Finalized PhD theses

Número de entradas: 80

Bayesian data analysis for LISA Pathfinder. Techniques applied to system identificaction experiments.

Estado: defended (13/01/2015)
Estudiante: Nikolaos Karnesis
Supervisada por: Carlos Sopuerta ; Miquel Nofrarias Serra
Universidad: Universitat Autònoma de Barcelona

LISA is a joint mission between the European Space Agency (ESA) and the US National Aeronautics and Space Administration (NASA) that will become the first space-based Gravitational-Wave (GW) detector. LISA is a constellation of three spacecrafts that will access GW signals at frequencies of 1mHz and below, around five orders of magnitude below the kHz band where Earth-based detectors, such as VIRGO and LIGO operate. LISA will open a new window to the observation of the Universe and is expected to provide revolutionary discoveries in the areas of Astrophysics, Cosmology, and Fundamental Physics. Due to the technological complexity of LISA, ESA approved a percursor mission, LISA PathFinder (LPF), to test the readiness of the main LISA technology. The scientific working principle of LISA is the detection of tiny relative displacements between pairs of proof masses in nominally geodesic motion, or free fall, induced by passing GWs. LPF consists in a single spacecraft hosting two proof masses in nominal free fall, whose motions are monitored by means of a Mach-Zender laser interferometer. LPF is expected to be launched around 2012 and its ultimate objective is to measure the noise in the proof masses motion, and to understand its physical origin. There are many sources of noise identified (thermal, magnetic, particles of cosmic origin, etc), and properly modelling them requires a careful planning of the measurement sequence, plus of course the use of suitable analysis tools to process the various data channels. The research work proposed for this PhD project consists of the following three points: 1. Development of Data Analysis Tools for the LTPDA software tool in order to perform the Data Analysis during the mission operations and also for the scientific parts that will be carried out by our Research Group. Also to participate in the Mock Data Analysis challenges organized by the LPF community. 2. To study how to develop a LISA noise model from the outcome of the LPF mission. 3. To develop Data Analysis Tools for LISA, which consists in the detection of GW signals and the estimation of the physical parameters of the associated sources. Also to participate in Mock Data Analysis challenges organized by the LISA scientific community (LISC).
The eLISA concept design consists of a constellation of three space-crafts forming a triangle in the sky. While in a sun centered orbit, it will constantly monitor the distance oscillations between the test bodies enclosed in the different space-crafts. Its principal goal, is to detect oscillations that…
Estado: defended (13/01/2015)
Estudiante: Nikolaos Karnesis
Supervisada por: Carlos Sopuerta ; Miquel Nofrarias Serra
Universidad: Universitat Autònoma de Barcelona

The eLISA concept design consists of a constellation of three space-crafts forming a triangle in the sky. While in a sun centered orbit, it will constantly monitor the distance oscillations between the test bodies enclosed in the different space-crafts. Its principal goal, is to detect oscillations that are caused by passing Gravitational-Waves. The technical complexity of this design was the reason for ESA and NASA to approve the LISA Pathfinder mission (LPF) which aims at testing all the key technologies for future Gravitational-Wave space observatories.
The LISA Technology Package (LTP) instrument onboard the LPF satellite, can be considered as one eLISA arm, squeezed from 1 million km to approximately 30 cm, and it aims to measure the differential acceleration between two test-bodies with unparalleled precision via a Mach-Zehnder interferometer. Among its objectives we have: The estimation of the acceleration noise models, the derivation of an accurate dynamical model of the system in all degrees-of-freedom, and the estimation of the systems’ parameters. In this thesis, we focus on a Bayesian analysis framework to set-up analysis strategies to process the planned system identification experiments.

We first model the system using different approximations, and then we develop and apply Markov Chain Monte Carlo (MCMC) algorithms to simulated data-sets. We report the accuracy on the parameters over the planned system identification experiments, that can be divided in two categories; the x-axis system identification experiments, that are performed over the sensitive axis defined by the line joining the two
test masses; and the so-called cross-talk experiments, where different degrees of freedom of the test bodies of the system are excited. The various cross-coupling physical effects that produce signal leakage on the sensitive differential interferometer channel,are then identified and estimated. In addition, the pipeline analysis designed for on-line
data analysis during operations is presented.

Finally, we also investigate the possible model selection problems in LPF data analysis, and we apply the reversible jump MCMC algorithm to simulated data sets. Different applications to the x-axis and the cross-talk experiments are considered, where the efficiency of the developed tools is demonstrated. We also show the association of
the model selection results to the design of the experiment itself. The above work is integrated to the LTP data analysis dedicated toolbox, the LTPDA. 

Stellar activity in exoplanet hosts

Estado: defended (06/10/2014)
Estudiante: Enrique Herrero Casas
Supervisada por: Ignasi Ribas Canudas
Universidad: Universitat de Barcelona

Stellar activity in exoplanet hosts Most of the efforts on the search and characterization of Earth-like exoplanets are currently focused on low mass stars. Some important properties related to the structure and processes in this type of stars are still unknown, so a careful characterization…
Estado: defended (06/10/2014)
Estudiante: Enrique Herrero Casas
Supervisada por: Ignasi Ribas Canudas
Universidad: Universitat de Barcelona

Stellar activity in exoplanet hosts Most of the efforts on the search and characterization of Earth-like exoplanets are currently focused on low mass stars. Some important properties related to the structure and processes in this type of stars are still unknown, so a careful characterization is essential as one of the next steps in exoplanet sciences. The characterization of stellar activity in low mass stars was carried out through several techniques that allowed us both to model and to simulate the relationships between the observational data and the stellar properties. Several empyrical relations for low mass stars allow to find correlations between certain activity indicators and the rotation period. These have permitted us to generate synthetic samples of stars with stochastic distributions of stellar and geometric properties allowing to estimate the inclination of the rotation axis from the distribution in the activity-vsini diagram. The methodology was applied to a sample of 1200 observed low mass stars and the best candidates for a targeted transit search were selected. Spot modelling techniques allow to obtain physical information about the stellar surface from time series photometric and spectroscopic data. In this work we analyse Kepler photometry of LHS 6343 A, an M-dwarf being eclipsed by a brown dwarf companion every 12.718 days, and showing photometric oscillations with the same periodicity and a phase lag of 100o from the eclipses. The accurate modeling of the Kepler data allowed to explain these oscillations with the presence of active regions appearing at a fixed longitude, thus suggesting a possible magnetic connection between both components. On the other hand, we also studied an alternative explanation for the photometric oscillations in LHS 6343 A in terms of the Doppler beaming effect, showing that this could be the main cause of the observed oscillations. Stellar activity effects are responsible for the noise observed at different amplitude and timescales on time series data. Such noise represents one of the main limitations for exoplanetary sciences. In order to characterize it, we designed a methodology to simulate the photosphere of an active rotating star through the integration of small surface elements from Phoenix atmosphere models. This allows to characterize the signal produced by activity and further study its relationship with the stellar properties, as well as the possible effects produced on exoplanet measurements. The methodology allowed us to present several strategies in order to correct or reduce the effects of spots on the photometry of exoplanet transits, as these may induce significant variations on the measurement of the planetary radius. We focused on a comprehensive analysis of HD 189733, a K5 star hosting a giant planet, which has simultaneous photometric (MOST) and spectroscopic (SOPHIE) data available. An accurate surface map was obtained using the methodology above, accurately reproducing the light curve and radial velocity observations. Such map was used in order to study the effects of activity on the exoplanet transits. We showed that the effects of spot-crossing events are significant even for mid-infrared wavelengths. Moreover, the chromatic effects of spots not occulted by the planet show a signal with a wavelength dependence and amplitude that are very similar to the signature of the atmosphere of a planet dom- inated by dust. The radial velocity theoretical curve is in agreement with the observations up to the typical instrumental systematics of SOPHIE. The results from this work conclude that it is essential to correctly model the stellar activity signals for exoplanetary sciences, and we provide some tools and strategies to characterize and reduce such effects and extract astrophysical information. 

Theory and observations of the PWN-SNR complex

Estado: defended (21/07/2014)
Estudiante: Jonatan Martín Rodríguez
Supervisada por: Diego F. Torres ; Nanda Rea
Universidad: Universitat Autònoma de Barcelona

In this work, we study theoretical and observational issues about pulsars (PSRs), pulsar wind nebulae (PWNe) and supernova remnants (SNRs). In particular, the spectral modeling of young PWNe and the X-ray analysis of SNRs with magnetars comparing their characteristics with those remnants surrounding…
Estado: defended (21/07/2014)
Estudiante: Jonatan Martín Rodríguez
Supervisada por: Diego F. Torres ; Nanda Rea
Universidad: Universitat Autònoma de Barcelona

In this work, we study theoretical and observational issues about pulsars (PSRs), pulsar wind nebulae (PWNe) and supernova remnants (SNRs). In particular, the spectral modeling of young PWNe and the X-ray analysis of SNRs with magnetars comparing their characteristics with those remnants surrounding canonical pulsars. The spectra of PWNe range from radio to $\gamma$-rays. They are the largest class of identified Galactic sources in $\gamma$-rays increasing the number from 1 to $\sim$30 during the last years. We have developed a detailed spectral code which reproduces the electromagnetic spectrum of PWNe in free expansion ($t_{age} \lesssim$10 kyr). We shed light and try to understand issues on time evolution of the spectra, the synchrotron self-Compton dominance in the Crab Nebula, the particle dominance in PWNe detected at TeV energies and how physical parameters constrain the detectability of PWNe at TeV. We make a systematic study of all Galactic, TeV-detected, young PWNe which allows to find correlations and trends between parameters. We also discuss about the spectrum of those PWNe not detected at TeV and if models with low magnetized nebulae can explain the lack of detection or, on the contrary, high-magnetization models are more favorable. Regarding the X-ray analysis of SNRs, we use X-ray spectroscopy in SNRs with magnetars to discuss about the formation mechanism of such extremely magnetized PSRs. The alpha-dynamo mechanism proposed in the 1990's produces an energy release that should have influence in the energy of the SN explosion. We extend the work done previously done by \cite{vink06} about the energetics of the SN explosion looking for this energy release and we look for the element ionization and the X-ray luminosity and we compare our results with other SNRs with an associated central source.

Weak Lensing Analysis of an All-Sky Simulation

Estado: defended (24/01/2014)
Estudiante: Carlos Lopez Arenillas
Supervisada por: Pablo Fosalba Vela; Enrique Gaztañaga
Universidad: Universitat de Barcelona

This Thesis is concerned with one of the most promising probes to constrain the "Dark Universe", and, particularly, the dark matter distribution. Based on MICE cosmological simulation, and the all-sky convergence maps generated by Fosalba, Gaztanaga, Castander & Manera (2003) we perform a mass calibration…
Estado: defended (24/01/2014)
Estudiante: Carlos Lopez Arenillas
Supervisada por: Pablo Fosalba Vela; Enrique Gaztañaga
Universidad: Universitat de Barcelona

This Thesis is concerned with one of the most promising probes to constrain the "Dark Universe", and, particularly, the dark matter distribution. Based on MICE cosmological simulation, and the all-sky convergence maps generated by Fosalba, Gaztanaga, Castander & Manera (2003) we perform a mass calibration of the dark matter halos there contained up to z=1. In order to do that, we analyse the average halo density proÖles of all the halos with masses ranging from 5E13 to 4E14 Msol/h , divided into four mass bins and three redshift bins. Through this analysis we address two main issues: the relatively low mass resolution of the simulation (mp=2.34 1011 h1M ) and the relatively high softening length (lsoft=50 h1 Kpc). We do that by using a two-step procedure. First, we simulate analytical pure NFW density profiles (with di§erent mass resolutions) using two input values: the virial radii of MICE halos and the expected concentrations, according to the Öxed mass-concentration relation from Oguri and Hamana [130]. Second, we model the e§ect of the softening length with a Gaussian Ölter, smoothing the halo core. The results show that MICE halos are, in average, NFW halos. Best-O NFW radii are in very good agreement with the average radii of our samples, overestimating the data by  1%, but best-fit NFW concentrations are in average 50% lower than the expected values. It is possible to account for part of this deviation by distinguishing between relaxed and unrelaxed halos, finding that, depending on the degree of relaxedness, the improvement can be as high as 30%. We also find that the analytical NFW halos simulated with MICE mass resolution have an overall concentration 40% lower than the input concentration, in the case of 3D proÖles, and 25% lower in that of the projected proÖles. The Gaussian-smoothed NFW profile is a good approximation for our projected halos. Additionally, we analyse the morphology of the halos, characterizing their triaxiality at R200 and calculating their orientation with respect to the line-of-sight (LOS). MICE halos tend to adopt a more prolate morphology, as might be expected from a  CDM simulation (Shaw et al. [159]), and the percentage of prolate halos grows as their mass grows. The mass resolution is, nonetheless, not good enough to draw conclusive inferences from the shape analysis, but it allows us to discern a trend and estimate the e§ect of halo shape and orientation on the weak lensing masses. Finally, we use the all-sky convergence maps to study the scatter in mass measurements of MICE halos. We determine the intrinsic scatter in the recovered masses by assuming the smoothed NFW profile as the ìtrueî profile, and creating two new convergence maps from different mass cuts. We estimate also the scatter due to the correlated structure by studying the angles between the major axes of the halos and the LOS, and also that due to projection e§ects (i.e. all the dark matter between observer and source). We find an irreducible scatter (intrinsic) of 10-14%, a scatter around a 30% of the intrinsic one due to correlated structure, and a scatter around 40-70% of the intrinsic one due to projection e§ects. The size of our halo sample allows us to improve the characterization of the cosmic noise, of great importance for present and future surveys.

CROSS-CORRELATING SPECTROSCOPIC AND PHOTOMETRIC GALAXY SURVEYS

Estado: defended (16/01/2014)
Estudiante: Martin B. Eriksen
Supervisada por: Enrique Gaztañaga
Universidad: Universitat Autònoma de Barcelona

CROSS-CORRELATING SPECTROSCOPIC AND PHOTOMETRIC GALAXY SURVEYS
Estado: defended (16/01/2014)
Estudiante: Martin B. Eriksen
Supervisada por: Enrique Gaztañaga
Universidad: Universitat Autònoma de Barcelona

CROSS-CORRELATING SPECTROSCOPIC AND PHOTOMETRIC GALAXY SURVEYS

Dynamically-generated baryon resonances with heavy flavor

Estado: defended (10/01/2014)
Estudiante: Romanets, O. (KVI, University of Groningen)
Supervisada por: Tolos, L.; Timmermans, R. (KVI, University of Groningen)

To study the properties of exotic hadrons with charm and strange content under extreme conditions of density and temperature, with applications for astrophysical observables in neutron stars and supernovae as well as for the future FAIR project at GSI.
Study the properties of dynamically-generated baryon resonaces with strange and charm content
Estado: defended (10/01/2014)
Estudiante: Romanets, O. (KVI, University of Groningen)
Supervisada por: Tolos, L.; Timmermans, R. (KVI, University of Groningen)

Study the properties of dynamically-generated baryon resonaces with strange and charm content

Theories of modified gravity and reconstruction schemes of cosmological models

Estado: defended (08/11/2013)
Estudiante: Antonio Jesús López Revelles
Supervisada por: Emilio Elizalde ; Sergei D Odintsov
Universidad: Universitat de Barcelona

The present thesis, aimed at obtaining the title of Philosophy Doctor in Physics, is based on the following papers published in referred journals, pre-prints and conference proceedings:  S. Capozziello, M. De Laurentis and A. J. Lopez-Revelles. Weak eld limit for F(R; G) modi ed gravities. In preparation. …
Estado: defended (08/11/2013)
Estudiante: Antonio Jesús López Revelles
Supervisada por: Emilio Elizalde ; Sergei D Odintsov
Universidad: Universitat de Barcelona

The present thesis, aimed at obtaining the title of Philosophy Doctor in Physics, is based on the
following papers published in referred journals, pre-prints and conference proceedings:
 S. Capozziello, M. De Laurentis and A. J. Lopez-Revelles. Weak eld limit for F(R; G) modi ed
gravities. In preparation.
 K. Bamba, A. J. Lopez-Revelles, R. Myrzakulov, S. D. Odintsov, and L. Sebastiani. Cosmic history
of viable exponential gravity: Equation of state oscillations and growth index from in
ation to dark
energy era. Class. Quant. Grav. 30:015008 (2013).
 K. Bamba, A. J. Lopez-Revelles, R. Myrzakulov, S. D. Odintsov, and L. Sebastiani. The universe
evolution in exponential F(R) -gravity. Proceedings of QFTG2013, published in TSPU Bulletin 3
(128), 2012, n 13 p.19-24.
 E. Elizalde and A. J. Lopez-Revelles.Reconstructing cosmic acceleration from modi ed and nonmin-
imal gravity: The Yang-Mills case. Phys. Rev. D, 82:063504 (2010).
 E. Elizalde, A. J. Lopez-Revelles, S. D. Odintsov, and S. Yu. Vernov. Cosmological models with
Yang-Mills elds. Phys.Atom.Nucl., 76:996 (2013).
 A. J. Lopez-Revelles. Growth of matter perturbations for realistic F(R) models. Phys. Rev. D,
87:024021 (2013).
 A. J. Lopez-Revelles. Reconstructing cosmic acceleration from f(R) modi ed gravity. Proceedings
of ERE2011, Madrid. ArXiv: 1301.2190.
 A. J. Lopez-Revelles and E. Elizalde. Universal procedure to cure future singularities of dark energy
models. Gen. Rel. Grav., 44:751 (2012).
 A. J. Lopez-Revelles, R. Myrzakulov and D. Saez-Gomez. Ekpyrotic universes in F(R) Horava-
Lifshitz gravity. Phys. Rev. D, 85:103521 (2012).

Measuring Large Scale Structure using angular cross-correlations

Estado: defended (27/09/2013)
Estudiante: Jacobo Asorey Barreiro
Supervisada por: Enrique Gaztañaga ; Martin Crocce
Universidad: Universitat Autònoma de Barcelona

