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  • Radiometric and spatial resolution constraints in millimeter-mave close-range passive screener systems

     Nova Lavado, Enrique; Romeu Robert, Jordi; Torres Torres, Francisco; Pablos Hernandez, Miriam; Riera Salis, Jose Manuel; Broquetas Ibars, Antoni; Jofre Roca, Luis
    IEEE transactions on geoscience and remote sensing
    Date of publication: 2013-04
    Journal article

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    This paper presents a comparative study of the radiometric sensitivity and spatial resolution of three near-field (NF) passive screener systems: real aperture, 1-D synthetic aperture (SA), and 2-D SA radiometers are compared. The analytical expressions for the radiometric resolution, the number of required antennas, and the number of pixels in the image are derived taking into account the distortion produced by the NF geometry at nonboresight directions where the distortion is dominant. Based on the theoretical results, a performance comparison among the studied systems is carried out to show the advantages and drawbacks when using the radiometers in a close-range screening application. Moreover, the screener performance in a close-range environment is discussed from the results obtained in the aforementioned comparison.

  • Towards a SMOS operational mission: SMOSOps-Hexagonal

     Zurita Campos, Alberto Manuel; Corbella Sanahuja, Ignasi; Martín Neira, Manuel; Plaza, Miguel Angel; Torres Torres, Francisco; Benito, Francisco Javier
    IEEE transactions on geoscience and remote sensing
    Date of publication: 2013-06-03
    Journal article

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    The Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) on-board the Soil Moisture and Ocean Salinity (SMOS) mission is providing useful data since November 2009, and proving the potential of 2D interferometry from space. With the end of its nominal operation phase in November 2012, the mission is expected to extend its lifetime for at least more than two additional years. Along with all the current improvements on data processing and exploitation, the SMOS trail might need to be continued with the aim of providing data to the users in the coming years. This paper presents a SMOS follow-on operational mission which is the result of integrating the actual lessons learnt from MIRAS with a novel hexagonal array geometry, proving robustness against radio-frequency interferences (RFI) and receiver failures. The performance and the instrument architecture enhancements are exposed, along with a practical deployment solution.

  • 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
    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.

  • SMOS calibration and instrument performance after one year in orbit

     Oliva Martínez, Ramon; Martín Neira, Manuel; Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Kainulainen, Juha; Tenerelli, Joseph; Cabot, François; Martín Porqueras, Fernando
    IEEE transactions on geoscience and remote sensing
    Date of publication: 2013
    Journal article

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    This paper summarizes the rationale for the European Space Agency's Soil Moisture and Ocean Salinity (SMOS) mission routine calibration plan, including the analysis of the calibration parameter annual variability, and the performances and stability of SMOS images after one year of data. SMOS spends 1.68% of the total observation time in calibration. The instrument performs well within expectations with regard to accuracy and radiometric sensitivity, although spatial ripples are present in SMOS images. Several mechanisms are currently used or under investigation to mitigate this problem. Also, a loss antenna model has recently been introduced to correct for physical temperature-induced effects. This antenna model successfully corrects observed orbital variations, but has difficulties in correcting brightness temperature long-term drifting, as assessed using relatively well-known targets other than the external calibration region-cold space.

    This paper summarizes the rationale for the European Space Agency's Soil Moisture and Ocean Salinity (SMOS) mission routine calibration plan, including the analysis of the calibration parameter annual variability, and the performances and stability of SMOS images after one year of data. SMOS spends 1.68% of the total observation time in calibration. The instrument performs well within expectations with regard to accuracy and radiometric sensitivity, although spatial ripples are present in SMOS images. Several mechanisms are currently used or under investigation to mitigate this problem. Also, a loss antenna model has recently been introduced to correct for physical temperature-induced effects. This antenna model successfully corrects observed orbital variations, but has difficulties in correcting brightness temperature long-term drifting, as assessed using relatively well-known targets other than the external calibration region-cold space.

  • Impact of the local oscillator calibration rate on the SMOS measurements and retrieved salinities

     Gabarro Prats, Carolina; Gonzalez Gambau, Verónica; Corbella Sanahuja, Ignasi; Torres Torres, Francisco
    IEEE transactions on geoscience and remote sensing
    Date of publication: 2013-09-02
    Journal article

