gAGE - grup d'Astronomia i GEomàtica
http://hdl.handle.net/2117/1128
2015-11-25T00:35:51ZIonospheric and plasmaspheric electron contents inferred from radio occultations and global ionospheric maps
http://hdl.handle.net/2117/79027
Ionospheric and plasmaspheric electron contents inferred from radio occultations and global ionospheric maps
González Casado, Guillermo; Juan Zornoza, José Miguel; Sanz Subirana, Jaume; Rovira Garcia, Adrià; Aragón Angel, Angela
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.
2015-11-11T13:07:44ZGonzález Casado, GuillermoJuan Zornoza, José MiguelSanz Subirana, JaumeRovira Garcia, AdriàAragón Angel, AngelaWe 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.Conditions of consistency for multicomponent stellar systems. II. Is a point-axial symmetric model suitable for the Galaxy?
http://hdl.handle.net/2117/28482
Conditions of consistency for multicomponent stellar systems. II. Is a point-axial symmetric model suitable for the Galaxy?
Cubarsí Morera, Rafael
Under a common potential, a finite mixture of ellipsoidal velocity distributions satisfying the Boltzmann collisionless
equation provides a set of integrability conditions that may constrain the population kinematics. They are referred to as
conditions of consistency and were discussed in a previous paper on mixtures of axisymmetric populations. As a corollary,
these conditions are now extended to point-axial symmetry, that is, point symmetry around the rotation axis or bisymmetry,
by determining which potentials are connected with a more flexible superposition of stellar populations. Under point-axial
symmetry, the potential is still axisymmetric, but the velocity and mass distributions are not necessarily. A point-axial stellar
system is, in a natural way, consistent with a flat velocity distribution of a disc population. Therefore, no additional integrability
conditions are required to solve the Boltzmann collisionless equation for such a population. For other populations, if the
potential is additively separable in cylindrical coordinates, the populations are not kinematically constrained, although under
point-axial symmetry, the potential is reduced to the harmonic function, which, for the Galaxy, is proven to be non-realistic.
In contrast, a non-separable potential provides additional conditions of consistency. When mean velocities for the populations
are unconstrained, the potential becomes quasi-stationary, being a particular case of the axisymmetric model. Then, the radial
and vertical mean velocities of the populations can differ and produce an apparent vertex deviation of the whole velocity
distribution. However, single population velocity ellipsoids still have no vertex deviation in the Galactic plane and no tilt in
their intersection with a meridional Galactic plane. If the thick disc and halo ellipsoids actually have non-vanishing tilt, as the
surveys of the solar neighbourhood that include RAdial Velocity Experiment (RAVE) data seem to show, the point-axial model
is unable to fit the local velocity distribution. Conversely, the axisymmetric model is capable of making a better approach. If,
in the end, more accurate data confirm a negligible tilt of the populations, then the point-axisymmetric model will be able to
describe non-axisymmetric mass and velocity distributions, although in the Galactic plane the velocity distribution will still be
axisymmetric.
2015-07-01T08:38:01ZCubarsí Morera, RafaelUnder a common potential, a finite mixture of ellipsoidal velocity distributions satisfying the Boltzmann collisionless
equation provides a set of integrability conditions that may constrain the population kinematics. They are referred to as
conditions of consistency and were discussed in a previous paper on mixtures of axisymmetric populations. As a corollary,
these conditions are now extended to point-axial symmetry, that is, point symmetry around the rotation axis or bisymmetry,
by determining which potentials are connected with a more flexible superposition of stellar populations. Under point-axial
symmetry, the potential is still axisymmetric, but the velocity and mass distributions are not necessarily. A point-axial stellar
system is, in a natural way, consistent with a flat velocity distribution of a disc population. Therefore, no additional integrability
conditions are required to solve the Boltzmann collisionless equation for such a population. For other populations, if the
potential is additively separable in cylindrical coordinates, the populations are not kinematically constrained, although under
point-axial symmetry, the potential is reduced to the harmonic function, which, for the Galaxy, is proven to be non-realistic.
In contrast, a non-separable potential provides additional conditions of consistency. When mean velocities for the populations
are unconstrained, the potential becomes quasi-stationary, being a particular case of the axisymmetric model. Then, the radial
and vertical mean velocities of the populations can differ and produce an apparent vertex deviation of the whole velocity
distribution. However, single population velocity ellipsoids still have no vertex deviation in the Galactic plane and no tilt in
their intersection with a meridional Galactic plane. If the thick disc and halo ellipsoids actually have non-vanishing tilt, as the
surveys of the solar neighbourhood that include RAdial Velocity Experiment (RAVE) data seem to show, the point-axial model
is unable to fit the local velocity distribution. Conversely, the axisymmetric model is capable of making a better approach. If,
in the end, more accurate data confirm a negligible tilt of the populations, then the point-axisymmetric model will be able to
describe non-axisymmetric mass and velocity distributions, although in the Galactic plane the velocity distribution will still be
axisymmetric.Conditions of consistency for multicomponent axisymmetric stellar systems. Is an axisymmetric model suitable yet?
http://hdl.handle.net/2117/28464
Conditions of consistency for multicomponent axisymmetric stellar systems. Is an axisymmetric model suitable yet?
