Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/654
2017-01-24T01:26:41ZImpact of amplitude calibration errors on SMOS global images
http://hdl.handle.net/2117/99432
Impact of amplitude calibration errors on SMOS global images
Durán Martínez, Israel; Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Duffo Ubeda, Núria; Oliva, Roger; Martín Neira, Manuel
Some of the artifacts observed in SMOS brightness temperature images are originated in an inconsistency between correlation and antenna temperature calibration errors, which produces a multiplicative bias that scales with the scene mean antenna temperature. Its most important effect, although not the only one, is a land-to-sea contamination near coastal areas, which cannot be easily mitigated by post-processing correction techniques. A simplified end-to-end simulator allows introducing separate errors in both antenna temperature and correlation, thus
providing an important insight on this problem and helping understanding its origin. Results from simulations compare very well with actual results from measured data.
2017-01-17T11:15:35ZDurán Martínez, IsraelCorbella Sanahuja, IgnasiTorres Torres, FranciscoDuffo Ubeda, NúriaOliva, RogerMartín Neira, ManuelSome of the artifacts observed in SMOS brightness temperature images are originated in an inconsistency between correlation and antenna temperature calibration errors, which produces a multiplicative bias that scales with the scene mean antenna temperature. Its most important effect, although not the only one, is a land-to-sea contamination near coastal areas, which cannot be easily mitigated by post-processing correction techniques. A simplified end-to-end simulator allows introducing separate errors in both antenna temperature and correlation, thus
providing an important insight on this problem and helping understanding its origin. Results from simulations compare very well with actual results from measured data.Mitigation of cross-polar antenna pattern errors in SMOS: simplified approach
http://hdl.handle.net/2117/99429
Mitigation of cross-polar antenna pattern errors in SMOS: simplified approach
Durán Martínez, Israel; Torres Torres, Francisco; Corbella Sanahuja, Ignasi; Duffo Ubeda, Núria; Lin, Wu; Martín Neira, Manuel
This paper analyzes a simplified image reconstruction method that exclusively takes into account the dominant antenna pattern terms to model image inversion artifacts and mitigate SMOS polarimetric spatial bias over the Ocean. This simplified method, that reduces computation time at the cost of small radiometric performance degradation, is useful to the L1 teams to process a large amount of data when full radiometric accuracy is not required (e.g. stability assessments).
2017-01-17T11:05:33ZDurán Martínez, IsraelTorres Torres, FranciscoCorbella Sanahuja, IgnasiDuffo Ubeda, NúriaLin, WuMartín Neira, ManuelThis paper analyzes a simplified image reconstruction method that exclusively takes into account the dominant antenna pattern terms to model image inversion artifacts and mitigate SMOS polarimetric spatial bias over the Ocean. This simplified method, that reduces computation time at the cost of small radiometric performance degradation, is useful to the L1 teams to process a large amount of data when full radiometric accuracy is not required (e.g. stability assessments).Millimeter-wave aperture synthesis radiometry for snow and ice mapping
http://hdl.handle.net/2117/98424
Millimeter-wave aperture synthesis radiometry for snow and ice mapping
Harvey, A.R.; Greenaway, A.H.; Camps Carmona, Adriano José; Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Bara Temes, Francisco Javier; Martín Neira, Manuel
An outline design for a dual-band mm-wave polarimetric SAIR has been presented and is considered to be tractable. The envisaged application is for snow and ice mapping and ocean wind vector measurement. The vastly increased complexity of the high-frequency waveband may not be justified by the scientific benefit and operation at an additional lower frequency such as 18 GHz may give improved classification, though with reduced spatial resolution. The authors describe the outline design for a polarimetric, mm-wave SAIR. One-dimensional aperture synthesis employs a hybrid technique in which a long linear array of real-aperture stick antennas form over-lapping fan beams on the ground and aperture synthesis within the fan beams enables synthesis of the mm-wave image. Critical aspects for building a high-resolution, mm-wave ESTAR are system calibration and the construction of stick antennas that will be 3 m long and about half a wavelength wide.