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    The local oscillators (LOs) of the Soil Moisture and Ocean Salinity mission payload are used to shift the operating frequency of the 72 receivers to an optimal intermediate frequency needed for the signal processing. The LO temperature variations produce phase errors in the visibility, which result in a blurring of the reconstructed brightness temperature (Tb) image. At the end of the commissioning phase, it was decided to calibrate the LO every 10 min while waiting for a more in-depth analysis. During short periods of time, the LOcalibration has been performed every 2 min to assess the impact of a higher calibration rate on the quality of the data. In this paper, by means of a decimation experiment, the relative errors of 6- and 10-min calibration interval data sets are estimated using the 2 min as a reference. A noticeable systematic across- and along-track pattern of amplitude ±0.3 K is observed for Tb differences between 10 and 2 min, whereas this is reduced between 6 and 2 min. A simulation experiment confirms that the nature of such systematic pattern is due to the visibility phase errors induced by the LO calibration rate. Such pattern is propagated into the sea surface salinity (SSS) retrievals. Overall, the SSS error increase (relative to the 2min SSS data) is about 0.39 and 0.14 psu for the 10- and 6-min data sets, respectively. This paper shows that a LO calibration rate of at least 6 min would noticeably improve the SSS retrievals.

  • Radio Frequency Interference in Microwave Radiometry: Statistical Analysis and Study of Techniques for Detection and Mitigation  Open access

     Tarongí Bauzá, José Miguel
    Defense's date: 2013-03-06
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    Microwave radiometry field has been increasing its performance with higher accuracy measurements, leading to a more presence in the remote sensing field. Several space-borne, air-borne and ground-based radiometers have been developed to perform measurement campaigns; however, the actual sensitivity of a radiometer is often limited by man-made radio emissions such as radars, broadcasting emissions, wireless communications and many other communication systems based on electromagnetic waves, limiting the improvement in the radiometers¿ performance. Consequently, in order to maintain the accuracy in the radiometric measurements, it has been researched in the Radio Frequency Interference (RFI) detection and mitigation systems and algorithms for the microwave radiometry field. The scope of this doctoral thesis is the development and testing of RFI detection and mitigation algorithms in order to enhance radiometric measurements performed by the Multifequency Experimental Radiometer with Interference Tracking for Experiments over Land and Littoral (MERITXELL). The MERITXELL has been developed during this thesis with the idea studying the RFI present in several radiometric bands and the way to mitigate it, as well as to obtain data from diverse frequency bands and devices in only one measurement campaign.

  • Radiometric and spatial resolution constraints in millimeter-wave close-range passive screener systems

     Nova Lavado, Enrique; Romeu Robert, Jordi; Torres Torres, Francisco; Pablos, M.; Riera, J.M.; Broquetas Ibars, Antoni; Jofre Roca, Luis
    IEEE transactions on geoscience and remote sensing
    Date of publication: 2013-04
    Journal article

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    This paper presents a comparative study of the radiometric sensitivity and spatial resolution of three near-field (NF) passive screener systems: real aperture, 1-D synthetic aperture (SA), and 2-D SA radiometers are compared. The analytical expressions for the radiometric resolution, the number of required antennas, and the number of pixels in the image are derived taking into account the distortion produced by the NF geometry at nonboresight directions where the distortion is dominant. Based on the theoretical results, a performance comparison among the studied systems is carried out to show the advantages and drawbacks when using the radiometers in a close-range screening application. Moreover, the screener performance in a close-range environment is discussed from the results obtained in the aforementioned comparison.

  • Spatial biases analysis and mitigation methods in SMOS images

     Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Wu, Lin; Duffo Ubeda, Nuria; Duran Martinez, Israel; Martín Neira, Manuel
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2013-07-22
    Presentation of work at congresses

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    SMOS brightness temperature images show some residual artifacts as a function of spatial directions. Due to having different antenna patterns in each element, even if knowing them perfectly, a minimum reconstruction error inherent to the inversion algorithm exists. On top of that, antenna patterns measurement errors and other effects such as cross-polarization terms, increase the spatial biases. Accurate characterization of these sources of error allows improving the quality of the SMOS images. Good results in this direction are reported.

  • In-orbit validations of SMOS full polarimetric equations

     Torres Torres, Francisco; Corbella Sanahuja, Ignasi; Wu, Lin; Duffo Ubeda, Nuria; Delwart, Steven; Martín Neira, Manuel
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2013-07-22
    Presentation of work at congresses

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    This paper analyzes the consistency of SMOS fully polarimetric measurement mode by comparing measured data over the ocean with the expected results. These last are based on an accurate ocean model provided by LOCEAN and simulated taking into account both the co- and cross-polar field antenna patterns. The successful image reconstruction by means of the so-called model full-pol G matrix (M-FPG) method validates SMOS main full-pol features: the full-pol switching scheme, the accuracy of the full-pol antenna pattern measurements and the full-polarimetric visibility equations.

