DSpace Collection:
http://hdl.handle.net/2117/1129
20150427T05:49:57ZA realtime worldwide ionospheric model for single and multifrequency precise navigation
http://hdl.handle.net/2117/27516
Title: A realtime worldwide ionospheric model for single and multifrequency precise navigation
Authors: Rovira Garcia, Adrià; Juan Zornoza, José Miguel; Sanz Subirana, Jaume
Abstract: The ionosphere plays an important role in satellitebased navigation, either in standard navigation, with single frequency massmarket receivers, or in precise navigation, with dual frequency receivers.
In this work, the requirements of a realtime ionospheric model suitable for GNSS applications are explored, in terms of accuracy and confidence bounds. Key factors for an ionospheric determination better than 1 Total Electron Content Unit (TECU) (16 centimeters in L1) are shown to be whether the model has been derived using an ambiguityfixing strategy and the number of layers used to reproduce the ionospheric delay. Different models are assessed both in midlatitudes and equatorial regions, near the Solar Cycle maximum.
It will be shown how dualfrequency users take benefit from a precise modelling of the ionosphere. If accurate enough, the convergence of the navigation filter is reduced to achieve high accuracy positioning quickly, (i.e., the Fast Precise Point Positioning technique). Satellite orbits and clocks computed for FastPPP will be shown to be accurate to few centimeters and few tenths of nanoseconds, respectively.
Singlefrequency users correct its measurements with the predictions provided by any ionospheric model. Thence, the accuracy of the FastPPP ionospheric corrections is directly translated to the measurements modelling and, consequently, to the user solution.
Horizontal and vertical 95% accuracies are shown to be better than 36 and 63 centimeters for singlefrequency users and 11 and 15 centimeters for dualfrequency users. The assessment is done for several locations, including the equatorial region, for a month of data close to the last Solar Maximum. The tradeoff between the formal and actual positioning errors has been carefully studied by means of the Stanford plots to set realistic confidence bounds to the corrections.20150422T12:46:58ZExperiments on the Ionospheric Models in GNSS
http://hdl.handle.net/2117/22728
Title: Experiments on the Ionospheric Models in GNSS
Authors: Vinh, La The; Quang, Phuong Xuan; García Rigo, Alberto; Rovira Garcia, Adrià; Ibáñez Segura, Marcos  Deimos
Abstract: In GNSS, one of the main error sources of the Standard Positioning Service (SPS) is introduced by the ionosphere.
Although
this error can be cancelled by combining two signals at different
frequencies, most of the single

frequency
mass

market receivers do not benefit from this cancel
l
ation. For that reason, a set of parameter
s
is included in the navigation
message in order to compute the ionospheric delay of any observation by the
Klobuchar model. The Klobuchar model is a very
simple model that is able to remove more than the 50% of the ionospheric delay.
Recently, more accurate ionospheric models
have been introduced such as Global Ionospheric Map (GIM) or the
F
ast
P
recise
P
oint
P
ositioning
(
F
PPP
) ionospheric model.
In previous works, with data gathered in Europe, it was shown the advantage of the
F
PPP’s ionospheric model. In this work,
we conduct experiments
to compare the performance of different ionospheric
modelling
methods including: Klobuchar, GIM
s
and
F
PPP. Our preliminary results show how
F
PPP and GIM
s
lead to better positioning precisions compared to the Klobuchar
model. However, since data is not wide enough to cover different ionospheric cond
itions, more experiments will be
carried out
in our future work to validate the current result
s
.20140428T12:39:21ZFast Precise Point Positioning based on realtime ionospheric modelling
http://hdl.handle.net/2117/22338
Title: Fast Precise Point Positioning based on realtime ionospheric modelling
Authors: Juan Zornoza, José Miguel; Hernández Pajares, Manuel; Sanz Subirana, Jaume; Samson, Jaron; Tossaint, Michel Mathias Maria
Abstract: Summary of main results of new technique Fast Precise Point Positioning developed in the framework of the “Enhanced Precise Point Positioning (EPPP) GNSS multifrequency user algorithm” ESA funded project.
