Global ionospheric maps : estimation and assessment in post-processing and real-time

The research of this paper-based dissertation is focused on Global Ionospheric Maps (GIM) generation and assessment. In summary, the novelty and thematic unity in this works relies on four different but complementary topics: 1. Defining a systematic procedure to validate and quantify the quality of GIMs based on independent data sources or techniques. 2. Applying this methodology to not only the GIMs computed at UPC, but also to most of the currently open accessible GIMs inside the scientific community. 3.Including newly available Global Navigation Satellite Systems (GNSS) data to the processing of UPC's GIMs. 4. Assessment and distribution also of real-time GIMs. More in detail, my first contribution has been to the definition of a complete GIM validation procedure. This procedure is based on two methods: direct VTEC (Vertical Total Electron Content) altimeter and GNSS difference of slant TEC (Total Electron Content), both of them giving complementary information of the GIM performance. The main advantage of using satellite altimeter data is the fact that we are using a truly independent information source with regard to the input data used for GIM generation. This allows assessing the TEC from a entirely different point-of-view, fully different and independent to any error that may affect GNSS systems and its processing. The second technique, relies on using the same type of input data but in this case from permanent GNSS stations not participating in the GIM generation. The main advantages of this second technique is twofold: first, it allows to asses the GIMs on land; and second its a low latency direct assessment of the GIM, given a more direct information about the processing and interpolation done with the GNSS input data. Afterwards, a second contribution has been to use the previously defined methodology to validate all the GIMs generated by the International GNSS Service (IGS) Associated Analysis Centers (IAAC), and some other candidates to join them, for a more than a full solar cycle (starting from end of 2001 to beginning of 2017). As a side result, it is also demonstrated that while the time interval of the GIM has little influence on its overall quality, the interpolation technique used by the IAACs has an important role. Finally, this work also lead to the acceptance of the previously mentioned IAAC candidates since it demonstrated the good quality of their GIMs. Another contribution has been, as part of the European GRC project, improving the currently in production UPC's TOMION (TOMographic IONospheric) software used to generate the UQRG (UPC's rapid GIM) map. The software input source data was restricted to GPS L1 and L2. Now it allows processing all current frequencies available for GPS, Galileo and Beidou. This software has been internally tested for some specific days with the previously explained altimeter method giving results with improved quality for specific combinations of GNSS systems and frequencies. Using this work flow but focused on single frequency processing, a last article was published analysing the ionospheric footprint of the solar eclipse over North America during 2017. Finally, another contribution has been to improve the data acquisition and distribution system for the real-time GIM generation processing chain. Furthermore, as part of UPC contribution to the Real Time Ionospheric Monitoring Working Group (RTIM-WG) of the International Association of Geodesy (IAG) and following the previously explained methodology, an assessment of the GIMs generated by the members of this sub-commission have been performed. As a result of all these efforts, UPC has been leading inside the IGS frame, and made a first implementation, of a new real-time combined map.La recerca realitzada en aquesta tesis en format compendi d’articles esta enfocada en la generació i validació de mapes ionosfèrics globals (GIM, del angles Global Ionospheric Maps). En resum, la novetat i unitat temàtica d’aquesta tesis esta basada en quatre temes diferents però complementaris: • Definició d’un procediment sistemàtic per validar i quantificar la qualitat dels GIMs basada en fonts de dades o tècniques independents. • Aplicar aquesta metodologia no nomes als GIMs generats a UPC, sinó també a la resta de GIMs d’accés obert actualment existent dintre la comunitat científica internacional. • Incloure en el processat per generar els GIMs de UPC dades de les noves constel·lacions GNSS (del angles Global Navigation Satellite Systems) disponibles. • Validació i distribució també dels GIMs en temps real. Com a conseqüència, també s’ha aconseguit generar un primer GIM combinat en temps real. Mes en detall, la meva primera contribució va ser definir un procediment complet de validació de GIM. Aquest procediment esta basat en dos mètodes: obtenció directa del contingut vertical total d’electrons (VTEC, del angles, Vertical Total Electron Content) a partir de dades d’altimetria i per diferencies del contingut total d’electrons (TEC, del angles Total Electron Content) inclinat de dades GNSS. Els dos donen informació complementaria de la qualitat dels GIM. L’avantatge principal d’utilitzar dades de satèl·lits altimètrics es que es una font de dades completament diferent de les que s’utilitzen per la generació dels GIMs. Aquest fet ens permet verificar el TEC des d’una perspectiva diferent, plenament independent de qualsevol font d’error que pugui afectar al propi sistema GNSS o el seu processat. El segon mètode, es basa en la mateix tipus de dades que s’utilitzen pel càlcul dels GIM però en aquest cas amb dades d’estacions permanent GNSS no involucrades en la generació dels GIMs a avaluar. L’avantatge principal d’aquest segon mètodes es doble: primer, permet avaluar el GIM sobre els continents; i segon, permet fer la anàlisis directa de baixa latència del GIM, a mes a mes donant informació directa sobre el processat i la interpolació aplicada sobre les dades GNSS. Seguidament, la meva segona contribució va ser utilitzar la metodologia prèviament definida per validar tots els GIM generats per part dels centres d’anàlisis associats al Servei Internacional de GNSS (IGS, del angles International GNSS Service) i altres centres candidats a unir-se a IGS, per mes d’un cicle solar (des de finals del 2001 fins al inici del 2017). Com a resultat secundari, també va permetre demostrar que per una banda l’interval temporal dels GIM te poca influencia sobre la seva qualitat global, però per altra banda la tècnica d’interpolació emprada per part dels centres te un impacte molt important. Finalment, aquest article va portar a l’admissió d’aquests candidats prèviament mencionats a centres d’anàlisis associats a IGS donat que es va demostrar la bona qualitat dels seus GIMs. Una altra contribució important va ser, com a part del projecte europeu GRC, millorar el software TOMION (TOMographic IONospheric) de UPC, actualment en producció generant el GIM UQRG (GIM ràpid de UPC). Aquest software nomes permetia utilitzar dades de GPS L1 i L2. Les millores realitzades durant aquesta tesis permeten processar totes les freqüències actualment existent de GPS, Galileo i Beidou. El software ha estat internament validat per certs dies específics amb el mètode explicat prèviament d’altimetria millorant els resultats en comparació a la versió anterior per certes combinacions de constel·lacions GNSS i freqüències. Utilitzant aquesta nova metodologia de processat aplicada a una sola freqüència, un últim article va ser publicat analitzant l’empremta ionosfèrica de l’eclipsi solar sobre Amèrica del nord durant el 2017. Finalment, una altre contribució va ser millorar el mètode d’adquisició i distribució del sistema de processat del GIM en temps real. Es mes, com a part de la contribució de la UPC, es va realitzar una validació dels GIMs generats pels participants del grup de treball de monitorització en temps real de la ionosfera (RTIM-WG, del angles Real Time Ionospheric Monitoring Working Group) de l’Associació Internacional de Geodèsia (IAG, del angles International Association of Geodesy) seguint la metodologia anteriorment citada. Com a resultat d’aquestes tasques la UPC ha liderat i mplementat un nou mapa combinat en temps real, en el marc de IGS.Postprint (published version