  • Spatial decorrelation of radiometric noise in SMOS measurements

     Torres Torres, Francisco; Wu, Lin; Duffo Ubeda, Nuria; Corbella Sanahuja, Ignasi; Martín Neira, Manuel
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2012-07-22
    Presentation of work at congresses

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  • Stability of the MIRAS amplitude calibration

     Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Duffo Ubeda, Nuria; Martín Neira, Manuel
    Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment
    Presentation's date: 2012
    Presentation of work at congresses

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    Efficient methods to characterize and mitigate longand short- term drifts in SMOS data have been developed after careful analysis of the external and internal calibration parameters and by accurate modeling of the individual receiver frontends. A method to characterize this drift has been successfully developed and used to reduce the measured antenna temperature variations.

    Efficient methods to characterize and mitigate long-and short- term drifts in SMOS data have been developed after careful analysis of the external and internal calibration parameters and by accurate modeling of the individual receiver front-ends. A method to characterize this drift has been successfully developed and used to reduce the measured antenna temperature variations.

  • Supermiras instrument development, technology and calibration

     Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Duffo Ubeda, Nuria; Martín Neira, Manuel
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2012-07-22
    Presentation of work at congresses

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  • Enhanced SMOS amplitude calibration using external target

     Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Duffo Ubeda, Nuria; Duran, Israel; Pablos, Miriam; Martín Neira, Manuel
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2012-07-22
    Presentation of work at congresses

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  • Optical cross-correlation of millimeter wave signals applied to interferometric radiometry

     Nova, Enrique; Romeu Robert, Jordi; Torres Torres, Francisco; Broquetas Ibars, Antoni; Jofre Roca, Luis
    International Conference on Infrared, Millimeter, and Terahertz Waves
    Presentation's date: 2012-07
    Presentation of work at congresses

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    This paper presents a method to perform in the opti- cal domain the correlations required when processing millimeter wave interferometric radiometer signals. The main problem when addressing the design of an interferometric radiometer working at W-band resides on the distribution and correlation of large bandwidth signals acquired by each radiometer receiver. In order to avoid the necessity of baseband processing of signals with large relative bandwidths, the signals coming from the radiometric receivers are up-converted to the optical domain using LiNbO3 optical phase modulators. The modulated signals from each receiver pairs are added and and detected by a photodiode. The correlation is obtained from the resulting photocurrent.

  • SMOS instrument performance and calibration

     Martín Neira, Manuel; Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Kainulainen, Juha; Oliva, R.; Cabot, François; Tenerelli, Joseph
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2012-07-22
    Presentation of work at congresses

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  • Performance of a spatial error correction technique in SMOS brightness temperature images

     Wu, Lin; Torres Torres, Francisco; Corbella Sanahuja, Ignasi; Duffo Ubeda, Nuria; Martín Neira, Manuel
    Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment
    Presentation's date: 2012-03-05
    Presentation of work at congresses

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    Soil Moisture and Ocean Salinity (SMOS) brightness temperature synthesized images are obtained after a comprehensive calibration and error correction procedure. However, the final images are still contaminated by small but non-negligible spatial errors: the so-called pixel bias. These errors have been found to be very stable in the SMOS Alias-Free Field of View (AF-FoV) and can be mitigated, to a large extent, by applying a multiplicative mask to the measured brightness temperatures at the antenna plane. This paper describes the procedure to upgrade this mask to cover SMOS Extended AF­ FoV.

  • 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
    Date of publication: 2012
    Journal article

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  • Reduction of Secondary Lobes in Aperture Synthesis Radiometry

     Corbella Sanahuja, Ignasi; Martín Neira, Manuel; Oliva, R.; Torres Torres, Francisco; Duffo Ubeda, Nuria
    IEEE Geoscience and Remote Sensing Letters
    Date of publication: 2012-09
    Journal article

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  • Minimization of Image Distortion in SMOS Brightness Temperature Maps Over the Ocean

     Torres Torres, Francisco; Corbella Sanahuja, Ignasi; Wu, Lin; Duffo Ubeda, Nuria; Gourrion, J.; Font Ferré, Jordi; Martín Neira, Manuel
    IEEE Geoscience and Remote Sensing Letters
    Date of publication: 2012-01
    Journal article

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  • Contribution to the characterization of interferometric radiometers devoted to Earth observation: application to the MIRAS/SMOS payload  Open access