2016-12-16T09:03:50ZHarvey, A.R.Greenaway, A.H.Camps Carmona, Adriano JoséCorbella Sanahuja, IgnasiTorres Torres, FranciscoBara Temes, Francisco JavierMartín Neira, ManuelAn outline design for a dual-band mm-wave polarimetric SAIR has been presented and is considered to be tractable. The envisaged application is for snow and ice mapping and ocean wind vector measurement. The vastly increased complexity of the high-frequency waveband may not be justified by the scientific benefit and operation at an additional lower frequency such as 18 GHz may give improved classification, though with reduced spatial resolution. The authors describe the outline design for a polarimetric, mm-wave SAIR. One-dimensional aperture synthesis employs a hybrid technique in which a long linear array of real-aperture stick antennas form over-lapping fan beams on the ground and aperture synthesis within the fan beams enables synthesis of the mm-wave image. Critical aspects for building a high-resolution, mm-wave ESTAR are system calibration and the construction of stick antennas that will be 3 m long and about half a wavelength wide.Scattering and emissivity of rain events using boundary element method
http://hdl.handle.net/2117/89163
Scattering and emissivity of rain events using boundary element method
Duffo Ubeda, Núria; Vall-Llossera Ferran, Mercedes Magdalena; Camps Carmona, Adriano José; Corbella Sanahuja, Ignasi; Bará Temes, Francisco Javier; Torres Torres, Francisco
The theory of thermal microwave emission from a bounded medium containing random nonspherical discrete scatters is studied. It is known that for a medium of constant temperature the emissivities can be related to the bistatic scattering coefficients. Such relations hold for the four Stokes parameters. The down-welling polarimetric emission of the rain can be computed by means of the radiative transfer equation, which contains the four Stokes parameters. In order to apply the above equation to a realistic rain event, raindrop shapes have to be taken into account in the computation of the scattering amplitudes. Those shapes were obtained by Pruppacher and Pitter and are quite different from a sphere when the size increases. In this paper a procedure based in the Boundary Element Method (B.E.M.) is presented to compute the scattering amplitudes for each drop shape. Results are then averaged for all drop radii with a weighting function given by the Laws-Parson law. This law establishes the relationship between the drop size distribution and the rain intensity. A Gaussian distribution of the drop canting angle due to the wind has been also considered. Finally, some numerical results are presented. The scenario consists of a rain cell of 4 Km height at a uniform temperature, considering the wind effect. The values of the rain intensity and wind speed and direction have been obtained from realistic measurements recorded by a meteorological station located in campus. In order to validate these results, the four Stokes parameters obtained with these simulations were compared with the ones measured by a X-band polarimetric radiometer developed in our laboratory.
2016-07-25T12:40:49ZDuffo Ubeda, NúriaVall-Llossera Ferran, Mercedes MagdalenaCamps Carmona, Adriano JoséCorbella Sanahuja, IgnasiBará Temes, Francisco JavierTorres Torres, FranciscoThe theory of thermal microwave emission from a bounded medium containing random nonspherical discrete scatters is studied. It is known that for a medium of constant temperature the emissivities can be related to the bistatic scattering coefficients. Such relations hold for the four Stokes parameters. The down-welling polarimetric emission of the rain can be computed by means of the radiative transfer equation, which contains the four Stokes parameters. In order to apply the above equation to a realistic rain event, raindrop shapes have to be taken into account in the computation of the scattering amplitudes. Those shapes were obtained by Pruppacher and Pitter and are quite different from a sphere when the size increases. In this paper a procedure based in the Boundary Element Method (B.E.M.) is presented to compute the scattering amplitudes for each drop shape. Results are then averaged for all drop radii with a weighting function given by the Laws-Parson law. This law establishes the relationship between the drop size distribution and the rain intensity. A Gaussian distribution of the drop canting angle due to the wind has been also considered. Finally, some numerical results are presented. The scenario consists of a rain cell of 4 Km height at a uniform temperature, considering the wind effect. The values of the rain intensity and wind speed and direction have been obtained from realistic measurements recorded by a meteorological station located in campus. In order to validate these results, the four Stokes parameters obtained with these simulations were compared with the ones measured by a X-band polarimetric radiometer developed in our laboratory.Modelo de transistores MESFET en régimen no lineal
http://hdl.handle.net/2117/88876
Modelo de transistores MESFET en régimen no lineal
Corbella Sanahuja, Ignasi; Legido, Jm; Pradell i Cara, Lluís
2016-07-19T07:29:03ZCorbella Sanahuja, IgnasiLegido, JmPradell i Cara, LluísMethod of moments applied to the analysis of rough surfaces modelled by fractals
http://hdl.handle.net/2117/88555
Method of moments applied to the analysis of rough surfaces modelled by fractals
Vall-Llossera Ferran, Mercedes Magdalena; Duffo Ubeda, Núria; Camps Carmona, Adriano José; Corbella Sanahuja, Ignasi; Bará Temes, Francisco Javier; Torres Torres, Francisco
The Scattering and Emissivity of rough surfaces involve solutions to non-linear differential equations. Different approaches have been used in the literature to obtain approximate solutions under some hypothesis. For example Kirchhoff solution is used when the roughness is gentle on the scale of the wavelength.