Global ionospheric maps : estimation and assessment in post-processing and real-time

The research of this paper-based dissertation is focused on Global Ionospheric Maps (GIM) generation and assessment. In summary, the novelty and thematic unity in this works relies on four different but complementary topics: 1. Defining a systematic procedure to validate and quantify the quality of GIMs based on independent data sources or techniques. 2. Applying this methodology to not only the GIMs computed at UPC, but also to most of the currently open accessible GIMs inside the scientific community. 3.Including newly available Global Navigation Satellite Systems (GNSS) data to the processing of UPC's GIMs. 4. Assessment and distribution also of real-time GIMs. More in detail, my first contribution has been to the definition of a complete GIM validation procedure. This procedure is based on two methods: direct VTEC (Vertical Total Electron Content) altimeter and GNSS difference of slant TEC (Total Electron Content), both of them giving complementary information of the GIM performance. The main advantage of using satellite altimeter data is the fact that we are using a truly independent information source with regard to the input data used for GIM generation. This allows assessing the TEC from a entirely different point-of-view, fully different and independent to any error that may affect GNSS systems and its processing. The second technique, relies on using the same type of input data but in this case from permanent GNSS stations not participating in the GIM generation. The main advantages of this second technique is twofold: first, it allows to asses the GIMs on land; and second its a low latency direct assessment of the GIM, given a more direct information about the processing and interpolation done with the GNSS input data. Afterwards, a second contribution has been to use the previously defined methodology to validate all the GIMs generated by the International GNSS Service (IGS) Associated Analysis Centers (IAAC), and some other candidates to join them, for a more than a full solar cycle (starting from end of 2001 to beginning of 2017). As a side result, it is also demonstrated that while the time interval of the GIM has little influence on its overall quality, the interpolation technique used by the IAACs has an important role. Finally, this work also lead to the acceptance of the previously mentioned IAAC candidates since it demonstrated the good quality of their GIMs. Another contribution has been, as part of the European GRC project, improving the currently in production UPC's TOMION (TOMographic IONospheric) software used to generate the UQRG (UPC's rapid GIM) map. The software input source data was restricted to GPS L1 and L2. Now it allows processing all current frequencies available for GPS, Galileo and Beidou. This software has been internally tested for some specific days with the previously explained altimeter method giving results with improved quality for specific combinations of GNSS systems and frequencies. Using this work flow but focused on single frequency processing, a last article was published analysing the ionospheric footprint of the solar eclipse over North America during 2017. Finally, another contribution has been to improve the data acquisition and distribution system for the real-time GIM generation processing chain. Furthermore, as part of UPC contribution to the Real Time Ionospheric Monitoring Working Group (RTIM-WG) of the International Association of Geodesy (IAG) and following the previously explained methodology, an assessment of the GIMs generated by the members of this sub-commission have been performed. As a result of all these efforts, UPC has been leading inside the IGS frame, and made a first implementation, of a new real-time combined map.La recerca realitzada en aquesta tesis en format compendi d’articles esta enfocada en la generació i validació de mapes ionosfèrics globals (GIM, del angles Global Ionospheric Maps). En resum, la novetat i unitat temàtica d’aquesta tesis esta basada en quatre temes diferents però complementaris: • Definició d’un procediment sistemàtic per