1,721,021 research outputs found
Derivation of Clear-Air Turbulence Parameters from High-Resolution Radiosonde Data
Full text linkThe knowledge of atmospheric refractive-index structure constant (Cn2) profiles is fundamental to determine the intensity of turbulence, and hence the impact of the scintillation impairment on the signals propagating in the troposphere. However, their relation with atmospheric variables is not straightforward, and profiles based on statistical considerations are normally employed. This can be a shortcoming when performing simulations for which scintillation disturbances need to be consistent with the assumed atmospheric conditions. In order to overcome this limitation, this work describes a procedure to obtain an estimate of the refractive-index structure constant profile under given atmospheric conditions. The procedure is based on the application of the vertical gradient approach to high resolution radiosonde data. The fact that turbulence is confined to vertically thin layers is accounted for by identifying the turbulent layers through the analysis of the Richardson number profiles, and the value of the outer scale length is estimated using the Thorpe length calculated from potential temperature profile. The procedure is applied to high resolution radiosonde data from the SPARC Data Center and the obtained results are consistent with measured Cn2 profiles previously published in the literature
Adaptive quadratic regularization for baseline wandering removal in wearable ECG devices
No full textThe electrocardiogram (ECG) is one of the most important physiological signals to monitor the health status of a patient. Technological advances allow the size and weight of ECG acquisition devices to be strongly reduced so that wearable systems are now available, even though the computational power and memory capacity is generally limited. An ECG signal is affected by several artifacts, among which the baseline wandering (BW), i.e., a slowly varying variation of its trend, represents a major disturbance. