http://hdl.handle.net/2117/1443 Search the Channel search http://upcommons.upc.edu/e-prints/simple-search http://hdl.handle.net/2117/2554 Title: Brightness-temperature retrival methods in synthetic aperture radiometers<br/><br/>Authors: Corbella Sanahuja, Ignasi; Torres Torres, Francesc; Camps Carmona, Adriano José; Duffo Ubeda, Núria; Vall-llossera Ferran, Mercè<br/><br/>Abstract: Bightness-temperature retrieval techniques for synthetic aperture radiometers are reviewed. Three different approaches to combine measured visibility and antennatemperatures, along with instrument characterization data,into a general equation to invert are presented. Discretizationand windowing techniques are briefly discussed, and formulasfor reciprocal grids using rectangular and hexagonal samplingsare given. Two known techniques are used to invert the equation,namely, inverse Fourier transform and G-matrix pseudoinverse.The proposed preprocessing approaches combined with these twoinversion methods are implemented with real data measured byan airborne Y-shaped interferometric radiometer over land andwater, and are compared. The images indicate that best resultsare obtained when inverting an incremental visibility obtainedafter substracting a term that includes the individual antennatemperatures, the physical temperatures of the receivers, and aflat-target response directly measured from cold-sky looks. http://hdl.handle.net/2117/2548 Title: Assessment of polarimetric SAR interferometry for improving ship classification based on simulated data<br/><br/>Authors: Margarit Martín, Gerard; Mallorquí Franquet, Jordi Joan<br/><br/>Abstract: This paper uses a complete and realistic SAR simulation processing chain, GRECOSAR,to study the potentialities of Polarimetric SAR Interferometry (POLInSAR) in thedevelopment of new classification methods for ships. Its high processing efficiency and scenario flexibility have allowed to develop exhaustive scattering studies. The results have revealed, first, vessels’ geometries can be described by specific combinations of Permanent Polarimetric Scatterers (PePS) and, second, each type of vessel could be characterized by aparticular spatial and polarimetric distribution of PePS. Such properties have been recently exploited to propose a new Vessel Classification Algorithm (VCA) working with POLInSAR data, which, according to several simulation tests, may provide promising performance in realscenarios. Along the paper, explanation of the main steps summarizing the whole researchactivity carried out with ships and GRECOSAR are provided as well as examples of the mainresults and VCA validation tests. Special attention will be devoted to the new improvements achieved, which are related to simulations processing a new and highly realistic sea surface model. The paper will show that, for POLInSAR data with fine resolution, VCA can help to classify ships with notable robustness under diverse and adverse observation conditions. http://hdl.handle.net/2117/2131 Title: SMOS REFLEX 2003: L-band emissivity characterization of vineyards<br/><br/>Authors: Vall-llossera Ferran, Mercè; Camps Carmona, Adriano José; Corbella Sanahuja, Ignasi; Torres Torres, Francesc; Duffo Ubeda, Núria; Monerris Belda, Alessandra; Sabia, Roberto; Selva, Daniel; Antolín, Carmen; López Baeza, Ernesto; Ferrer, Joan Ferran; Saleh, Kauzar<br/><br/>Abstract: The goal of the Soil Moisture and Ocean Salinity mission over land is to infer surface soil moisture from multiangular L-band radiometric measurements. As the canopy affects the microwave emission of land, it is necessary to characterize different vegetation layers. This paper presents the Reference Pixel L-Band Experiment (REFLEX), carried out in June-July 2003 at the Vale/spl grave/ncia Anchor Station, Spain, to study the effects of grapevines on the soil emission and on the soil moisture retrieval. A wide range of soil moisture (SM), from saturated to completely dry soil, was measured with the Universitat Polite/spl grave/cnica de Catalunya's L-band Automatic Radiometer (LAURA). Concurrently with the radiometric measurements, the gravimetric soil moisture, temperature, and roughness were measured, and the vines were fully characterized. The opacity and albedo of the vineyard have been estimated and found to be independent on the polarization. The /spl tau--//spl omega/ model has been used to retrieve the SM and the vegetation parameters, obtaining a good accuracy for incidence angles up to 55/spl deg/. Algorithms with a three-parameter optimization (SM, albedo albedo, and opacity) exhibit a better performance than those with one-parameter optimization (SM). http://hdl.handle.net/2117/2130 Title: Sea state effect on the sea surface emissivity at L-band<br/><br/>Authors: Miranda, J.; Vall-llossera Ferran, Mercè; Camps Carmona, Adriano José; Duffo Ubeda, Núria; Corbella