A compression tool for satellite based imagery of the earth's land and atmosphere is presented. Orthogonal wavelet filters are adopted for this purpose. The ability of the technique to compress images has been applied to AVHRR images of cloud fields and the earth's surface. Compression by a factor as large as 50 is possible in clear sky condition without any significant loss of information, whereas for frontal cloud fields, which are the most interesting in terms of meteorological studies, factors of ten are easily achieved

The problems of smoothing data through a transform in the Fourier domain and of retrieving a function from its Fourier coefficients are analyzed in the present paper. For both of them a solution, based on regularization tools, is known. Aim of the paper is to prove strong results of convergence of the regularized solution and optimality of the Generalized Cross Validation criterion for choosing the regularization parameter.

We consider the problem of determining quantitative information about corrosion occurring on an inaccesible part of a specimen. The data for the problem consist of prescribed current flux and voltage measurements on an accessible part of the specimen boundary. The problem is modelled by Laplace's equation with an unknown term in the boundary conditions. Our goal is recovering from the data. We prove uniqueness under certain regularity assumptions and construct a regularized numerical method for obtaining approximate solutions to the problem. The numerical method, which is based on the assumption that the specimen is a thin plate, is tested in numerical experiments using synthetic data.

organizzazione dell'evento (scientifica, logistica ecc.)

The authors study the convergence and the stability of a collocation and a discrete collocation method for Cauchy singular integral equations with weakly singular perturbation kernels in some weighted uniform norms. Uniform error estimates are also given. © 1997 Rocky Mountain Mathematics Consortium.

The Hilbert transform of a function g, H(g) is an important tool in many mathematical fields. Expecially its numerical evaluation is often useful in some procedures for searcing solutions of the singular integral equations. In this context an approximation of (HV^alpha,beta,f;t), |t|1, where f is a continuous function in [-1,1] and v^alpha,beta, alpha,beta>-1 is a Jacobi weight, is required. In the last decade more then one paper appeared on this subject and among others we recall [1,2,3,4,5,14,15,20]. The procedure used in these papers can be described as follows. Approximate the function f with a Lagrange interpolating polynomial and obtain a quadrature formula with coefficients depending on the singularity t. The error of the quadrature formula was estimated assuming t in a "more or less" wide neighborhood of zero since (HV^alpha,beta,f;t) is unbounded at the endpoints of (-1,1). In this paper we propose a more accurate procedure: since (HV^alpha,beta,f;t) is unbounded at the endpoints, itis more natural to consider its approximation in some functional spaces equipped with weighted uniform norms. In Section 2 (see theorems 2.1 and 2.2) we state the behaviour of (HV^alpha,beta,f;t) in [-1,1] and we give new conditions for its exstence. In sections 3 and 4 we cosntruct approximations of (HV^alpha,beta,f;t) which converge to the exact value in weighted uniform norm. The L^p convergence of the formula is also briefly treated. Finally since the considered procedures are numerically stable, these can be used for the numerical evaluation of (HV^alpha,beta,f;t) . In this sense the present paper is a short survey on the subject.

Alcuni modelli di dispersione di sostanze inquinanti prodotte dal traffico autoveicolare in un area urbana vengono presentati. In particolare si descrive il modello OMG-Volume Source che sembra essere in grado di analizzare realisticamente l'effetto "canyon", tipico di un area urbana. I parametri del modello vengono determinati tenendo soprattutto in considerazione le caratteristiche spaziali dell'insediamento urbano.

Alcuni modelli di dispersione di sostanze inquinanti prodotte dal traffico autoveicolare in un area urbana vengono presentati. In particolare si descrive il modello OMG-Volume Source che sembra essere in grado di analizzare realisticamente l'effetto "canyon", tipico di un area urbana. I parametri del modello vengono determinati tenendo soprattutto in considerazione le caratteristiche spaziali dell'insediamento urbano.

Remote sounding of earth's atmosphere from upwelling infrared radiances is highly non-linear. A linearization step is typically involved in seeking for suitable solutions. This letter discusses possible problems which arise when combining the linearization step with schemes aimed at solving the inverse problem. Possible strategies which could be able to get rid of such problems are discussed, too. Copyright 1996 by the American Geophysical Union.