The precise ionospheric corrections facilitate the resolution of undifferenced carrier phase ambiguities, ambiguity validation and integrity monitoring.
The FPPP performance is shown in terms of accuracy, convergence time and integrity, with actual GPS and simulated Galileo data.
Very limited bandwidth requirements for future EPPP users (less than 300 bps for dualfrequency GPS data).20140321T16:20:20ZFast Precise Point Positioning for decimetererrorlevel navigation for multi and singlefrequency users of Global Navigation Satellite Systems
http://hdl.handle.net/2117/22336
Title: Fast Precise Point Positioning for decimetererrorlevel navigation for multi and singlefrequency users of Global Navigation Satellite Systems
Authors: Juan Zornoza, José Miguel; Hernández Pajares, Manuel; Sanz Subirana, Jaume; Samson, J.; Tossaint, M.
Abstract: This manuscript summarizes the new algorithm of Fast Precise Point Positioning (FPPP) the developed during the projects "Enhanced PPP GNSS multifrequency user algorithm" nd “Precise Real Time Orbit Determination and Time synchronisation”, both funded by the European Space Agency (ESA). The main innovations achieved during the overall project comprise the application of precise ionospheric corrections to facilitate the fast resolution of undifferenced carrier phase ambiguities, ambiguity validation and integrity monitoring for both multi and singlefrequency users. Among the integrity, detailed in previous works, the performance of the FPPP algorithm in terms of improved accuracy and convergence time is demonstrated with actual GPS and simulated Galileo data. The 10centimeters error level realtime kinematic positioning can be achieved in few minutes for dualand singlefrequency users, almost instantaneous for threefrequency users (or once the tropospheric delay is well estimated in few minutes in cold start), and with very limited bandwidth requirements for the FPPP users (less than 300 bps for dualfrequency GPS).20140321T16:01:06ZSolar EUV flux rate estimation during mid and strong flares from the ionospheric electron content response signature in GNSS observations
http://hdl.handle.net/2117/22153
Title: Solar EUV flux rate estimation during mid and strong flares from the ionospheric electron content response signature in GNSS observations
Authors: Hernández Pajares, Manuel; García Rigo, Alberto; Juan Zornoza, José Miguel; Sanz Subirana, Jaume; Monte Moreno, Enrique; Aragón Ángel, María Ángeles
Abstract: A simple and precise technique to measure the sudden Extreme Ultraviolet (EUV) radiation increase of the Sun, during mid and strong flares, has been formulated and demonstrated for the most active part of the last Solar Cycle. On the one hand, it is based on the short time scale of these events, which allows the validity of a simple global overionization model. And on the other hand on the prompt ionospheric response to the EUV ionization, which signature (in terms of the Global Navigation Satellite Systems GNSSSolar Flare Activity Indicator, GSFLAI) is accurately measured in realtime from the existing global networks of dualfrequency GNSS receivers, and with a time resolution higher that those of dedicated space probes. Moreover the sensitivity of this approach enables the detection of not only extreme Xclass flares, but also the detection of variations of one order of magnitude lower or even smaller (such as for Mclass flares): 100% successful detection for all the Xclass solar flares during 20002006 with registered location outside of the solar limb (i.e. detection of 94% of all of Xclass solarflares) and about 65% for Mclass ones, obtained with the associated SISTED detector. In summary, its full availability, continuity, high precision and integrity for mid and high solar flare effects on Ionosphere, can make GSFLAI an useful indicator of potential Space Weather activity for many users in radio propagation. These results, which have been recently published by the authors, are extended in this work up to one complete solar cycle, and using a lower sampling rate (30 seconds), demonstrating the better behaviour of this indirect solar EUV variability proxy (GSFLAI30), when comparisons are made with direct measurements from space probes, providing readings which can be affected by the late enhancement of particles.20140317T13:19:16ZDefinition of an SBAS ionospheric activity indicator and its assessment over Europe and Africa During the last solar cycle
http://hdl.handle.net/2117/22085
Title: Definition of an SBAS ionospheric activity indicator and its assessment over Europe and Africa During the last solar cycle
Authors: Sanz Subirana, Jaume; Juan Zornoza, José Miguel; Hernández Pajares, Manuel; Prieto Cerdeira, Roberto; Schlueter, Stefan
