Enhancing PPP-AR with satellite attitude data from ORBEX files

Abstract

Over the past decades, Precise Point Positioning (PPP) has become a well-established technique for determining the user's position with the signals of Global Navigation Satellite Systems (GNSS). PPP is characterized by applying precise satellite products (orbits, clocks, and biases) and accurately modeling a wide range of error sources to estimate the user's position. This way, a position accuracy at the centimeter or even millimeter level is accomplished. However, the convergence time until the coordinates have reached this accuracy is well known as the primary concern of PPP. In that regard, PPP with integer ambiguity resolution (PPP-AR) has proven as an effective way to dramatically reduce the convergence time of PPP, especially in the east coordinate component.

Currently, the so-called Orbit Exchange (ORBEX) format is under revision. Its main philosophy is larger flexibility for the description of the satellite state than in different existing formats. Besides other advantages, the ORBEX format can provide information on the satellite orientation in attitude records. Several Analysis Centers have started to provide such data in addition to their satellite orbits, clocks, and biases. Consequently, the PPP user can accurately calculate the satellite orientation instead of relying on the usually adopted IGS convention.

Since the satellites' orientation is essential for accurately modeling several error sources and recovering the integer property of the phase ambiguities, the performance of PPP is usually improved by using accurate satellite attitude information. This contribution illustrates the effect of attitude data on ambiguity fixing, convergence time (time to first fix), and coordinate accuracy in several test cases. Especially, satellite eclipse seasons are investigated. The PPP calculations are performed with our software raPPPid, the PPP module of the Vienna VLBI and Satellite Software (VieVS PPP).