGS users. Accordingly, our focus generally centered on the GNSS-based POD of Low-Earth Orbiting (LEO) satellites and, specifically, on data from NASA’s Gravity Recovery and Climate Experiment (GRACE) mission. We assessed both the effects and orbit accuracy using a number of tests, including analyses of orbital fits, Satellite Laser Ranging (SLR) residuals, K-Band Ranging (KBR) residuals and external orbit comparisons. The results presented in this paper show that there are no significant differences between IGS combined and individual products for GNSS-based POD. The SLR residuals and external orbit comparison indicate that the accuracy of 3-dimensional orbits is about 2 centimeters. Moreover, the external orbit comparison shows that the orbit accuracy in radial and normal directions is better than 1 centimeter.