La propuesta de proyecto de tesis se enmarca en el estudio de la evolución cósmica a través de cartografiados extragalácticos. Será llevada a cabo dentro del grupo de Cosmología del Instituto de Ciencias del Espacio (IEEC-CSIC), el cual participa activamente en la construcción de grandes cartografiados como son el Physics of the Accelerating Universe Survey (PAU Survey), el Dark Energy Survey (DES) y el ESA-EUCLID. El proyecto consistirá en estudiar y entender la ciencia básica relacionada con los catálogos de galaxias resultantes de tales cartografiados, además de desarrollar métodos de análisis que nos permitan optimizar la información sobre el contenido de materia y energía del Universo, que condicionan tanto la evolución cósmica como la formación de estructuras a grandes escalas. Esto nos permitiría discriminar entre diferentes modelos, tanto los que se basan en la energía oscura como el fluido responsable de la expansión acelerada del Universo como aquellos que proponen modificaciones de la teoría de la gravedad para explicar dicha aceleración. Para ello tendremos en cuenta la distribución espacial de las galaxias, las distorsiones en el espacio de redshift producidas por el campo de velocidades de las galaxias y el efecto de lente gravitatoria causado sobre las imágenes de galaxias más lejanas por la materia que hay entre nosotros y dichas fuentes. Especialmente, en el caso de PAU, al basarse en la estimación de coordenadas radiales de las galaxias usando redshifts fotométricos de alta resolución, mediante la toma de imágenes de las galaxias contenidas en el volumen del catálogo con una cámara con 40 filtros de banda estrecha, estudiaremos la manera óptima de analizar el catálogo que resulte cuando finalice el cartografiado al tratarse de una nueva técnica observacional para la obtención de cartografiados extragalácticos. La obtención del redshifts fotométricos de alta resolución, nos permite dividir en capas muy finas el volumen del catálogo, pudiendo estudiar como están correlacionadas las galaxias en cada capa y entre ellas, abriendo nuevos horizontes en el análisis de la distribución de galaxias y materia oscura. Además será posible llegar hasta una profundidad de z ~ 1.2 lo que también amplia la capacidad de posibles análisis. Se realizarán predicciones de los errores estadísticos a los que estarán sujetos los cartografiados en construcción utilizando métodos analíticos, numéricos e incluso simulaciones cosmológicas. Así mismo, se aplicarán las herramientas desarrolladas en los datos una vez disponibles. En particular intentaremos desarrollar técnicas que nos permitan combinar los relacionados a los catálogos de galaxias con datos procedentes de otros experimentos como son el espectro de anisotropías en la temperatura de la radiación de fondo de microondas dados por WMAP o Planck o catálogos de Supernovas de tipo Ia. Un objetivo final es realizar una determinación de parámetros conjunta que nos permita obtener todavía mayor precisión en la determinación del contenido energético del Universo y en la parametrización de la Energía Oscura.
In this thesis we propose to use galaxy clustering, more concretely angular cross-correlations, as a tool to understand the late-time expansion of the Universe and the growth of large-scale structure. Galaxy surveys measure the position of galaxies (what traces the dark- matter field) in spherical coordinates…
Estado: defended (27/09/2013)
Estudiante: Jacobo Asorey Barreiro
Supervisada por: Enrique Gaztañaga ; Martin Crocce
Universidad: Universitat Autònoma de Barcelona

In this thesis we propose to use galaxy clustering, more concretely angular cross-correlations, as a tool to understand the late-time expansion of the Universe and the growth of large-scale structure. Galaxy surveys measure the position of galaxies (what traces the dark- matter field) in spherical coordinates (z,θ,φ). Most galaxy clustering analyses convert these positions to distances assuming a background cosmology. This approach thus requires doing the full data analysis for each background cosmological model one wants to test. Instead we propose to select galaxies in radial shells, according to their redshifts, and then measure and analyse the angular (2D) correlations in each bin circumventing the model assumption. Remarkably, we find that if we include in the analysis also the angular cross-correlations between different shells, we can recover the radial modes corresponding to the separations between radial bins. We extend this analysis to photometric galaxy surveys, such as Physics of the Accelerating Universe (PAU) and Dark Energy Survey (DES). Angular analysis in redshift bins is then the natural framework for such surveys. We show that we can obtain competitive constraints on the growth history of the Universe at high redshifts (z~1). Finally, we built galaxy survey mocks from the MICE simulations, including non-linear gravitational effects and observational ones such as redshift-space distortions and photo-z errors.  We found a good agreement between theory and simulation measurements. In the future, we expect to apply this framework for cosmological parameter estimation, especially focusing on DES and PAU surveys.