Cubarsí Morera, Rafael
Solving the Boltzmann collisionless equatio n under the axisymmetric hypot hesis introduces serious lim itations on describing the kinematics of a single stellar system according to the local Galactic observables. Instead of relaxing the hypothesis of axisymmetry, one alternative is to assume a mixture model. For a finite mixture of ellipsoidal velocity distributions, the coexistence of several stellar populations sharing a co mmon potential introduces a set of conditions of consistency that m ay also constrain the population kinematics. For only a few potentials, the populations may have independent mean veloc ities and unconstrained velocity ellipsoids. In this paper, we determine which axisymmetric potentials are connect ed with a more flexible superposition of the stellar populations. The conditions of consistency are checked against recent results derived from kinematic surveys of the solar neighbourhood that include RAdial Velocity Experiment (RAVE) data. Several key observables are used to determine whether the axisymmetric mixture model is able to account for the main features of the local velocity distribution, such as the vertex deviation associated with the second central moment µ ¿ , the population radial mean velocities, the radial gradient of the moment µ z , the tilt of the velocity ellipsoids, and the existence of stars with no net rotation. In addition, the mixture moments for an arbitrary number of populations are derived in terms of the one-to-one mean velocity di ff erences in order to study whether a more populated mixture could add any new features to the velocity distribution that remain unnoticed in a two-component mixture. According to this analysis, the quasi-stationary potential is the only potential allowing arbitrary directions of the population mean velocities. Then, the apparent vertex deviation of the total velocity distribution is due to the di ff erence of the mean velocities of the populations whose velocity ellipsoids hav e no vertex deviation. For a non-separable pot ential, the population v elocity ellipsoids have the same orientation and point towards the Galactic centre. For a potential separable in addition in cylindrical coordinates, the population velocity ellipsoids may ha ve arbitrary tilt.
2015-06-30T08:51:39ZCubarsí Morera, RafaelSolving the Boltzmann collisionless equatio n under the axisymmetric hypot hesis introduces serious lim itations on describing the kinematics of a single stellar system according to the local Galactic observables. Instead of relaxing the hypothesis of axisymmetry, one alternative is to assume a mixture model. For a finite mixture of ellipsoidal velocity distributions, the coexistence of several stellar populations sharing a co mmon potential introduces a set of conditions of consistency that m ay also constrain the population kinematics. For only a few potentials, the populations may have independent mean veloc ities and unconstrained velocity ellipsoids. In this paper, we determine which axisymmetric potentials are connect ed with a more flexible superposition of the stellar populations. The conditions of consistency are checked against recent results derived from kinematic surveys of the solar neighbourhood that include RAdial Velocity Experiment (RAVE) data. Several key observables are used to determine whether the axisymmetric mixture model is able to account for the main features of the local velocity distribution, such as the vertex deviation associated with the second central moment µ ¿ , the population radial mean velocities, the radial gradient of the moment µ z , the tilt of the velocity ellipsoids, and the existence of stars with no net rotation. In addition, the mixture moments for an arbitrary number of populations are derived in terms of the one-to-one mean velocity di ff erences in order to study whether a more populated mixture could add any new features to the velocity distribution that remain unnoticed in a two-component mixture. According to this analysis, the quasi-stationary potential is the only potential allowing arbitrary directions of the population mean velocities. Then, the apparent vertex deviation of the total velocity distribution is due to the di ff erence of the mean velocities of the populations whose velocity ellipsoids hav e no vertex deviation. For a non-separable pot ential, the population v elocity ellipsoids have the same orientation and point towards the Galactic centre. For a potential separable in addition in cylindrical coordinates, the population velocity ellipsoids may ha ve arbitrary tilt.A methodology to assess ionospheric models for GNSS
http://hdl.handle.net/2117/27981
A methodology to assess ionospheric models for GNSS
Rovira Garcia, Adrià; Juan Zornoza, José Miguel; Sanz Subirana, Jaume; González Casado, Guillermo; Ibáñez Segura, Marcos - Deimos
2015-05-20T12:32:18ZRovira Garcia, AdriàJuan Zornoza, José MiguelSanz Subirana, JaumeGonzález Casado, GuillermoIbáñez Segura, Marcos - DeimosNovel ionospheric activity indicator specifically tailored for GNSS users
http://hdl.handle.net/2117/27928
Novel ionospheric activity indicator specifically tailored for GNSS users
Sanz Subirana, Jaume; Juan Zornoza, José Miguel; González Casado, Guillermo; Prieto Cerdeira, Roberto; Schlüter, S.; Orús Pérez, Raul
This work introduces a novel ionospheric activity indicator useful for identifying disturbed periods affecting performance for GNSS users, at regional level. This indicator is based in the “Along Arc TEC Rate (AATR) and can be easily computed from GNSS data. The AATR indicator has been assessed over more than one Solar Cycle (2002-2013) involving 140 receivers distributed world-wide. Results show that it is well correlated with the ionospheric activity and, unlike other global indicators linked to the geomagnetic activity (i.e. DST, Ap), it is sensitive to regional behaviour the ionosphere and identifies specific effects on GNSS users. Moreover from a devoted analysis of EGNOS performances in different ionospheric conditions, it follows that the AATR indicator is able to predict SBAS user availability anomalies linked to the ionosphere. The AATR indicator has been chosen as the metric to characterise the ionosphere operational conditions in the frame of EGNOS activities. This indicator has been also proposed for joint analysis in the International SBAS-Ionosphere Working Group.
