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  • Common mathematical framework for real and synthetic aperture by interferometry radiometers

     Bosch Lluis, Xavier; Ramos Pérez, Isaac; Camps Carmona, Adriano Jose; Rodríguez Álvarez, Nereida; Valencia Domenech, Enric; Park, Hyuk
    IEEE transactions on geoscience and remote sensing
    Date of publication: 2014-01
    Journal article

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    This work focuses on the relationship between real and synthetic aperture radiometers giving a general and common mathematical framework for both of them. It will be demonstrated that a real aperture radiometer array can be understood as a synthetic aperture one, with a high level of redundancy. Therefore, all the recent results from synthetic aperture radiometry can be translated to real aperture radiometer arrays. This fact can be used to create beamforming arrays in a new way. To do this, the beamforming array equation will be written in terms of cross-correlations between all pair of antenna signals (visibility samples). By properly combining the visibility samples, a new type of digital beamforming radiometer can be implemented, which will benefit from the high calibration accuracy achieved in synthetic aperture radiometers (e.g., The Y-shaped MIRAS radiometer used in the Soil Moisture and Ocean Salinity mission of the European Space Agency) and the flexibility to electronically steer the beam. © 1980-2012 IEEE.

  • GNSS-R derived centimetric sea topography: an airborne experiment demonstration

     Carreño Luengo, Hugo; Park, Hyuk; Camps Carmona, Adriano Jose; Fabra Cervellera, Fran; Rius Jordán, Antonio
    IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing
    Date of publication: 2013-06
    Journal article

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    The results of two airborne experiments performed to test the precision and the relative accuracy of the conventional Global Navigation Satellite Systems Reflectometry (GNSS-R) technique employing only the C/A code are presented. The first and the second experiments demonstrate, respectively, a 17 cm precision for a 500 m flight altitude with a 8 km along-track spatial resolution, and a 6 cm precision for a 3000 m flight altitude with a 6.6 km along-track spatial resolution. In both, the Relative Mean Dynamic Topography (RMDT) is compared with results derived from traditional radar altimetry provided by Jason-2. The Root Mean Square (RMS) of the RMDTdifference between both measurement systems is 48 cm for the first flight, and 198 cm for the second flight. During the second flight, the feasibility of the proposed technique to measure the sea slopes is demonstrated by superposing over the aircraft ground track the measured sea surface height with the geoid undulations, which are about 1 meter.

  • Wind speed maping from the ISS using GNSS-R? A simulation study

     Camps Carmona, Adriano Jose; Park, Hyuk; Alonso Arroyo, Alberto
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2013-07-21
    Presentation of work at congresses

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    Reflectometry using Global Navigation Satellite System's signals of opportunity (GNSS-R) was originally conceived for mesoscale altimetry, but it can be applied to sea state determination (i.e. wind speed), among many other applications. The feasibility to create scattering coefficient and wind speed maps over the ocean using the Delay-Doppler Maps (DDMs) has also been analyzed. In this work a case study is presented to show the evolution of some features of the DDM (shape and peak) as seen from a PAU-like GNSS-R instrument aboard the International Space Station (ISS), while overpassing the Sandy hurricane on October 27th, 2012 in front of the coast of Florida. © 2013 IEEE.

  • Comparison of GPS L1 and Galileo E1 signals for GNSS-R ocean altimetry

     Pascual Biosca, Daniel; Park, Hyuk; Camps Carmona, Adriano Jose; Alonso Arroyo, Alberto; Onrubia Ibañez, Raul
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2013-07-21
    Presentation of work at congresses

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    In the last years, the GPS signals have been validated as opportunity signals in a wide range of reflectometry-based remote sensing applications for sea, land or ice scenarios. Recently, the first Galileo satellites have started transmitting the new signal E1, which shares the band with the GPS L1 signal. This work compares the performance of both signals in space and airborne scenarios for sea state and altimetry determination. © 2013 IEEE.

  • Digital back-end for RFI detection and mitigation in earth observation

     Forte Veliz, Giuseppe Francesco; Querol Borras, Jorge; Park, Hyuk; Camps Carmona, Adriano Jose
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2013-07
    Presentation of work at congresses

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    A powerful real time Radio-frequency interference (RFI) mitigation back-end system is presented in this work. The interfering signals are estimated by using the wavelet transform to utilize its effective denoising capability. The estimated RFI signals are then subtracted from the total received signal, and ultimately the RFI-mitigated signal is obtained. Here, the hardware implementation and the system tests are demonstrated, showing sinusoid, chirp, and PRN interference mitigation under different Interference to Noise Ratios (INRs).

