Molpeceres, C.; Colina, M.A.; Holgado, M.; Morales, M.; Sánchez, M.; Lauzurica, S.; García, J.; Ocaña, J. Proceedings - SPIE Vol. 7202, p. 72020R-1-72020R-10 DOI: 10.1117/12.809514 Data de publicació: 2009-02-24 Article en revista
Recently, there is a growing interest in Scanning SAR systems (ScanSAR) for their wider swaths. In this framework, efficient algorithms for generating ScanSAR images from raw data are demanded for browsing purposes or for on-board image generation. The SPECtral ANalysis method (SPECAN) and its variations are very appropriate for efficient SAR processing in both range and azimuth, when no full resolution is demanded. In the case of azimuth ScanSAR, that condition is naturally met due to the burst mode that does not acquire the whole Doppler spectrum. However, several problems arise due to the spectral analysis operation and its practical implementation. On the other hand, matched filtering for range processing presents a different scenario related to SPECAN processing because the signal contains a fixed quadratic phase, but different amplitude envelope. This work studies the processing of raw SAR data by the SPECAN techniques in both range and azimuth dimensions. The main contributions of this study are the analysis of the signals and the identification of their practical limitations related to SPECAN processing. The results show that SPECAN is a very promising method for efficient two-dimensional ScanSAR image generation when a specially designed algorithm concerning the signal dimension is applied.
Medical therapeutic applications using lasers involves understanding the light tissue interaction, in particular the rate ofphotochemical and thermal reactions. Tissue is composed ofa mix ofturbid media. Light propagation in turbid media can be described by the so-called Equation of Radiative Transfer, an integro-differential equation where scattering, absorption and internal reflection are significant factors in determining the light distribution in tissue. The Equation of Radiative Transfer however can not commonly be solved analytically.' In order to visualize and simulate the effects of laser light on heart tissues (myocardium) in relation to the treatment of irregular heart rates or so called arrhythmias, a fast interactive computer program has been developed in Java. 2000 SPIE.
Recently developed Scanning Synthetic Aperture Radar (ScanSAR) instruments require new algorithms for the processing stages because the classical approaches to SAR image generation are not well suited to ScanSAR data. Therefore, other techniques must be investigated. Spectral Analysis (SPECAN) is an efficient implementation of chirp de-correlation and it is specially well adapted to ScanSAR bursts of data. It consists of deramping and a spectral analysis stage that can be implemented by several techniques. One of them is Fast Fourier Transform (FFT) that is very efficient but presents some drawbacks concerning pixel spacing. A recently proposed method is the Chirp Z-Transform (CZT) SPECAN that obtains spectrum information at arbitrary positions. CZT can be efficiently implemented by FFTs and mixing operations and it provides the desired flexibility to the user. The main contribution of this study is the analysis of SPECAN techniques for processing ScanSAR data by comparing spectral estimation methods and new multilook strategies. The new CZT-SPECAN technique is compared with the classical SPECAN approach showing its advantages avoiding interpolation steps. The new multilook strategy implemented by SPECAN also reduces the scalloping effect. The results show that the new method is very promising for obtaining fast and simple ScanSAR image generation.
The present work consists on the generation of a DEM using ERS satellites interferometric data over a wide area (50 X 50 Km) with an error study using a high accuracy reference DEM, focusing on the atmosphere induced errors. The area is heterogeneous with flat and rough topography ranging from sea level up to 1200 m in the inland ranges. The ERS image has a 100 X 100 Km2 area and has been divided in four quarters to ease the processing. The phase unwrapping algorithm, which is a combination of region growing and least squares techniques, worked out successfully the rough topography areas. One quarter of the full scene was geocoded over a local datum ellipsoid to a UTM grid. The resulting DEM was compared to a reference one provided by the Institut Cartografic de Catalunya. Two types of atmospheric error or artifacts were found: a set of very localized spots, up to one phase cycle, which generated ghost hills up to 100, and a slow trend effect which added up to 50 m to some areas in the image. Besides of the atmospheric errors, the quality of the DEM was assessed. The quantitative error study was carried out locally at several areas with different topography.
The mass production of SAR products and its usage on monitoring emergency situations (oil spill detection, floods, etc.) requires high-speed SAR processors. Two different parallel strategies for near real time SAR processing based on a multiblock version of the Chirp Scaling Algorithm (CSA) have been studied. The first one is useful for small companies that would like to reduce computation times with no extra investment. It uses a cluster of heterogeneous UNIX workstations as a parallel computer. The second one is oriented to institutions, which have to process large amounts of data in short times and can afford the cost of large parallel computers. The parallel programming has reduced in both cases the computational times when compared with the sequential versions.
Antenna arrays collect multidimensional data that contains signals arriving from different sources. Neural Network Architectures can separate the different signals, thus enabling parallel processing structures. These structures can solve a multi-signal estimation problem more efficiently than the corresponding single signal estimator. Various of these parallel architectures are evaluated in the context of array signal processing. Specifically, the scheme developed in this paper (section 2) uses the spatial diversity supplied by the aperture associated with the sensors to separate the signals and to apply them to a bank of parallel adaptive filters. These filters are then designed in accordance with a mean square error minimization criterion (i.e., a criterion based on Second Order Statistics). As Second Order Statistics assume linearity or Gaussianity they are sometimes overly restrictive. It is shown how High Order Statistics can be very useful when more general criteria such as statistical independence between the signals to be separated are imposed.
In this paper we introduce the use of normalized parameters to study an electrooptically active Y-Junction, by means of a five-layer model and the step approximation method. In a similar way as it is done for three-layer and four-layer waveguides, we find a set of dimensionless parameters for five-layer waveguides that allows the description of their waveguiding features.
In the present work we analyse the nonlinear, nonlocal response tensor describing optical second-harmonic processes in centrosymmetric free-electron-like bulk metals with a flat surface. On the basis of the classical infinite barrier (CIB)-model and the Boltzmann equation in the relaxation time approximation we present new analytic results for the fully nonlocal nonlinear response tensor. Via numerical calculations the nonlinear, fully nonlocal response tensor's dependence on the fundamental frequency is discussed and compared with that of the near-local (hydrodynamic) response tensor. Finally, the significance of the contribution to the nonlinear, nonlocal optical response stemming for single-particle excitations, i.e. Landau interactions, is considered.
A simple procedure has been developped which allows us to obtain the phase matching and the coupling coefficient in multilayer magnetooptical waveguides using the "Transfer Matrix Method". This procedure gives the TE-TM mode conversion parameters of a waveguide without having to solve analytically the non-perturbed system.
The propagation modes in a five-layer magnetooptical waveguide have been calculated as a function of the permeability and permitivity tensors of the material. TE-TM mode conversion caused by magnetic linear birrefringence has been studied for a plane magnetooptic wave guide consisting in a three-layer thin film epitaxially grown on a substrate and placed in the air, where the active element corresponds to the top layer. This structure makes it possible to obtain single mode propagation and mode conversion between different modes, which is of great interest in the making of optical devices (1). A relation between the thickness of the active layer and the width and refraction indexes of the intermediate layers in order to obtain single mode conversion has been established. Calculations were performed for wavelenghts of 1.152 µm.