Abstract: In this work, an ionospheric activity indicator is defined based in the “weighted” Along Arc TEC rate (AATR). It is shown that this indicator, which can be easily computed from the GPS carrier phases, is well correlated with the ionospheric activity and, unlike other global indicators linked to the geomagnetic activity, can be sensitive to regional behaviours of ionospheric activity20140314T16:48:26ZCharacterization and modelling of the ionosphere for EGNOS development and qualification
http://hdl.handle.net/2117/22082
Title: Characterization and modelling of the ionosphere for EGNOS development and qualification
Authors: Schlüter, S.; Prieto Cerdeira, Roberto; Orús Pérez, Raul; Lam, J.P.; Juan Zornoza, José Miguel; Sanz Subirana, Jaume; Hernández Pajares, Manuel
Abstract: The availability of representative data samples, models and statistical information derived from the analysis of parameters that adequately describe the state of the ionosphere are key elements for the design, verification and qualification of EGNOS algorithms. As part of the ongoing evolutions of EGNOS V2 releases, and also in
support to the development of a future multiconstellation and dualfrequency SBAS (EGNOS V3), ESA has started a refinement process of the tools, data and precise definition of the ionospheric operational conditions. A particular driver for this process is the improvement of the availability performance of the current and future system especially under solar max and severe ionospheric conditions, without
degradation of integrity and accuracy performances. The paper provides an overview about the concept and the data and models used for EGNOS development and qualification. It outlines the approaches to generate reference models and describes the parameter used for the characterization of nominal and perturbed ionospheric conditions from an SBAS perspective.20140314T15:53:04ZImpact of higher order ionospheric delay on precise GNSS computation
http://hdl.handle.net/2117/22065
Title: Impact of higher order ionospheric delay on precise GNSS computation
Authors: Hernández Pajares, Manuel; Aragón Ángel, María Ángeles; Defraigne, Pascale; Bergeot, Nicolas; Prieto Cerdeira, Roberto; Sanz Subirana, Jaume20140314T12:52:30ZThe shape of a galaxy is not much influenced by the potential as it might seem
http://hdl.handle.net/2117/21962
Title: The shape of a galaxy is not much influenced by the potential as it might seem
Authors: Cubarsí Morera, Rafael
Abstract: The dynamics of a galaxy as a stellar system in statistical equilibrium is usually obtained from the superposition principle, based on the linearity of the Boltzmann collisionless equation (BCE) in regard to the phase space density function. The term statistical equilibrium is a notion coming from statistical dynamics, although, from an analytical dynamics viewpoint, it should be associated with an invariant (conservative) density function under the BCE in the phase space. Similarly, dissipative forces like dynamical friction, which are essential to statistical dynamics, emerge in analytical dynamics via non steadystate phase density functions and/or potentials as solutions of the BCE. When some kinematic knowledge about the stellar integrals of motion or the velocity distribution function is already known, Jeans’ inverse problem leads, from an statistical viewpoint, to the most probable timedependent potential function. For a mixture of several galactic components, the natural approach is the Jeans’ inverse problem, by associating a generalised quadratic velocity distribution with each stellar population. The BCE relates the dynamics of each stellar population to a potential, which is shared by all of the population components. The coexistence of several stellar populations introduces integrability conditions of consistency for a population mixture, that forces the potential function to adopt a relatively simple functional form, while the velocity distribution function has a higher number of degrees of freedom. Due to the conditions of consistency, axially symmetric potentials are proven to be still suitable to describe nonaxially symmetric conservative stellar systems. A paradigm of this situation is the pointaxial symmetry model, build for mass and velocity distributions to allow spiral or bar structures. The BCE yields an axially symmetric potential, although the mass and velocity distributions still maintain pointaxial symmetry.20140310T12:12:06ZIonospheric activity in the South East Asian region
http://hdl.handle.net/2117/20963
Title: Ionospheric activity in the South East Asian region
Authors: Juan Zornoza, José Miguel; Sanz Subirana, Jaume; Prieto, Roberto; Schlueter, Stefan
Abstract: A SBAS Ionospheric Activity indicator, based in the RMS of Along Arc TEC Rate (AATR) computations has been defined by the gAGE/UPC authors in the context of previous studies on EGNOS Ionosphere. This indicator can be easily computed from GNSS data and, unlike other global indices which are related with the geomagnetic activity, it is sensible to the regional behaviour of the ionosphere.