Sanahuja, Ignasi; Etcheto, Jacqueline<br/><br/>Abstract: In May 1999, the European Space Agency (ESA) selected the Earth Explorer Opportunity Soil Moisture and Ocean Salinity (SMOS) mission to obtain global and frequent soil moisture and ocean salinity maps. SMOS' single payload is the Microwave Imaging Radiometer by Aperture Synthesis (MIRAS), an L-band two-dimensional aperture synthesis radiometer with multiangular observation capabilities. At L-band, the brightness temperature sensitivity to the sea surface salinity (SSS) is low, approximately 0.5 K/psu at 20/spl deg/C, decreasing to 0.25 K/psu at 0/spl deg/C, comparable to that to the wind speed /spl sim/0.2 K/(m/s) at nadir. However, at a given time, the sea state does not depend only on local winds, but on the local wind history and the presence of waves traveling from far distances. The Wind and Salinity Experiment (WISE) 2000 and 2001 campaigns were sponsored by ESA to determine the impact of oceanographic and atmospheric variables on the L-band brightness temperature at vertical and horizontal polarizations. This paper presents the results of the analysis of three nonstationary sea state conditions: growing and decreasing sea, and the presence of swell. Measured sea surface spectra are compared with the theoretical ones, computed using the instantaneous wind speed. Differences can be minimized using an "effective wind speed" that makes the theoretical spectrum best match the measured one. The impact on the predicted brightness temperatures is then assessed using the small slope approximation/small perturbation method (SSA/SPM). http://hdl.handle.net/2117/2129 Title: Synthesis of large low-redundancy linear arrays<br/><br/>Authors: Camps Carmona, Adriano José; Cardama Aznar, Ángel; Infantes, D.<br/><br/>Abstract: Aperture synthesis interferometric radiometers can overcome mass, weight and mechanical scan limitations of present-day radiometers. A full antenna array is "thinned" by eliminating selected antennas, while keeping all possible antenna separations. This paper describes a new technique for the direct synthesis of low-redundancy large arrays, consisting in growing small arrays by inserting a seed repeatedly. This technique has achieved the largest thinned arrays with the least redundancy reported in the literature. http://hdl.handle.net/2117/2128 Title: A two-dimensional doppler-radiometer for earth observation<br/><br/>Authors: Camps Carmona, Adriano José; Swift, Calvin T.<br/><br/>Abstract: Compared to synthetic aperture radars (SARs), the angular resolution of microwave radiometers is quite poor. Traditionally, it has been limited by the physical size of the antenna. However, the angular resolution can be improved by means of aperture synthesis interferometric techniques. A narrow beam is synthesized during the image formation processing of the cross-correlations measured at zero-lag between pairs of signals collected by an array of antennas. The angular resolution is then determined by the maximum antenna spacing normalized to the wavelength (baseline). The next step in improving the angular resolution is the Doppler-Radiometer, somehow related to the super-synthesis radiometers and the Radiometer-SAR. This paper presents the concept of a three-antenna Doppler-Radiometer for 2D imaging. The performance of this instrument is evaluated in terms of angular/spatial resolution and radiometric sensitivity, and an L-band illustrative example is presented. http://hdl.handle.net/2117/2127 Title: A model of the wind direction signature in the Stokes emission vector from the ocean surface at microwave frequencies<br/><br/>Authors: Camps Carmona, Adriano José; Reising, S. C.<br/><br/>Abstract: This paper presents a model of the Stokes emission vector from the ocean surface. The ocean surface is described as an ensemble of facets with Cox and Munk's (1954) Gram-Charlier slope distribution. The study discusses the impact of different up-wind and cross-wind rms slopes, skewness, peakedness, foam cover models and atmospheric effects on the azimuthal variation of the Stokes vector, as well as the limitations of the model. Simulation results compare favorably, both in mean value and azimuthal dependence, with SSM/I data at 53° incidence angle and with JPL's WINDRAD measurements at incidence angles from 30° to 65°, and at wind speeds from 2.5 to 11 m/s. http://hdl.handle.net/2117/2126 Title: Polarimetric radar interferometry for improved mine detection and surface clutter rejection<br/><br/>Authors: Sagués Piella, Lluís; López Márquez, Miguel Ángel; Fortuny, Joaquim; Fàbregas Cànovas, Xavier; Broquetas Ibars, Antoni; Sieber, Alois<br/><br/>Abstract: A recently developed technique, polarimetric radar interferometry, is applied to tackle the problem of the detection of buried objects embedded in surface clutter. An experiment with a fully polarimetric radar in an anechoic chamber has been carried out using different frequency bands and baselines. The processed results show the ability of this technique to detect buried plastic mines and to measure their depth. This technique enables the detection of plastic mines even if their backscatter response is much lower than that of the surface clutter. http://hdl.handle.net/2117/2125 Title: SAR Interferometric phase noise reduction using wavelet transform<br/><br/>Authors: López Martínez, Carlos; Cànovas, Xavier Fàbregas; Chandra, A. M.