Archive for March, 2010

PPP now supporting ETRS89 in Spain

March 8th, 2010 by Ricardo Píriz

magicGNSS now supports the ETRS89 coordinate reference system in Precise Point Positioning (PPP). ETRS89 has been recently declared the official reference frame in continental Spain. ETRS89 stands for European Terrestrial Reference System 1989. In this system the coordinates are “frozen” at the 1989.0 epoch (1st of January 1989), in order to maintain a network of stable reference landmarks throughout the country, considering that the Eurasian tectonic plate drift is around 2 cm per year on Spain.

PPP uses as input satellite orbits given in the global ITRF05 system (actually IGS05, the IGS realization of ITRF05). Therefore the resulting user receiver coordinates are given in ITRF05 too, and they are estimated at the date of the user measurements. For users in Spain we are now converting these ITRF05 coordinates to ETRS89 and reporting them in the PPP outputs.

How do we do the conversion from ITRF05 to ETRS89? We take as reference a set of 23 fiducial GNSS stations located all over Spain and maintained by the IGN, the Spanish national mapping agency. Only stations on the Iberian Peninsula are chosen. For these stations, every month we process offline one day of data in PPP, and then we do a Helmert transformation between the official ETRS89 coordinates published by the IGN and our PPP solution in ITRF05. Then, at PPP user level, we apply the Helmet transformation parameters in the opposite direction in order to obtain the ETRS89 user coordinates.

The residual fit after the Helmert transformation between ITRF05 and ETRS89 for the 23 IGN stations is around 6 mm only (3-D RMS). This means that the loss of accuracy at user level due to the conversion to ETRS89 is well below the cm, which is at the same level as the PPP accuracy itself.

The Chile earthquake observed by GPS and GLONASS

March 1st, 2010 by Ricardo Píriz

On February 27, 2010, at 06:34 UTC, Chile was hit by an earthquake rating a magnitude of 8.8. The earthquake epicenter was offshore from the Maule Region, approximately 115 km (71 mi) north-northeast of Chile’s second largest city, Concepción.

The University of Concepción hosts the GNSS station called conz, tracking GPS and GLONASS satellites. conz survived the earthquake during several hours and continued recording data until 20:00 UTC.

The following plot shows the conz station displacement as a consequence of the earthquake. The plot shows the comparison of coordinates between two GPS+GLONASS Precise Point Positioning solutions, the first one using 5 hours of data before the earthquake, and the second one using 6 hours of data after the earthquake.

See also the IGS mail about predicted site displacement.