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  • Contributions to Radio Frequency Interference Detection and Mitigation in Earth Observation

     Forte Veliz, Giuseppe Francesco
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    El problema més comú en els sistemes electrònics de mesura són les interferències electromagnètiques. La presència d'aquests senyals pot danyar les mesures preses per instruments molt sensibles, com radiòmetres de microones o sistemes de navegació. L'exactitud i precisió es veuen compromeses. El primer pas per mitigar aquests efectes no desitjats és estudiar les propietats de les interferències electromagnètiques. Diversos algoritmes han estat proposats per detectar interferències, però no hi ha mètode que funcioni bé en tots els casos .Aquest treball comprèn el disseny, implementació i comprovació de diferents mètodes de detecció i mitigació en temps real. Els estudis i caracterització de les fonts d'interferències són una gran contribució per a optimitzar les tècniques de mitigació actuals. En el tema de mitigació, dos sistemes en temps real han estat implementats en hardware: un sistema que utilitza wavelets per modelar la interferència i mitigar-la, i un circuit que permet a un sistema de navegació continuar funcionant sota els efectes d'un interferidor comercial ( jammer ).

  • Pràctiques de laboratori de Projecte Bàsic d'Enginyeria (ETSETB-UPC)

     Fabregas Canovas, Francisco Javier; Torres Torres, Francisco; Duffo Ubeda, Nuria; Vall-llossera Ferran, Mercedes Magdalena
    Date: 2014-02-03
    Report

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  • Grup de Teledetecció, Antenes, Microones i Superconductivitat

     Aguasca Sole, Alberto; Barlabe Dalmau, Antoni; Blanch Boris, Sebastian; Broquetas Ibars, Antoni; Camps Carmona, Adriano Jose; Cardama Aznar, Angel; Elias Fuste, Antonio; Duffo Ubeda, Nuria; Fabregas Canovas, Francisco Javier; Jofre Roca, Luis; Heldring, Alexander; López Martínez, Carlos; Mallorqui Franquet, Jordi Joan; O'callaghan Castella, Juan Manuel; Pradell Cara, Lluis; Rius Casals, Juan-manuel; Romeu Robert, Jordi; Torres Torres, Francisco; Ubeda Farre, Eduardo; Vall-llossera Ferran, Mercedes Magdalena; Duran Martinez, Israel; Wu, Lin; Gilasgar, Mitra; Lort Cuenca, Marc; Imbert Villa, Marc; Martin Alemany, Francisco; Chaparro Danon, David; Pablos Hernandez, Miriam; Pascual Biosca, Daniel; Park, Hyuk; Alonso Arroyo, Alberto; Onrubia Ibañez, Raul; Yam Ontiveros, Luis Eduardo; Rodriguez Silva, Juan Carlos; Piles Guillem, Maria; Deng, Xinping; Querol Borras, Jorge; Corbella Sanahuja, Ignasi
    Competitive project

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  • Radiación y propagación (RP): colección de problemas

     Corbella Sanahuja, Ignasi; Fabregas Canovas, Francisco Javier; Torres Torres, Francisco; Vall-llossera Ferran, Mercedes Magdalena
    Date: 2013-09-02
    Report

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  • Radiació i propagació. Fulls de resposta laboratori

     Corbella Sanahuja, Ignasi; Fabregas Canovas, Francisco Javier; Torres Torres, Francisco; Vall-llossera Ferran, Mercedes Magdalena
    Date: 2013-07-09
    Report

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  • Radiation and Propagation (RP-2B). Exercises. October 2013

     Corbella Sanahuja, Ignasi; Fabregas Canovas, Francisco Javier; Torres Torres, Francisco; Vall-llossera Ferran, Mercedes Magdalena
    Date: 2013-10-07
    Report

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  • Radiació i propagació. Pràctiques de laboratori

     Corbella Sanahuja, Ignasi; Fabregas Canovas, Francisco Javier; Torres Torres, Francisco; Vall-llossera Ferran, Mercedes Magdalena
    Date: 2013-07-03
    Report

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  • PRODUCTOS Y APLICACIONES AVANZADOS DE SMOS Y FUTURAS MISIONES. PARTE UPC

     Vall-llossera Ferran, Mercedes Magdalena
    Competitive project

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  • Radiometric performance of SMOS full polarimetric imaging

     Wu, Lin; Torres Torres, Francisco; Corbella Sanahuja, Ignasi; Duffo Ubeda, Nuria; Duran Martinez, Israel; Vall-llossera Ferran, Mercedes Magdalena; Camps, Adiano; Delwart, Steven; Martín Neira, Manuel
    IEEE Geoscience and Remote Sensing Letters
    Vol. 10, num. 6, p. 1454-1458
    DOI: 10.1109/LGRS.2013.2260128
    Date of publication: 2013-11
    Journal article

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    This work has been conducted in the framework of several projects devoted to assess the performance of the Soil Moisture and Ocean Salinity (SMOS) mission full-pol measurement mode. Since its launch in November 2009, SMOS is producing dual-polarization brightness temperature synthesized images that are yielding a high scientific return. However, these images are affected by a non-negligible spatial amplitude error, the so-called spatial bias (SB), that degrades geophysical parameter retrieval. This effect is particularly detrimental in SMOS polarimetric images where spatial bias is masking the polarimetric physical signature to a large extend. This paper presents a method to mitigate SMOS spatial bias by taking into account the co-and cross-polar antenna patterns in the image reconstruction algorithm through the, so called, full-pol G-matrix (FPG). The method is validated by producing spatial bias maps out of the comparison between SMOS full-pol images and an accurate polarimetric brightness temperature model of the ocean. This model has been provided to SMOS ESLs (Expert Support Laboratories) by LOCEAN (Laboratoire d'Océanographie et du Climat, France) as a test bench to validate and improve SMOS Level 1 (L1) data. Finally, a radiometric performance summary table comparing spatial bias and radiometric sensitivity between this new FPG approach and SMOS current co-polar G-matrix approach (CPG) is provided. This paper presents the best quality SMOS polarimetric images, which may lead a breakthrough in the science returns of the mission.

  • Real-time RFI detection and mitigation system for microwave radiometers

     Forte Veliz, Giuseppe Francesco; Querol Borras, Jorge; Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena
    IEEE transactions on geoscience and remote sensing
    Vol. 51, num. 10, p. 4928-4935
    DOI: 10.1109/TGRS.2013.2267595
    Date of publication: 2013-10
    Journal article

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    Microwave radiometers are very sensitive passive sensors that measure the power of the thermal noise within a determined bandwidth. Therefore, any other signal present in the band modifies the value of the measured power, and the corresponding estimated antenna temperature, from which the geophysical parameters are retrieved. Due to the high sensitivity and accuracy required for these instruments, radio frequency interference (RFI) is becoming more and more a serious problem. On one hand, ground-based or global RFI surveys are helping to understand the occurrence and types of RFI sources. If RFI does not necessarily affect the whole bandwidth, or it is not present during the whole integration time, the application of either frequency blanking, time blanking or signal spectrogram techniques can be applied. However, it would be desirable to apply techniques to estimate the RFI signal so that it can be subtracted from the received signal itself so that some useful measurements are still possible. Such a real-time system is currently being developed for RFI detection and mitigation. This work focuses however in the description and performance of a wavelet-based RFI-mitigation technique implemented in a FPGA hardware back-end. The interfering signal is estimated by using the powerful denoising capabilities of the wavelet transform, and it is then subtracted from the total received signal to obtain a RFI-mitigated noise signal. © 2012 IEEE.

  • Experimental study on the performance of RFI detection algorithms in microwave radiometry: Toward an optimum combined test

     Forte Veliz, Giuseppe Francesco; Tarongí Bauzá, José Miguel; Depau, Veronica; Vall-llossera Ferran, Mercedes Magdalena; Camps Carmona, Adriano Jose
    IEEE transactions on geoscience and remote sensing
    Vol. 51, num. 10, p. 4936-4944
    DOI: 10.1109/TGRS.2013.2273081
    Date of publication: 2013-10
    Journal article

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    Radio-frequency interference (RFI) is probably today's most serious limitation to the accurate retrieval of geophysical parameters from microwave radiometric measurements. Strong RFI inducing a change in the detected power larger than the natural variability is simple to detect. Moderate or weak RFI can be masked by the natural variability of the measurements, passing undetected and corrupting them. A number of techniques have been devised in the past years to detect and, eventually, mitigate RFI present in microwave radiometry measurements: 1) time domain; 2) frequency domain; 3) spectrogram techniques looking for anomalously high power peaks; 4) statistical techniques testing the hypothesis of Gaussianity of the received signal; 5) polarimetric techniques looking for anomalous signatures in the third and fourth Stokes parameters; or 6) wavelet techniques to estimate the RFI signal and cancel it (if any). In this paper, the first four techniques are evaluated with real data gathered with a multifrequency microwave radiometer. It will be shown how spectrogram techniques can detect RFI signals concentrated in narrow frequency bands and/or time intervals that may pass undetected with time-domain and/or frequency-domain techniques alone or with statistical methods. A combined approach is proposed to take advantage of the best performance of each technique. On one side, for strong localized RFI, the approach is spectrogram blanking or, if it is too demanding in terms of computational resources, simple time- and frequency-domain blanking. On the other side, for weak RFI, the approach is the Kurtosis statistical test, which exhibits the best performance among the ten normality tests evaluated, in conjunction with the Anderson-Darling test to detect potential RFI in the blind spots of the Kurtosis test. © 2012 IEEE.

    Radio-frequency interference (RFI) is probably today's most serious limitation to the accurate retrieval of geophysical parameters from microwave radiometric measurements. Strong RFI inducing a change in the detected power larger than the natural variability is simple to detect. Moderate or weak RFI can be masked by the natural variability of the measurements, passing undetected and corrupting them. A number of techniques have been devised in the past years to detect and, eventually, mitigate RFI present in microwave radiometry measurements: 1) time domain; 2) frequency domain; 3) spectrogram techniques looking for anomalously high power peaks; 4) statistical techniques testing the hypothesis of Gaussianity of the received signal; 5) polarimetric techniques looking for anomalous signatures in the third and fourth Stokes parameters; or 6) wavelet techniques to estimate the RFI signal and cancel it (if any). In this paper, the first four techniques are evaluated with real data gathered with a multifrequency microwave radiometer. It will be shown how spectrogram techniques can detect RFI signals concentrated in narrow frequency bands and/or time intervals that may pass undetected with time-domain and/or frequency-domain techniques alone or with statistical methods. A combined approach is proposed to take advantage of the best performance of each technique. On one side, for strong localized RFI, the approach is spectrogram blanking or, if it is too demanding in terms of computational resources, simple time- and frequency-domain blanking. On the other side, for weak RFI, the approach is the Kurtosis statistical test, which exhibits the best performance among the ten normality tests evaluated, in conjunction with the Anderson-Darling test to detect potential RFI in the blind spots of the Kurtosis test.

  • Sistema de estabilización para la compensación del movimiento angular en plataformas LIDAR móviles

     Rocadenbosch Burillo, Francisco; Tiana Alsina, Jordi; Bermejo Sanchez, Sergio; Vall-llossera Ferran, Mercedes Magdalena; Camps Carmona, Adriano Jose
    Date of request: 2013-07-22
    Invention patent

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  • Inter-comparison of SMOS and aquarius brightness temperatures at L-band over selected targets

     Pablos Hernandez, Miriam; Piles Guillem, Maria; Gonzalez Gambau, Verónica; Vall-llossera Ferran, Mercedes Magdalena; Camps Carmona, Adriano Jose
    IEEE International Geoscience and Remote Sensing Symposium
    p. 386-389
    DOI: 10.1109/IGARSS.2013.6721173
    Presentation's date: 2013-07
    Presentation of work at congresses

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    The spectral window at L-band (1.400 - 1.427 GHz) is reserved for passive microwave remote sensing. This band is well-suited to retrieve soil moisture and ocean salinity due to emissivity of soil and seawater decreases with moisture and salinity, respectively, affecting microwave radiation of the Earth's surface. Nowadays, there are two space missions devoted to Earth observation with L-band radiometers on-board: the SMOS mission from the ESA and the Aquarius/SAC-D mission from the NASA and CONAE. Both missions are providing the first TB measurements of the Earth's surface at 1.413 GHz. Thus, it is a great opportunity to compare SMOS and Aquarius TBs and verify the continuity and consistency of the data. This inter-comparison is a key requirement needed to use data of both radiometers for meteorological, hydrological and climatological studies on a long term.