     González Gambau, Veronica
    Defense's date: 2012-09-05
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    The variability of soil moisture and ocean salinity controls the continuous exchange of water between the oceans, the atmosphere and the land. Therefore, the accurate and periodic measurements of these geophysical variables are paramount to improve the climate change prediction and extreme-event forecasting. However, until very recently, global measurements of these parameters with a suitable spatial and temporal resolution have not been available. Real aperture radiometers have been frequently used for Earth observation applications. Nevertheless, for space-borne sensors at a low Earth orbit, the requirements on spatial resolution and coverage, at the operating frequencies (L-band), would require an unfeasibly large antenna. Conversely, synthetic aperture radiometry achieves high resolution using an array of small antennas, becoming a sound alternative to real aperture radiometry at low microwave frequencies. The ESA's SMOS (Soil Moisture and Ocean Salinity) mission, successfully launched on November 2009, is the first mission ever attempted to frequently and globally measure soil moisture over the continents and sea surface salinity over the oceans. The single payload of the mission, the MIRAS (Microwave Imaging Radiometer by Aperture Synthesis) instrument, is the first spaceborne L-band two dimensional synthetic aperture radiometer. This completely new type of instrument implies a technological challenge, for which the development of a detailed error model denition, dedicated calibration and image reconstruction algorithms have been needed. The calibration of MIRAS tackles all activities devoted to retrieve the SMOS scientic products from raw data measurements with the accuracy required by the scientic community. Characterization activities of the MIRAS instrument, mainly performed prior to the beginning of the in-orbit operation, have been required to develop and test the calibration activities. Within the framework of the SMOS mission, this Ph.D. Thesis is focused on the characterization of the interferometric radiometers devoted to Earth observation. The main contributions of this Thesis, which are directly related to the MIRAS payload performance assessment, are: (i) the denition of tests for the characterization campaigns, data processing methods and success criteria and (ii) the development of calibration algorithms and tools to fine-tune the instrument in order to fully achieve the system requirements and therefore the scientific requierements of the mission. Most of the work has been done in the framework of the MIRAS/SMOS Pre-Commissioning Phase activities and it has been completed in the framework of the Commissioning Phase preparatory work. Calibration tools and techniques developed for the MIRAS ground characterization have been adapted to fulfill in-orbit instrument characterization during the first months of the Commissioning Phase and contributed to the development and consolidation of the SMOS operational level-1 processing.

    La variabilidad de la humedad del suelo y de la salinidad de los oc´eanos controla el continuo intercambio de agua entre los oc´eanos, la atm´osfera y la tierra. Por tanto, la obtenci´on de medidas precisas y peri´odicas de estas dos variables geof´ısicas es fundamental para la mejora de la predicci´on del cambio clim´atico y de la previsi´on de desastres naturales. Sin embargo, hasta hace muy poco no se dispon´ıa de medidas globales de estos par´ametros con la resoluci´on temporal y espacial necesaria para este tipo de aplicaciones. Los radi´ometros de apertura real se han utilizado frecuentemente para aplicaciones de observaci´on de la Tierra. Sin embargo, para sensores situados en ´orbitas bajas, los requerimientos de resoluci´on espacial y cobertura, a la frecuencia de trabajo (banda L), implicar´ıan el uso de una antena de unas dimensiones que no son viables tecnol´ogicamente. Por el contrario, la radiometr´ıa de apertura sint´etica permite obtener una alta resoluci´on utilizando un array de peque˜nas antenas, convirti´endose en una s´olida alternativa a la radiometr´ıa de apertura real para frecuencias bajas de microondas. La misi´on SMOS, de la Agencia Espacial Europea, lanzada con ´exito en Noviembre de 2009, es la primera misi´on para la medida frecuente y global de la humedad del suelo y la salinidad de los oc´eanos. La ´unica carga ´util de la misi´on, el instrumento MIRAS, es el primer radi´ometro de apertura sint´etica en dos dimensiones que es lanzado al espacio. Este tipo de instrumento, completamente novedoso, implica todo un reto tecnol´ogico, por lo que han sido necesarios la definici´on de un modelo detallado de errores y el desarrollo de algoritmos espec´ıficos de calibraci´on e inversi´on de imagen. La calibraci´on del radi´ometro MIRAS comprende todas las actividades dedicadas a recuperar los productos cient´ıficos de SMOS a partir de los datos crudos con la precisi´on requerida por la comunidad cient´ıfica. Para poder desarrollar y probar las actividades de calibraci´on ha sido preciso realizar campa˜nas de caracterizaci´on del instrumento, llevadas a cabo en tierra principalmente. En el marco de la misi´on SMOS, esta tesis se centra en la caracterizaci´on de radi´ometros interfer´ometricos para la observaci´on de la Tierra. Las principales contribuciones de esta tesis, relacionadas directamente con la evaluaci´on de las prestaciones del radi´ometro MIRAS, son: (i) la definici´on de las medidas para las campa˜nas de caracterizaci´on, m´etodos de procesado de datos y criterios de ´exito y (ii) el desarrollo de algoritmos de calibraci´on y herramientas que permitan el ajuste del intrumento para cumplir los requerimientos del sistema y por lo tanto, los requerimientos cient´ıficos de la misi´on. La mayor parte de este trabajo se ha realizado en el marco de las actividades previas al lanzamiento de la misi´on y se ha completado en el marco del trabajo preparatorio de la fase de comisionado (primeros meses de medidas en ´orbita). Las herramientas de calibraci´on y las t´ecnicas desarrolladas para la caracterizaci´on en tierra del instrumento se han adaptado para completar la caracterizaci´on del instrumento durante los primeros meses en ´orbita, contribuyendo al procesado de nivel 1 operacional.

