Marco Roggero

Reference frames for GNSS positioning services: Some problems and proposed solutions

Abstract Positioning services based on GNSS Permanent Networks (PNs) disseminate the reference frame to users; hence the networks must be adjusted by constraining the ITRF coordinates of some permanent stations (PS), with the satellite orbits and clocks constrained to the values published by the International GNSS Service (IGS). Furthermore, the positioning service provider must use analysis methods, conventions and practices fully consistent with IGS standards. In this framework some problems arise. A first one is that long term solutions for the IGS PS coordinates are not always fully consistent with weekly IGS products, requiring an appropriate use of IGS PS weekly solutions. Moreover, the consistence of the reference frame implied by different positioning services must be checked, to avoid discontinuities between neighbouring networks. Clearly, in order to monitor the PS coordinates, the adjustment of a network needs to be performed on a quasi real time continuous (daily or weekly) basis. However, from a practical point of view, a continuous update of the PS coordinates is neither appropriate nor possible and alternative proposals will be presented. Finally, most users of real-time positioning services need coordinates in another reference frame, perhaps a local one or the national one. In this case the real-time service provider must distribute the transformation between the broadcasted frame and the user required reference frame. In this work some possible solutions of the aforementioned problems are presented, based on experiences obtained during data processing and adjustments of the Piemonte and Lombardia (Northern Italy) networks.

Low cost DGPS wireless network

This article depicts the development and test of a low cost wireless sensor network intended for use in severe environmental conditions. The test site is a serac located at 4100m above a populated area. It was needed to put in place a monitoring system able to trace displacement continuously and in all weather conditions. To achieve this goal starting from a professional but cheap single frequency GNSS module we developed the needed electronics to control it, log the data and transmit them over a long distance. The final board is working at 2.4 GHz and the network protocol is based on a proprietary implementation of a listen before talk approach. The high DGPS precision is obtained by using local GNSS permanent stations.

Extensive Analysis of IGS REPRO1 Coordinate Time Series

The work describes the analysis conducted on the IGS REPRO1 coordinate time series, in order to detect GNSS permanent stations periodic behavior. Frequency analysis requires cyclostationary time series, while observed coordinates time series are not cyclostationary because of discontinuities of different kind and origin and of long term linear or non linear trend. For this reason time series offsets and trends must be estimated and eliminated, prior to conduct the harmonic analysis.

A Review on Non Iterative Closed Form Configuration Matching and Rotations Estimation

Orthonormal matrices, Procrustes and quaternion analysis are closed form solutions of the configuration matching problem, common in geodesy as in the datum transformation problem. Literature reports more Procrustes based geodetic applications than Quaternions, which are more used in other application fields, such as aerospace navigation, robotics and computer vision. The large popularity of Procrustes in geodesy is mainly due to its capability to take into account a priori observation weighting in a simple way.