1,720,988 research outputs found
X-band SAR measurements to extract motion-related parameters of offshore wind farms
No full textThis study deals with the observation of off-shore wind turbines using X-band Synthetic Aperture Radar (SAR) measurements acquired by the Spanish PAZ satellite mission. Wind turbines are installed increasingly offshore in utility scale wind farms equipped with enough capacity to satisfy the demand for renewable energy. Especially in northern Europe, the number of large offshore wind farms is increasing rapidly.Hence, in this study, spectral information is extracted from X-band SAR measurements to monitor wind turbines belonging to the Robin Rigg off-shore wind farm in Scotland, UK. Experimental results demonstrate the ability of SAR measurements to provide information about motion parameters associated to the wind turbines
A spatio-temporal variability assessment of the C33 iceberg using multi-polarisation C-band SAR satellite data
No full textIn this study, relevant features are extracted from multi-polarization Sentinel-1 synthetic aperture radar measurements and investigated to characterize the spatial pattern and the temporal evolution of the C33 iceberg formed on 7 April 2016 by partial collapsing of the Nansen Ice Shelf (Terra Nova Bay, Ross Sea, Antarctica). A time series consisting of four dual-polarimetric (HH+HV) C-band synthetic aperture radar measurements is collected from 9 April to 3 May 2016 and processed to extract the iceberg profile - according to an unsupervised state-of-the-art methodology - from three multi-polarization features, namely HH- and HV-polarized normalised radar cross-section and the product of HH- and HV-polarized scattering amplitudes. Once the edge of the C33 icberg is obtained, meaningful features as displacement, drift velocity and rotation are estimated to characterize its spatio-temporal variability.Results show that in such complex environment the HV-polarized NRCS performs best in extracting the iceberg profile and that the C33 iceberg drifted offshore for more than 65 km with an average velocity of about 3 km per day, experiencing non-negligible rotation and stabilizing its behavior over time
A multi-polarization analysis of Terra Nova Bay polynya
No full textThis study focuses on the analysis of Terra Nova Bay polynya, Antarctica, using multi-polarization C-band Sentinel-1 synthetic aperture radar (SAR) measurements. The study aims at analyzing the added-value of polarimetric measurements in observing the polynya and its inhomogeneities with respect to the single-polarization backscattering measurements. The analysis contrasts single-polarization co-And cross-polarized SAR measurements with dual-polarimetric coherent ones using the following metrics: single-polarization normalized radar cross sections and dual-polarimetric eigen-decomposition parameters. Experimental results show the extra benefits carried on by partial polarimetric SAR measurements that allow a more roboust and effective separation between ice-free water and ice streaks
Multi-Frequency and Multi-Polarisation Analysis of the Scattering From Offshore Wind Turbines
No full textIn this study, a scattering analysis of wind turbines is performed using a multi-frequency and multi-polarisation synthetic aperture radar dataset. The latter includes L-, C- and X-band synthetic aperture radar imagery collected by Alos PalSAR-2, Sentinel-1 and PAZ, respectively. Multi-polarization normalized radar cross sections and reflecion symmetry are considered to characterize the backscattering properties of the Robin Rigg offshore wind farm (Solway Firth, UK) turbines, whose features are evaluated with reference to a target-free surrounding sea surface. The experimental results show that the detectability of the wind turbines is severely influenced by the incident wavelength, with the reflection symmetry being a robust and effective parameter to characterize wind turbines. Co-polarized backscattering is always larger than the corresponding cross-polarized one at that HH-polarized backscattering is larger at L-band rather than at X-band, while the C-band VV-polarized backscattering is the lowest. Considering cross-polarized channel, wind turbines call for the largest (lowest) backscattering at X-band (C-band). Results also show that wind turbines are characterized by a correlation between co- and cross-polarized channels much larger than the surrounding sea surface, which satisfies reflection symmetry. In particular, the HH-HV correlation is, on average, larger at X-rather than L-band, while the C-band VV-VH correlation is much lower
On the extraction of the reservoirs’ waterline using polarimetric X-band SAR measurements: the case study of the San Giuliano reservoir, Italy
Full text linkAccording to the World Bank data catalogue, (Formula presented.) records of reservoirs and their associated dams are present summing up a capacity of (Formula presented.) km3 of water. They play a crucial role in providing potable and irrigation water and, therefore, it is of paramount interest to effectively monitor such critical infrastructures. An effective approach is based on satellite remote sensing and, in particular, on the Synthetic Aperture Radar (SAR). In this paper, we critically investigate the use of polarimetric SAR measurements for reservoirs’ waterline estimation. Measurements of the novel COSMO-SkyMed Second Generation (CSG) X-band quad-polarimetric SAR related to the San Giuliano reservoir, in the South of Italy, are used to carry out an electromagnetic analysis of the different polarimetric scattering returns. Experimental results show that the cross-polarized channel, as well as the inter-channel phase, are noisy and, therefore, uninformative when used to design coherent polarimetric waterline extraction methods. From an electromagnetic viewpoint, this is due to the peculiarities of the reservoirs that call for low surface roughness and negligible wave pattern that, at once, result in a joint combination of un-tilted Bragg scattering and specular reflection. This implies that a low co-polarized backscatter and a cross-polarized signal largely below the system noise floor are to be expected. As a consequence, waterline extraction approaches that do not exploit the inter-channel phase, the so-called incoherent approaches, are shown to outperform the coherent ones
A multi-polarization analysis of Terra Nova Bay polynya
No full textThis study focuses on the analysis of Terra Nova Bay polynya, Antarctica, using multi-polarization C-band Sentinel-1 synthetic aperture radar (SAR) measurements. The study aims at analyzing the added-value of polarimetric measurements in observing the polynya and its inhomogeneities with respect to the single-polarization backscattering measurements. The analysis contrasts single-polarization co-And cross-polarized SAR measurements with dual-polarimetric coherent ones using the following metrics: single-polarization normalized radar cross sections and dual-polarimetric eigen-decomposition parameters. Experimental results show the extra benefits carried on by partial polarimetric SAR measurements that allow a more roboust and effective separation between ice-free water and ice streaks
A Machine Learning Approach to Forecast Economic Recessions—An Italian Case Study
Full text linkIn economic activity, recessions represent a period of failure in Gross Domestic Product (GDP) and usually are presented as episodic and non-linear. For this reason, they are difficult to predict and appear as one of the main problems in macroeconomics forecasts. A classic example turns out to be the great recession that occurred between 2008 and 2009 that was not predicted. In this paper, the goal is to give a different, although complementary, approach concerning the classical econometric techniques, and to show how Machine Learning (ML) techniques may improve short-term forecasting accuracy. As a case study, we use Italian data on GDP and a few related variables. In particular, we evaluate the goodness of fit of the forecasting proposed model in a case study of the Italian GDP. The algorithm is trained on Italian macroeconomic variables over the period 1995:Q1-2019:Q2. We also compare the results using the same dataset through Classic Linear Regression Model. As a result, both statistical and ML approaches are able to predict economic downturns but higher accuracy is obtained using Nonlinear Autoregressive with exogenous variables (NARX) model
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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