validar i quantificar la qualitat dels GIMs basada en fonts de dades o tècniques independents. • Aplicar aquesta metodologia no nomes als GIMs generats a UPC, sinó també a la resta de GIMs d’accés obert actualment existent dintre la comunitat científica internacional. • Incloure en el processat per generar els GIMs de UPC dades de les noves constel·lacions GNSS (del angles Global Navigation Satellite Systems) disponibles. • Validació i distribució també dels GIMs en temps real. Com a conseqüència, també s’ha aconseguit generar un primer GIM combinat en temps real. Mes en detall, la meva primera contribució va ser definir un procediment complet de validació de GIM. Aquest procediment esta basat en dos mètodes: obtenció directa del contingut vertical total d’electrons (VTEC, del angles, Vertical Total Electron Content) a partir de dades d’altimetria i per diferencies del contingut total d’electrons (TEC, del angles Total Electron Content) inclinat de dades GNSS. Els dos donen informació complementaria de la qualitat dels GIM. L’avantatge principal d’utilitzar dades de satèl·lits altimètrics es que es una font de dades completament diferent de les que s’utilitzen per la generació dels GIMs. Aquest fet ens permet verificar el TEC des d’una perspectiva diferent, plenament independent de qualsevol font d’error que pugui afectar al propi sistema GNSS o el seu processat. El segon mètode, es basa en la mateix tipus de dades que s’utilitzen pel càlcul dels GIM però en aquest cas amb dades d’estacions permanent GNSS no involucrades en la generació dels GIMs a avaluar. L’avantatge principal d’aquest segon mètodes es doble: primer, permet avaluar el GIM sobre els continents; i segon, permet fer la anàlisis directa de baixa latència del GIM, a mes a mes donant informació directa sobre el processat i la interpolació aplicada sobre les dades GNSS. Seguidament, la meva segona contribució va ser utilitzar la metodologia prèviament definida per validar tots els GIM generats per part dels centres d’anàlisis associats al Servei Internacional de GNSS (IGS, del angles International GNSS Service) i altres centres candidats a unir-se a IGS, per mes d’un cicle solar (des de finals del 2001 fins al inici del 2017). Com a resultat secundari, també va permetre demostrar que per una banda l’interval temporal dels GIM te poca influencia sobre la seva qualitat global, però per altra banda la tècnica d’interpolació emprada per part dels centres te un impacte molt important. Finalment, aquest article va portar a l’admissió d’aquests candidats prèviament mencionats a centres d’anàlisis associats a IGS donat que es va demostrar la bona qualitat dels seus GIMs. Una altra contribució important va ser, com a part del projecte europeu GRC, millorar el software TOMION (TOMographic IONospheric) de UPC, actualment en producció generant el GIM UQRG (GIM ràpid de UPC). Aquest software nomes permetia utilitzar dades de GPS L1 i L2. Les millores realitzades durant aquesta tesis permeten processar totes les freqüències actualment existent de GPS, Galileo i Beidou. El software ha estat internament validat per certs dies específics amb el mètode explicat prèviament d’altimetria millorant els resultats en comparació a la versió anterior per certes combinacions de constel·lacions GNSS i freqüències. Utilitzant aquesta nova metodologia de processat aplicada a una sola freqüència, un últim article va ser publicat analitzant l’empremta ionosfèrica de l’eclipsi solar sobre Amèrica del nord durant el 2017. Finalment, una altre contribució va ser millorar el mètode d’adquisició i distribució del sistema de processat del GIM en temps real. Es mes, com a part de la contribució de la UPC, es va realitzar una validació dels GIMs generats pels participants del grup de treball de monitorització en temps real de la ionosfera (RTIM-WG, del angles Real Time Ionospheric Monitoring Working Group) de l’Associació Internacional de Geodèsia (IAG, del angles International Association of Geodesy) seguint la metodologia anteriorment citada. Com a resultat d’aquestes tasques la UPC ha liderat i mplementat un nou mapa combinat en temps real, en el marc de IGS.Postprint (published version