  • On the synergy of SMOS and Terra/Aqua MODIS: high resolution soil moisture maps in near real-time

     Piles Guillem, Maria; Vall-llossera Ferran, Mercedes Magdalena; Camps Carmona, Adriano Jose; Sanchez, Nilda; Martinez Fernandez, Jose; Martinez, Justino; Gonzalez Gambau, Verónica; Riera, R.
    IEEE International Geoscience and Remote Sensing Symposium
    p. 3423-3426
    DOI: 10.1109/IGARSS.2013.6723564
    Presentation's date: 2013-07
    Presentation of work at congresses

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    An innovative downscaling approach to obtain fine-scale soil moisture estimates from 40 km SMOS observations has been developed. It optimally blends SMOS multi-angular and full-polarimetric information with MODIS visible/data into high resolution soil moisture maps. The core of the algorithm is a model that linksmicrowave/optical sensitivity to soilmoisture and linearly relates the two instruments across spatial scales. This algorithm has been implemented at SMOS-BEC facilities and near real-time maps of disaggregated soil moisture over the Iberian Peninsula are being distributed. In this work, the temporal and spatial variability of these maps is evaluated through comparison with ground-basedmesurements acquired at the REMEDHUS soil moisture network, in the central part of the Duero basin, Spain. Results from a two-year time-series comparison show that downscaled soil moisture maps compare well with in situ data and nicely reproduce soil moisture dynamics at a 1 km spatial scale.

  • UPCSAT-1, demostrador CubeSat para observación terrestre

     Jove Casulleras, Roger; Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena; Bou Balust, Elisenda; Ramos Castro, Juan Jose; Alarcon Cot, Eduardo Jose; Alonso Arroyo, Alberto
    Congreso de la Asociación Española de Teledetección
    p. 49-52
    Presentation's date: 2013-10
    Presentation of work at congresses

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    UPCSat-1, es el primer proyecto de la Universitat Politécnica de Catalunya para construir y lanzar un pico- satélite. El objetivo principal de este proyecto es construir, ensamblar, testear y poner en órbita baja terrestre (LEO) un sensor óptico y un sensor de oxígeno monoatómico entre otros demostradores tecnológicos. Empezado en 2007 y actualmente en fase de integración, el satélite UPCSat-1 pretende demostrar la validez de la plataforma y las tecnologías que incorpora. Su objetivo es adquirir el know-how para la fabricación de CubeSats para preparar misiones más complejas en un futuro cercano. Por otro lado el proyecto tiene un fuerte componente educacional puesto que algunos de los subsistemas han sido desarrollados por nuestros estudiantes a través de sus proyectos finales de carrera. Se espera el lanzamiento para antes de 2015.

  • Study of radio frequency interference effects on radiometry bands in urban environments

     Forte Veliz, Giuseppe Francesco; Camps Carmona, Adriano Jose; Tarongí Bauzá, José Miguel; Vall-llossera Ferran, Mercedes Magdalena
    IEEE International Geoscience and Remote Sensing Symposium
    p. 1069-1072
    DOI: 10.1109/IGARSS.2012.6351364
    Presentation's date: 2013-07
    Presentation of work at congresses

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    Microwave radiometers are very accurate passive sensors that have been successfully used in Earth remote sensing during the last decades. Microwave radiometers measure thermal noise, therefore any other signal (radio-frequency interference or RFI) present in the band modifies the value of the measured power, and the corresponding estimated antenna temperature, from which the geophysical parameters will be retrieved. An on-going RFI survey shows how corrupted is the spectrum “protected” L-band in the city of Barcelona. This type of studies should help to validate or discard the measurements made there, and in other locations, and also to take further actions against RFI. Detection and mitigation techniques are used to validate results.

  • Calibration, performance, and imaging tests of a fully digital synthetic aperture interferometer radiometer

     Ramos Perez, Isaac; Forte Veliz, Giuseppe Francesco; Camps Carmona, Adriano Jose; Bosch Lluis, Xavier; Rodríguez Álvarez, Nereida; Valencia Domenech, Enric; Park, Hyuk; Vall-llossera Ferran, Mercedes Magdalena
    IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
    Vol. 5, num. 3, p. 723-734
    DOI: 10.1109/JSTARS.2012.2193118
    Date of publication: 2012-06-28
    Journal article

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    This work presents the calibration, characterization, and imaging tests of the Passive Advanced Unit-Synthetic Aperture instrument (PAU-SA). PAU-SA is a fully digital -shaped two-dimensional synthetic aperture interferometric radiometer operating at the Global Positioning System (GPS) L1 band ( GHz), conceived as a test-bed for potential technological improvements in future instruments. Calibration of instrumental offsets is performed by looking to a microwave absorber and the “cold” sky. Since the instrument operates in the GPS L1 band, GPS satellites are imaged therefore, a new way to compute the Flat Target Response (FTR) has been devised. Internal phase/amplitude calibration is performed using a new technique that consists of injecting pseudo-random noise signals. Different paths from the input switch to the antennas are calibrated by means of an external beacon. A near-field to far-field transformation is applied to compensate for differences in the propagation paths. Finally, absolute amplitude calibration is achieved by imaging the GPS satellites constellation when pointing to the zenith. Evaluation of the images’ quality in terms of angular resolution, radiometric resolution and precision, show the goodness of the techniques applied to compensate for instrumental errors, the imaging capabilities of the instrument, and demonstrate their applicability in future missions.