Gamma-ray emission of young stellar objects and discovery of superorbital variability at high energies

Estado: defended (30/07/2013)
Estudiante: Daniela Hadasch
Supervisada por: Diego F. Torres ; Font, Ll. (UAB)
Universidad: Universitat Autònoma de Barcelona

UAB Abstract - Department of Physics - Doctor of Physics   Gamma-ray emission of young stellar objects and discovery of super orbital variability at high energies   by Daniela Hadasch   This thesis is structured in three parts: 1.) Observations of binary systems with the Fermi…
Estado: defended (30/07/2013)
Estudiante: Daniela Hadasch
Supervisada por: Diego F. Torres ; Font, Ll. (UAB)
Universidad: Universitat Autònoma de Barcelona

UAB Abstract - Department of Physics - Doctor of Physics   Gamma-ray emission of young stellar objects and discovery of super orbital variability at high energies   by Daniela Hadasch   This thesis is structured in three parts: 1.) Observations of binary systems with the Fermi satellite and first discovery of superorbital modulation at high energies in the system LS I +61 ◦303, 2.) Studies of magnetars at high and at very high energies and deriving first upper limits on their γ-ray emission and 3.) Studies of the prospects forobservations of binary systems with the forthcoming Cherenkov Telescope Array.

GNSS-R as a Source of Opportunity for Remote Sensing of the Cryosphere

Estado: defended (13/05/2013)
Estudiante: Fran Fabra Cervellera
Supervisada por: Estel Cardellach Galí
Universidad: Universitat Politècnica de Catalunya

This work evaluates the potential use of signals from the Global Navigation Satellite Systems (GNSS) that scatter off the Earth surface for the retrieval of geophysical information from the cryosphere. For this purpose, the present study is based on data collected with a dedicated reflectometry GNSS…
Estado: defended (13/05/2013)
Estudiante: Fran Fabra Cervellera
Supervisada por: Estel Cardellach Galí
Universidad: Universitat Politècnica de Catalunya

This work evaluates the potential use of signals from the Global Navigation Satellite Systems (GNSS) that scatter off the Earth surface for the retrieval of geophysical information from the cryosphere. For this purpose, the present study is based on data collected with a dedicated reflectometry GNSS receiver during two field campaigns, which were focused on two types of characteristic surfaces of the cryosphere: thin sea ice covers and thick dry snow accumulations. During the first experiment, the complete process of formation, evolution and melting of sea ice was monitorized for more than seven months in a bay located in Greenland. This type of ice is typically characterized by its thickness, concentration and roughness. Different observables from GNSS reflections are analyzed to try to infer these properties. The ice thickness is linked to the free-board level, defined as the height of the sea ice
surface. Accurate phase altimetry is achieved, showing good agreement with an Arctic tide model. In addition, the long term results of ellipsoidal height retrievals are consistent with the evolution of the ice surface temperature product given by MODIS, which is a key parameter in the rate of growth of sea ice. On the other hand, the presence of salinity in the sea ice modifies its dielectric properties, resulting in different amplitude and phase for the co- and cross-polar components of the complex Fresnel coefficients. The polarimetric measurements obtained show good agreement with visual inspections of ice concentration from an Arctic weather station. Finally, the shape of the reflected signals and its phase dispersion are tested as potential signatures of surface roughness. For comparison, ice charts of the experimental area are employed. In particular, maximums in roughness given by the GNSS observables coincide with fast ice events. Fast ice is defined as ice anchored to the coast, where the tidal movements contribute to the development of strange patterns, cracks, and fissures on its surface, thus consistent with the GNSS-R roughness retrievals. The second experiment took place on Antarctica, monitoring a pristine snow area which is well-known for the calibration of remote sensing instruments. Due to the relative stability of the snow layers, the data acquisition was limited to ten continuous days. Interferometric beats were found after a first analysis of the amplitude from the collected signals, which were consistent with a multipath model where the reflector lies below the surface level. Motivated by these results, a forward model is developed that reconstructs the complex received signal as a sum of a finite number of reflections, coming from different snow layers (a snow density profile obtained from in-situ measurements). The interferometric information is then retrieved from the spectral analysis applied to time series from both real and modeled signals (lag-holograms). We find that the frequency bands predicted by the model are in general consistent with the data and the lag-holograms show repeatability for different days. Then, we attempt a proper inversion of the collected data to determine the dominant layers of the dry snow profile that contribute to L-band reflections, which are related to significant gradients of snow density/permittivity.
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