Global distribution of ionospheric scintillations from the Real-Time GPS ROTI

A global real-time monitoring system has been implemented in the frame of ESA-ESTEC/EGNOS-POfunded project MONITOR. It is based on world-wide GNSS datastreams distributed by means of NTRIP and provides multiple ionospheric indices and products to the scientific community and industry. In particular, the Rate Of Total Electron Content Index (ROTI) proxy, which is correlated with scintillation activity and has been running for several years for real-time detection and monitoring. It shall also be pointed out that the multiple products, also aiming at the identification of Travelling Ionospheric Disturbances (TIDs), Solar Flares overionization, among other ionospheric perturbations, are useful to properly characterize scenarios where these could occur simultaneously to scintillations. In addition, there is also a new proxy suitable for radio-occultation GNSS measurements, named OSPI. In this context, a climatological ionospheric scintillation study has been conducted in different latitudinal regions from the UPC-IonSAT database of global ROTI. For this purpose, we have obtained results from several receivers in 30-degree latitudinal strips and distinguishing between North- and South-Hemisphere locations.Postprint (published version

Design of a camera for the Image Stabilization System for the Solar Orbiter project

Diseño del hardware y firmware para una cámara de correlación apta para un proyecto del espacio.[ANGLÈS] The Correlation Tracking Camera (CTC) is a high frame rate low resolution camera. It is used by the Image Stabilization System (ISS), which function is to detect and correct the jitter introduced by the spacecraft. The CTC provides images which are processed by the ISS using a correlation tracking algorithm and it detects displacements with subpixel resolution. Based on its results a mirror is tipped and tilted, in order to stabilize the image position for the FPA (Focal Plane Assembly) image cameras. The FPA will provide high-resolution and full-disk measurements of the photospheric magnetic field, goal of the Polarimetric and Helioseismic Imager (PHI) instrument of the Solar Orbiter mission.[CASTELLÀ] Diseño del hardware y firmware para una cámara de correlación apta para un proyecto del espacio.[CATALÀ] Disseny del hardware i firmware per una càmara de correlació apta per un projecte del espai

Disseny d'una càmera pel sistema d'estabilització d'imatges del projecte Solar Orbiter

Projecte Final de Carrera d'Enginyeria Electrònica, Universitat de Barcelona, Facultat de Física. Director: Gómez Cama, José María. Any: 201