<br/><br/>Abstract: The problem of synthetic aperture radar interferometric phase noise reduction is addressed. A new technique based on discrete wavelet transforms is presented. This technique guarantees high resolution phase estimation without using phase image segmentation. Areas containing only noise are hardly processed. Tests with synthetic and real interferograms are reported. http://hdl.handle.net/2117/2124 Title: Linear and nonlinear terrain deformation maps from a reduced set of interferometric SAR images<br/><br/>Authors: Mora Sacristán, Óscar; Mallorquí Franquet, Jordi Joan; Broquetas Ibars, Antoni<br/><br/>Abstract: In this paper, an advanced technique for the generation of deformation maps using synthetic aperture radar (SAR) data is presented. The algorithm estimates the linear and nonlinear components of the displacement, the error of the digital elevation model (DEM) used to cancel the topographic terms, and the atmospheric artifacts from a reduced set of low spatial resolution interferograms. The pixel candidates are selected from those presenting a good coherence level in the whole set of interferograms and the resulting nonuniform mesh tessellated with the Delauney triangulation to establish connections among them. The linear component of movement and DEM error are estimated adjusting a linear model to the data only on the connections. Later on, this information, once unwrapped to retrieve the absolute values, is used to calculate the nonlinear component of movement and atmospheric artifacts with alternate filtering techniques in both the temporal and spatial domains. The method presents high flexibility with respect to the required number of images and the baselines length. However, better results are obtained with large datasets of short baseline interferograms. The technique has been tested with European Remote Sensing SAR data from an area of Catalonia (Spain) and validated with on-field precise leveling measurements. http://hdl.handle.net/2117/2123 Title: Considerations about antenna pattern measurements of 2-D aperture synthesis radiometers<br/><br/>Authors: Camps Carmona, Adriano José; Skou, N.; Torres Torres, Francesc; Corbella Sanahuja, Ignasi; Duffo Ubeda, Núria<br/><br/>Abstract: Accurate measurement of the antenna voltage patterns of large-aperture synthesis radiometers is critical in order to achieve good radiometric accuracy, and a very time consuming and expensive task. Measurement requirements and a tradeoff study relating radiometric accuracy degradation and number of elements to be measured are presented. http://hdl.handle.net/2117/2122 Title: Performance of sea surface salinity and soil moisture retrieval algorithms with different auxiliary datasets in 2-D L-band aperture synthesis interferometric radiometers<br/><br/>Authors: Camps Carmona, Adriano José; Vall-llossera Ferran, Mercè; Batres Gonzalez, Luis; Torres Torres, Francesc; Duffo Ubeda, Núria; Corbella Sanahuja, Ignasi<br/><br/>Abstract: The Soil Moisture and Ocean Salinity (SMOS) Earth Explorer Opportunity Mission was selected in May 1999 by the European Space Agency Earth Observation Programme Board to provide global and frequent soil moisture (SM) and sea surface salinity (SSS) maps. SMOS' single payload is the Microwave Imaging Radiometer by Aperture Synthesis (MIRAS) sensor, an L-band two-dimensional aperture synthesis interferometric radiometer with multiangular and polarimetric imaging capabilities. The definition of the SMOS Level 2 Processor requires the selection of the optimum operation mode (dual-polarization or full-polarimetric) for each application, the specification of the required auxiliary data, and the optimum retrieval algorithms. Using the SMOS simulator and based on the experience gained in previous works, this paper presents a study of the SM and SSS retrieval capabilities over homogeneous pixels, in the two modes of operation with different auxiliary data. It is found that SSS retrievals using the first Stokes parameter measured in the dual-polarization mode perform somewhat worse than using the vertical (T/sub vv/) and horizontal (T/sub hh/) brightness temperatures measured in the full-polarimetric mode, and the performance degrades for cold waters due to the lower sensitivity of the brightness temperature to SSS at low sea surface temperature (SST). Due to the larger angular variation of