  • Comparison of GNSS-R processing techniques for spaceborne ocean altimetry

     Martin Alemany, Francisco; d'Addio, Salvatore; Camps Carmona, Adriano Jose; Martín Neira, Manuel; Park, Hyuk; Pascual Biosca, Daniel
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2013-07
    Presentation of work at congresses

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    Earth-reflected Global Navigation Satellite System (GNSS) have become an attractive tool to be employed in low-Earth-orbit spaceborne missions, for applications such as ocean mesoscale altimetry and scatterometry. For such techniques, several on-board processing strategies have been proposed, either based on the correlation with on-board generated signal or based on 'blind' interferometric processing, which involves the correlation between received direct and reflected signals. This paper will provide a comparison of these two proposed GNSS-R processing techniques, highlighting the possible achieved performance for a typical spaceborne scenario. The performance comparison will be carried out by analyzing the widely used Cramer-Rao Bound, which takes into account the full statistical properties of the reflected signals and provides accurate comparison.

  • MIR: the microwave interferometric reflectometer, a new airborne sensor for GNSS-R advanced research

     Onrubia Ibañez, Raul; Pascual Biosca, Daniel; Camps Carmona, Adriano Jose; Alonso Arroyo, Alberto; Park, Hyuk
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2013-07-21
    Presentation of work at congresses

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    The use of Global Navigation Satellite Signals (GNSS) in reflectometric applications (GNSS-R) is highly extended in remote sensing applications, such as sensing sea state, soil moisture or ice layer characterization. There are two main techniques in this field: the conventional GNSS-R, that achieves high SNRs by cross-correlating the received signal with a replica of the transmitted one but, with a low resolution due to narrow bandwidth of the signals, and the interferometric GNSS-R, which achieves better resolutions but with lower SNRs since it directly correlates the direct and reflected signals. The Microwave Interferometric Reflectometer (MIR) is a new sensor that will use high-directivity, multiband and steerable arrays to achieve higher SNRs in the interferometric technique. Additionally, it will also apply the conventional technique. All these capabilities will be applied simultaneously to two beams at each band (L1 and L5 / E1 and E5). This work describes this concept instrument and the first prototypes will be presented at the conference. © 2013 IEEE.

  • Improvement of the PAU/PARIS End-to-end Performance Simulator (P^2 EPS) in preparation for upcoming GNSS-R missions

     Park, Hyuk; Camps Carmona, Adriano Jose; Pascual Biosca, Daniel; Alonso Arroyo, Alberto; Martin Alemany, Francisco; Carreño Luengo, Hugo
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2013-07-21
    Presentation of work at congresses

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    PAU/PARIS End-to-end Performance Simulator (P2EPS) has been developed for studying and design tools for GNSS-R space mission. For the purpose of accuracy and various scenario, P2EPS has recently improved in many features. Especially, the wide range of the simulation inputs enables to simulate the upcomming GNSS-R space missions. This paper presents the recent improvement of the P2EPS. © 2013 IEEE.

  • Soil moisture mapping using forward scattered GPS L1 signals

     Alonso Arroyo, Alberto; Forte Veliz, Giuseppe Francesco; Camps Carmona, Adriano Jose; Park, Hyuk; Pascual Biosca, Daniel; Onrubia Ibañez, Raul; Jove Casulleras, Roger
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2013-07-21
    Presentation of work at congresses

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    This work presents a novel technique for the determination of soil moisture obtaining 2-D Soil Moisture (SM) information with a single instrument. Both the instrument and the retrieval algorithm used, which is based on inferring the reflection coefficient of the terrain by direct and forward scattering polarimetric measurements of Global Navigation Satellite Systems (GNSS) Signals, are briefly described. Some preliminary results of a field campaign performed on La Pobla de Mafumet (Tarragona, Spain) are presented. This instrument and retrieval algorithm can be used for different applications, such as, an input for the irrigation algorithm (Smart-Irrigation) or forest fire prevention among others.

  • SAIRPS: a generic simulator for evaluation of synthetic aperture interferometric radiometers

     Camps Carmona, Adriano Jose; Park, Hyuk; Kang, Yujin; Barbosa, José; Bandeiras, J.; Vieira, Paula; Friaças, Ana; d'Addio, Salvatore
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2013-07-21
    Presentation of work at congresses

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    ESA's SMOS mission has been a cornerstone in passive Earth Observation, since it has provided for the first time ever with global and frequent observations of Soil Moisture and Ocean Salinity (where the mission acronym comes from). SMOS' single payload is MIRAS: the Microwave Imaging Radiometers by Aperture Synthesis in two dimensions. After SMOS' success, today, a number of instruments are planned or under study: the GeoStar instrument is the baseline payload for the Precipitation and All-weather Temperature and Humidity (PATH) mission from NASA (USA), the Geostationary Atmospheric Sounder (GAS) instrument is under study for post-MSG operational satellites observations (Europe), and the Geostationary Interferometric Microwave Sounder (GIMS) instrument from NSSC-CAS (China). The study of the instrument performance in terms of angular resolution and radiometric performance (radiometric sensitivity and accuracy), and the optimization of this new type of instruments is a complex task that requires dedicated ad-hoc tools. In this work the SAIRPS (Synthetic Aperture Interferometric Radiometer Performance Simulator) is presented. This complex simulator allows to analyze arbitrary receiver topologies, arbitrary array geometries, and includes noise injection calibration algorithms, and new external robust calibration algorithms, and image reconstruction algorithms that allow to evaluate the performance of almost any instrument. At present, the full simulator has been coded in Matlab, translated into C++, and integrated in OpenSF. This work summarizes the key aspects of the architecture of this simulator, completing the presentation made in IGARSS 2012, and presents a few examples of the simulation results using different instrument configurations. © 2013 IEEE.

  • Altimetry performance and error budget of the PARIS in-orbit demonstration mission

     Camps Carmona, Adriano Jose; Pascual Biosca, Daniel; Park, Hyuk; Martin Alemany, Francisco; Rius, Antonio; Ribó Vedrilla, Serni; Benito, Javier; Andrés, Ana; Saameno, Paula; Staton, Gavin; Martín Neira, Manuel; d'Addio, Salvatore; Willemsen, Philip
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2013-07-21
    Presentation of work at congresses

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    Reflectometry using Global Navigation Satellite System's signals of opportunity (GNSS-R) was originally conceived for mesoscale altimetry [1], although its applicability to sea state determination, soil moisture, vegetation, snow monitoring. has already been demonstrated. In December 2012 the Phase A studies of ESA's PAssive Reflectometry and Interferometry System In-orbit Demonstration (PARIS IoD) mission ended. In conventional GNSS-R the GNSS signals scattered over the Earth's surface are cross-correlated with a locally generated replica of the transmitted signal shifted in frequency (¿fd) and in delay (¿t). PARIS is called an interferometric GNSS-R (iGNSS-R) system because the direct and the scattered signals are cross-correlated in order to use the whole signal's bandwidth, and improve the altimetric precision, despite the large bandwidth signals are not publicly available. This work presents a methodology to evaluate the performance of iGNSS-R altimeters. It is then applied to a PARIS IoD-like case, in which the receivers' bandwidths have been optimized in terms of altimetric resolution. © 2013 IEEE.

  • Delay Tracking in Spaceborne GNSS-R Ocean Altimetry

     Park, Hyuk; Valencia Domenech, Enric; Camps Carmona, Adriano Jose; Rius, Antonio; Ribó Vedrilla, Serni; Martín Neira, Manuel
    IEEE Geoscience and Remote Sensing Letters
    Date of publication: 2013-01
    Journal article

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    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
    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.

  • Interferometric GNSS-R achievable altimetric performance and compression/denoising using the wavelet transform: An experimental study

     Camps Carmona, Adriano Jose; Martin Alemany, Francisco; Park, Hyuk; Valencia Domenech, Enric; Rius, Antonio; d'Addio, Salvatore
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2012-07
    Presentation of work at congresses

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  • A generic simulator for aperture synthesis radiometers

     Camps Carmona, Adriano Jose; Park, Hyuk; Barbosa Torralbo, José; Bandeiras, J.; d'Addio, Salvatore
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2012-07
    Presentation of work at congresses

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    ESA's SMOS mission has demonstrated that Synthetic Aperture Interferometric Radiometers can be a useful tool for Earth observation. Today, the NASA's GeoStar instrument (USA), ESA's GAS instrument (Europe), or CSSAR's GIMS instrument (China) are just three examples of planned geostationary millimeter-wave sounders using synthetic aperture interferometric radiometry for continuous atmospheric monitoring with a much improved spatial resolution. The study of the performance in terms of angular resolution and radiometric performance, and the optimization of this new type of instruments is a complex task that requires dedicated ad-hoc simulators. The SAIPRS (Synthetic Aperture Interferometric Radiometer Performance Simulator) is an ESA project aiming at the development of a generic simulator in terms of receiver architecture and array configuration, including moving antennas (and eventually changing polarization reference frames). This work summarizes the key aspects of the architecture of this simulator.

  • Submeter ocean altimetry with GPS L1 C/A signal

     Carreño Luengo, Hugo; Park, Hyuk; Camps Carmona, Adriano Jose; Fabra Cervellera, Fran; Rius, Antonio
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2012-07
    Presentation of work at congresses

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    The ultimate accuracy and precision of conventional1 and interferometric2 Global Positioning Satellite System Rerflectometry (GNSS-R) techniques for mesoscale ocean altimetry are still a matter of debate in the scientific community. The results obtained depend on the techniques used to identify the point of the specular delay in the waveform, and to perform the different delay corrections to derive the geometric delay. Also, the geometric model assumed for the scenario determines the accuracy of the altimeter range. This work presents the results of two ESA-sponsored airborne experiments using conventional GNSS-R showing subdecimeter altimetric precision with the Global Positioning System (GPS) L1 C/A code only. The Relative Mean Dynamic Topography (RMDT) obtained in both experiments is compared with results derived from traditional radar altimetry provided by Jason 2. The Root Mean Square (RMS) of the RMDT difference between both measurement systems is 48 cm for the first flight, and 198 cm for the second flight. Additionally, results from the second flight experiment show the capability of the proposed technique to retrieve sea slope measurements by superposing the ground track with EM96 geoid undulations.

  • Impact of doppler frequency compensation errors on spaceborne GNSS-R altimetry

     Park, Hyuk; Camps Carmona, Adriano Jose; Valencia Domenech, Enric
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2012-07
    Presentation of work at congresses

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    The compensation of the Doppler frequency error is important to accurately estimate the sea height in spaceborne GNSSR altimetry. This work presents the impact of the residual Doppler error on the altimetric performance. The GNSS-R altimetric observables (waveforms) are simulated with various observation parameters, and the degradation is analyzed vs. the Doppler errors. It is shown that the Doppler error causes a bias, a decrease of the waveform value, and consequently the altimetric performance degradation in accuracy and precision.

  • 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
    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.

  • PAU instrument aboard INTA MicroSAT-1: initial results of the FM model from an airborne experiment

     Alonso Arroyo, Alberto; Camps Carmona, Adriano Jose; Pascual Biosca, Daniel; Park, Hyuk; Alcayde, Antonio; Chavero, Sergio; Martinez, Pedro; Crespo, Luis; Angulo, Manuel; Rius, Antonio
    Workshop on Reflectometry Using GNSS and Other Signals of Opportunity
    Presentation's date: 2012-10
    Presentation of work at congresses

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    This work presents the PAU instrument aboard the satellite INTA MicroSAT-1. The PAU instrument is a combination of a Radiometer and a GNSS Reflectometer designed to study the relationship GNSS-R observables (Delay Doppler Maps) and the L-Band brightness temperature measurements to improve the Sea Surface Salinity (SSS) retrievals. This work describes an airborne experiment conducted to preliminary test the PAU instrument GNSS-R observables sensibility to sea state and to explore other applications of the instrument

  • GNSS-R altimeter performance: analysis of Cramer-Rao lower bounds

     d'Addio, Salvatore; Martín Neira, Manuel; Martin Alemany, Francisco; Park, Hyuk; Camps Carmona, Adriano Jose
    Workshop on Reflectometry Using GNSS and Other Signals of Opportunity
    Presentation's date: 2012-10
    Presentation of work at congresses

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    Earth-reflected Global Navigation Satellite Systemsignals have become an attractive tool for remote sensing, being proposed as a means to perform ocean altimetry, among many other applications. The technique exploiting navigation signals is widely known as GNSS-R. In this paper the well-known Cramer- Rao lower bound is used to predict the sea surface height estimation precision of a GNSS-R based spaceborne altimeter, exploiting the open-access GPS L1 C/A code signal. Real spaceborne data acquired by the GPS-R receiver on-board UKDMC satellite is used to extract statistical properties of spaceborne GPS reflected signals.