The polarimetric and helioseismic imager on solar orbiter

This paper describes the Polarimetric and Helioseismic Imager on the Solar Orbiter mission (SO/PHI), the first magnetograph and helioseismology instrument to observe the Sun from outside the Sun-Earth line. It is the key instrument meant to address the top-level science question: How does the solar dynamo work and drive connections between the Sun and the heliosphere? SO/PHI will also play an important role in answering the other top-level science questions of Solar Orbiter, as well as hosting the potential of a rich return in further science. SO/PHI measures the Zeeman effect and the Doppler shift in the FeI 617.3nm spectral line. To this end, the instrument carries out narrow-band imaging spectro-polarimetry using a tunable LiNbO_3 Fabry-Perot etalon, while the polarisation modulation is done with liquid crystal variable retarders (LCVRs). The line and the nearby continuum are sampled at six wavelength points and the data are recorded by a 2kx2k CMOS detector. To save valuable telemetry, the raw data are reduced on board, including being inverted under the assumption of a Milne-Eddington atmosphere, although simpler reduction methods are also available on board. SO/PHI is composed of two telescopes; one, the Full Disc Telescope (FDT), covers the full solar disc at all phases of the orbit, while the other, the High Resolution Telescope (HRT), can resolve structures as small as 200km on the Sun at closest perihelion. The high heat load generated through proximity to the Sun is greatly reduced by the multilayer-coated entrance windows to the two telescopes that allow less than 4% of the total sunlight to enter the instrument, most of it in a narrow wavelength band around the chosen spectral line

High-resolution ionosphere corrections for single-frequency positioning

The ionosphere is one of the main error sources in positioning and navigation; thus, information about the ionosphere is mandatory for precise modern Global Navigation Satellite System (GNSS) applications. The International GNSS Service (IGS) and its Ionosphere Associated Analysis Centers (IAAC) routinely provide ionospheric information in terms of global ionosphere maps (final GIM). Typically, these products are modeled using series expansion in terms of spherical harmonics (SHs) with a maximum degree of n=15 and are based on post processed observations from Global Navigation Satellite Systems (GNSS), as well as final satellite orbits. However, precise applications such as autonomous driving or precision agriculture require real-time (RT) information about the ionospheric electron content with high spectral and spatial resolution. Ionospheric RT-GIMs are disseminated via Ntrip protocol using the SSR VTEC message of the RTCM. This message can be streamed in RT, but it is limited for the dissemination of coefficients of SHs of lower degrees only. It allows the dissemination of SH coefficients up to a degree of n=16. This suits to most the SH models of the IAACs, but higher spectral degrees or models in terms of B-spline basis functions, voxels, splines and many more cannot be considered. In addition to the SHs, several alternative approaches, e.g., B-splines or Voxels, have proven to be appropriate basis functions for modeling the ionosphere with an enhanced resolution. Providing them using the SSR VTEC message requires a transfer to SHs. In this context, the following questions are discussed based on data of a B-spline model with high spectral resolution; (1) How can the B-spline model be transformed to SHs in order to fit to the RTCM requirements and (2) what is the loss of detail when the B-spline model is converted to SHs of degree of n=16? Furthermore, we discuss (3) what is the maximum necessary SH degree n to convert the given B-spline model and (4) how can the transformation be performed to make it applicable for real-time applications? For a final assessment, we perform both, the dSTEC analysis and a single-frequency positioning in kinematic mode, using the transformed GIMs for correcting the ionospheric delay. The assessment shows that the converted GIMs with degrees n=30 coincide with the original B-spline model and improve the positioning accuracy significantly.Peer ReviewedPostprint (published version

Methodology and consistency of slant and vertical assessments for ionospheric electron content models

The final publication is available at Springer via http://dx.doi.org/10.1007/s00190-017-1032-zA summary of the main concepts on global ionospheric map(s) [hereinafter GIM(s)] of vertical total electron content (VTEC), with special emphasis on their assessment, is presented in this paper. It is based on the experience accumulated during almost two decades of collaborative work in the context of the international global navigation satellite systems (GNSS) service (IGS) ionosphere working group. A representative comparison of the two main assessments of ionospheric electron content models (VTEC-altimeter and difference of Slant TEC, based on independent global positioning system data GPS, dSTEC-GPS) is performed. It is based on 26 GPS receivers worldwide distributed and mostly placed on islands, from the last quarter of 2010 to the end of 2016. The consistency between dSTEC-GPS and VTEC-altimeter assessments for one of the most accurate IGS GIMs (the tomographic-kriging GIM ‘UQRG’ computed by UPC) is shown. Typical error RMS values of 2 TECU for VTEC-altimeter and 0.5 TECU for dSTEC-GPS assessments are found. And, as expected by following a simple random model, there is a significant correlation between both RMS and specially relative errors, mainly evident when large enough number of observations per pass is considered. The authors expect that this manuscript will be useful for new analysis contributor centres and in general for the scientific and technical community interested in simple and truly external ways of validating electron content models of the ionosphere.Peer ReviewedPostprint (author's final draft