2015-05-15T08:41:11ZSanz Subirana, JaumeJuan Zornoza, José MiguelGonzález Casado, GuillermoPrieto Cerdeira, RobertoSchlüter, S.Orús Pérez, RaulThis work introduces a novel ionospheric activity indicator useful for identifying disturbed periods affecting performance for GNSS users, at regional level. This indicator is based in the “Along Arc TEC Rate (AATR) and can be easily computed from GNSS data. The AATR indicator has been assessed over more than one Solar Cycle (2002-2013) involving 140 receivers distributed world-wide. Results show that it is well correlated with the ionospheric activity and, unlike other global indicators linked to the geomagnetic activity (i.e. DST, Ap), it is sensitive to regional behaviour the ionosphere and identifies specific effects on GNSS users. Moreover from a devoted analysis of EGNOS performances in different ionospheric conditions, it follows that the AATR indicator is able to predict SBAS user availability anomalies linked to the ionosphere. The AATR indicator has been chosen as the metric to characterise the ionosphere operational conditions in the frame of EGNOS activities. This indicator has been also proposed for joint analysis in the International SBAS-Ionosphere Working Group.A Worldwide ionospheric model for fast precise point positioning
http://hdl.handle.net/2117/27895
A Worldwide ionospheric model for fast precise point positioning
Rovira Garcia, Adrià; Juan Zornoza, José Miguel; Sanz Subirana, Jaume; González Casado, Guillermo
Fast precise point positioning (Fast-PPP) is a satellite-based navigation technique using an accurate real-time ionospheric modeling to achieve high accuracy quickly. In this paper, an end-to-end performance assessment of Fast-PPP is presented in near-maximum Solar Cycle conditions; from the accuracy of the Central Processing Facility corrections, to the user positioning. A planetary distribution of permanent receivers including challenging conditions at equatorial latitudes, is navigated in pure kinematic mode, located from 100 to 1300 km away from the nearest reference station used to derive the ionospheric model.
It is shown that satellite orbits and clocks accurate to few centimeters
and few tenths of nanoseconds, used in conjunction with an ionosphere with an accuracy better than 1 Total Electron Content Unit (16 cm in L1) reduce the convergence time of dual-frequency Precise Point Positioning, to decimeter-level (3-D) solutions. Horizontal convergence times are shortened 40% to 90%, whereas the vertical components are reduced by 20% to 60%. A metric to evaluate the quality of any ionospheric model for Global Navigation Satellite System is also proposed. The ionospheric modeling accuracy is directly translated to mass-market single-frequency
users. The 95th percentile of horizontal and vertical accuracies is shown to be 40 and 60 cm for single-frequency users and 9 and 16 cm for dual-frequency users. The tradeoff between the formal and actual positioning errors has been carefully studied to set realistic confidence levels to the corrections.
2015-05-12T11:44:15ZRovira Garcia, AdriàJuan Zornoza, José MiguelSanz Subirana, JaumeGonzález Casado, GuillermoFast precise point positioning (Fast-PPP) is a satellite-based navigation technique using an accurate real-time ionospheric modeling to achieve high accuracy quickly. In this paper, an end-to-end performance assessment of Fast-PPP is presented in near-maximum Solar Cycle conditions; from the accuracy of the Central Processing Facility corrections, to the user positioning. A planetary distribution of permanent receivers including challenging conditions at equatorial latitudes, is navigated in pure kinematic mode, located from 100 to 1300 km away from the nearest reference station used to derive the ionospheric model.
