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Global Navigation Satellite Systems (GNSS) are systems that continuously acquire data and provide position time series. Many monitoring applications are based on GNSS data and their efficiency depends on the capability in the time series analysis to characterize the signal content and/or to predict incoming coordinates. In this work we propose a suitable Network Architecture, based on Long Short Term Memory Recurrent Neural Networks, to solve two main tasks in GNSS time series analysis: denoising and prediction. We carry out an analysis on a synthetic time series, then we inspect two real different case studies and evaluate the results. We develop a non-deep network that removes almost the 50% of scattering from real GNSS time series and achieves a coordinate prediction with 1.1 millimeters of Mean Squared Error.

La rete di stazioni GNSS permanenti attualmente presente in Italia è costituita da più di 700 siti. Queste stazioni sono distribuite in modo non omogeneo sul territorio e sono caratterizzate da una forte disomogenietà; infatti possono differire tra loro per diversi motivi, quali ad esempio: le caratteristiche della strumentazione utilizzata; la collocazione dell'antenna ricevente (roccia, edificio); il tipo di supporto antenna utilizzato (tripode INGV, supporto UNIBO-Max, staffa), gli scopi per cui è stata realizzata la stazione (studio e monitoraggio scientifico, supporto per il posizionamento in tempo reale o altro). Questi fattori possono influire pesantemente sulle caratteristiche delle serie temporali giornaliere della posizione introducendo segnali periodici e non ed influire in modo non trascurabile sulle caratteristiche del rumore presente nelle serie temporali della posizione di queste. Per cercare di individuare possibili correlazioni tra questi fattori e le caratteristiche delle stazioni permanenti italiane, le serie temporali della posizione ottenute elaborando le osservazioni giornaliere con due diversi software (Gipsy/OASIS e Gamit /Globk) sono state analizzate. In particolare, è stata utilizzata l'analisi spettale per individuare i principali segnali periodici presenti nelle serie temporali della posizione. Inoltre, le serie temporali sono state analizzate per determinare le caratteristiche del rumore presente per tentare di correlarlo con le diverse tipologie di installazione e/o gestione presenti nella rete rete italiana. E' stata anche utilizzata un'analisi di tipo principal component analysis (PCA) allo scopo di individuare possibili segnali comuni a stazioni presenti in determinate aree o a siti che presentano tipologie di installazione o gestione simili.

I sistemi di riferimento geodetici, ed i frame che li materializzano, costituiscono struttura di base che permette di confrontare coerentemente le rappresentazioni geometriche del territorio acquisite con rilievi diversi. Nell’ultimo secolo si è vista una continua evoluzione nella definizione dei frame geodetici, dovuta principalmente alle nuove esigenze, e possibilità, introdotte dalle tecniche di geodesia spaziale. È cambiata la scala alla quale si affronta il problema, sono cambiate le precisioni delle misure e delle accuratezze richieste, sono cambiati gli approcci e le definizioni. L’esigenza di un sistema di riferimento valido su scala globale ha imposto la definizione di frame dinamici, che seguano le evoluzioni della crosta terrestre nel suo complesso, introducendo così la necessità di una coordinata temporale oltre alle classiche coordinate geometriche. Proprio la natura dinamica della Terra implica delle variazioni nel tempo delle coordinate, espresse nel riferimento globale, troppo elevate per essere gestite nelle applicazioni cartografiche a scala continentale/nazionale, per cui si è resa necessaria la definizione di altri sistemi di riferimento, vincolati alle placche tettoniche. Di fondamentale importanza sono diventati quindi i parametri di conversione delle coordinate che premettono il passaggio da sistemi globali a regionali, e viceversa. Nel percorso di questa tesi ci si è occupati del monitoraggio dei frame di riferimento dinamici, in particolare di quello nazionale realizzato dalla Rete Dinamica Nazionale. È stato affrontato il problema delle velocità residue che caratterizzano il territorio italiano nel sistema di riferimento europeo, definendo un nuovo sistema ad hoc per il territorio nazionale. È stata indagata la tecnica di calcolo Precise Point Positioning, sia dal punto di vista geodetico e dell’inquadramento delle coordinate nel sistema globale, sia dal punto di vista del rilievo tecnico. Infine, ci si è occupati delle reti geodetiche diffuse sul territorio di Regione Emilia-Romagna, e della funzione che queste ancora devono avere nell’era dei GNSS., The geodetic reference systems, and the related frames, constitute the basic structure that allows to compare geometric representations of the earth acquired by different surveys. The last century has seen a continuous evolution in the definition of geodetic frames, mainly due to new needs, and possibilities, introduced by the space geodesy techniques. Are changed the scale of the problem, the precision of the measurements and the required accuracies, and also the approaches and definitions. The requirement of a global reference system has imposed the definition of dynamic frames, which follow the evolution of the earth's crust as a whole, so the need for introducing a time coordinate in addition to usual geometric coordinates. The dynamic nature of the Earth involves variations in time of coordinates, when expressed in the global reference system, too quick to be handled in mapping applications on a continental / national scale. So it was necessary the definition of other reference systems, linked to the tectonic plates. Thus, fundamental are the transformation parameters needed to switch from regional systems to global systems, and vice versa. In this thesis the topic of the monitoring of dynamic reference frames has been addressed, in particular the Italian Rete Dinamica Nazionale. The matter of the high residual ETRS velocities that characterize the Italian peninsula has been addressed, and a new ad hoc reference system was defined. The calculation technique of Precise Point Positioning has been investigated, both from the geodetic point of view, addressing the strategies to align the coordinates in the global system, than from the point of view of technical surveys. Finally, the geodetic networks of the Emilia-Romagna Region were analyzed, evaluating their importance in the age of GNSS.

