Evaluation of earth rotation parameters from modernized GNSS navigation messages

Modernized navigation messages of global navigation satellite systems like GPS CNAV include earth rotation parameters (ERPs), namely the pole coordinates and UT1-UTC (∆UT1) as well as their rates. Broadcast ERPs are primarily needed for space-borne GNSS applications that require transformations between earth-fixed and inertial reference frames like navigation in earth orbit as well as to the moon. Based on a global tracking network of 23 stations, broadcast ERP values are obtained for the global systems GPS and BeiDou as well as the regional QZSS and IRNSS. Subsequent data sets at daily intervals show polar motion discontinuities of 0.4 to 0.7 mas for GPS, QZSS, and IRNSS, whereas BDS is worse by a factor of about two. Discontinuities in ∆UT1 range from 0.17 to 0.45 ms. External comparison with the C04 series of the International Earth Rotation and Reference Systems Service results in polar motion RMS differences of 0.3 to 1.0 mas and ∆UT1 differences of about 0.13 ms for GPS, QZSS, and IRNSS. Due to less frequent update intervals, BDS performs worse by a factor of 2 – 4. In view of the current GNSS-based positioning errors at geostationary or even lunar distances, the accuracy of GPS, QZSS, and IRNSS broadcast ERPs is sufficient to support autonomous spacecraft navigation without the need for external data

Performance Evaluation of the Early CNAV Navigation Message

The GPS Directorate initiated a pre-operational routine generation and transmission of the Civil Navigation Message (CNAV) starting on 28 April 2014. CNAV data of the Block IIR-M and IIF satellites have been collected with a small set of globally distributed receivers. Starting in 2015, CNAV uploads are performed on a daily basis. Since then, the Signal-in-Space Range Error (SISRE) amounts to roughly 0.6 m, which is essentially identical to the LNAV SISRE for the same satellites. The new broadcast Inter-Signal Corrections (ISCs) agree with differential code biases derived in the frame of the IGS Multi-GNSS Experiment and DCBs from the Center for Orbit Determination in Europe on the 0.1–2 ns level depending on the ISC type. Use of these ISCs enables, for the first time, a consistent point positioning based on the exclusive use of civil L1C/A and L2C observations

Characterization of GPS/GIOVE Sensor Stations in the CONGO Network

The Cooperative Network for GIOVE Observation (CONGO) is a global network of real-time capable multi-constellation GNSS receivers, which has been established by the German Aerospace Center (DLR) and the German Federal Agency for Cartography and Geodesy (BKG) as a test bed for experimentation with the new Galileo signals. The CONGO network employs a variety of different antennas and receivers which have become available for public use over the last 2 years. Following an overview of the network and the employed user equipment, the paper discusses the achieved GPS/GIOVE tracking performance. This includes a characterization of antenna gain patterns as well as receiver noise and multipath errors. Special attention is given to the discussion of inter-system biases. The nature and variation of these biases is illustrated based on a set of three different receivers operated in a zero-baseline configuration at the Wettzell site

CONGO - First GPS/GIOVE Tracking Network for Science, Research

Selected results from the COoperative Network for GIOVE Observation (CONGO) demonstrate how the global network provides early familiarization with the new Galileo signals and access to precise GIOVE orbit and clock information, to develop new processing techniques for multi-constellation, multi-frequency GNSS

Monitoring of Antenna Changes at IGS Stations in Iceland

GNSS antenna changes are in particular critical for the long-term stability of the coordinate time series and the reference systems realized with these stations. Depending on the antenna types and the available antenna calibrations, discontinuities of up to several centimeters can be introduced. Therefore, a monitoring of the antenna changes is important to verify the continuity of the time series.In order to add Galileo tracking capability the GNSS equipment at the Icelandic IGS stations Reykjavik and Hoefn had to be replaced. Temporary GNSS sites were set up in the vicinity of both sites. These short baselines are analyzed with different observables. In addition, the temporary sites were included in the routine processing of the Center for Orbit Determination in Europe analysis center of the IGS. The equipment changes introduced discontinuities of up to 1.5 cm in the coordinates derived from the global solution. Depending on the analysis strategy and observables used, the results of the short baselines differ by up to 2.5 cm