About this Web Page

Background

To investigate the interoperability of the various GNSS constellations we compute epochwise the positions of European permanent GNSS receivers by analyzing data simultaneously from different GNSS constellations.

Method

Use RINEX 3.02 data freely available within the MGEX data base. Process pseudoranges in ionofree combination, and broadcast ephemeris. Use as apriori coordinates official ITRF2008/IGb08 values.

Solve for 3 coordinates, 1 clock offset for each GNSS constellation, 1 Tropospheric Zenith Delay (ZTD) at each computation epoch.

The computation is made daily for a sample of European GNSS sites, and different receiver types. This Web site is updated on a weekly basis, beginning Jan.1, 2014.

Goal

Our goal is to provide data, in tabular and plot format (see Keyword File Type), enabling one to assess (see Keyword Parameter):

-Parameter = Position: epochwise departures in North East Up from a priori position

-Parameter = Post fit residuals : differences between measured ionofree pseudorange and computed pseudoranges, using estimated coordinates, clock offsets and TZD

-Parameter = Time Offset: Offset of the GNSS time scale relative to the GPS time scale

-Parameter = TZD: estimate of the TZD from the combined multiGNSS solution

In addition we provide in Daily estimates of clock offsets and drift relative to GPS  daily values obtained, for each day, by Matlab’s “robust linear regression” of the epochwise values of the parameter Time Offset.

What do these results tell us

-          The Position data enable to assess the accuracy of the multiGNSS point positioning relative to exact coordinate values, and the stability in time;

-          The Post fit residuals tell us about the goodness of the fit, and the removal of GNSS dependent biases, particularly time biases.

-          The Time Offset data tell us about the amount of misalignment of the time scales kept by the various GNSS relative to a reference time scale, which we assume to be GPS

-          The TZD data tell us about the epoch by epoch Tropospheric Zenith Delay.

-          The Time Offsets of the same receivers are very close, for a given GNSS. However Time Offsets measured with different receivers for the same GNSS may vary. This leads to a quantitative estimate of  receiver dependent biases.

 More details in

An analysis of intersystem biases for multi-GNSS positioning

Andrea Dalla Torre Alessandro Caporali

GPS Solutions (2014) DOI 10.1007/s10291-014-0388-2

Questions?

Alessandro.caporali@unipd.it