Papers by Angela Aragon Angel
The main focus of this paper is to show how the better knowledge of the behaviour of the more com... more The main focus of this paper is to show how the better knowledge of the behaviour of the more common ionospheric perturbations (the so called Medium Scale Travelling Ionospheric Disturbances, MSTIDs) can significantly improve the precise GNSS real-time positioning. In order to do this, three main studies has been carried out: 1) To develop a simple but accurate MSTID detection and characterization algorithm. 2) To apply this technique to extract the MSTID worldwide behaviour, in terms of occurrence, velocity, azimuth and period. 3) To form a simple blind MSTID model, summarizing these results (the main point detailed in this manuscript). This model is applied to realtime positioning scenarios, to show the significant reduction of positioning error. This increase of performance is achieved in both “classical” short baselines of few tens of kilometres (those covered by RTK and VRS techniques), as well as in very long baselines of hundreds of kilometres (by using the Wide Area RTK tech...
High precision positioning and time transfer are required by a large number of scientific applica... more High precision positioning and time transfer are required by a large number of scientific applications: seismic ground deformations, sea level monitoring or land survey applications require sub-centimeter precision in kinematic position; monitoring of stable atomic frequency standards requires an increasing sub –nanosecond precision. Differential GNSS is presently the best tool to reach such precisions, as it removes the majority of the errors affecting the GNSS signals. However, the associated need for dense GNSS observation networks is not fulfilled for many locations (e.g. Pacific, Africa). An alternative is to use Precise Point Positioning (PPP), but this technique requires correcting signal delays at the highest level of precision, including high order ionospheric effects. It is thus essential to accurately characterize the higher order ionospheric terms (I2+), i.e. I2, I3, I4, geometric bending and differential STEC bending, which is the goal of this paper. For that, we used a...
Users of the Global Navigation Satellite System (GNSS) using a single-frequency receiver need to ... more Users of the Global Navigation Satellite System (GNSS) using a single-frequency receiver need to use an Ionospheric Correction Algorithm (ICA) to compensate the delay introduced by the Ionosphere on radio waves. The European GNSS, Galileo, uses an ICA named NeQuick-G since it is an adaptation to real time use of the 3D climatological model NeQuick, whereas the American Global Positioning Service (GPS) uses the Klobuchar ICA, which was also adopted initially by the Chinese GNSS, Beidou. In an effort to foster the adoption of NeQuick-G by final users, two implementations in C language were made publicly available by the European Space Agency (ESA) and the Joint Research Centre (JRC) of the European Commission (EC) respectively. The latter, was chosen to be integrated in the GNSS laboratory tool suite (gLAB), developed by the research group of Astronomy and Geomatics (gAGE) of the Universitat Politecnica de Catalunya (UPC) because its open license and its processing speed. The aim of t...
The Ionosphere, such partially ionized atmospheric region between ~60 to +1000 km height, is typi... more The Ionosphere, such partially ionized atmospheric region between ~60 to +1000 km height, is typically affected by spatial and temporal variations, driven by Local Time (solar illumination), Latitude (magnetic field and solar illumination) and time (space weather, among seasonal and solar cycle dependence). And it can be studied by assuming the first order ionospheric approximation from the dual L-band frequency GNSS measurements. Nevertheless the Ionosphere can be affected as well by other "hidden" effects which are not so evident, which are going to be summarized: 1) The frequent ionospheric waves (Medium Scale Travelling Ionospheric Disturbances). 2) The daylight sudden overionization generated by Solar Flares. 3) The four high order ionospheric effects affecting L-band GNSS measurements for very precise applications. IonSAT 3 GPS and the Ionosphere The UV (and X) Solar radiation ionizes the region above 50-100 km: Ionosphere (to 1000 km) and Protonosphere/Plasmasphere (above 1000 km). The GPS signals are affected by the free electrons: carrier phase advance and code/pseudorange delays. IonSAT GPS signal is very sensitive to free electron distribution, which reacts to the EM field, oscilating and generating a secondary EM wave which overimposes and changes the velocity of the GPS signals (main iono. effect on GPS code and phase). 4 GNSS+ IGS: Global Iono. scanner "Ionoscope" Worldwide scanner of the Ionosphere that can be used to monitor the Space Weather signatures on VTEC, such as Storm Enhanced Densities (SED), X-Flares, Scintillation, TIDs. Low orbiting GPS receivers (CHAMP, SAC-C…) are also available adding 3D estimation capability (electron density) with great vertical resolution. GPS+ IGS Sat. Rec. IonSAT 5 Vertical and Horizontal electron content distribution Global vertical TEC map computed from ~100 GPS dual frequency receivers (units: 0.1 TECU) Electron density (Ne) profile computed from LEO GPS data (units: Te-/m**3) •Typical horizontal distribution: Maximum values at both sides of the geomagnetic equator (equatorial anomalies), correlated with the Sun position as well. •Typical vertical distribution: Maximum density height at 200-400 km (or higher during the night) with maximum electron densities of 10 11-10 12 e-/m 3 (lower in the night).