  • 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
    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.

  • SMOS brightness temperature measurements and end-to-end calibration

     Torres Torres, Francisco; Corbella Sanahuja, Ignasi; Duffo Ubeda, Nuria; Martín Neira, Manuel
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2011-07
    Presentation of work at congresses

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    SMOS is the acronym for the Soil Moisture and Ocean Salinity mission by the European Space Agency (ESA) [1]. Its single payload, the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS), was launched in November 2009. After a six months Commissioning Phase SMOS entered in operational mode in May 2010. Since then SMOS has been delivering a large amount of data to successfully produce the first relevant scientific results. In order to provide accurate measurements, MIRAS requires a complex multi-step calibration procedure that was successfully tested both during pre-flight ground tests and Commissioning Phase activities. Additionally, an assessment of SMOS system performance in terms of short and long term stability, radiometric sensitivity and radiometric accuracy was also produced. In this context, this work is devoted to provide a high level overview of MIRAS calibration scheme by focusing on the rationale behind it.

  • Correction of spatial errors in SMOS brightness temperature images

     Wu, Lin; Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Duffo Ubeda, Nuria; Martín Neira, Manuel
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2011-07
    Presentation of work at congresses

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    Systematic spatial errors in SMOS brightness temperature images are successfully estimated by using a statistical analysis of measured data. A constant multiplicative mask is derived by averaging spatial errors of a large number of snapshots over the ocean. The mask has been obtained for the aliasfree field of view region without the need of any geophysical model. It can be considered as part of the instrument characterization and is totally independent of the target to measure. When this mask is applied to regular SMOS brightness temperatures, the spatial artifacts are clearly reduced.

  • Interferometric radiometry measurement concept: The visibility equation

     Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Duffo Ubeda, Nuria; Martín Neira, Manuel
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2011-07
    Presentation of work at congresses

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    The fundamental concept of interferometric aperture synthesis microwave radiometry for Earth observation is reviewed. The measurement principles and a discussion on the signal processing techniques for image reconstruction are briefly summarized. Examples of real measurements from the sensor onboard the ESA SMOS mission are used to illustrate the image reconstruction techniques.

  • Phase error assessment of MIRAS/SMOS by means of the redundant space calibration

     Dávila, Rubén; Torres Torres, Francisco; Duffo Ubeda, Nuria; Corbella Sanahuja, Ignasi; Pablos, Miriam; Martín Neira, Manuel
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2011-07
    Presentation of work at congresses

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    SMOS is the acronym for the Soil Moisture and Ocean Salinity mission by the European Space Agency (ESA) [1]. Its single payload, the Microwave Imaging Radiometer using Aperture Synthesis (MIRAS), was successfully launched in November 2009. A six months Commissioning Phase was devoted to bring the satellite into a fully operational condition and to characterize the payload using specific orbits to check all instrument modes [2]. An ongoing activity is devoted to analyze the contribution of each single calibration procedure to the overall radiometric accuracy in order to assess the dominant sources of spatial errors. In this framework, this paper is devoted to assess the performance of the phase calibration procedures by means of the so called Redundant Space Calibration (RSC)1.

  • W-band radiometric imager with mechanical beam-scanning

     Nova, Enrique; Abril, Jordi; Romeu Robert, Jordi; Broquetas Ibars, Antoni; Torres Torres, Francisco; Jofre Roca, Luis
    International Conference on Infrared, Millimeter, and Terahertz Waves
    Presentation's date: 2011-10-02
    Presentation of work at congresses

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    The design of a 94 GHz Total Power Radiometer system for imaging purposes is presented in this paper. A mechanical beam-scanning antenna system is used to acquire passive raster images. The main performance parameters of the imaging system are described as well as their impact on the resulting image quality. A temperature resolution below 1K and a spatial resolution around 4 cm at 1 meter standoff distance are obtained with this system. Moreover, radiometric images acquired in indoor and outdoor environments are shown and compared.

  • Characterization of a 94 GHz radiometric imager with mechanical beam-scanning

     Nova, Enrique; Abril, Jordi; Romeu Robert, Jordi; Broquetas Ibars, Antoni; Torres Torres, Francisco; Jofre Roca, Luis
    IEEE International Microwave Workshop
    Presentation's date: 2011-08-24
    Presentation of work at congresses

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    This paper presents the characterization in terms of spatial resolution and radiometric sensitivity of a W-band Total Power Radiometer (TPR). The TPR is based on a heterodyne receiver with 64 dB of gain and 6.5 dB of noise figure. An antenna system consisting on a pan-tilt scanner has been designed and built in order to aim a 100 mm offset parabolic reflector. With this system, relative temperature images of targets at a 1 m standoff range are obtained in indoor environments with an spatial resolution of 4 cm.

