Query: rnav gnss BAD WEATHER

title: A New GNSS Based Approach for Volcanic Crater Location During Lava Fountains
abstract: Recent studies have focused on the capability of the global navigation satellite system (GNSS) instruments to detect volcanic plumes by means of either variation in signal to noise ratio or products from positioning processing. These new approaches can be extremely useful for volcanoes worldwide, which may not have advanced monitoring systems or during bad weather conditions when other techniques may fail. In this letter, we show how the GNSS stations can provide a new tool to locate the volcanic crater during highly explosive events. The proposed method has been tested on the lava fountains at Mt. Etna (Italy) that has characterized most of the eruptive activity from different craters since 2011. Our results confirm that not only there are evidences of detectable interaction between volcanic plumes and GNSS data but also, for the first time on a large data set, we are able to discriminate the erupting crater with great precision.

title: Urban Heat Island Monitoring with Global Navigation Satellite System (GNSS) Data
abstract: The Urban Heat Island (UHI) effect occurs when the temperature in an urban area is higher than the temperature at a rural area. UHIs are monitored using remote sensing techniques such as satellite imagery or using temperature sensors deployed in a metropolitan area. In this chapter we propose a methodology to monitor the UHI intensity from Global Navigation Satellite Systems (GNSS) data. As the GNSS signal travels from the satellite to the receiver it propagates through the troposphere. A delay (Tropospheric delay) affects the signal. The delay is proportional to environmental variables. Also, the tropospheric delay in zenith direction (ZTD) is estimated as part of the Precise Point Positioning (PPP) technique. Therefore, in this chapter it is shown how to use process GNSS data to obtain ZTD and obtain temperature at an urban and a rural site simultaneously from the ZTD. The advantages of using GNSS data is its availability and many GNSS networks have been deployed in different cities so no need to deploy sensor networks. Furthermore, GNSS signal is less affected by bad weather conditions than satellite imagery.

title: Performance Enhancement of a USV INS/CNS/DVL Integration Navigation System Based on an Adaptive Information Sharing Factor Federated Filter
abstract: To improve the ability of autonomous navigation for Unmanned Surface Vehicles (USVs) multi sensor integrated navigation based on Inertial Navigation System (INS) Celestial Navigation System (CNS) and Doppler Velocity Log (DVL) is proposed. The CNS position and the DVL velocity are introduced as the reference information to correct the INS divergence error. The autonomy of the integrated system based on INS/CNS/DVL is much better compared with the integration based on INS/GNSS alone. However, the accuracy of DVL velocity and CNS position are decreased by the measurement noise of DVL and bad weather, respectively. Hence, the INS divergence error cannot be estimated and corrected by the reference information. To resolve the problem, the Adaptive Information Sharing Factor Federated Filter (AISFF) is introduced to fuse data. The information sharing factor of the Federated Filter is adaptively adjusted to maintaining multiple component solutions usable as back ups, which can improve the reliability of overall system. The effectiveness of this approach is demonstrated by simulation and experiment, the results show that for the INS/CNS/DVL integrated system, when the DVL velocity accuracy is decreased and the CNS cannot work under bad weather conditions, the INS/CNS/DVL integrated system can operate stably based on the AISFF method.

title: A Robust and Effective GNSS/INS Integration Optimizing Cost and Effort
abstract: Meeting all requirements for ying approaches in bad weather conditions is one of the most demanding and challenging aspects of present day airborne navigation. Stand alone satellite navigation has not yet reached the point of being suciently robust and accurate in order to reach certication level. Therefore, in this work the performance of an integrated satellite/inertial navigation system (GNSS/INS) is investigated in order to cope with short term losses of GNSS signals. We consider a low cost Micro Electronic Mechanical System (MEMS) INS which is constantly reinitialized with information coming solely from GNSS. It takes over navigational responsibility when a loss of signal occurs or other failures in the satellite navigation system are detected. For the GNSS to provide all information necessary to initialize an INS, a minimum of three antennas is needed to measure the aircraft's attitude along with its speed and position. Error models for positioning, speed and attitude estimation are used to create a model for initialization uncertainties. Together with error models for the accelerometers and gyros in the Inertial Measurement Unit (IMU) the behavior of the whole proposed architecture is determined via performance simulations. As a maximum allowable error 15.3 meters (which corresponds to the CAT III horizontal alert limit for GNSS approaches) are taken. Our simulations show that this limit is not exceeded for at least 14 seconds after the take over of navigational responsibility by the INS.

