DOI: 10.13127/epos_gnss_ppp_pos
title: INGV PPP GNSS daily solutions for EPOS
title: EPOS_GNSS_PPP_POS

description: Data from the GNSS Data Gateway Portal is validated and analysed in different GNSS analysis centres and made available in the GNSS Product Portal. 
The portal enables access to the GNSS observations and derived products, such as daily and weekly time series, estimated velocities and strain rate maps from various regions in Europe. Graphical interfaces enable station visualisation and multiple queries over stations and associated metadata, allowing users to retrieve the desired information. 

INGV provides daily GNSS solutions using the ppp (precise-point-positioning) approach in sinex format for the stations affiliated in the EPOS GNSS infrastructure.
description: GPS data from GNSS stations were reduced using the Jet Propulsion Laboratory (JPL) GIPSY-OASIS II software (version 6.3) in a precise point positioning mode (Bertiger et al., 2010) applied to ionospheric-free carrier phase and pseudorange data and using JPL’s final fiducial-free GPS orbit products (JPL GNSS Products). A detailed description of the data analysis strategy and models is reported in this table.

The observable model includes:
(1) ocean tidal loading and companion tides (Scherneck, 1991) computed by the Ocean Tide Loading Provider (Scherneck1991) using the FES2004 ocean tidal model (Lyard et al., 2006) and applied it as a station motion model;
(2) estimation of wet zenith troposphere and two gradient parameters every 5 minutes as a random walk process (Bar-Sever et al., 1998) using troposphere mapping functions (Vienna Mapping Functions 1, VMF1, (Boehm et al., 2006) developed based on data from numerical weather models (e.g. from the European Centre for Medium-Range Weather Forecasts (ECMWF);
(3) antenna calibrations for ground receivers and satellite transmitters (Schmid et al., 2007);
(4) second order ionospheric correction (Kedar et al., 2003);
(5) estimation of station clocks as a white-noise process.

Ambiguity resolution was applied using the wide lane and phase bias (WLPB) method, which phase-connects individual stations to IGS stations in common view (Bertiger et al., 2010). Resolving ambiguities reduces significantly the scatter mostly in the east component of time series. Satellite orbits and clock parameters were provided by JPL who determine them in a global fiducial free analysis using a subset of the available IGS core stations as tracking sites. The fiducial-free daily GPS solutions are aligned to IGS14 (Rebischung et al., 2016) by applying a daily seven-parameter Helmert transformation (three rotations, three translations, and a scale component) using parameters obtained from JPL (x-files). In order to reduce the common mode signal we also align daily solutions in the IGS14 reference frame defined by Cartesian coordinates and velocities for 132 stations selected by specific quality criteria. This frame is aligned in origin and scale with IGS14 and it is implemented to have no-net rotation with respect to the stable interior of the Eurasian plate, realized by subtracting a rigid rotation estimated from a 32-station core subset. This reference frame realization method transforms the station time series into a plate-fixed frame and effectively applies a continental-scale spatial filter to the station coordinates, leading to a reduction of the common-mode errors (Wdowinski et al., 1997), and to an increase of the signal-to-noise ratio.

Bibliography 

Bar-Sever, Y. E. (1996), "A new model for GPS yaw attitude", Journal of Geodesy, 70:714-723

Bar-Sever, Y. E., and D. Kuang (2004), New empirically-derived solar radiation pressure model for GPS
satellites, IPN Progress Reports 42-159, JPL. Available online: http://ipnpr.jpl.nasa.gov/progress_report/42-160/title.htm

Bassiri, S., and G. A. Hajj, (1993), Higher-order ionospheric effects on the global positioning systems
observables and means of modeling them, Manuscripta Geodtica, 18, 280-289, 1993

Blewitt, G., (1990), An automatic editing algorithm for GPS data. Geophysical Research Letters, Vol. 17,
No. 3, p. 199-202

Boehm, J., A.E. Niell, P. Tregoning, H. Schuh (2006), "Global Mapping Functions (GMF): A new empirical
mapping function based on numerical weather model data", Geophysical Research Letters, Vol. 33, L07304
DOI:10.1029/2005GL025545. 

Boehm J, Werl B, Schuh H (2006a), "Troposphere mapping functions for GPS and very long baseline
interferometry from European Centre for Medium-Range Weather Forecasts operational analysis data","
Journal Geophys Res 111:B02406. doi:10.1029/2005JB003629

Boehm, J., R. Heinkelmann and H. Schuh (2007), "Short Note: A global model of pressure and temperature
for geodetic applications", Journal of Geodesy, DOI: 10.1007/s00190-007-0135-3 

IERS Conventions 2003, D.D. McCarthy & G. Petit (editors), IERS Technical Note 32, Frankfurt am Main:
Verlag des Bundesamts fuer Kartographie und Geodaesie, 2004.

Kedar, S., G. Hajj, B. Wilson, and M. Heflin (2003), The effect of the second order GPS ionospheric
correction on receiver positions, Geophys. Res. Lett., 30(16), 1829, doi:10.1029/2003GL017639

Moyer, T.D., (2000) Formulation of observed and computed values of deep space network data types for
navigation, Deep Space Communications and Navigation Series, Jet Propulsion Laboratory, California
Institute of Technology, Pasadena, CA, Chapter 4, pp, 19-28.

Sibois, A., C. Selle, S. Desai, A. Sibthorpe, and J. Weiss, GSPM13: An updated empirical model for solar
radiation pressure forces acting on GPS satellites, IGS Workshop 2014, Pasadena, CA, 2014. 

Sibthorpe, A., J. Weiss, N. Harvey, D. Kuang, and Y. Bar-Sever, Empirical modeling of solar radiation
pressure forces affecting GPS satellites, AGU Fall Meeting, San Francisco, CA, 2010.
description: INGV PPP solutions are internally consistent  and well-suited for geodynamic, tectonic and seismological studies.