Journal of Geophysical Research: Space Physics, 2015
We introduce a methodology to extract the separate contributions of the ionosphere and the plasma... more We introduce a methodology to extract the separate contributions of the ionosphere and the plasmasphere to the vertical total electron content, without relying on a fixed altitude to perform that separation. The method combines two previously developed and tested techniques, namely, the retrieval of electron density profiles from radio occultations using an improved Abel inversion technique and a two-component model for the topside ionosphere plus protonosphere. Taking measurements of the total electron content from global ionospheric maps and radio occultations from the Constellation Observing System for Meteorology, Ionosphere, and Climate/FORMOSAT-3 constellation, the ionospheric and plasmaspheric electron contents are calculated for a sample of observations covering 2007, a period of low solar and geomagnetic activity. The results obtained are shown to be consistent with previous studies for the last solar minimum period and with model calculations, confirming the reversal of the winter anomaly, the hemispheric asymmetry of the semiannual anomaly, and the existence in the plasmasphere of an annual anomaly in the South American sector of longitudes. The analysis of the respective fractional contributions from the ionosphere and the plasmasphere to the total electron content shows quantitatively that during the night the plasmasphere makes the largest contribution, peaking just before sunrise and during winter. On the other hand, the fractional contribution from the ionosphere reaches a maximum value around noon, which is nearly independent of season and geomagnetic latitude.
ABSTRACT GPS radio occultations allow the sounding of the Earth's atmosphere, in particul... more ABSTRACT GPS radio occultations allow the sounding of the Earth's atmosphere, in particular the ionosphere. The physical observables estimated with this technique allow to test theoretical models of the ionosphere, as, for example, the Chapman and the Vary-Chap models. The former is characterized by a constant scale height, whereas the latter considers a more general function of the scale height and the height. We propose to investigate the feasibility of a novel and simple model where the scale height varies linearly with the height. The scale height data provided by the radio occultations from a receiver on board a low Earth orbit (LEO) satellite, obtained by iterating with a local Chapman model at every point of the vertical profile provided by the GNSS satellite occultation, are fitted with the height, by means of a linear least squares fit (LLS), in order to test this hypothesis. Preliminary results, based on FORMOSAT-3/COSMIC GPS occultation data, show that the scale height presents a more clear linear trend above the F2 layer peak height (hmF2) which can be in agreement with a temperature dependence, following ionospheric models like the IRI. Moreover, according to this preliminary analysis, the parameters of the linear fit do not depend significantly on the local time, whereas they do on latitude.
Physics and Chemistry of the Earth, Parts A/B/C, 2008
Tide gauges measure sea level changes relative to land. To separate absolute changes in sea level... more Tide gauges measure sea level changes relative to land. To separate absolute changes in sea level from vertical land movements tide gauges are often co-located with Continuous GPS (CGPS). In order to achieve an accuracy of better than 1 mm/yr, as required for sea level ...
Remote Sensing
Users of the global navigation satellite system (GNSS) operating with a single-frequency receiver... more Users of the global navigation satellite system (GNSS) operating with a single-frequency receiver must use an ionospheric correction algorithm (ICA) to account for the delay introduced on radio waves by the upper atmosphere. Galileo, the European GNSS, uses an ICA named NeQuick-G. In an effort to foster the adoption of NeQuick-G by final users, two implementations in C language have been recently made available to the public by the European Space Agency (ESA) and the Joint Research Centre (JRC) of the European Commission (EC), respectively. The aim of the present contribution is to compare the slant total electron content (STEC) predictions of the two aforementioned implementations of NeQuick-G. For this purpose, we have used actual multi-constellation and multi-frequency data for several hundreds of stations distributed worldwide belonging to the Multi GNSS Experiment (MGEX) network of the International GNSS Service (IGS). For each first day of the month during year 2019, the STECs...