After a deep assessment done over Europe and Africa during the last Solar Cycle, this AATR indicator has been chosen as the metric to characterise the ionospheric operational conditions in the frame of ESA EGNOS activities (EGNOS V3 Mission Requirements).
In this work we summarise the results of the application of the AATR indicator to the analysis of the ionospheric activity during an entire Solar Cycle in the South of Asia (SEA) Region. This region has special interest from the ionospheric point of view, because the larger Slant Total Electron Content (STEC) values and gradients experienced due to its proximity to the ionospheric equatorial anomaly.20131210T16:09:05ZPlasmaspheric Electron Content contribution inferred from ground and radio occultation derived Total Electron Content
http://hdl.handle.net/2117/18480
Title: Plasmaspheric Electron Content contribution inferred from ground and radio occultation derived Total Electron Content
Authors: Aragón Ángel, María Ángeles; Sanz Subirana, Jaume; Juan Zornoza, José Miguel; Hernández Pajares, Manuel; Altadill, D.
Abstract: The FORMOSAT3/COSMIC satellite constellation
has become an important source of remote sensing data globally
distributed for the sounding of the atmosphere of the Earth and,
in particular, the ionosphere. In this study, electron density
profiles derived using the Improved Abel transform inversion in
Radio Occultation (RO) scenarios are used as input data to
derive some features regarding the topside and outside
ionospheric contribution, hence, the plasmasphere in great
extend, by means of the analysis of the integral values of the
shape functions corresponding to each density profile. The
novelty presented in this paper, with respect to previous works, is
the use of experimental data from the FORMOSAT3/COSMIC
ROderived electron densities to infer global characterizations
and distribution of the Total Electron Content (TEC) into its
main components: ionospheric TEC and plasmaspheric TEC,
both contributing to TEC. The results show agreement with
earlier modeled and observational data from previous local
studies of the plasmaspheric contribution. The main conclusion
of this research is that the plasmasphere contributes significantly
to TEC and the ratio between plasmaspheric TEC and TEC has
been climatologically analyzed for the whole year 2007
confirming that the major relative impact of the plasmasphere is
during night time. The added value of this study is that the
results obtained are globally distributed and can help to infer a
proxy for the plasmaspheric contribution at any location over the
globe thanks to the FORMOSAT3/COSMIC coverage.20130322T10:59:58ZReal time Ionospheric determination at global scale
http://hdl.handle.net/2117/15912
Title: Real time Ionospheric determination at global scale
Authors: Hernández Pajares, Manuel; Sanz Subirana, Jaume; García Rigo, Alberto
Abstract: The global ionospheric determination has been possible in the last 15 years thanks to the availability of
a new type of ionospheric sensor with a very high spatial and temporal sampling: the dualfrequency
GPS receivers. Indeed, several hundreds of them, worldwide distributed, are freely available, tracking
typically 6+ GPS satellites in view, providing at every epoch several thousands of lineofsight integrated
free electron densities (Slant Total Electron Content, STEC). This has allowed in particular to compute
and freely distribute global Vertical Total Electron Content (VTEC) maps, in the context of the open
product organization called International GNSS Service (IGS), which applications run from single frequency
receivers (accurate mitigation of ionospheric delay), calibration of new altimeters (such as the SMOS
mission) up to the potential use for increasing the performance of positioning based on carrier phase
measurements.
One of the next challenges, in particular in IGS, is computing the global VTEC maps, in realtime, which
involves much less permanent receivers, increasing much more the di cult task of interpolating in a realistic
way the electron content over large regions with few receivers (south hemisphere, oceans...).