  • A new space technology for ocean observation: the SMOS mission

     Font Ferré, Jordi; BALLABRERA POY, JOAQUIM; Camps Carmona, Adriano Jose; Corbella Sanahuja, Ignasi; Duffo Ubeda, Nuria; Duran Martínez, Israel; Emelianov Kolomitski, Mikhail; Enrique González, Luis; Fernández Gallego, Pedro; Gabarro Prats, Carolina; González, Cristina; Gonzalez Gambau, Verónica; Gourrion, J.; Guimbard, Sébastien Arnaud; Hoareau, N.; Julià, A; Kalaroni, S.; Konstantinidou, Anna; Aretxabaleta, L.; Martínez, Justino; Miranda, Jorge Miguel; Monerris Belda, Alessandra; Montero, Sergio; Mourre, B.; Pablos Hernandez, Miriam; Pérez Villar, Fernando; Piles Guillem, Maria; Portabella, Marcos; Sabia, Roberto; Salvador, Joaquin; Talone, Marco; Torres Torres, Francisco; Turiel Martínez, Antonio; Vall-llossera Ferran, Mercedes Magdalena; Villarino, Ramon
    Scientia marina
    Vol. 76, num. Supl. 1, p. 249-259
    DOI: 10.3989/scimar.03621.19K
    Date of publication: 2012
    Journal article

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    Capability for sea surface salinity observation was an important gap in ocean remote sensing in the last few decades of the 20th century. New technological developments during the 1990s at the European Space Agency led to the proposal of SMOS (Soil Moisture and Ocean Salinity), an Earth explorer opportunity mission based on the use of a microwave interferometric radiometer, MIRAS (Microwave Imaging Radiometer with Aperture Synthesis). SMOS, the first satellite ever addressing the observation of ocean salinity from space, was successfully launched in November 2009. The determination of salinity from the MIRAS radiometric measurements at 1.4 GHz is a complex procedure that requires high performance from the instrument and accurate modelling of several physical processes that impact on the microwave emission of the ocean’s surface. This paper introduces SMOS in the ocean remote sensing context, and summarizes the MIRAS principles of operation and the SMOS salinity retrieval approach. It describes the Spanish SMOS high-level data processing centre (CP34) and the SMOS Barcelona Expert Centre on Radiometric Calibration and Ocean Salinity (SMOS-BEC), and presents a preliminary validation of global sea surface salinity maps operationally produced by CP34.

  • Snow thickness monitoring using GNSS measurements

     Rodríguez Álvarez, Nereida; Aguasca Sole, Alberto; Valencia Domenech, Enric; Bosch Lluis, Xavier; Camps Carmona, Adriano Jose; Ramos Perez, Isaac; Park, Hyuk; Vall-llossera Ferran, Mercedes Magdalena
    IEEE Geoscience and Remote Sensing Letters
    Vol. 9, num. 6, p. 1109-1113
    DOI: 10.1109/LGRS.2012.2190379
    Date of publication: 2012
    Journal article

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  • Optimum intercalibration time in synthetic aperture interferometric radiometers: application to SMOS

     Ramos Perez, Isaac; Bosch Lluis, Xavier; Camps Carmona, Adriano Jose; González Gambau, Veronica; Valencia Domenech, Enric; Rodríguez Álvarez, Nereida; Park, Hyuk; Vall-llossera Ferran, Mercedes Magdalena; Forte Veliz, Giuseppe Francesco
    IEEE Geoscience and Remote Sensing Letters
    Vol. 9, num. 4, p. 774-777
    DOI: 10.1109/LGRS.2011.2181483
    Date of publication: 2012
    Journal article

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    Interpolation strategies for calibration of the Soil Moisture and Ocean Salinity (SMOS) mission of the European Space Agency are tested and compared. Calibration strategy (how and how often) is critical in achieving the required performance of any instrument, but it is even more important in very complex instruments such as the new family of synthetic aperture interferometric radiometers and, in particular, in the Microwave Imaging Radiometer by Aperture Synthesis instrument aboard the SMOS mission. On one hand, frequent calibration reduces the available observation time. On the other hand, the calibration requirements for soil moisture applications are more relaxed than those for ocean salinity, so the intercalibration time requirements are very different. Since SMOS drifts are stationary, half-orbit information is available to perform different interpolation strategies. In this letter, these approaches are tested to estimate the calibration parameters between consecutive calibrations. The average root-mean-square phase error is then used to find the optimum interpolation strategy and intercalibration time. On the other side, in real-time instruments, the “future” calibration data are not available at the time of taking the measurements, and predictors are required to estimate the evolution of the calibration parameters from past data only. For these systems, the extended Kalman filter can be used. The intercalibration time in a real-time instrument is evaluated, and the requirements and performances are compared to offline instruments.

  • Vegetation water content estimation using GNSS measurements

     Rodriguez Alvarez, Nereida; Bosch Lluis, Xavier; Camps Carmona, Adriano Jose; Ramos Perez, Isaac; Valencia Domenech, Enric; Park, Hyuk; Vall-llossera Ferran, Mercedes Magdalena
    IEEE Geoscience and Remote Sensing Letters
    Vol. 9, num. 2, p. 282-286
    DOI: 10.1109/LGRS.2011.2166242
    Date of publication: 2012-03
    Journal article

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    Global Navigation Satellite Systems (GNSS) opportunity signals reflected at or near the Earth's surface have already shown their potential to perform retrievals of a number of geophysical parameters. Radio occultations using GNSS signals are also used for atmospheric sensing. This letter presents a GNSS technique to retrieve vegetation water content (VWC). This technique measures the received powers of the GPS signals in open sky and under the vegetation layer. From these two powers, the attenuation due to the vegetation is computed, which is related to the VWC. This letter presents the results obtained after deploying the instrument in a walnut-tree stand for 11 months.

  • Access to the full text
    PAU-SA: a synthetic aperture interferometric radiometer test bed for potential improvements in future missions  Open access

     Ramos Perez, Isaac; Camps Carmona, Adriano Jose; Bosch Lluis, Xavier; Rodríguez Álvarez, Nereida; Valencia Domenech, Enric; Park, Hyuk; Forte Veliz, Giuseppe Francesco; Vall-llossera Ferran, Mercedes Magdalena
    Sensors
    Vol. 12, num. 6, p. 7738-7777
    DOI: 10.3390/s120607738
    Date of publication: 2012-06
    Journal article

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    The Soil Moisture and Ocean Salinity (SMOS) mission is an Earth Explorer Opportunity mission from the European Space Agency (ESA). Its goal is to produce global maps of soil moisture and ocean salinity using the Microwave Imaging Radiometer by Aperture Synthesis (MIRAS). The purpose of the Passive Advanced Unit Synthetic Aperture (PAU-SA) instrument is to study and test some potential improvements that could eventually be implemented in future missions using interferometric radiometers such as the Geoestacionary Atmosferic Sounder (GAS), the Precipitation and All-weather Temperature and Humidity (PATH) and the Geostationary Interferometric Microwave Sounder (GIMS). Both MIRAS and PAU-SA are Y-shaped arrays with uniformly distributed antennas, but the receiver topology and the processing unit are quite different. The purpose of this work is to identify the elements in the MIRAS’s design susceptible of improvement and apply them in the PAU-SA instrument demonstrator, to test them in view of these future interferometric radiometer missions.