  • Analysis of GNSS-R delay and doppler tracking errors

     Park, Hyuk; Camps Carmona, Adriano Jose; Valencia Domenech, Enric; Carreño Luengo, Hugo; Martin Alemany, Francisco; Alonso Arroyo, Alberto; Pascual Biosca, Daniel
    Workshop on Reflectometry Using GNSS and Other Signals of Opportunity
    Presentation's date: 2012-10
    Presentation of work at congresses

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    The compensation of the delay and Doppler errors using tracking is important to accurately estimate the sea height in spaceborne GNSS-R. This work presents the impacts of the tracking residual errors on the GNSS-R observables, and potential tracking strategies for spaceborne GNSS-R. Tracking error impacts are visually demonstrated by using the P2EPS (PAU/PARIS End-to-end Performance Simulator) spaceborne simulation.

  • Impact of the observation geometry on the GNSS-R direct descriptors used for sea state monitoring

     Valencia Domenech, Enric; Camps Carmona, Adriano Jose; Park, Hyuk; Rodríguez Álvarez, Nereida; Ramos Perez, Isaac
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2012-07
    Presentation of work at congresses

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    In recent years GNSS-R has been proposed for ocean remote sensing, both for altimetry and scatterometry. For the later, two main approaches are available: fitting the measurements with a model, or using some observable from the measurements (either the waveform or the delay-Doppler Map) to be directly linked to ocean surface's roughness. For ground-based and airborne experiments, several direct observables have been proposed to describe ocean surface's roughness, and they have been used assuming that the observation geometry had little impact on them. However, it may not be true for a spaceborne scenario, since the dynamics are higher. In this work an extensive simulation study is performed, and the first results on how the observation geometry does impact different GNSS-R direct observables is presented

    In recent years GNSS-R has been proposed for ocean remote sensing, both for altimetry and scatterometry. For the later, two main approaches are available: fitting the measurements with a model, or using some observable from the measurements (either the waveform or the delay-Doppler Map) to be directly linked to ocean surface’s roughness. For groundbased and airborne experiments, several direct observables have been proposed to describe ocean surface’s roughness, and they have been used assuming that the observation geometry had little impact on them. However, it may not be true for a spaceborne scenario, since the dynamics are higher. In this work an extensive simulation study is performed, and the first results on how the observation geometry does impact different GNSS-R direct observables is presented.

  • Cross-correlation waveform mode: a critical review

     Martin Alemany, Francisco; Park, Hyuk; Camps Carmona, Adriano Jose; d'Addio, Salvatore; Martín Neira, Manuel
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2012-07
    Presentation of work at congresses

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    Earth-reflected Global Navigation Satellite System (GNSS) signals have become an attractive tool for remote sensing. Recently it has been proposed as an alternative to the conventional altimetry to estimate the surface height However GNSS-R altimetry offers lower bandwidths and signals power compared to radar altimeters. This implies a poorer altimetry precision, accuracy and resolution per pulse.Also the altimetry precision will be impacted by the impact of the thermal, and speckle noise mainly. This paper gives a critical review of the cross-correlation waveform model.

  • 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
    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.

  • 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
    Date of publication: 2012
    Journal article

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  • 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
    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.

  • Retracking considerations in spaceborne GNSS-R altimetry

     Park, Hyuk; Camps Carmona, Adriano Jose; Valencia Domenech, Enric; Rodriguez Alvarez, Nereida; Bosch Lluis, Xavier; Ramos Perez, Isaac; Carrero Luengo, Hugo
    Gps solutions
    Date of publication: 2012-10
    Journal article

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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 Geoscience and Remote Sensing Letters
    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.