  • MIRAS calibration and performance: results from the SMOS in-orbit commissioning phase

     Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Duffo Ubeda, Nuria; González Gambau, Veronica; Pablos Hernandez, Miriam; Duran Martínez, Israel; Martín Neira, Manuel
    IEEE transactions on geoscience and remote sensing
    Date of publication: 2011-09
    Journal article

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    After the successful launching of the Soil Moisture and Ocean Salinity satellite in November 2009, continuous streams of data started to be regularly downloaded and made available to be processed. The first six months of operation were fully dedicated to the In-Orbit Commissioning Phase, with an intense activity aimed at bringing the satellite and instrument into a fully operational condition. Concerning the payload Microwave Imaging Radiometer with Aperture Synthesis, it was fully characterized using specific orbits dedicated to check all instrument modes. The procedures, already defined during the on-ground characterization, were repeated so as to obtain realistic temperature characterization and updated internal calibration parameters. External calibration maneuvers were tested for the first time and provided absolute instrument calibration, as well as corrections to internal calibration data. Overall, performance parameters, such as stability, radiometric sensitivity and radiometric accuracy were evaluated. The main results of this activity are presented in this paper, showing that the instrument delivers stable and well-calibrated data thanks to the combination of external and internal calibration and to an accurate thermal characterization. Finally, the quality of the visibility calibration is demonstrated by producing brightness temperature images in the alias-free field of view using standard inversion techniques. Images of ocean, ice, and land are given as examples.

  • Smos payload performance assessment

     Martín Neira, Manuel; Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Cabot, François; Closa Dominguez, Josep M.; Kainulainen, Juha; Castro, J.; Barbosa Torralbo, José; Gutierrez, A.; Martín Porqueras, Fernando; Oliva, R.; Anterrieu, E.; Brown, N.; McMulan, K.
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2010-07-25
    Presentation of work at congresses

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  • Combined passive and active millimeter-wave imaging system for concealed objects detection

     Abril, Jordi; Nova, Enrique; Broquetas Ibars, Antoni; Torres Torres, Francisco; Romeu Robert, Jordi; Jofre Roca, Luis
    Infrared Millimeter and Terahertz Waves (IRMMW-THz), 2010 35th International Conference on
    Presentation's date: 2010-09-06
    Presentation of work at congresses

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  • Active and passive THz systems for short-range imaging applications

     Abril, Jordi; Nova, Enrique; Capdevila Cascante, Santiago; Broquetas Ibars, Antoni; Torres Torres, Francisco; Jofre Roca, Luis
    European Conference on Antennas and Propagation
    Presentation's date: 2010-04-13
    Presentation of work at congresses

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    Some results on SMOS-MIRAS calibration and Imaging  Open access

     Martín Neira, Manuel; Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Cabot, François; Duffo Ubeda, Nuria; Closa Dominguez, Josep M.; Kainulainen, Juha; Castro, R.; Barbosa Torralbo, José; Gutierrez, A.; Martín Porqueras, Fernando; Oliva, R.; Anterrieu, E.; Brown, N.; McMulan, K.
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2010-07-23
    Presentation of work at congresses

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    The performance requirements of the SMOS payload are demanding in terms of spatial resolution, accuracy, stability and precision, all critical to fulfill its scientific objectives. For this reason a commissioning plan for MIRAS was carefully devised to verify, calibrate and characterize all instrument parameters which could have an impact on its performance. This presentation describes the most important results from the instrument commissioning phase.

  • One point calibration in interferometric radiometers: MIRAS/SMOS preliminary results

     Torres Torres, Francisco; Corbella Sanahuja, Ignasi; Duffo Ubeda, Nuria; González Gambau, Veronica; Pablos Hernandez, Miriam; Duran Martínez, Israel; Martín Neira, Manuel
    Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment
    Presentation's date: 2010-03-01
    Presentation of work at congresses

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  • First results on MIRAS calibration and overall SMOS performance

     Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Duffo Ubeda, Nuria; González Gambau, Veronica; Pablos Hernandez, Miriam; Duran Martínez, Israel; Martín Neira, Manuel
    Specialist Meeting on Microwave Radiometry and Remote Sensing of the Environment
    Presentation's date: 2010-03-01
    Presentation of work at congresses

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  • Far field condition in passive interferometry for security screening applications

     Torres Torres, Francisco; Abril, Jordi; Nova, E.; Broquetas Ibars, Antoni; Jofre Roca, Luis
    European Conference on Antennas and Propagation
    Presentation's date: 2010-04-12
    Presentation of work at congresses

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    This work presents the main geometric constraints that affect the performance of a passive interferometer at 94 GHz for security screening applications by means of a reviewed definition of the Far Field condition in close range detection applications. This new approach allows to easily give, in a first order approximation, the number of antennas, the array size and the target range by using well known far field tools.

