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A wavelet technique to extract the backscatter signatures from SAR images of the sea
No full textSAR images of the sea often show backscatter patterns linked to the horizontal structure of the Marine Atmospheric Boundary Layer (MABL) at the interface with the sea surface. In general, their dimensions are spread over a wide range of length scales, presenting spatial periodicity as well as intermittence. With the aim to isolate such backscatter structures, the two-dimensional Continuous Wavelet Transform (CWT2) analysis has been applied to SAR, images of the sea. The CWT2 analysis permits to highlight the backscatter cells associated to the structure of MABL, as well as to evidence the structure of the atmospheric gravity waves occurring at the lee side of islands and coast. The cells detected in the range 0.3 km divided by 4 km are directly associated to the wind spatial structure deriving, in turns, from the turbulent characteristics of the wind flow. They have an elliptic shape, with the major axis along the (aliased) wind direction. Those with size falling inside the spatial range 4 km divided by 20 km describe, instead, the atmospheric gravity waves structure (if present) and the structures linked to the wind shading. The technique developed is the background for several applications: it has been used to compute the wind fields without any a priori information, as well as to study the inner structure of the Langmuir atmospheric circulation. Other applications could be on the detection of sea surface oil slicks
A joint analysis of microwave radiometer and scatterometer data to characterize meso-scale structures in the Mediterranean Sea
No full textAn analysis of a large set of data, collected from the Special Sensor Microwave/Imager (SSM/I) radiometer and from the NASA SeaWinds scatterometer over the Mediterranean Sea is presented, with the aim of studying the mean behavior of various geophysical parameters, such as water vapor, surface rain rate, wind speed and Ekman pumping for the years 2000 and 2001. This paper presents the results of the study of two different meteorological situations occurring, in the Mediterranean basin. Moreover, ability of these instruments for analyzing extreme events is shown through examples
Small time scale properties of the experimental radar backscatter from the sea surface at off nadir angles
No full textAnalysis of ENVISAT RA2 altimeter sigma-nought bloom events for S and Ku bands backscattering intercomparison
No full textThe RA2 radar altimeter onboard the European Satellite Envisat is a double band microwave instrument working at Ku- and S-band. The S-band measurements provide appropriate atmospheric corrections for the more precise Ku-band measurements, but are also used in conjunction with the Ku-band data in order to investigate the underlying surface. In this study we try to identify differences and similarities of the backscatter signal in the two bands. We focus our attention on the condition of specular alike radar returns, which mostly occur on sea-ice regions. An attempt to find situations in which highly correlated radar waveforms in the two bands can be ascribed to simple scattering mechanisms is made in order to find indications on the mutual calibration of the two channels. The paper reports a number of cases ancountered while analyzing RA-2 data. Both level 2 (1 Hz geophysical parameters) and level 1 (18 Hz waveforms) have been used
Computation of Wind Direction from SAR Images without External a Priori Information
No full textWe present here the follow-up of a previously published work [1], where we described a wavelet based method to characterize the sea surface backscatter structures present in the SAR images. The method relies on the ability of the two-dimensional continuous wavelet technique to detect the spatial structure of the marine atmospheric boundary layer and to isolate wind-related cells and features. The analysis of the cells' geometry, moulded by the radiometric characteristics of the sea surface, permits the identification of the wind direction inside the cells and thus the computation of the wind speed through standard algorithms. About twenty SAR images (ERS-2 and ASAR Wide Swath) over the Mediterranean Sea have been analyzed, and the results compared with NSCAT and QuikSCAT satellites wind fields. These images cover a wide range of meteorological conditions, from low (2 m/s) to moderate winds (12 m/s), presenting many kinds of signature, i.e. wind cells, atmospheric gravity waves, convective structures and radiometric flatness. The main difference of this method, with respect to the majority of those already proposed, is that it does not require a-priori information about the wind direction as well as any periodicity of the backscatter structures. The aliased wind directions are estimated from the texture of the SAR reconstructed map, while the dealiasing is possible due to the asymmetries present in the detected backscatter structures. The resulting SAR derived wind fields have been compared with those provided by satellite scatterometers. Results indicate a good score in detecting the wind direction (≈ 70%). The developed methodology, once tested over an adequate quantity of images to derive statistically reliable results, could be routinely used to enrich SAR images with the wind field, as well as to characterize other backscatter structures displayed by SAR not depending directly on the wind
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Soft tissue and tendon reconstruction after achilles tendon rupture : adipofascial sural turnover flap associated with cryopreserved gracilis tendon allograft for complicated soft tissue and achilles tendon losses. A case report and literature review
No full textSoft tissue and tendon reconstruction after Achilles tendon rupture:Adipofascial sural turnover flap associated with cryopreserved gracilis tendon allograft for complicated soft-tissue tendon losses.A case report and literature review Achilles tendon rupture is often complicated by skin substance loss around the tendon, which is a poorly-vascularized site. Treatment may be conservative or surgical, but the former is not generally accepted by the orthopedic community and is reserved for selected cases, while surgery remains the most widely-used approach. Soft tissue repair at this site is a crucial reconstruction problem, and becomes very complex if skin reconstruction has to be associated with a complex tendon repair. The Authors describe a new approach to the repair of Achilles tendon substance loss compounded by a soft tissue defect, using a cryopreserved gracilis tendon allograft in combination with a distally-based adipofascial sural flap
Studio multivariato di parametri oceanografici chimici e fisici caratterizzanti l’area Nord-Adriatica
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