In this paper the Method of Moments is used to analyze the scattering of arbitrary surfaces. No approximation about the scale roughness is necessary. Both Gaussian and Fractal surfaces have been modeled and compared. The introduction of fractal geometry provides a new tool to describe natural rough surfaces. A first inside to the properties and parameters that describe fractal geometry has been done in order to characterize them statistically. It has been demonstrated that geometrical and scattering characteristics are controlled by Fractal descriptors, including fractal dimension.
As a first step, our simulations refer to a (topological) one-dimensional (1-D) profile embedded in a two-dimensional (2-D) space. Physically, this corresponds to assume that both the electromagnetic field and the surface height are constant along a fixed direction. Extension to the case of a 2-D surface embedded in a three-dimensional (3-D) space is not conceptually difficult, but any simulation run requires a much longer computational time. Furthermore, scattering results obtained for 1-D profiles give also a good indication of scattering dependence on 2-D surface parameters.
2016-07-06T13:26:55ZVall-Llossera Ferran, Mercedes MagdalenaDuffo Ubeda, NúriaCamps Carmona, Adriano JoséCorbella Sanahuja, IgnasiBará Temes, Francisco JavierTorres Torres, FranciscoThe Scattering and Emissivity of rough surfaces involve solutions to non-linear differential equations. Different approaches have been used in the literature to obtain approximate solutions under some hypothesis. For example Kirchhoff solution is used when the roughness is gentle on the scale of the wavelength.
In this paper the Method of Moments is used to analyze the scattering of arbitrary surfaces. No approximation about the scale roughness is necessary. Both Gaussian and Fractal surfaces have been modeled and compared. The introduction of fractal geometry provides a new tool to describe natural rough surfaces. A first inside to the properties and parameters that describe fractal geometry has been done in order to characterize them statistically. It has been demonstrated that geometrical and scattering characteristics are controlled by Fractal descriptors, including fractal dimension.
As a first step, our simulations refer to a (topological) one-dimensional (1-D) profile embedded in a two-dimensional (2-D) space. Physically, this corresponds to assume that both the electromagnetic field and the surface height are constant along a fixed direction. Extension to the case of a 2-D surface embedded in a three-dimensional (3-D) space is not conceptually difficult, but any simulation run requires a much longer computational time. Furthermore, scattering results obtained for 1-D profiles give also a good indication of scattering dependence on 2-D surface parameters.Evaluation of MIRAS space borne instrument performance: snap shot radiometric accuracy and its improvement by means of pixel averaging
http://hdl.handle.net/2117/88554
Evaluation of MIRAS space borne instrument performance: snap shot radiometric accuracy and its improvement by means of pixel averaging
Camps Carmona, Adriano José; Torres Torres, Francisco; Bará Temes, Francisco Javier; Corbella Sanahuja, Ignasi; Martín Neira, Manuel
2016-07-06T13:19:37ZCamps Carmona, Adriano JoséTorres Torres, FranciscoBará Temes, Francisco JavierCorbella Sanahuja, IgnasiMartín Neira, ManuelCalibration procedures in 2-D large interferometric radiometers study applied to the MIRAS/SMOS instrument
http://hdl.handle.net/2117/88084
Calibration procedures in 2-D large interferometric radiometers study applied to the MIRAS/SMOS instrument
Torres Torres, Francisco; Camps Carmona, Adriano José; Corbella Sanahuja, Ignasi; Bará Temes, Francisco Javier; Vall-Llossera Ferran, Mercedes Magdalena; Duffo Ubeda, Núria
2016-06-16T12:42:55ZTorres Torres, FranciscoCamps Carmona, Adriano JoséCorbella Sanahuja, IgnasiBará Temes, Francisco JavierVall-Llossera Ferran, Mercedes MagdalenaDuffo Ubeda, NúriaNew radiometers: SMOS-a dual pol L-band 2D aperture synthesis radiometer
http://hdl.handle.net/2117/88045
