IGS RTS precise orbits and clocks verification and quality degradation over time

Tomasz Hadas,Jaroslaw Bosy

doi:10.1007/s10291-014-0369-5

Tomasz Hadas, Jaroslaw Bosy

Open Access

https://doi.org/10.1007/s10291-014-0369-5

Copy DOI

Abstract

The International GNSS Service (IGS) real-time service (RTS) provides access to real-time precise products such as orbits, clocks and code biases, which can be used as a substitute for ultra-rapid products in real-time applications. The true performance of these products can be assessed by the Analysis Centers daily statistics derived from the comparison with IGS rapid products. Additionally, indirect verification is performed by their application to various precise point positioning strategies. Monitoring results and basic descriptions of these products are available at the official RTS Web page ( http://rts.igs.org/ ). We present a more detailed description of RTS products. Information from various sources is collected to provide products application methodology and describe their important features. We provide extended verification of the products using 1 week of real-time correction data. Results are presented separately for GNSS constellations, considering satellite block and type of onboard clock. Comparison with ESA/European Space Operations Centre final products proves the high accuracy of RTS orbits and clocks, which is 5 cm for GPS orbits, 8 cm for GPS clocks, 13 cm for GLONASS orbits and 24 cm for GLONASS clocks. The real-time correction performance is also examined regarding availability and latency. In general, the availability of corrections was beyond 95 % for GPS and beyond 90 % for GLONASS. Since the increasing degradation of product quality with latency is critical for real-time applications, the relation between product latency and accuracy is analyzed. It confirms that high-rate stream update intervals are suitable for the data provided and that the obsolete data should not be used. To avoid this, we propose a method of short-term prediction of RTS corrections that extends the application period of obsolete correction data without a significant loss in orbit quality. Using polynomial fitting, it is possible to forecast the orbit corrections reliably up to 8 min for GPS and 4 min for GLONASS.

Highlights

Since 1994, the GNSS user community takes advantage of precise GPS orbit products provided by International GNSS Service (IGS)
The International GNSS Service (IGS) realtime service (RTS) provides access to real-time precise products such as orbits, clocks and code biases, which can be used as a substitute for ultra-rapid products in real-time applications
The combined product is just a mean value from individual clocks provided by the different Analysis Center (AC); corresponding code biases are not provided for combined products

Summary

Introduction

Since 1994, the GNSS user community takes advantage of precise GPS orbit products provided by International GNSS Service (IGS). Available official real-time IGS products include only corrections to GPS satellite broadcast orbits and clocks. Results show that the minimum time required to provide combined orbit and clock corrections is about 31 s for the IGS03 stream (Fig. 3) and about 28 s for IGS01 This difference is caused by the application of the Kalman filter in the IGS03 stream, while IGS01 is only single-epoch combination solution. Another two subsets of data (separately for orbit and clock corrections), containing only the data available just before the update occurrence in the stream, were selected.

99 GLO mean

GLO 19

Conclusions