Innovative concepts for high-accuracy local geodetic networks
Background & Objectives
The proposed research project addressed the use of GNSS local networks for geophysical monitoring. Among many geophysical events requiring highly precise and fast update monitoring, crystal and seismogenic faults monitoring is the most demanding one, as a performing informatics tool for other geophysical events (landslide, subsidence, etc.) monitoring can be a by-product derived from a professional tool developed using this reference application. Deformation monitoring through GNSS measurements, integrated with seismological studies and geophysical forward modelling, is becoming of paramount importance to discriminate areas prone to earthquake events with a given magnitude.
These results are obtained by applying the so-called intermediate-term middle-range earthquake prediction algorithms and the geophysical forward modelling, which translate surface strain fields obtained by GNSS data analysis in deep stress field at the level of the seismogenic fault. The objective of geophysical forward modelling is to derive seismic hazard maps.
However, seismic hazard maps are associated with time and space uncertainties that are respectively of a few years and a few hundred kilometres, thus not allowing an effective early warning service to protect the local population. More refined monitoring of active faults, based on a near-real-time processing of data collected by local geodetic networks and on local seismic analysis that is bridged together through geophysical forward modelling in the areas prone to earthquake events, is the current goal to further reduce time and space uncertainties in the prediction of seismic events.
The objective of the proposed research was to develop and validate innovative algorithms, models and procedures to improve the accuracy and to promote the use of local geodetic networks for Earth crust deformation monitoring. The proposed research aimed to fully exploit the new expected performances of the Galileo system.
A preliminary requirement definition phase was carried out to set the objectives. During the early phase of the project the Galileo data simulator (GSSF) was analysed and understood. Algorithm studies and definitions for the three frequencies of Galileo data preceded the implementation phase where the already existing Galileian Plus software called NDA Professional was upgraded with the aim of processing three frequencies of Galileo data. Innovative algorithm implementations concerned cycle slips removal, ionosphere and three frequencies of ambiguity fixing. Meanwhile, the test bed, including GPS (two frequencies of real and three frequencies of simulated) data and Galileo (three frequencies of simulated) data, was prepared. Mobile equipment was set up and data was acquired by Harpha Sea, which provided micrometric movements for the NRT test bed.
GEOLOCALNET investigates the feasibility of the synergistic use of the Galileo signals (three frequencies) and geophysical models for near-real-time (NRT) monitoring of earth crust deformations. The objective is to decrease the GNSS observation time while maintaining the maximum accuracy achievable today with geodetic networks, through the use of Galileo’s third carrier frequency. In the long term, the aim is to achieve an early warning system for seismic activity, subsidence and landslide events.
Key activities in the project include:
- Identification of the monitoring requirements for NRT geodetic networks, in terms of the trade-off between accurate and observable durations.
- Testing of GSSF (Galileo System Simulation Facility) simulator for GPS- and Galileo-like signal outputs.
- Development and testing of new algorithms based on three frequencies for upgrading the Galileian Plus NDA (network deformation analysis) product for geodetic networks.
- Comparison of the use of GPS, simulated GPS and simulated Galileo signals (the latter from the GSSF) within an existing geodetic network in Slovenia using the upgraded NDA analysis software.
- Awareness activities to promote the use of Galileo in geodetic network monitoring.
Work performed & results
GEOLOCALNET demonstrated that by using three frequencies of simulated data a remarkable improvement in very precise positioning could be achieved by exploiting Galileo data. Both repeatability tests and near-real-time tests demonstrated the increased capability of Galileo. These tests were carried out by using an upgraded version of NDA professional, a Galileian Plus product for GNSS data analysis, which has been upgraded during the project for three frequencies of Galileo data processing. In particular, using the same observation time a more precise relative positioning was obtained. For the same precision, i.e. repeatability, shorter observation times could be exploited. This will allow for a reduction in the costs of mobile GNSS campaigns. In general, Galileo will allow the measurement of small movements in shorter time periods thus opening up new interesting scenarios for applications such as pre-seismic non-linear deformation monitoring. This will bring important improvements in early warning services to protect the local population against a seismic hazard.