The present Italian kinematic field has been estimated by a network of about 780 GNSS permanent stations. The daily observations acquired with a sampling rate of 30 seconds from January 01, 2001 to December, 31, 2015 have been analysed through the GAMIT/GLOBK software, adopting a distributed procedure. The position component time series (North, East and Vertical) are analysed in order to obtain a reliable estimation of: average velocity, amplitude and periods of seasonal signals, dimension of instrumental and/or seismic steps and noise. These characteristics have been studied in order to verify possible correlations with some characteristics of GNSS installation and/or natural and anthropogenic phenomena present in some areas. The average velocity of the 414 sites characterized by a time span greater than 2.5 years and an efficiency greater than 50% have been used in order to estimate the present kinematic pattern in the Italian peninsula and surrounding areas. The horizontal velocity field is characterized by some interesting features that are compatible with the long term deformation pattern deduced from geological observations. The vertical velocity field is characterized to an heterogeneous distribution probably due to the strong influence that anthropogenic activities have on this component .

In this paper the main results obtained by a study on a subnetwork of the EUREF Permanent Network has been reported. The study focus the impact of different methods to align PPP solution into ITRS Reference System using both global and regional transformation parameters. In particular we demonstrate as the regional parameter transformation improve accuracy and repeatability without remove any local periodical signal detected by the permanent stations. The considered dataset is constituted by 6 years of 14 permanent stations located in Italy and neighbor regions. This work is a review of a more complete work published in 2015 in GPS solution entitled “Improved PPP performance in regional networks” by the same coauthors of this contribute.

GNSS technology is still not considered as a suitable method for structural monitoring because of its relatively low precision, despite the increase in acquisition frequencies. This paper aims to evaluate a strategy for filtering a daily kinematic GNSS solution using a movement smoothing model based on the observations of previous days, so as to obtain a less scattered solution. A test was conducted with a permanent GNSS station located on top of the medieval Garisenda tower in Bologna (Italy), as it is an important part of the city’s cultural heritage and a reliable test site. Because of the presence of the adjacent Asinelli tower, which is taller than the Garisenda, sky visibility is not optimal here, and for this reason a particular sequential filtering can be adopted in order to obtain more accurate solutions. The test was performed using RTKLIB software to calculate 1 Hz baselines between the test station and a master one located on a stable area about one kilometer away from the tower. In order to obtain reliable results, several variables were considered both in the data processing phase and in defining the filter. All results are reported and discussed in detail in the paper. The test results reveal a reduction in scatter of about 20% in the filtered kinematic time series, especially in weaker geodetic components.