  • Linearity characterization of detectors for interferometric radiometers

     Gonzalez-Haro, Cristina; Torres Torres, Francisco; Duffo Ubeda, Nuria; Corbella Sanahuja, Ignasi; Vilaseca, R; de Paco Sánchez, Pedro Antonio; Martín Neira, Manuel
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2009-07-12
    Presentation of work at congresses

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  • One point calibration in interferometric radiometers: error assessment

     Torres Torres, Francisco; Corbella Sanahuja, Ignasi; Duffo Ubeda, Nuria; González Gambau, Veronica
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2009-07-12
    Presentation of work at congresses

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  • Phase noise requirements in interferometric radiometers

     Torres Torres, Francisco; Corbella Sanahuja, Ignasi; Castro, E.; Segarra, M.; Vilaseca, R
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2009-07-12
    Presentation of work at congresses

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  • On-flight characterization of the SMOS payload during the commissioning phase

     Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Duffo Ubeda, Nuria; Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena; González Gambau, Veronica
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2009-09-12
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    Correlation denormalization in interferometric or polarametric radiometers: a unified approach  Open access

     Colliander, A; Torres Torres, Francisco; Corbella Sanahuja, Ignasi
    IEEE transactions on geoscience and remote sensing
    Date of publication: 2009-02
    Journal article

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    This paper presents a general analysis of correlation measurements in an interferometer or a radiometer based on noise injection and/or switching and measurement of normalized correlations (e.g., imaging synthetic aperture or polarimetric radiometers). A compact unifying notation for denormalizing the measured normalized correlations in the presence of noise injection in one or both of the receiving channels is presented. Technological limitations are also assessed by evaluating the effect of associated approximations. Finally, the approach is validated by experimental results of the measurement and calibration of related front-end nonidealities, namely, the finite isolation of the front-end switch. The methods presented in this paper are illustrated by a thorough analysis of the so-called mixed baselines of microwave imaging radiometer using aperture synthesis, which refer to those baselines which are formed between the regular receivers (light-weight cost-efficient front-end) and the reference radiometers. These baselines require special attention, since the reference radiometers are noise-injection radiometers, which inject noise to the measured signal, whereas the regular receivers are total power receivers.

  • CONCEPTOS AVANZADOS EN TELEDETECCION ACTIVA Y PASIVA DE MICROONDAS: TECNOLOGIA Y APLICACIONES

     Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Broquetas Ibars, Antoni; Mallorqui Franquet, Jordi Joan; Duffo Ubeda, Nuria; Aguasca Sole, Alberto; López Martínez, Carlos; Fabregas Canovas, Francisco Javier
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    On-ground characterization of the SMOS payload  Open access

     Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Duffo Ubeda, Nuria; Martín Neira, Manuel; González Gambau, Veronica; Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena
    IEEE transactions on geoscience and remote sensing
    Date of publication: 2009-09
    Journal article

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    The on-ground characterization of the synthetic aperture radiometer onboard the Soil Moisture and Ocean Salinity mission is described. Characterization includes basic functionality, internal calibration, thermal cycling, response to point and flat sources, self-radio-frequency interference, and others. The description of the different tests performed as well as the detailed results are provided. The results show that the instrument is very stable and has all gains and offsets consistent with the ones obtained at subsystem level. On the other hand, the phase of the visibility has a larger variation with temperature than expected, a small signal leakage from the local oscillators is present, and a small interference from the X-band transmitter during short periods of time has been detected. The implementation of internal-calibration procedures, along with the accurate thermal characterization performed, have been used to produce highly accurate brightness-temperature values well within specifications.

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    Polarimetric emission of rain events: simulation and experimental results at X-Band  Open access

     Duffo Ubeda, Nuria; Vall·Llosera, M; Camps Carmona, Adriano Jose; Corbella Sanahuja, Ignasi; Torres Torres, Francisco
    Remote Sensing
    Date of publication: 2009-06
    Journal article

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    Accurate models are used today for infrared and microwave satellite radiance simulations of the first two Stokes elements in the physical retrieval, data assimilation etc. of surface and atmospheric parameters. Although in the past a number of theoretical and experimental works have studied the polarimetric emission of some natural surfaces, specially the sea surface roughened by the wind (Windsat mission), very limited studies have been conducted on the polarimetric emission of rain cells or other natural surfaces. In this work, the polarimetric emission (four Stokes elements) of a rain cell is computed using the polarimetric radiative transfer equation assuming that raindrops are described by Pruppacher-Pitter shapes and that their size distribution follows the Laws-Parsons law. The Boundary Element Method (BEM) is used to compute the exact bistatic scattering coefficients for each raindrop shape and different canting angles. Numerical results are compared to the Rayleigh or Mie scattering coefficients, and to Oguchi’s ones, showing that above 1-2 mm raindrop size the exact formulation is required to model properly the scattering. Simulation results using BEM are then compared to the experimental data gathered with a X-band polarimetric radiometer. It is found that the depolarization of the radiation caused by the scattering of non-spherical raindrops induces a non-zero third Stokes parameter, and the differential phase of the scattering coefficients induces a non-zero fourth Stokes parameter.