New radiometers: SMOS-a dual pol L-band 2D aperture synthesis radiometer
Kerr, Yann H.; Waldteufel, Philippe; Camps Carmona, Adriano José; Bará Temes, Francisco Javier; Corbella Sanahuja, Ignasi; Torres Torres, Francisco; Duffo Ubeda, Núria; Vall-Llossera Ferran, Mercedes Magdalena
Since the mid 1980s, aperture synthesis interferometric radiometers have received increased attention to monitor the Earth at low microwave frequencies (L-band), where there is a maximum sensitivity to soil moisture and ocean salinity. At L-band, classic radiometers require large steerable antennas to meet the spatial resolution requirements (30-50 km at most, 10-20 km wished for), from a low polar orbit platform. During the 1990s, technological studies were conducted by the ESA with an eye to design a 2D synthetic aperture L-Band radiometer (the Microwave Imaging Radiometer by Aperture Synthesis project: MIRAS). In 1998, in answer to a call for Earth Explorer Opportunity Missions issued by ESA, the Soil Moisture and Ocean Salinity Mission proposal (SMOS), based upon a radiometer concept derived from the MIRAS studies, was submitted, In 1999, following a selection procedure, ESA approved the SMOS mission for an extended phase. This paper summarize part of the work carried out on the interferometric radiometry concept and the optimization of the instrument configuration.
2016-06-15T15:08:06ZKerr, Yann H.Waldteufel, PhilippeCamps Carmona, Adriano JoséBará Temes, Francisco JavierCorbella Sanahuja, IgnasiTorres Torres, FranciscoDuffo Ubeda, NúriaVall-Llossera Ferran, Mercedes MagdalenaSince the mid 1980s, aperture synthesis interferometric radiometers have received increased attention to monitor the Earth at low microwave frequencies (L-band), where there is a maximum sensitivity to soil moisture and ocean salinity. At L-band, classic radiometers require large steerable antennas to meet the spatial resolution requirements (30-50 km at most, 10-20 km wished for), from a low polar orbit platform. During the 1990s, technological studies were conducted by the ESA with an eye to design a 2D synthetic aperture L-Band radiometer (the Microwave Imaging Radiometer by Aperture Synthesis project: MIRAS). In 1998, in answer to a call for Earth Explorer Opportunity Missions issued by ESA, the Soil Moisture and Ocean Salinity Mission proposal (SMOS), based upon a radiometer concept derived from the MIRAS studies, was submitted, In 1999, following a selection procedure, ESA approved the SMOS mission for an extended phase. This paper summarize part of the work carried out on the interferometric radiometry concept and the optimization of the instrument configuration.Banco automatizado para la medida de parámetros S, de ruido y características DC de transistores en oblea
http://hdl.handle.net/2117/88024
Banco automatizado para la medida de parámetros S, de ruido y características DC de transistores en oblea
Pradell i Cara, Lluís; Purroy, Francesc; Subirats, M.; Ballester, A.; Torres Torres, Francisco; O'Callaghan Castellà, Juan Manuel; Corbella Sanahuja, Ignasi
The AMR Group has an automatized bench for the measurement of DC-characteristics, [S] parameters (45 MHz- 40 GHz) and noise parameters (2-26.5 GHz) of microwave on-wafer transistors. The hardware configuration is described, as well as the software applications developed. The measurement procedures are commented in detail, in particular those concerning the noise-parameters extraction techniques. Experimental results show the bench performances.
2016-06-15T13:11:03ZPradell i Cara, LluísPurroy, FrancescSubirats, M.Ballester, A.Torres Torres, FranciscoO'Callaghan Castellà, Juan ManuelCorbella Sanahuja, IgnasiThe AMR Group has an automatized bench for the measurement of DC-characteristics, [S] parameters (45 MHz- 40 GHz) and noise parameters (2-26.5 GHz) of microwave on-wafer transistors. The hardware configuration is described, as well as the software applications developed. The measurement procedures are commented in detail, in particular those concerning the noise-parameters extraction techniques. Experimental results show the bench performances.