  • Review of the CALIMAS Team Contributions to European Space Agency¿s Soil Moisture and Ocean Salinity Mission Calibration and Validation

     Camps Carmona, Adriano Jose; Font Ferré, Jordi; Corbella Sanahuja, Ignasi; Vall-llossera Ferran, Mercedes Magdalena; Portabella, Marcos; BALLABRERA POY, JOAQUIM; Gonzalez Gambau, Verónica; Piles Guillem, Maria; Aguasca Sole, Alberto; Acevo Herrera, René; Gabarro Prats, Carolina; Duffo Ubeda, Nuria; Bosch, Xavier; Fernández Gallego, Pedro; Gourrion, J.; Guimbard, Sébastien Arnaud; Marín, Anna; Martínez, Justino; Monerris Belda, Alessandra; Pérez, Baptiste; Pérez Villar, Fernando; Salvador, Joaquin; Sabia, Roberto; Talone, Marco; Torres Torres, Francisco; Pablos, Miriam; Martínez-Fernández, José; ANTONIO, TURIEL MARTÍNEZ; Valencia Domenech, Enric; Rodríguez Álvarez, Nereida; Sanchez, Nilda; Pérez Gutiérrez, Carlos; Baroncini Turricchia, Guido; Rius, Antonio; Ribó Vedrilla, Serni
    Remote sensing of environment
    Vol. 4, num. 5, p. 1272-1309
    DOI: 10.3390/rs4051272
    Date of publication: 2012
    Journal article

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  • Validation and experimental tests of the PAU-synthetic aperture radiometer

     Ramos Perez, Isaac; Forte Veliz, Giuseppe Francesco; Camps Carmona, Adriano Jose; Bosch Lluis, Xavier; Rodríguez Álvarez, Nereida; Valencia Domenech, Enric; Park, Hyuk; Vall-llossera Ferran, Mercedes Magdalena
    IEEE International Geoscience and Remote Sensing Symposium
    p. 4656-4659
    DOI: 10.1109/IGARSS.2012.6350427
    Presentation's date: 2012-07
    Presentation of work at congresses

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    This paper presents calibration and the radiometric performance of the Passive Advanced Unit Synthetic Aperture (PAU-SA) in order to verify the instrument's characterization.

  • SMOS CP34 soil moisture and ocean salinity maps

     Font Ferré, Jordi; Gabarró, Carolina; BALLABRERA POY, JOAQUIM; Turiel Martínez, Antonio; Martínez, Justino; Umbert, M.; Pérez, Francisco C.; Hoareau, N.; Portabella, Marcos; González Gambau, Veronica; Gourrion, J.; Guimbard, Sébastien Arnaud; Piles Guillem, Maria; Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena
    Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment
    p. 1-4
    DOI: 10.1109/MicroRad.2012.6185236
    Presentation's date: 2012
    Presentation of work at congresses

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    This paper presents the soil moisture and ocean salinity maps from the SMOS mission generated operationally by the Spanish SMOS Level 3 and 4 data processing center (CP34) and experimentally by the SMOS Barcelona Expert Center (SMOS-BEC).

  • A downscaling approach to combine SMOS multi-angular and full-polarimetric observations with MODIS VIS/IR data into high resolution soil moisture maps

     Piles Guillem, Maria; Vall-llossera Ferran, Mercedes Magdalena; Laguna, Laia; Camps Carmona, Adriano Jose
    IEEE International Geoscience and Remote Sensing Symposium
    p. 1247-1250
    DOI: 10.1109/IGARSS.2012.6351316
    Presentation's date: 2012-07
    Presentation of work at congresses

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    A downscaling algorithmfor SMOS which combines MODIS Visible/Infrared data and SMOS horizontal brightness temperatures at 42.5◦ incidence angle into high-resolution soil moisture maps has been shown to nicely reproduce soil moisture dynamics at a 1 km spatial scale. The core of this algorithm is a linking model that depicts the synergy between SMOS and MODIS observations and their sensitivity to soil moisture. In this work, the impact of adding SMOS observations at horizontal and vertical polarizations and at multiple incidence angles to this linking model has been evaluated using 6 months of observations over the Murrumbidgee catchment, South-East Australia, and a robust alternative formulation is proposed. Results show that adding SMOS observations at multiple incidence angles and both polarizations the algorithm is more stable over time and its minimization error is reduced. By comparing with in situ data, a remarkable improvement of the linear regression between downscaled and in situ data is also observed (slope of 0.95).

  • Spatial patterns of SMOS downscaled soil moisture maps over the remedhus network (Spain)

     Sanchez, Nilda; Piles Guillem, Maria; Scaini, Anna; Martinez Fernandez, Jose; Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena
    IEEE International Geoscience and Remote Sensing Symposium
    p. 714-717
    DOI: 10.1109/IGARSS.2012.6351465
    Presentation's date: 2012-07
    Presentation of work at congresses

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    This paper describes the relationships found between remotely sensed soil moisture, in situ observed soil moisture, and spatial distribution of soil and climatic factors. For the comparison between remote and in situ soil moisture, soil moisture map series at high resolution, obtained by applying a downscaling approach that combines Soil Moisture and Ocean Salinity (SMOS) and MODIS imagery is extracted. The in situ soil moisture series are obtained from the Soil Moisture Measurement Stations Network (REMEDHUS) in Spain. For the spatial analysis, factors such as topography, precipitation, and land uses were mapped from the climatic and cartographic database of REMEDHUS. The comparison between downscaled and in situ soil moisture data resulted in correlation coefficient (R) values between 0.40 and 0.70, bias between -0.04 and 0.16 m3m-3, and root mean squared difference (RMSD) between 0.07 and 0.19 m3m-3. Regarding the spatial correlations between downscaled and spatial factors, no clear patterns were found when considering the topography (Topographic Wetness Index, TWI), and the land uses (Landsat classification). Nevertheless, the downscaled soil moisture was more related with the spatial distribution of precipitation (Antecedent Precipitation Index, API), with significant correlations varying between 0.24 and 0.55.