Precise ionospheric electron content monitoring from single-frequency GPS receivers

The number of existing global positioning system (GPS) single-frequency receivers continues growing. More than 90% of GPS receivers are implemented as low-cost single-frequency chipsets embedded in smartphones. This provides new opportunities, in particular for ionospheric sounding. In this context, we present the new sidereal days ionospheric graphic (SIg) combination of single-frequency GNSS measurements. SIg is able to monitor, for each given GNSS transmitter-receiver pair, the vertical total electron content (VTEC) relative to the previous observation with the same or almost the same line-of-sight (LOS) vector. In such arrangements the SIg multipath error mostly cancels, thus increasing the accuracy of the ΔVTEC significantly. This happens for the GPS constellation after one sidereal day (about 23 h 56 m) and for Galileo after 10 sidereal days approximately. Moreover, we show that the required calibration of the corresponding carrier phase ambiguity can be accurately performed by means of VTEC global ionospheric maps (GIMs). The results appear almost as accurate as those based on the dual-frequency technique, i.e., about 1 TECU or better, and with much more precision and resolution than the GIM values in the ionospheric region sounded by each given single-frequency receiver. The performance is demonstrated using actual data from 9 permanent GPS receivers during a total solar eclipse on August 21, 2017 over North America, where the corresponding ionospheric footprint is clearly detected in agreement with the total solar eclipse predictions. The advantages of extending SIg to lower carrier frequencies and the feasibility of applying it to other global navigation satellite system (GNSS) systems are also studied. This is shown in terms of a fully consistent VTEC depletion signature of the same eclipse phenomena, obtained with Galileo-only data in North America at mid and low latitude. Finally the SIg feasibility, including the cycle slip detection, is shown as well with actual mass-market single frequency GPS receivers at mid and high latitude

Precise ionospheric electron content monitoring from single- frequency GPS receivers

This is a post-peer-review, pre-copyedit version of an article published in Gps solutions. The final authenticated version is available online at: http://dx.doi.org/10.1007/s10291-018-0767-1The number of existing global positioning system (GPS) single-frequency receivers continues growing. More than 90% of GPS receivers are implemented as low-cost single-frequency chipsets embedded in smartphones. This provides new opportunities, in particular for ionospheric sounding. In this context, we present the new sidereal days ionospheric graphic (SIg) combination of single-frequency GNSS measurements. SIg is able to monitor, for each given GNSS transmitter–receiver pair, the vertical total electron content (VTEC) relative to the previous observation with the same or almost the same line-of-sight (LOS) vector. In such arrangements the SIg multipath error mostly cancels, thus increasing the accuracy of the ¿VTEC significantly. This happens for the GPS constellation after one sidereal day (about 23 h 56 m) and for Galileo after 10 sidereal days approximately. Moreover, we show that the required calibration of the corresponding carrier phase ambiguity can be accurately performed by means of VTEC global ionospheric maps (GIMs). The results appear almost as accurate as those based on the dual-frequency technique, i.e., about 1 TECU or better, and with much more precision and resolution than the GIM values in the ionospheric region sounded by each given single-frequency receiver. The performance is demonstrated using actual data from 9 permanent GPS receivers during a total solar eclipse on August 21, 2017 over North America, where the corresponding ionospheric footprint is clearly detected in agreement with the total solar eclipse predictions. The advantages of extending SIg to lower carrier frequencies and the feasibility of applying it to other global navigation satellite system (GNSS) systems are also studied. This is shown in terms of a fully consistent VTEC depletion signature of the same eclipse phenomena, obtained with Galileo-only data in North America at mid and low latitude. Finally the SIg feasibility, including the cycle slip detection, is shown as well with actual mass-market single frequency GPS receivers at mid and high latitude.Peer ReviewedPostprint (author's final draft