The networks of GNSS permanent stations are extremely useful infrastructures for whom those are involved in precise positioning issues and tracking with satellite techniques. For a full and proper use of those networks it’s fundamental the availability of archives containing the daily records as completely as possible both in the aspect of the datum that in the aspect of metadata associated with. One aim of this paper is to find a way to analyze, by means of objective parameters, an archive generated by a network of GNSS permanent stations with the purpose of identifying a parameter of quality to be attributed to each of the stations of the network, and in perspective to evaluate the reliability of the entire network. A method to evaluate the efficiency of a GNSS network can be based on the analysis of consistency of the recorded data, and to do that it’s been implemented a software procedure able to analyze GNSS data and evaluate the various aspects that characterize it. These archives, generally containing files in RINEX format, should be accompanied, according to international standards, by metadata describing the ancillary parameters of each station (and its “history”) in order to be properly managed in the geodetic calculation phase. Often, however, especially at the national scale, these metadata are non-existent or incomplete and this aspect makes particularly difficult the correct use of the recorded data. The work that’s subject of this paper addresses the problem with two different viewpoints: the first one is the detailed analysis of the archive’s data consistency, the second one is the reorganization of the archive in accordance with international standards, accompanied by proper metadata (log_site). The software procedure has been tested on various archives, and in particular on RDN network.

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.

Per il calcolo geodetico di grandi reti di stazioni permanenti GNSS, in particolare quando la gestione di queste non rispetti gli standard internazionali, è necessario predisporre l’archivio dati, rilevando e correggendo i frequenti errori formali e le eventuali criticità dei singoli file. Per svolgere questa onerosa operazione è stata quindi sviluppato un pacchetto di scripts in ambiente Linux, scritti nel linguaggio Perl, in grado di riordinare un qualunque archivio dati, separando i files corrotti da quelli pronti per il processamento geodetico, e fornire per esso una completa analisi statistica. Mediante il pacchetto presentato è possibile ottenere automaticamente i files ancillari necessari ai software di calcolo, identificando inoltre gli eventuali errori formali presenti negli header dei RINEX che possano rivelarsi compromettenti per l’elaborazione e correggendoli poi nel modo più automatizzato possibile.

The knowledge of the so-called geoid undulation, which represents the height of the geoid above a reference ellipsoid, is a fundamental step to link ellipsoidal heights measured using satellite systems and orthometric heights. Several geoid models are available at the time both at the national or global scale, which can be used for the purpose. Another way to define the geoid undulation is to perform joint measures with GNSS and spirit levelling over common benchmarks. This requires onerous measurements that is seldom possible to perform due to their cost. In this work, we evaluated the possibility to define a local model of the geoid undulation using already available spirit levelling orthometric heights and GNSS ellipsoidal heights measured about 13 years later. The test area is the Emilia-Romagna Adriatic coastline, an area of great interest both from the environmental and economic point of view, which is also undergoing consistent subsidence phenomena.Test results show that the available measurements allow defining a geoid undulation that is coherent with the shape defined by the gravimetric models and also allows to transform ellipsoidal heights into orthometric ones more consistent with the height reference available on the surveyed area. A 7 cm overall bias with respect to the ITALGEO05 was found, whereas ITG2009 and EGM2008 have higher differences. The use of subsidence models to align over time the coordinates used to define the geoid undulation has proven to be a fundamental step. The analysis on the a-priori uncertainty in the geoid height definition shown that the combined use of much more precise GNSS coordinates and contemporary spirit levelling campaign is necessary to significantly improve the resulting geoid height.

Among several instruments and techniques that can be used for monitoring purposes, GNSS technology has undergone a fast evolution and provides a large choice of solutions. Despite the best performances can be achieved by using double frequency geodetic receivers, capable to maintain high precisions even for wide-scale monitoring, in the recent years, several interesting solutions were presented in the low-cost market. In this work, a monitoring system based on a couple of low-cost GNSS receivers has been developed and tested in the field (Ponte Motta in Cavezzo - Modena, Italy). The two receivers were positioned about 50 m from each other and data were acquired at 1-Hz frequency. The position solutions were calculated both in post processing, through two different free and open-source software packages, and using an embedded RTK processor. The analysis aims to assess on one hand the capability of the system to perform the monitoring of slow displacements with the best possible precision, and, on the other hand, the performances of the real-time solutions that can be used for early warning purposes. The precisions evidenced by the tests show that such low-cost instrumentation can be used for many monitoring purposes, especially considering the cost that is about a tenth of geodetic instruments.