In this paper the actual status of the problem will be presented, from the perspective of gAGE/UPC, one
of the four IGS Ionospheric Analysis Centers, participating in the RealTime IGS Pilot Project.20120523T11:19:44ZAnalyzing the effect of power control algorithms on the receiver's computing resource consumption
http://hdl.handle.net/2117/12590
Title: Analyzing the effect of power control algorithms on the receiver's computing resource consumption
Authors: Gómez Miguelez, Ismael; Marojevic, Vuk; Salazar Hernández, Dagoberto José; Gelonch Bosch, Antonio José
Abstract: Traditional SoftwareDefined Radios are limited in their ability to share the computational infrastructure between different channel flows of different demands. Future terminals should move to a shared resource model to further improve resource utilization and link availability. For this purpose, an accurate characterization and prediction of the consumed resources by a new user entering the cell is important. At the receiver side, iterative channel decoding algorithms, which exhibit the highest contribution of processing time and energy consumption, consume resources as a function of the signal quality. Therefore, power control has an impact on the computing resources of the receiver. This paper presents a model to characterize the available computing resources of a receiver. This model may be useful for utilitybased power control algorithms.20110518T08:57:01ZOptimal seggregation of a twocomponent sample based on maximim population entropy: an application to astronomy
http://hdl.handle.net/2117/12402
Title: Optimal seggregation of a twocomponent sample based on maximim population entropy: an application to astronomy
Authors: Alcobé López, Santiago; CatalaPoch, M.A.; Cubarsí Morera, Rafael
Abstract: Determination of stellar population parameters from statistics of global samples is extremely sensitive to the noise introduced by few nontypical stars. In order to obtain a nearlypure twopopulation mixture a subsample is drawn from the nearby stars catalogue by applying a noninformative filtering. The method is used to study the trivariate velocity distribution of stars, which can be locally approximated by a superposition of two normal components. Thus, an auxiliar parameter P, depending or not on the velocity variables, such as the absolute velocity referred to the lower population mean, the absolute value of one peculiar velocity component alone, the distance to the galactic plane, etc. is introduced. This parameter must induce an ordered incorporation of stars to the population components, in the sense that the greater the P value, the greater the number of stars in each component, Then a subsample S(P) is drawn from the global one. Depending on this parameter the population entropy H(P) of the mixture is computed from the mixing proportions and an optimal subsample S(P) is selected in order to maximize H(P). On the other hand, for each subsample S(P), the goodness of the superposition approximation is estimated by reconstructing the sample central moments up to fourthorder from the mixture parameters. A chisquare test taking into account the sampling distribution moments, is evaluated to measure the fitting error. For different subsamples S(P) a total accordance between the minimum chisquare and the maximum population entropy H(P) is produced. Furthermore, this method can be used recursively in order to segregate a global sample is more than two populations.20110418T08:28:40ZNoninformative filtering of the local stellar velocity distribution to obtain two nearlypure statistical populations
http://hdl.handle.net/2117/12400
Title: Noninformative filtering of the local stellar velocity distribution to obtain two nearlypure statistical populations
Authors: Cubarsí Morera, Rafael; Alcobé López, Santiago; CatalaPoch, M.A.
Abstract: The determination of stellar population constants from the statistics of a global sample is extremely sensitive to the noise introduced by a few nontypical stars. The local velocity distribution can be better determined from a catalogue of nearby stars including Hipparcos data and by applying a noninformative filtering to the global sample. In order to produce an optimal segregation into two population components an auxiliary parameter P, depending on the distribution of variables such as the absolute velocity referred to the slower subcentroid, is introduced. The parameter must induce an ordered incorporation of stars to the population components, in the sense that the greater the P value, the greater the number of stars in each component. Then a subsample S(P) is drawn from the global one. Depending on this parameter the statistical entropy H(P) of the mixture probability is computed, and the optimal subsample S(P) is selected in order to maximize H(P). The method is applied to segregate the local velocity distribution into two main trivariate normal components (Cubarsi et. al) where a total accordance between the best fit from the chisquared test and the maximum population entropy H(P) is produced. Furthermore the method can be used recursively in order to separate a global sample into more than two populations.20110418T07:57:58Z