title: An Improved Tomography Approach Based on Adaptive Smoothing and Ground Meteorological Observations
abstract: Using the Global Navigation Satellite System (GNSS) to sense three dimensional water vapor (WV) has been intensively investigated. However, this technique still heavily relies on the a priori information. In this study, we propose an improved tomography approach based on adaptive Laplacian smoothing (ALS) and ground meteorological observations. By using the proposed approach, the troposphere tomography is less dependent on a priori information and the ALS constraints match better with the actual situation than the constant constraints. Tomography experiments in Hong Kong during a heavy rainy period and a rainless period show that the ALS method gets superior results compared with the constant Laplacian smoothing (CLS) method. By validation with radiosonde and European Centre for Medium Range Weather Forecasts (ECMWF) data, we found that the introduction of ground meteorological observations into tomography can solve the perennial problem of resolving the wet refractivity in the lower troposphere and thus significantly improve the tomography results. However, bad data quality and incompatibility of the ground meteorological observations may introduce errors into tomography results.

title: New role of GNSS in the Safety of maritime navigation
abstract: IMO introduces the issue of maritime safety as follows: Shipping is perhaps the most international of all the world's great industries and one of the most dangerous. Ship casualties and incidents can result in serious loss of life and pollution of the marine environment as modern ship can carry over 5,000 people and over 500,000 tons of petroleum. Maritime safety is of paramount importance in the new role of GNSS. Increased safety at sea should be considered while taking into account the most critical issue of supplying the master of a vessel and those responsible for the safety of shipping ashore with modern, proven tools to make marine navigation and communications more reliable thereby reducing errors, especially those with the potential to cause equipment damage, pollution harm to the marine nvironment, injury and loss of life. Maritime safety in this case means to address the particular needs of enhancing the prevention of collisions and groundings. According to statistics, the number of ship collisions and groundings has not appreciably changed over the last ten years despite the growing technology. Furthermore, it should be considered that there are serious concerns about the secondary disasters resulting from collisions and groundings, for example, loss of human life and oil spills. The EMSA statistics show that 762 vessels were involved in 715 accidents (sinkings, collisions, groundings, fires/explosions and other significant accidents) in and around EU waters during 2007. The majority of vessels in the 2007 EMSA survey were involved in collisions and contacts (around 40% and roundings (around 26% while sinkings accounted for around 7% of the total and fires and explosions for around 12% (other 15% It is acknowledged that there is evidence to show that the great majority of accidents have a human error component, and also that seafarers often make mistakes under difficult circumstances (eg bad weather, geographical/infrastructure restrictions, fatigue, task overload, training shortcomings, etc. There are numerous examples of collisions and groundings that might have been avoided had there been suitable input into the navigation decisionmaking process.

title: GPS/GNSS reflectometry nanosatellite demonstration mission
abstract: Loss of life, injury and huge economic losses are incurred annually due to irregular and insufficient sea state information. Figures indicate that, each year, the marine insurance industry pays out over $2 billion in claims for weather related accidents, while bad weather causes one ship of over 500 t to sink somewhere on the globe every week. Accurate knowledge of local ocean conditions is therefore crucial in providing forecasts and early warnings of severe weather conditions. Space borne systems, particularly satellites, provide the ideal platform for global monitoring of sea conditions via altimetric measurements. As an alternative to active altimetry, another concept is passively receiving reflected signals from the Global Positioning System (GPS) and other Global Navigation Satellite System (GNSS) satellites. This concept was first developed by Dr Manuel Martin Neira at ESA ESTEC. ESA's Passive Reflectometry and Interferometry System makes use of GPS/GNSS signals from satellites and their reflection off the ocean surface to derive oceanic properties such as surface height, significant wave height, wind speed and wind direction. Surrey Satellite Technology Ltd are proposing a nanosatellite demonstration mission to ascertain the feasibility of the GPS ocean reflectometry concept.

title: Velocity estimation of Grandes Jorasses glacier in the framework of GlaRiskAlp project
abstract: The Grandes Jorasses hanging glacier, located at 4100 m asl above a populated area, is monitored by Fondazione Montagna sicura since 2007, on account of the Geological Service of the Aosta Valley Autonomous Region. The serac dynamic shows a periodic trend of mass increasing, interrupted by a collapse: The collapse is preceded by an exponential acceleration that lasts few days, as revealed in 1997 98 by Prof. M Funk (ETH Zurich) By tracking the velocity of the ice mass it is therefore possible to forecast its breakdown. At the early stage of the project the native monitoring system consisted of poles with prisms placed on the glacier surface, monitored by an automatic total station (motorized total station) sited at the valley bottom. During bad weather conditions the system could loss measurements, so alternative monitoring systems were designed, installed and tested in the framework of the GlaRiskAlp project (Alcotra program) In particular the new monitoring systems consisted of a low cost, single frequency, GNSS wireless sensors network, able to trace continuously (H24) the receivers positions to measure the displacement in real time, and a seismometer at the top of the glacier was placed in order to follow the seismic activity (that is proportional to the velocity) Furthermore, in order to better characterize the mass evolution, photogrammetric activities were carried out to reconstruct the glacier surface. Prototypes, results and outlooks of these monitoring systems for Grandes Jorasses glacier will be presented