T/sub hh/ and T/sub vv/, SM retrievals using T/sub hh/ and T/sub vv/ measured in the full-polarimetric mode exhibit a significant better performance over bare soils than over vegetation-covered soils. Over vegetation-covered soils vegetation parameters (opacity and albedo) can be inferred over a 550-km swath width in the full-polarimetric mode. However, since the first Stokes parameter is independent of both geometric and Faraday rotations, it is very robust in the presence of instrumental and geophysical errors. In the SSS retrieval problem and in the SM retrieval problem (with T/sub hh/ and T/sub vv/ measured in the full-polarimetric mode), the performance of the retrieval algorithms tested is not significantly altered if the model parameters are not exactly known, but are left as adjustable parameters in the optimization process. http://hdl.handle.net/2117/2121 Title: Topography dependent motion compensation for repeat-pass interferometric SAR systems<br/><br/>Authors: Prats Iraola, Pau; Reigber, Andreas; Mallorquí Franquet, Jordi Joan<br/><br/>Abstract: This letter presents a new motion compensation algorithm to process airborne interferometric repeat-pass synthetic aperture radar (SAR) data. It accommodates topography variations during SAR data processing, using an external digital elevation model. The proposed approach avoids phase artifacts, azimuth coregistration errors, and impulse response degradation, which usually appear due to the assumption of a constant reference height during motion compensation. It accurately modifies phase history of all targets before azimuth compression, resulting in an enhanced image quality. Airborne L-band repeat-pass interferometric data of the German Aerospace Center experimental airborne SAR (E-SAR) is used to validate the algorithm. http://hdl.handle.net/2117/2120 Title: General electromagnetic simulation tool to predict the microwave nonlinear response of planar, arbitrarily-shaped HTS structures<br/><br/>Authors: Parrón Granados, Josep; Collado Gómez, Juan Carlos; Mateu Mateu, Jordi; Rius, J. M.; Duffo Ubeda, Núria; O'Callaghan Castellà, Joan<br/><br/>Abstract: This work describes a simulation tool being developed at UPC to predict the microwave nonlinear behavior of planar superconducting structures with very few restrictions on the geometry of the planar layout. The software is intended to be applicable to most structures used in planar HTS circuits, including line, patch, and quasi-lumped microstrip resonators. The tool combines Method of Moments (MoM) algorithms for general electromagnetic simulation with Harmonic Balance algorithms to take into account the nonlinearities in the HTS material. The Method of Moments code is based on discretization of the Electric Field Integral Equation in Rao, Wilton and Glisson Basis Functions. The multilayer dyadic Green's function is used with Sommerfeld integral formulation. The Harmonic Balance algorithm has been adapted to this application where the nonlinearity is distributed and where compatibility with the MoM algorithm is required. Tests of the algorithm in TM010 disk resonators agree with closed-form equations for both the fundamental and third-order intermodulation currents. Simulations of hairpin resonators show good qualitative agreement with previously published results, but it is found that a finer meshing would be necessary to get correct quantitative results. Possible improvements are suggested. http://hdl.handle.net/2117/2119 Title: A Novel Algorithm for Ship Detection in SAR Imagery Based on the Wavelet Transform<br/><br/>Authors: Tello Alonso, Mª Victoria; López Martínez, Carlos; Mallorquí Franquet, Jordi Joan<br/><br/>Abstract: Carrying out an effective control of fishing activities is essential to guarantee a sustainable exploitation of sea resources. Nevertheless, as the regulated areas are extended, they are difficult and time consuming to monitor by means of traditional reconnaissance methods such as planes and patrol vessels. On the contrary, satellite-based synthetic aperture radar (SAR) provides a powerful surveillance capability allowing the observation of broad expanses, independently from weather effects and from the day and night cycle. Unfortunately, the automatic interpretation of SAR images is often complicated, even though undetected targets are sometimes visible by eye. Attending to these particular circumstances, a novel approach for ship detection is proposed based on the analysis of SAR images by means of the discrete wavelet transform. The exposed method takes advantage of the difference of statistical behavior among the ships and the surrounding sea, interpreting the information through the wavelet coefficients in order to provide a more reliable detection. The analysis of the detection performance over both simulated and real images confirms the robustness of the proposed algorithm.