It is shown that satellite orbits and clocks accurate to few centimeters
and few tenths of nanoseconds, used in conjunction with an ionosphere with an accuracy better than 1 Total Electron Content Unit (16 cm in L1) reduce the convergence time of dual-frequency Precise Point Positioning, to decimeter-level (3-D) solutions. Horizontal convergence times are shortened 40% to 90%, whereas the vertical components are reduced by 20% to 60%. A metric to evaluate the quality of any ionospheric model for Global Navigation Satellite System is also proposed. The ionospheric modeling accuracy is directly translated to mass-market single-frequency
users. The 95th percentile of horizontal and vertical accuracies is shown to be 40 and 60 cm for single-frequency users and 9 and 16 cm for dual-frequency users. The tradeoff between the formal and actual positioning errors has been carefully studied to set realistic confidence levels to the corrections.A real-time world-wide ionospheric model for single and multi-frequency precise navigation
http://hdl.handle.net/2117/27516
A real-time world-wide ionospheric model for single and multi-frequency precise navigation
Rovira Garcia, Adrià; Juan Zornoza, José Miguel; Sanz Subirana, Jaume
The ionosphere plays an important role in satellite-based navigation, either in standard navigation, with single frequency mass-market receivers, or in precise navigation, with dual frequency receivers.
In this work, the requirements of a real-time 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 ambiguity-fixing strategy and the number of layers used to reproduce the ionospheric delay. Different models are assessed both in mid-latitudes and equatorial regions, near the Solar Cycle maximum.
It will be shown how dual-frequency 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 Fast-PPP will be shown to be accurate to few centimeters and few tenths of nanoseconds, respectively.
Single-frequency users correct its measurements with the predictions provided by any ionospheric model. Thence, the accuracy of the Fast-PPP 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 single-frequency users and 11 and 15 centimeters for dual-frequency users. The assessment is done for several locations, including the equatorial region, for a month of data close to the last Solar Maximum. The trade-off 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.
2015-04-22T12:46:58ZRovira Garcia, AdriàJuan Zornoza, José MiguelSanz Subirana, JaumeThe ionosphere plays an important role in satellite-based navigation, either in standard navigation, with single frequency mass-market receivers, or in precise navigation, with dual frequency receivers.
In this work, the requirements of a real-time 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 ambiguity-fixing strategy and the number of layers used to reproduce the ionospheric delay. Different models are assessed both in mid-latitudes and equatorial regions, near the Solar Cycle maximum.
It will be shown how dual-frequency 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 Fast-PPP will be shown to be accurate to few centimeters and few tenths of nanoseconds, respectively.
Single-frequency users correct its measurements with the predictions provided by any ionospheric model. Thence, the accuracy of the Fast-PPP 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 single-frequency users and 11 and 15 centimeters for dual-frequency users. The assessment is done for several locations, including the equatorial region, for a month of data close to the last Solar Maximum. The trade-off 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.Biomedical applications of bacterial inclusion bodies
http://hdl.handle.net/2117/27044
Biomedical applications of bacterial inclusion bodies
Ratera, Imma; Peternel, Espela; Seras Franzoso, Joaquín; Cano Garrido, Olivia; García Fruitós, Elena; Cubarsí Morera, Rafael; Vazquez, Esther; Corchero Nieto, Jose Luis; Rodriguez-Carmona, Escar; Veciana Miró, Jaume; Villaverde, A.
2015-03-26T11:05:24ZRatera, ImmaPeternel, EspelaSeras Franzoso, JoaquínCano Garrido, OliviaGarcía Fruitós, ElenaCubarsí Morera, RafaelVazquez, EstherCorchero Nieto, Jose LuisRodriguez-Carmona, EscarVeciana Miró, JaumeVillaverde, A.Consolidated characterisation of an ionospheric indicator for the definition of EGNOS Ionospheric Conditions
http://hdl.handle.net/2117/23040
Consolidated characterisation of an ionospheric indicator for the definition of EGNOS Ionospheric Conditions
Juan Zornoza, José Miguel; Sanz Subirana, Jaume
2014-05-23T18:17:49ZJuan Zornoza, José MiguelSanz Subirana, JaumeFeasibility analysis of a methodology to estimate hourly DCBs for Feared Events Characterization
http://hdl.handle.net/2117/23039
Feasibility analysis of a methodology to estimate hourly DCBs for Feared Events Characterization
Juan Zornoza, José Miguel; Sanz Subirana, Jaume
Analysis of Hardware Biases Feared Events
2014-05-23T17:48:23ZJuan Zornoza, José MiguelSanz Subirana, JaumeAnalysis of Hardware Biases Feared Events