Although thermal imaging is a widely used technique in many applications and is under continuous development, one of its limits is the relatively coarse spatial resolution. Nevertheless, in the last years, a number of super-resolution algorithms have been developed which allow to enhance the resolution of the images. They can be divided in two main different categories: single-image or multiple image-based algorithms. In this work, a multiple image-based algorithm for the super-resolution was implemented, tested and applied to terrestrial thermal imaging with the aim to overcome the limitation of the low resolution. In particular, the method relies on the use of many images acquired from slightly different positions to obtain, thanks to the redundancy of observations, a super-resolution frame having an upsampling factor of four. Several tests were performed on synthetic datasets, and the accuracy of the obtained super-resolution images was investigated. Moreover, an original algorithm capable to identify gross errors during the image registration phase, which is one of the crucial phases, is presented and its reliability assessed. Results showed the effectiveness of the proposed method on both common visible images and thermal infrared ones, since discrepancies between reconstructed and reference values are reduced by 18 and 25% respectively, when compared with a conventional bicubic algorithm. Finally, the proposed method was tested on a case study concerning the thermal survey of the facade of a historical building in Bologna (Palazzo D’Accursio). A dataset of real thermal frames was acquired and a super-resolution image of the subject was generated through the developed algorithm. Strengths and weaknesses of the method were analysed and discussed in the paper.

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.

In 2011, Italy established a new geodetic reference system, the European Terrestrial Reference System 1989 (ETRS89), which was based upon the ETRF2000 reference frame at epoch 2008.0. In order to maintain this reference, the IGMI defined a permanent GNSS network within the EPN densification project, known as the “Rete Dinamica Nazionale” (RDN) and composed of 99 tracking stations located in and around Italy. Eight years of data are now available and the aim of this work is to estimate the velocities of the official RDN sites. It was necessary to pre-analyze the data accurately because of the incomplete maintenance of the associated repository. The network was calculated using a PPP approach and applying the GIPSY-OASIS II software package, and the solutions were aligned to ITRS using a customized procedure. After they were transformed into ETRF2000, the time series of the solutions were properly analyzed to find discontinuities and solve jumps caused by earthquakes and instrumental changes. Results highlighted the residual velocities with respect to ETRS89, which can reach 5 mm/year in some areas. The velocity field is shown to be very inhomogeneous, with clusters of sites presenting very different behaviours.

Il litorale emiliano-romagnolo costituisce un'importante ricchezza naturalistica e socio-economica a livello nazionale, per questo motivo la difesa della costa è tra i temi d’interesse dell’azione di governo della Regione Emilia-Romagna e di diversi Enti locali. La conoscenza dello stato attuale della costa e della sua evoluzione nel tempo sono tra i requisiti fondamentali per una corretta definizione delle politiche di salvaguardia del patrimonio paesaggistico – ambientale e di tutela del quadro economico della fascia costiera. Per questo motivo da diversi decenni l’Agenzia regionale per la prevenzione, l’ambiente e l’energia dell’Emilia-Romagna (Arpae), su incarico della Regione, svolge attività di monitoraggio per l’individuazione delle dinamiche costiere ed il riconoscimento dei vari fattori incidenti sulla dinamica litoranea e le criticità presenti. In questo ambito si inseriscono le periodiche campagne di rilievo topografico e/o batimetrico della spiaggia emersa e dei fondali antistanti. Queste misure sono indispensabili per monitorare la continua evoluzione del litorale dovuto al fenomeno dell’erosione costiera e decidere quali politiche adottare per la sua conservazione nel tempo. Una delle tecniche di conservazione è il ripascimento, tecnica che prevede l’apporto di sabbia proveniente da accumuli litoranei e giacimenti sottomarini nelle zone più colpite dall’erosione. Per svolgere adeguatamente questa attività è fondamentale conoscere la quantità di materiale eroso dal mare e questo valore viene solitamente stimato confrontando tra loro i rilievi topografici e/o batimetrici eseguite nella medesima area in tempi diversi. Al fine di poter correttamente confrontare rilievi eseguiti in periodi diversi, e anche da ditte differenti, è necessario definire in modo univoco un sistema di riferimento a cui riferire tutti i rilievi. Tale sistema di riferimento è bene che sia adeguato per precisione e materializzazione alle tecniche di rilievo che si intendono utilizzare. Per questo motivo l’Unità Mare Costa di Arpae, per conto della Regione Emilia-Romagna, ha riscontrato la necessità di costruire una struttura geodetica di riferimento per le future attività di monitoraggio lungo il litorale emiliano–romagnolo. In questo lavoro vengono descritte le varie fasi che hanno condotto alla creazione di questa struttura di riferimento denominata Rete Geodetica Costiera (RGC), realizzata dall’Unità Mare Costa di Arpae in collaborazione con il Dipartimento di Ingegneria Civile, Chimica, Ambientale e dei Materiali (DiCAM) dell’Università di Bologna.