Blind Speckle Decorrelation for SAR Image Despeckling

In the past few decades, several methods have been developed for despeckling synthetic aperture radar (SAR) images. A considerable number of them have been derived under the assumption of a fully-developed speckle model in which the multiplicative speckle noise is supposed to be a white process. Unfortunately, the transfer function of SAR acquisition systems can introduce a statistical correlation, which decreases the despeckling efficiency of such filters. In this paper, a whitening method is proposed for processing a complex image acquired by a SAR system. We demonstrate that the proposed approach allows the successful application of classical despeckling algorithms. First, we perform an estimation of the SAR system frequency response based on some statistical properties of the acquired image and by using realistic assumptions. Then, a decorrelation process is applied on the acquired image, taking into account the presence of point targets. Finally, the image is despeckled. The experimental results show that the despeckling filters achieve better performance when they are preceded by the proposed whitening method; furthermore, the radiometric characteristics of the image are preserve

A Tutorial on Speckle Reduction in Synthetic Aperture Radar Images

Speckle is a granular disturbance, usually modeled as a multiplicative noise, that affects synthetic aperture radar (SAR) images, as well as all coherent images. Over the last three decades, several methods have been proposed for the reduction of speckle, or despeckling, in SAR images. Goal of this paper is making a comprehensive review of despeckling methods since their birth, over thirty years ago, highlighting trends and changing approaches over years. The concept of fully developed speckle is explained. Drawbacks of homomorphic filtering are pointed out. Assets of multiresolution despeckling, as opposite to spatial-domain despeckling, are highlighted. Also advantages of undecimated, or stationary, wavelet transforms over decimated ones are discussed. Bayesian estimators and probability density function (pdf) models in both spatial and multiresolution domains are reviewed. Scale-space varying pdf models, as opposite to scale varying models, are promoted. Promising methods following non-Bayesian approaches, like nonlocal (NL) filtering and total variation (TV) regularization, are reviewed and compared to spatial- and wavelet-domain Bayesian filters. Both established and new trends for assessment of despeckling are presented. A few experiments on simulated data and real COSMO-SkyMed SAR images highlight, on one side the costperformance tradeoff of the different methods, on the other side the effectiveness of solutions purposely designed for SAR heterogeneity and not fully developed speckle. Eventually, upcoming methods based on new concepts of signal processing, like compressive sensing, are foreseen as a new generation of despeckling, after spatial-domain and multiresolution-domain method

Tucidide e il sistema numerale acrofonico (proposta di correzione a 6.31.5)

In this passage, πολλά does not make sense near τὰ πάντα: the corrupted ΠΟΛΛΑ probably originated from ΠΔΔΔΔ, i.e. 80 talents, the likely cost of the 100 ships for the Sicilian expedition

Amplitude vs intensity Bayesian despeckling in the wavelet domain for SAR images

In this paper, the problem of despeckling SAR images when the input data is either an intensity or an amplitude signal is revisited. State-of-the-art despeckling methods based on Bayesian estimators in the wavelet domain, recently proposed in the literature, are taken into consideration. First, how these methods proposed for one format (e.g., intensity) can be adapted to the other format (e.g., amplitude) is investigated. Second, the performance of such algorithms in both cases is analyzed. Experimental results carried out on simulated speckled images and on true SAR data are presented and discussed in order to assess the best strategy. From these results, it can be observed that filtering in the amplitude domain yields better performances in terms of objective quality indexes, such as preservation of structural details, as well as in terms of visual inspection of the filtered SAR dat

Claudiano, De sext. cons. Hon. Aug. 557

The author proposes correcting the transmitted cura to cana in Claudian, De sexto consulatu Honorii Augusti 557

Scrivere in latino oggi

ItL'autore traccia un breve bilancio sull'uso del latino filologico degli ultimi decenni. Ricorda come la praefatio latina delle edizioni critiche dei classici sia stata ormai soppiantata dalla preface in inglese. Ma se i filologi rinunciano al latino nelle prefazioni, dovrebbero rinunciarvi anche negli apparati critici, nei titoli e nelle abbreviazioni. Solo nella Bibliotheca Teubneriana resistono le praefationes, ma sempre più spesso viziate da imperfezioni ed errori. La conclusione è che l'inglese sostituisce il latino a causa dei nostri limiti, non per una scelta di modernità. Sottomettendosi ogni volta a chi chiede di abbassare l'asticella, il mondo delle Humanities pensa di evitare l'estinzione sacrificando l'onore, ma avrà sia l'estinzione che il disonore.EnThe author draws a brief balance sheet on the use of philological latin in recent decades. He recalls how the Latin praefatio in critical editions of classical texts has now been supplanted by the English preface. But if philologists abandon Latin in their prefaces, they should also abandon it in their critical apparatus, titles, and abbreviations. Only in the Bibliotheca Teubneriana do praefationes survive, but they are increasingly tainted by imperfections and errors. The conclusion is that English replaces Latin because of our limitations, not because of a choice of modernity. By bowing time and again to those who demand that we lower the bar, the world of the Humanities thinks it can avoid extinction by sacrificing honour, but it will face both extinction and dishonour