  • Altimetry with GNSS-R interferometry: first proof of concept experiment

     Rius, A.; Nogués Correig, O.; Ribó Vedrilla, Serni; Cardellach, Estel; Oliveras, S.; Valencia Domenech, Enric; Park, Hyuk; Tarongí Bauzá, José Miguel; Camps Carmona, Adriano Jose; Van Der Marel, H.; van Bree, R.; Altena, B.; Martín Neira, Manuel
    Gps solutions
    Date of publication: 2012-04
    Journal article

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    The Global Navigation Satellite System Reflectometry (GNSS-R) concept was conceived as a means to densify radar altimeter measurements of the sea surface. Until now, the GNSS-R concept relied on open access to GNSS transmitted codes. Recently, it has been proposed that the ranging capability of the technique for ocean altimetric applications can be improved by using all the signals transmitted in the bandwidth allocated to GNSS, which includes open access as well as encrypted signals. The main objective of this study is to provide experimental proof of this enhancement through a 2-day experiment on the Zeeland Bridge (The Netherlands). In the experiment, we used a custom built GNSS-R system, composed of high gain GPS antennas, calibration subsystem, and an FPGAbased signal processor which implemented the new concepts, an X-band radar altimeter and a local geodetic network. The results obtained indicate that the new approach produces a significant improvement in GNSS-R altimetric performance.

  • Oil slicks detection using GNSS-R

     Valencia Domenech, Enric; Camps Carmona, Adriano Jose; Park, Hyuk; Rodriguez Alvarez, Nereida; Bosch Lluis, Xavier; Ramos Perez, Isaac
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2011-07-25
    Presentation of work at congresses

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  • PAU instrument aboard INTA MicroSat-1: A GNSS-R demonstration mission for sea state correction in L-band radiometry

     Camps Carmona, Adriano Jose; Marchan Hernandez, Juan Fernando; Valencia Domenech, Enric; Ramos Perez, Isaac; Bosch Lluis, Xavier; Rodriguez Alvarez, Nereida; Park, Hyuk; Alcayde, Antonio; Mollfulleda, Antonio; Galindo, Juan Jose; Martinez, Pedro; Chavero, Sergio; Angulo, Manuel; Rius, Antonio
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2011-07-29
    Presentation of work at congresses

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    Global Navigation Satellite System (GNSS) Reflectometry was originally proposed for mesoscale altimetry, but today its feasibility for sea state, soil moisture, vegetation and snow height has already been demonstrated. This paper describes a GNSS-Reflectometer develop to perform the sea state correction in L-band radiometric measurements, and therefore, improve the quality of the sea surface salinity retrievals. The instrument is currently being developed as a secondary payload to be launched aboard INTA (Instituto Nacional de Técnicas Aerospaciales, Spanish Aerospace Center) MicroSat-1. The basic principles of operation and the instrument development status are presented.

  • 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
    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
    Presentation's date: 2011-07-25
    Presentation of work at congresses

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  • A radiometer concept to retrieve the 3-D radiometric emission from atmospheric temperature and water vapor density

     Bosch Lluis, Xavier; Park, Hyuk; Camps Carmona, Adriano Jose; Reising, Steve C.; Sahoo, S.; Padmanabhan, Sharmila; Rodriguez Alvarez, Nereida; Ramos Perez, Isaac; Valencia Domenech, Enric
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2011-07-29
    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
    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
    Presentation's date: 2011-07-25
    Presentation of work at congresses

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  • New approach to sea surface wind retrieval from GNSS-R measurements

     Park, Hyuk; Valencia Domenech, Enric; Rodriguez Alvarez, Nereida; Bosch Lluis, Xavier; Ramos Perez, Isaac; Camps Carmona, Adriano Jose
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2011-07-28
    Presentation of work at congresses

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  • Preliminary error budget of a GNSS-r spaceborne mission

     Camps Carmona, Adriano Jose; Park, Hyuk; Valencia Domenech, Enric; Rius, A.
    IEEE International Geoscience and Remote Sensing Symposium
    Presentation's date: 2011-07-24
    Presentation of work at congresses

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    Reflectometry using Global Navigation Satellite System's (GNSS) opportunity signals was originally conceived for altimetry [1], but it has been demonstrated today that it can be applied to sea state determination, soil moisture, vegetation, snow monitoring... So far, GPS signals scattered over the Earth's surface have been cross-correlated with a local replica of the transmitted signal (typically the only GPS available: the C/A code) shifted in frequency (Δfd) and in delay (τ). However, to achieve the full potential (bandwidth) of these signals the direct and reflected signals can be directly cross-correlated, but in this case, high gain antennas are required to increase the signal-to-noise ratio. Therefore these antennas must be steerable so as to track the direct satellite and the specular reflection point. This is the concept of the European Space Agency PARIS In Orbit Demonstrator (IoD) mission [2], a new concept that was demonstrated experimentally for the first time in 2010 [3]. This work deals with the analysis of the preliminary instrument error budget of this mission to address the critical design parameters.