  • Determination of the sea surface emissivity at L-band and application to SMOS salinity retrieval algorithms: Review of the contributions of the UPC-ICM

     Camps Carmona, Adriano Jose; Font, J; Vall-llossera Ferran, Mercedes Magdalena; Corbella Sanahuja, Ignasi; Duffo Ubeda, Nuria; Torres Torres, Francisco; Blanch Boris, Sebastian; Aguasca Sole, Alberto; Villarino, R; Gabarro, C; Enrique, L; Miranda, J; Sabia, Roberto
    Radio science
    Date of publication: 2008-06-20
    Journal article

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  • AMIRAS - An Airborne MIRAS Demonstrator

     Martín Neira, Manuel; Cabeza, I; Perez, C; Palacios, M A; Guijarro, M A; Ribó Vedrilla, Serni; Corbella Sanahuja, Ignasi; Blanch Boris, Sebastian; Torres Torres, Francisco; Duffo Ubeda, Nuria; Gonzalez Gambau, Verónica; Beraza, S; Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena
    IEEE transactions on geoscience and remote sensing
    Date of publication: 2008-03
    Journal article

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  • Angular and radiometric resolution of Y-shaped non-uniform synthetic aperture radiometers for Earth observation

     Camps Carmona, Adriano Jose; Vall-llossera Ferran, Mercedes Magdalena; Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Duffo Ubeda, Nuria
    IEEE Geoscience and Remote Sensing Letters
    Date of publication: 2008-10
    Journal article

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  • Interferometric radiometers: fringe washing function estimation

     Duffo Ubeda, Nuria; Corbella Sanahuja, Ignasi; Torres Torres, Francisco; González Gambau, Veronica; Martín Neira, Manuel
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2008-07-07
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  • Assessment on linearity errors in detectors for interferometric radiometers

     Torres Torres, Francisco; Duffo Ubeda, Nuria; Gonzalez-Haro, Cristina; Vilaseca, R; Sagués, L; Martín Neira, Manuel
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2008-07-06
    Presentation of work at congresses

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    The performance of the power detectors used to denormalize the digital correlations in interferometric radiometers is degraded due to the non-linear behavior of the diode response. This work presents a comprehensive analysis of the impact of detector non-linearity and related correction techniques in the performance of the MIRAS (Microwave Imaging Radiometer with Aperture Synthesis) instrument, which is the single payload of the European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) mission.

    The performance of the power detectors used to denormalize the digital correlations in interferometric radiometers is degraded due to the non-linear behavior of the diode response. This work presents a comprehensive analysis of the impact of detector non-linearity and related correction techniques in the performance of the MIRAS (Microwave Imaging Radiometer with Aperture Synthesis) instrument [1], which is the single payload of the European Space Agency (ESA) Soil Moisture and ocean Salinity (SMOS) mission

  • Calibration consistency tool for interferometric radiometers

     Gonzalez Gambau, Verónica; Torres Torres, Francisco; Duffo Ubeda, Nuria; Martín Neira, Manuel
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2008-07-06
    Presentation of work at congresses

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    This paper presents a method to check the consistency of the amplitude calibration in interferometric radiometers devoted to Earth observation This tool is based in the intrinsic properties of the internal calibration scheme and can be used to systematically assess in-orbit the quality of the amplitude calibration coefficients. This technique is illustrated taking into account the results of the validation and system performance tests recently undertaken by the MIRAS instrument, the single payload of the Soil Moisture and Ocean Salinity mission of the European Space Agency.

    This paper presents a method to check the consistency of the amplitude calibration in interferometric radiometers devoted to Earth observation This tool is based in the intrinsic properties of the internal calibration scheme and can be used to systematically assess in-orbit the quality of the amplitude calibration coefficients. This technique is illustrated taking into account the results of the validation and system performance tests recently undertaken by the MIRAS instrument, the single payload of the Soil Moisture and Ocean Salinity mission of the European Space Agency.

  • MIRAS-SMOS Antenna Relative Phase Calibration

     Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Benito Paramo, Jose Antonio; Martín Neira, Manuel
    IEEE International Symposium on Antennas and Propagation
    Presentation of work at congresses

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