    This paper describes the relationships found between remotely sensed soil moisture, in situ observed soil moisture, and spatial distribution of soil and climatic factors. For the comparison between remote and in situ soil moisture, soil moisture map series at high resolution, obtained by applying a downscaling approach that combines Soil Moisture and Ocean Salinity (SMOS) and MODIS imagery is extracted. The in situ soil moisture series are obtained from the Soil Moisture Measurement Stations Network (REMEDHUS) in Spain. For the spatial analysis, factors such as topography, precipitation, and land uses were mapped from the climatic and cartographic database of REMEDHUS. The comparison between downscaled and in situ soil moisture data resulted in correlation coefficient (R) values between 0.40 and 0.70, bias between -0.04 and 0.16 m3m-3, and root mean squared difference (RMSD) between 0.07 and 0.19 m3m-3. Regarding the spatial correlations between downscaled and spatial factors, no clear patterns were found when considering the topography (Topographic Wetness Index, TWI), and the land uses (Landsat classification). Nevertheless, the downscaled soil moisture was more related with the spatial distribution of precipitation (Antecedent Precipitation Index, API), with significant correlations varying between 0.24 and 0.55.

  • Digital back-end for RFI detection and mitigation in microwave radiometers

     Forte Veliz, Giuseppe Francesco; Camps Carmona, Adriano Jose; Ramos, I.; Vall-llossera Ferran, Mercedes Magdalena
    IEEE International Geoscience and Remote Sensing Symposium
    p. 2953-2955
    DOI: 10.1109/IGARSS.2012.6350706
    Presentation's date: 2012-07
    Presentation of work at congresses

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    Radio-frequency interference (RFI) is a serious problem in microwave radiometry. In order to process the received data in real time, a powerful back-end for RFI detection and mitigation system must be implemented. This system includes many techniques against RFI, like time, frequency domain and spectrogram analysis. A wavelet-based RFI-mitigation technique is implemented in hardware. The interfering signal is estimated by using the powerful denoising capabilities of the wavelet transform. Then, this estimate of the RFI signal is subtracted from the total received signal to obtain a RFI-mitigated noise signal. Statistical analysis helps to validate the mentioned methods.

  • CONTRIBUTIONS TO EARTH OBSERVATION USING GNSS-R OPPORTUNITY SIGNALS  Open access

     Rodriguez Alvarez, Nereida
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    During years a number of satellites have been developed to remotely sense Earth geophysical parameters for weather forecasting and other climate studies. In recent years the use of reflected Global Navigation Satellite System Signals (GNSS-R) has shown its potential to retrieve geophysical parameters over the ocean, mainly altimetry and sea state, and over land, mainly soil moisture. It is known that sea roughness has an impact on L-band radiometric measurements, and therefore on the retrieved sea surface salinity (SSS). GNSS-R is an interesting tool to help improving the sea state effect correction to reduce the final SSS retrieval error. To demonstrate this idea the Passive Advanced Unit (PAU) project was proposed to the European Scienc Foundation (ESF) under the EURYI 2004 call. The main objective was the study of the direct relationship between the radiometric brightness temperatures and some GNSS-R observables to perform the state correction without using emission/scattering models. Once this goal was successfully addressed, the PAU objectives were broaden including the development of new GNSS-R instruments and techniques, and the study of retrieving geophysical parameters from different surfaces. The present Ph.D. dissertation describes one of the research lines of the the PAU project, undertaken between February 2007 and December 2011, within the Passive Remote Sensing Group of the Remote Sensing Lab, at the Department of Signal Theory and Communications of the Universitat Politènica de Catalunya. The present Ph.D. dissertation focuses on GNSS-R techniques applied to the observation of different types of scattering surfaces (land surfaces: bare soils, vegetation-covered soils, snow-covered soils; inland-water surfaces and ocean surfaces) and the retrieval of different geophysical parameters. Two main GNSS-R techniques have been studied and applied to real data obtained during seven field experiments, the Delay-Doppler Map (DDM) processing technique and the Interference-Pattern Technique (IPT), selecting the one most appropriate to the observed surface. Furthermore, in the context of this Ph.D dissertation a new type of GNSS-R instrument has been developed, being the main tool for the application of the IPT and the retrieval of several geophysical parameters over land and inland-water surfaces. After an introduction on GNSS-R and the PAU-project, the methodology, the instruments and the techniques used to retrieve soil moisture, vegetation height and topography in agricultural areas, snow thickness, water level in reservoirs, and wind speed in ocean surfaces, are described. These retrievals show the potential that these opportunity signals have for monitoring a broad kind of effects. After that, some studies related to space-borne GNSS-R techniques are summarized. Finally a summary of the work performed in this Ph. D. dissertation, the main conclusions and the future work lines are presented. The presented results contribute to promote the use of the GNSS opportunity signals for monitoring geophysical parameters to increase the understanding of the Earth¿s water cycle, and position these techniques as suitable tools that enhance water resources management.

  • Q-00002

     Tiana Alsina, Jordi; Bermejo Sanchez, Sergio; Vall-llossera Ferran, Mercedes Magdalena; Camps Carmona, Adriano Jose; Rocadenbosch Burillo, Francisco
    Competitive project

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  • Radio-frequency interference detection and mitigation algorithms for synthetic aperture radiometers

     Camps Carmona, Adriano Jose; Gourrion, J.; Tarongí Bauzá, José Miguel; Vall-llossera Ferran, Mercedes Magdalena; Gutiérrez, A.; Barbosa Torralbo, José; Castro, Rita
    Algorithms
    Vol. 4, num. 3, p. 155-182
    DOI: 10.3390/a4030155
    Date of publication: 2011
    Journal article

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  • Analysis of a Least-Squares Soil Moisture Retrieval Algorithm from L-band Passive Observations