  • Access to the full text
    A general analysis of the impact of digitization in microwave correlation radiometers  Open access

     Bosch Lluis, Xavier; Ramos Perez, Isaac; Camps Carmona, Adriano Jose; Rodriguez Alvarez, Nereida; Valencia Domenech, Enric; Park, Hyuk
    Sensors
    Date of publication: 2011-06
    Journal article

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    This study provides a general framework to analyze the effects on correlation radiometers of a generic quantization scheme and sampling process. It reviews, unifies and expands several previous works that focused on these effects separately. In addition, it provides a general theoretical background that allows analyzing any digitization scheme including any number of quantization levels, irregular quantization steps, gain compression, clipping, jitter and skew effects of the sampling period.

  • Radiometric resolution of motion-induced synthetic aperture radiometer

     Park, Hyuk; Camps Carmona, Adriano Jose; Choi, Min Gyu; Kim, Yong-Hoon
    IEEE Geoscience and Remote Sensing Letters
    Date of publication: 2011-07
    Journal article

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    The radiometric resolution of a motion-induced synthetic aperture radiometer (MISAR) is analytically obtained from the standard deviation of a baseline response, an observation scenario, and the imaging method of the MISAR. The intrinsic long integration time given by the whole dwell time on moving platforms improves the radiometric resolution compared with the snapshot resolution of other nominal synthetic aperture radiometers. In addition, it is illustrated that the MISAR imaging holds the tradeoff relationship between the radiometric and spatial resolutions.

  • 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
    Date of publication: 2011-10-15
    Journal article

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  • Ocean surface's scattering coefficient retrieval by delay-doppler map inversion

     Valencia Domenech, Enric; Camps Carmona, Adriano Jose; Marchan Hernandez, Juan Fernando; Park, Hyuk; Bosch Lluis, Xavier; Rodriguez Alvarez, Nereida; Ramos Perez, Isaac
    IEEE Geoscience and Remote Sensing Letters
    Date of publication: 2011-07
    Journal article

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    Global navigation satellite system reflectometry of signals is a promising technique to remotely sense a number of Earth’s geophysical parameters, and it has been proposed for ocean monitoring applications such as mesoscale altimetry or sea state monitoring. So far, the following two main approaches have been considered to retrieve a sea state descriptor from measured delay waveforms or delay–Doppler (DD) maps (DDMs): 1) fitting the measurements to a model tuned with the desired parameter or 2) directly linking a property of the measurements with the parameter to be retrieved (e.g., volume of the normalized DDM). However, these approaches provide a single sea state descriptor related to the overall glistening zone where sea state conditions may not be homogeneous. In this letter, the relationship between the physical space and the DD domains is exploited, and a method to retrieve the bistatic scattering coefficient distribution over the observation ocean surface from measured DDMs is proposed.

  • Improving the accuracy of sea surface salinity retrieval using GNSS-R data to correct the sea state effect

     Valencia Domenech, Enric; Camps Carmona, Adriano Jose; Rodriguez Alvarez, Nereida; Ramos Perez, Isaac; Bosch Lluis, Xavier; Park, Hyuk
    Radio science
    Date of publication: 2011
    Journal article

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  • SISTEMA GNSS-R PARA FUTURAS MISIONES SMOS

     Tarongí Bauzá, José Miguel; Park, Hyuk; Camps Carmona, Adriano Jose
    Participation in a competitive project

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  • Correction to "A Two-Dimensional Doppler Radiometer for Earth Observation"

     Park, Hyuk; Kim, Y H; Camps Carmona, Adriano Jose
    IEEE transactions on geoscience and remote sensing
    Date of publication: 2007-12
    Journal article

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