GNSS radio occultation (RO) measurements have become crucial to provide valuable information on t... more GNSS radio occultation (RO) measurements have become crucial to provide valuable information on the vertical electron density structure of the Ionosphere. Ionospheric key parameters such as the maximum electron density (NmF2) and the corresponding peak height of the F2 layer (hmF2) can be easily derived. In the current work, in order to assess the accuracy of NmF2 and hmF2 inferred from Formosat-3/COSMIC (F-3/C) RO measurements, an efficient electron density retrieval method, previously developed at the UPC (Barcelona, Spain), has been applied for a period of more than half a solar cycle between 2006 and 2014. Ionosonde measurements from the Space Physics Interactive Data Resource (SPIDR) network have been used as reference. Results show that relative variations of NmF2 differences are in the range of 22%–30% and 10%–15% for hmF2. Equatorial and midlatitude sectors at daytime and dawn present the highest consistency whereas degradations have beendetected in the polar regions during ...
Proceedings of the 33rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2020), 2020
The adoption of the Galileo Ionospheric Correction Algorithm, NeQuick-G, by the GNSS community ha... more The adoption of the Galileo Ionospheric Correction Algorithm, NeQuick-G, by the GNSS community has been hampered in the past due to its complexity. During 2019, the Joint Research Centre (JRC) was involved in the review, recoding and testing of the NeQuick-G algorithm, with the objective to provide a professional version, open-source, fit for integration in any GNSS software suite and fully portable on any platform. Since December 2019, the JRC NeQuick-G code is being distributed through the European GNSS Service Centre web portal under an EU Public License (EUPL). This effort is expected to contribute greatly to the adoption of NeQuick-G model at user level. This version of the code has been designed to be highly modular, rendering it more legible for a potential programmer with no specific knowledge of the ionosphere. A library has been also developed to enable its quick integration into existing applications. This library should be of high interest for the European GNSS Agency's GNSS Raw Measurements Task Force. The introduction of Google Android 7.0 revision allows for direct access to raw GNSS pseudoranges observed by smartphones and the NeQuick-G library is ready to be easily integrated in any embedded system.
The Ionosphere Prediction Service (IPS), project funded by European Commission within Horizon 202... more The Ionosphere Prediction Service (IPS), project funded by European Commission within Horizon 2020 and currently ongoing, provides a prototype for a monitoring and prediction service of potential ionosphere-related disturbances affecting GNSS (Global Navigation Satellite System) user communities, to help these communities cope with the effects of the ionosphere and mitigate the related effects for the specific GNSS-based application/services. The aim of the IPS project is to design and develop a prototype platform able to translate the prediction and forecast of the ionosphere effects into a service customized for specific GNSS user communities. The objective is to alert the GNSS users in due time of an upcoming ionospheric event potentially harmful for GNSS and for the related operations in the given application field. The project team is composed of Telespazio (coordinator),
Journal of Space Weather and Space Climate, 2020
We introduce a novel empirical model to forecast, 24 h in advance, the Total Electron Content (TE... more We introduce a novel empirical model to forecast, 24 h in advance, the Total Electron Content (TEC) at global scale. The technique leverages on the Global Ionospheric Map (GIM), provided by the International GNSS Service (IGS), and applies a nonlinear autoregressive neural network with external input (NARX) to selected GIM grid points for the 24 h single-point TEC forecasting, taking into account the actual and forecasted geomagnetic conditions. To extend the forecasting at a global scale, the technique makes use of the NeQuick2 Model fed by an effective sunspot number R12 (R12eff), estimated by minimizing the root mean square error (RMSE) between NARX output and NeQuick2 applied at the same GIM grid points. The novel approach is able to reproduce the features of the ionosphere especially during disturbed periods. The performance of the forecasting approach is extensively tested under different geospatial conditions, against both TEC maps products by UPC (Universitat Politècnica de ...