     Piles Guillem, Maria; Vall-llossera Ferran, Mercedes Magdalena; Camps Carmona, Adriano Jose; Talone, Marco; Monerris Belda, Alessandra
    Remote Sensing
    Vol. 2, num. 1, p. 352-374
    DOI: 10.3390/rs2010352
    Date of publication: 2011-01-20
    Journal article

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  • Downscaling SMOS-derived soil moisture using MODIS visible/infrared data

     Piles Guillem, Maria; Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena; Corbella Sanahuja, Ignasi; Panciera, Rocco; Rudiger, Christoph; Kerr, Yann H.; Walker, Jeffrey
    IEEE transactions on geoscience and remote sensing
    Vol. 49, num. 9, p. 3156-3166
    DOI: 10.1109/TGRS.2011.2120615
    Date of publication: 2011-09
    Journal article

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    A downscaling approach to improve the spatial resolution of Soil Moisture and Ocean Salinity (SMOS) soil moisture estimates with the use of higher resolution visible/infrared (VIS/IR) satellite data is presented. The algorithm is based on the so-called “universal triangle” concept that relates VIS/IR parameters, such as the Normalized Difference Vegetation Index (NDVI), and Land Surface Temperature (Ts), to the soil moisture status. It combines the accuracy of SMOS observations with the high spatial resolution of VIS/IR satellite data into accurate soil moisture estimates at high spatial resolution. In preparation for the SMOS launch, the algorithm was tested using observations of the UPC Airborne RadIomEter at L-band (ARIEL) over the Soil Moisture Measurement Network of the University of Salamanca (REMEDHUS) in Zamora (Spain), and LANDSAT imagery. Results showed fairly good agreement with ground-based soil moisture measurements and illustrated the strength of the link between VIS/IR satellite data and soil moisture status. Following the SMOS launch, a downscaling strategy for the estimation of soil moisture at high resolution from SMOS using MODIS VIS/IR data has been developed. The method has been applied to some of the first SMOS images acquired during the commissioning phase and is validated against in situ soil moisture data from the OZnet soil moisture monitoring network, in South-Eastern Australia. Results show that the soil moisture variability is effectively captured at 10 and 1 km spatial scales without a significant degradation of the root mean square error.

  • Review of crop growth and soil moisture monitoring from a ground-based instrument implementing the Interference Pattern GNSS-R Technique

     Rodriguez Alvarez, Nereida; Bosch Lluis, Xavier; Camps Carmona, Adriano Jose; Aguasca Sole, Alberto; Vall-llossera Ferran, Mercedes Magdalena; Valencia Domenech, Enric; Ramos Perez, Isaac; Park, Hyuk
    Radio science
    Vol. 46, num. RS0C03, p. 1-11
    DOI: 10.1029/2011RS004680
    Date of publication: 2011-10-15
    Journal article

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  • Error Covariance Matrices Characterization in the Ocean Salinity Retrieval Cost Function within the SMOS Mission

     Talone, Marco; Gabarro Prats, Carolina; Camps Carmona, Adriano Jose; Sabia, Roberto; Gourrion, J.; Vall-llossera Ferran, Mercedes Magdalena; Font, J.
    Journal of atmospheric and oceanic technology
    Vol. 28, num. 9, p. 1155-1166
    DOI: 10.1175/2011.JTECHO813.1
    Date of publication: 2011-09
    Journal article

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  • Land Geophysical Parameters Retrieval Using the Interference Pattern GNSS-R Technique

     Rodriguez Alvarez, Nereida; Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena; Bosch Lluis, Xavier; Monerris Belda, Alessandra; Ramos Perez, Isaac; Valencia Domenech, Enric; Marchan Hernandez, Juan Fernando; Martinez Fernandez, Jose; Baroncini Turricchia, Guido; Pérez Gutiérrez, Carlos; Sanchez, Nilda
    IEEE transactions on geoscience and remote sensing
    Vol. 49, num. 1, p. 71-84
    DOI: 10.1109/TGRS.2010.2049023
    Date of publication: 2011-01
    Journal article

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  • Snow monitoring using GNSS-R techniques

     Rodriguez Alvarez, Nereida; Aguasca Sole, Alberto; Valencia Domenech, Enric; Bosch Lluis, Xavier; Ramos Perez, Isaac; Park, Hyuk; Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena
    IEEE International Geoscience and Remote Sensing Symposium
    p. 4375-4378
    DOI: 10.1109/IGARSS.2011.6050201
    Presentation's date: 2011-07-25
    Presentation of work at congresses

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    GNSS-R techniques are currently being studied to remotely sense a number of geophysical parameters over different types of surfaces [1-6]. The Interference Pattern Technique (IPT) is based on the measurement of the interference pattern of the GPS direct and reflected signals, after reflecting over the surface, as the GPS satellites move. This paper extends previous studies [7-11], in which water level was monitored [7] and land areas were observed retrieving soil moisture, topography and vegetation height for different kinds of crops (wheat, barley and maize) [8-10], to a snowcovered soils studies.

    GNSS-R techniques are currently being studied to remotely sense a number of geophysical parameters over different types of surfaces [1-6]. The Interference Pattern Technique (IPT) is based on the measurement of the interference pattern of the GPS direct and reflected signals, after reflecting over the surface, as the GPS satellites move. This paper extends previous studies [7-11], in which water level was monitored [7] and land areas were observed retrieving soil moisture, topography and vegetation height for different kinds of crops (wheat, barley and maize) [8-10], to a snow- covered soils studies.