title: Single frequency GPS monitoring of glacial displacements: the case of Grand Jorasses glacier
abstract: Since 2008 Fondazione Montagna sicura is in charge of the monitoring system of the Grandes Jorasses's serac. It is an unbalanced hanging glacier standing above Ferret Valley, a famous and highly populated area. The glacier is subject to periodic icefalls which (especially in winter) can trigger snow and ice avalanches. Thankfully the serac dynamic was studied in 1997 98 by prof. M Funk (ETH Zurich) revealing an exponential acceleration the days before the collapse. Forecasting the breakdown is then possible by tracking the ice mass velocity. The current monitoring system consists of stakes with prisms placed on the surface of the serac and an automatic total station (theodolite plus distantiometer) sited on the valley floor. The major drawback of this system is that fog or bad weather could impair its operation, thus causing loss of information about the serac movement. This paper presents an alternative monitoring system developed and tested during the 2010. The idea is to use single channel GNSS receivers installed on the serac, transmit data with a wireless network and gain high accuracy exploiting permanent GNSS stations and the DGPS technique. The system must be characterized by low cost (throwaway sensors due to the environment) high precision (mean velocity is about 5 cm/day) self recovery and stand alone electric supply. The solution was to adopt the Magellan AC12, a professional GNSS receiver, and develop the needed electronics to log and transmit data. The electronic board is able to start and configure the GNSS receiver and to recover possible failures. During the normal operation the system is optimized to reduce current consumption logging data and minimizing the transmission time to only once every 30 minutes. The developed network is composed by three slave nodes (GNSS receiver plus PCB) one relay station(the final installation is 4 km away from the valley floor) and one receiving station. The communication protocol in this first release is a single direction custom implementation of the "Listen before Talk" principle. The slave nodes probe the channel and if no one is transmitting the communication start. The receiving station logs the data in RINEX format closing one hourly file for each GNSS station. The high accuracy is than obtained by means of differential computation using local permanent GNSS stations. The whole system was tested in august 2010 during one field campaign in Val Veny (Courmayeur, Italy) The slave nodes were installed on a stake with a prism on its top and then moved for some centimetres and the movement recorded with a total station. In post processing was possible to compare the GNSS log with the total station measurements and appreciate an accordance lower than one centimetre. Nel gruppo del Monte Bianco numerose sono le situazioni di rischio glaciale. Una di queste, oggetto di un progetto pilota di monitoraggio gestito dall'Ufficio Ghiacciai e Permafrost di Fondazione Montagna Sicura (FMS) e il seracco delle Grandes Jorasses, una enorme massa di ghiaccio in continuo accrescimento e altamente instabile, posta tra i 4000 e i 4200 m di quota e alimentata dalla neve che si deposita sul versante sottovento dello spartiacque italo francese. Il seracco e controllato integrando tecniche di osservazione diverse, che vanno dal monitoraggio topografico classico, possibile grazie a prismi posizionati sul ghiacciaio, fino alla fotogrammetria da elicottero, che permette di ottenere da immagini oblique un modello tridimensionale del fronte glaciale con la tecnica del dense matching. Tutti questi dati confluiscono in un modello numerico di simulazione, gestito dal Prof. Martin Funk dell'ETH di Zurigo. Solo il GPS pero e teoricamente in grado di fornire osservazioni con continuita in ogni stagione, anche di notte e in ogni condizione di visibilita. Per questo motivo e stata messa a punto una stazione GPS remota posizionata sul seracco a quota 4100 m. Nella progettazione di questa stazione, che puo essere perduta in caso di crollo, abbiamo perseguito l'obiettivo di limitarne al massimo il costo, che nell'attuale prototipo e di circa 1000 EUR. Il ricevitore scelto e un Ashtech AC12 a singola frequenza; l'alimentazione e fotovoltaica con batteria tampone e le osservazioni grezze sono trasmesse via ponte radio wireless in formato NMEA ogni 30 secondi. Nei pressi delle Grandes Jorasses sono installate alla quota di 2350 m la stazione permanente del Ferrachet (FERR) anch'essa gestita da FMS e a quota 1670 m la stazione di Morgex (MRGE) gestita dall'INGV. I dati delle basi JORA FERR (3.2 km) e JORAMRGE (13.3 km) sono elaborati automaticamente a cadenza giornaliera con il software Bernese; le coordinate sono monitorate in automatico e il sistema e in grado di attivare degli allarmi in caso di spostamenti anomali