Journal of Space Weather and Space Climate, 2019
The effect of the Earth’s ionosphere represents the single largest contribution to the Global Nav... more The effect of the Earth’s ionosphere represents the single largest contribution to the Global Navigation Satellite System (GNSS) error budget and abnormal ionospheric conditions can impose serious degradation on GNSS system functionality, including integrity, accuracy and availability. With the growing reliance on GNSS for many modern life applications, actionable ionospheric forecasts can contribute to the understanding and mitigation of the impact of the ionosphere on our technology based society. In this context, the Ionosphere Prediction Service (IPS) project was set up to design and develop a prototype platform to translate the forecast of the ionospheric effects into a service customized for specific GNSS user communities. To achieve this overarching aim, four different product groups dealing with solar activity, ionospheric activity, GNSS receiver performance and service performance have been developed and integrated into a service chain, which is made available through a web...
International Technical Symposium on Navigation and Timing 2018, 2018
holds the position of Project Manager in Telespazio with more than 18 years of technical and mana... more holds the position of Project Manager in Telespazio with more than 18 years of technical and managing experience. He is managing EC and ESA projects mostly focused on GNSS evolution and currently he is the coordinator of the Ionosphere Prediction Service programme for EC and the technical coordination of the Galileo PRS navigation performance monitoring tool development for the GSOp (the Galileo Service Operator). He has two degrees in Telecommunication Engineering and Astronautics Engineering and a PHD in Control Systems Engineering. He holds two patents in GNSS technology Stefano Di Rollo received is MSc in Telecommunication Engineering from the University of Rome La Sapienza (2008) and a II level specializing master in advanced systems for satellite communication and navigation (2010). From 2012 he was a Navigation System expert at Telespazio serving as system engineer and technical responsible on several projects regarding Galileo KPI monitoring and evolution, ionospheric activity monitoring and development of GNSS-based solutions for several applications. Roberto Ronchini holds a M.Sc. in Computer Science and a Ph.D. in Systems Engineering both from Sapienza University of Rome. He is currently employed in Telespazio as a GNSS Research Engineer and Technical Manager, and has been working on many international research projects since 2001. His research interests in GNSS include navigation systems integrity and failure detection, ionosphere monitoring and, more in general, GNSS systems performance modelling and forecast with focus on Civil Aviation and ATM Applications. Angela Aragon-Angel has two degrees in Mathematics and Physics and obtained her Ph.D. in the Aerospace Science and Technology Aerospace Doctoral Program of the Technical University of Catalonia (UPC) in 2010. She is currently a scientific/technical officer at the Joint Research Centre (JRC) of the European Commission (EC), Italy. Her working topics range from ionospheric radio occultation to ionospheric modeling for positioning and navigation within the area of GNSS data processing.
2016 International Conference on Localization and GNSS (ICL-GNSS), 2016
The European Commission has recently released the official document describing the particular ion... more The European Commission has recently released the official document describing the particular ionospheric model developed for the Galileo satellite navigation system. Such publication allows GNSS receiver manufacturers starting the implementation of the specific algorithm targeted for their Galileo related products in order to be compliant with the Galileo system. According to the European GNSS (Galileo) Open Service Signal In Space Interface Control Document, Issue 1.1, among the parameters that are broadcast in the Galileo navigation message, one can find five Ionospheric Disturbance Flags for Regions 1 to 5 (SF1, SF2, SF3, SF4 and SF5 respectively). Nevertheless, in the current version of the model presented in the Galileo-Iono document, the Ionospheric Disturbance flags are not used within the Galileo ionospheric correction calculation. In this work, a potential approach to account for this information is being investigated. This approach includes the update of the Galileo ionospheric correction model, NeQuick-G, by specifying the use of these flags. Hence a customized version of the NeQuick-G model has been developed and tested.
Modelling in Science Education and Learning, 2011
La implantación de la modelización matemática en elámbito del Espacio Europeo de Educación Superi... more La implantación de la modelización matemática en elámbito del Espacio Europeo de Educación Superior (EEES) necesita de una revisión y adaptación de los contenidos y estrategias para abordar las asignaturas, en particular, aquellas más teóricas y abstractas, para fomentar su carácter interdisciplinario. Se presenta una nueva propuesta metodológica para la asignatura de Análisis Vectorial (cálculo multivariable) ofertada durante losúltimos años por l'
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Papers by Angela Aragon Angel