  • Water level monitoring using the interference pattern GNSS-R technique

     Rodriguez Alvarez, Nereida; Bosch Lluis, Xavier; Camps Carmona, Adriano Jose; Ramos Perez, Isaac; Valencia Domenech, Enric; Park, Hyuk; Vall-llossera Ferran, Mercedes Magdalena
    IEEE International Geoscience and Remote Sensing Symposium
    p. 2334-2337
    DOI: 10.1109/IGARSS.2011.6049677
    Presentation's date: 2011-07-25
    Presentation of work at congresses

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  • First results of the PAU-SA synthetic aperture radiometer

     Ramos Perez, Isaac; Forte, Giuseppe; Bosch Lluis, Xavier; Camps Carmona, Adriano Jose; Valencia Domenech, Enric; Rodriguez Alvarez, Nereida; Park, Hyuk; Vall-llossera Ferran, Mercedes Magdalena
    IEEE International Geoscience and Remote Sensing Symposium
    p. 3633-3636
    DOI: 10.1109/IGARSS.2011.6050011
    Presentation's date: 2011-07-28
    Presentation of work at congresses

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  • Downscaling SMOS-derived soil moisture using MODIS visible/infrared data

     Piles Guillem, Maria; Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena; Corbella Sanahuja, Ignasi; Panciera, Rocco; Rudiger, Chris; Kerr, Yann H.; Walker, Jeff
    IEEE International Geoscience and Remote Sensing Symposium
    p. 3156-3166
    DOI: 10.1109/TGRS.2011.2120615
    Presentation's date: 2011-07-28
    Presentation of work at congresses

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  • Vegetation water content estimation using GNSS measurements

     Rodriguez Alvarez, Nereida; Bosch Lluis, Xavier; Camps Carmona, Adriano Jose; Ramos Perez, Isaac; Valencia Domenech, Enric; Park, Hyuk; Vall-llossera Ferran, Mercedes Magdalena
    IEEE International Geoscience and Remote Sensing Symposium
    p. 282-286
    DOI: 10.1109/LGRS.2011.2166242
    Presentation's date: 2011-07-25
    Presentation of work at congresses

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  • Enhancing the spatial resolution of SMOS soil moisture data over Spain

     Piles Guillem, Maria; Monerris Belda, Alessandra; Vall-llossera Ferran, Mercedes Magdalena; Camps Carmona, Adriano Jose
    IEEE International Geoscience and Remote Sensing Symposium
    p. 3121-3124
    DOI: 10.1109/IGARSS.2011.6049879
    Presentation's date: 2011-07-28
    Presentation of work at congresses

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  • Sea surface salinity retrievals from HUT-2D L-band radiometric measurements

     Talone, Marco; Sabia, Roberto; Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena; Gabarro Prats, Carolina; Font Ferré, Jordi
    Remote sensing of environment
    Vol. 114, num. 8, p. 1756-1764
    DOI: 10.1016/j.rse.2010.03.006
    Date of publication: 2010-08-16
    Journal article

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  • Performance of soil moisture retrieval algorithms using multiangular L band brightness temperatures

     Piles Guillem, Maria; Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena; Monerris Belda, Alessandra; Talone, Marco; Sabater, J.M.
    Water resources research
    Vol. 46, num. W06506, p. 1-9
    DOI: 10.1029/2009WR008554
    Date of publication: 2010-06-09
    Journal article

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  • Determination of the Sea Surface Salinity Error Budget in the Soil Moisture and Ocean Salinity Mission

     Sabia, Roberto; Camps Carmona, Adriano Jose; Talone, Marco; Vall-llossera Ferran, Mercedes Magdalena; Font Ferré, Jordi
    IEEE transactions on geoscience and remote sensing
    Vol. 48, num. 4, p. 1684-1693
    DOI: 10.1109/TGRS.2009.2034648
    Date of publication: 2010-03
    Journal article

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  • Access to the full text
    Study of maize plants effects in the retrieval of soil moisture using the interefence Ppttern GNSS-R technique  Open access

     Rodriguez Alvarez, Nereida; Bosch Lluis, Xavier; Acevo Herrera, René; Aguasca Sole, Alberto; Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena; Ramos Perez, Isaac; Valencia Domenech, Enric
    IEEE International Geoscience and Remote Sensing Symposium
    p. 3813-3816
    DOI: 10.1109/IGARSS.2010.5651724
    Presentation's date: 2010-07-30
    Presentation of work at congresses

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    The use of Global Navigation Satellite Signals Reflections (GNSS-R) techniques to retrieve geophysical parameters from surfaces has been increased in the recent years. These techniques have resulted in suitable tools to obtain information about the sea state of oceans, which is very useful to improve the ocean salinity retrieval, and also, information about the soil moisture of lands. The present work focuses on the use of the Interference Pattern Technique (IPT), a particular type of GNSS-R technique, to study vegetation-covered soils. The IPT consists mainly of the measurement of the interference pattern between the GPS direct and reflected signals (the interference power), after they impinge over the ensemble soil surface and vegetation layer. The measured interference signal provides information on the soil moisture of the surface and also, on the vegetation height.

  • Access to the full text
    Altimetry study performed using an airborne GNSS-reflectometer  Open access

     Rodriguez Alvarez, Nereida; Acevo Herrera, René; Aguasca Sole, Alberto; Valencia Domenech, Enric; Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena; Bosch Lluis, Xavier; Ramos Perez, Isaac
    IEEE International Geoscience and Remote Sensing Symposium
    p. 3833-3836
    DOI: 10.1109/IGARSS.2010.5653872
    Presentation's date: 2010-07-30
    Presentation of work at congresses

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    The Global Navigation Satellite Signals Reflections (GNSSR)techniques have been widely used for remote sensing purposes retrieving geophysical parameters over different types of surfaces. Over the ocean, altimetry or sea state can be retrieved. Over land, soil moisture can be inferred and over ice, altimetry, and ice age are also retrieved. This paper presents the results of using GNSS-R techniques to retrieve altimetry from the measurements of an airborne GNSS-Reflectometer.

  • Simulated SMOS Levels 2 and 3 Products: The Effect of Introducing ARGO Data in the Processing Chain and Its Impact on the Error Induced by the Vicinity of the Coast

     Talone, M; Camps Carmona, Adriano Jose; Mourre, B; Sabia, Roberto; Vall-llossera Ferran, Mercedes Magdalena; Gourrion, J; Gabarro, C
    IEEE transactions on geoscience and remote sensing
    Vol. 47, num. SI:9, p. 3041-3050
    Date of publication: 2009-09
    Journal article

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  • Soil Moisture Retrieval Using GNSS-R Techniques: Experimental Results Over a Bare Soil Field

     Rodriguez Alvarez, Nereida; Bosch Lluis, Xavier; Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena; Valencia Domenech, Enric; Marchan Hernandez, Juan Fernando; Ramos Perez, Isaac
    IEEE transactions on geoscience and remote sensing
    Vol. 47, num. 11, p. 3616-3624
    DOI: 10.1109/TGRS.2009.2030672
    Date of publication: 2009-11
    Journal article

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