della stazione. La scelta di un ricevitore a singola frequenza non implica particolari problemi, essendo la stazione FERR a soli 3.2 km di distanza; tuttavia l'Ashtech AC12 e pur sempre un ricevitore a basso costo: il rumore delle osservazioni di codice e fase su L1 e l'effetto di multipath dovuto alla neve richiedono di essere mediati su finestre di osservazione ampie. Attualmente la procedura automatizzata di calcolo e gestita su base giornaliera, ma si prevede di ripetere il calcolo delle coordinate con frequenza superiore su sessioni di misura di 12 e 6 ore. Le ripetibilita giornaliere delle coordinate, valutate in una fase di test preliminare all'installazione sul seracco, sono dell'ordine del centimetro in planimetria e di 3 cm in quota. La stima dei parametri troposferici e particolarmente critica, dato che la rete e caratterizzata da elevati dislivelli su limitate lunghezze di base. Sono stimati ad intervalli di 12 ore i soli ritardi troposferici relativi; si e evitata una stima a maggiore frequenza, che conduce a sovra parametrizzare il sistema normale e non porta sostanziali benefici in termini di miglioramento delle ripetibilita giornaliere. La stazione remota JORA e stata installata sul seracco ed ha iniziato ad acquisire il 21 luglio 2009. L'antenna GPS e montata su di un tubo Innocenti da 6 m, infisso verticalmente nel ghiaccio ad una profondita di 4 m. Sullo stesso tubo sono fissate l'antenna wireless, il pannello fotovoltaico e una cassetta stagna e coibentata che accoglie il ricevitore GPS e la batteria. La perforazione e stata realizzata con sonda a vapore. Nella fase operativa di acquisizione le maggiori criticita si sono verificate nella trasmissione dei dati via wireless, probabilmente a causa della formazione di ghiaccio sull'antenna. Altro aspetto da tenere presente e l'effetto del vento sul palo, con conseguenti vibrazioni anche forti, in quanto il palo non e controventato. L'inclinazione del palo e controllata mensilmente per mezzo di misure topografiche, grazie a due bande catarifrangenti applicate sul palo, e le coordinate di JORA sono depurate dell'effetto dovuto a tale inclinazione. Nel mese di agosto 2009 sono state determinate una velocita orizzontale di 30 mm/giorno in direzione SSW e verticale di 60 mm/giorno. Il piano di scorrimento del seracco ha un'inclinazione di circa 45deg, per cui ci si potrebbe aspettare valori simili di velocita orizzontale e verticale. Il maggiore abbassamento deve invece essere attribuito alla fusione dovuta alle elevate temperature registrate nel mese di agosto. Ci attendiamo tuttavia un rallentamento gia dal mese di settembre. Un crollo importante e atteso dalla fronte del seracco e il sindaco di Courmayeur con un'ordinanza del 20 agosto ha vietato l'accesso al rifugio Boccalatte Piolti e alle aree sottostanti il ghiacciaio Whimper. I primi due mesi di attivita della stazione JORA hanno mostrato che e possibile attuare soluzioni di basso costo per il monitoraggio GPS di movimenti macroscopici, dell'ordine dei decimetri/mese. Hanno mostrato anche che, nonostante i problemi dovuti alla trasmissione dei dati in tempo reale, e possibile ottenere risultati affidabili con procedure totalmente automatizzate e gestire quindi un sistema di allertamento. Bibliografia Aoudia A. K.  (2004) "Il progetto Alps GPS QuakeNet" in Atti della VIII Conferenza ASITA, Roma. Baldo M. Cina A. Manzino A. M. Roggero M. (2002) "Utilizzo geodetico e in tempo reale di ricevitori GPS di basso costo" In Atti della VI Conferenza Nazionale ASITA, Perugia,  (2005) "Realizzazione della rete geodetica GAIN in Piemonte e Valle d'Aosta" In Atti della IX Conferenza ASITA, Catania, pp. 309 314, Vol. 1. Thales Navigation (2005) A12TM, B12 TM &AC12 TM, Reference manual, Part Number: 630871, Revision D.

title: Modeling of the Galileo signals near a sea surface
abstract: The Galileo system is obviously seen as a huge opportunity for the air traffic management since it is built to deliver guaranteed signals at sub meter accuracies. In the same way, the Galileo system has to play a big role in the maritime transport. The accuracy and the reliability of the positioning based on Galileo can be of a great importance for shipping containers management or navigation in port areas, for maritime safety (avoiding shipwreck system) for search and rescue (specially in bad weather conditions) Nevertheless, these opportunities of development for the Galileo positioning system in maritime domains are only available if the performances of the Galileo system are proved to be valid in any maritime environment. As a matter of facts, due the multiple electromagnetic reflection from the sea surface, the GNSS signal received above the sea surface could be significantly perturbed by the electromagnetic contributions from the sea, see figures 1 and 2. And so the maritime environment could seriously impact the performances of the Galileo system.