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The increasing number of GNSS permanent stations both in Italy and around the world can have a huge amount of data that may be monitored continuously and in accurate and precise wise. From some years the calculation approach known as Precise Positioning Point (PPP) constitutes a valid alternative to the differential approach, since it allows to obtain precision and accuracies of the same order of magnitude but in the face of a flexibility of calculation certainly advantageous and computation time significantly reduced. These accuracies are reachable applying an ambiguity resolution strategy and a successive framing approach. As known PPP estimate coordinates of points (GNSS stations) into the same reference frame (RF) of the orbits that can be different from the International or National RF (IGS08 or others). In this work, the computing architecture that allows to manage the monitoring of several networks of permanent stations is shown. This procedure is already running and it will be shown from a 16 GNSS permanent stations network evenly distributed on Italy and neighboring areas in a time window of 11 years.

GNSS is one of the most used technique to monitor Reference Frame, Plate motion, Landslides, Structures, etc... Data acquired by GNSS satellites have to be processed considering models, approaches and strategies which are influencing the final results and, if wrongly done, may introduce biases. In this work the Precise Point Positioning (PPP) approach for GNSS data processing has been considered and investigated. As well-known PPP is faster and more flexible compared to the carrier phase differenced approach. On the other hand the differenced approach has been generally characterized by a better repeatability, especially for quite small baselines. Until few years ago one of the major limits of PPP was the impossibility to resolve the ambiguity as integer but nowadays some methods are available to resolve this aspect expecting an increasing of the precision. Starting from two subsets of the IGS Tracking network (one located in Europe and composed by 16 stations around Italy and another one, composed by 9 stations and located in Antarctica) processed respectively for 11 and 3 years, the impact of some data processing strategies has been considered. For both the networks different kind of solutions has been obtained, each one using more refined strategies, considering the ambiguity phase resolution, the possibility to frame the solution using global transformation parameters (provided by JPL), or framing the solution using regional transformation parameters. Furthermore, with the aim to evaluate in polar regions the impact of different tropospheric models in GNSS solutions the Antarctica network has been processed also considering the Vienna Mapping function instead of the Niell MF. The results will be synthetized by two parameters which are accuracy and precision: accuracy has been obtained comparing each solution with the reference ITRF2008 solution (ITRF2008-TRF-IGS.SNX.gz) and precision has been estimated considering the scattering of the solutions (time series) around a straight line obtained by a least square approach.

Le finalità delle reti di stazioni permanenti GNSS, in ambito geodetico, sono: l’erogazione di servizi di posizionamento di precisione in tempo reale, la definizione ed il monitoraggio dei sistemi di riferimento, e il controllo del territorio e delle strutture. In particolare, nei casi di monitoraggio, può essere utile disporre di un dato continuo. Il metodo di calcolo denominato Precise Point Positioning è una valida alternativa all’approccio differenziato e presenta vantaggi in termini di flessibilità, in quanto non impone correlazioni tra stazioni. Esso, così come l’approccio differenziato, consente quindi il calcolo in quasi tempo reale di una qualsiasi rete di stazioni GNSS. In questo lavoro si intende mostrare una procedura, realizzata ad hoc completamente automatica in grado di elaborare grandi reti di stazioni permanenti con ritardo giornaliero o settimanale e precisioni centimetriche sulla singola stima. Tale procedura può essere riassunta in 4 macrofasi: prelievo dati (download dati GNSS e file ancillari), pre-analisi (valutazione consistenza del dataset e individuazione di eventuali errori di natura formale), processamento, post-trattamento (la conversione in diversi sistemi di riferimento o di coordinate, individuazione e successiva rimozione di eventuali outlier nell’ipotesi di comportamento lineare, redazione di risultati grafici). Il campione di dati utilizzati per valutare l’applicabilità della procedura in termini generali consiste in una rete GNSS costituita da 16 stazioni permanenti omogeneamente distribuite sul territorio italiano e zone limitrofe.

Over the past decade, precise point positioning (PPP) has become a tool widely used in many Global Navigation Satellite Syste applications and the performance levels of the method are often close to those that can be achieved through a differenced approach. The aim of this paper is to analyze the dependency of the precision of a PPP solution output from the GIPSY-OASIS II software on the observing-session durations. In detail, starting from real data acquisitions spanning 24, 12, 6, 3 h, 1 h, and ½ an hour, all processed through the PPP, a continuous function has been defined and the related coefficients have been estimated. The original dataset consists of daily RINEX files provided from 44 sites of both International GNSS Service (IGS) and European Permanent Network (EPN) permanent networks acquired over one year. Each RINEX file was split into several shorter files according to the above listed time spans and processed by using GIPSY-OASIS II together with jet propulsion laboratory (JPL) precise post-processed products. The uncertainty of the proposed function was also estimated and a complete analysis of its compliance with the data sample has been provided. The estimated model is demonstrated to reach a millimeter accuracy level within a statistical confidence level of 99% using the experimental data.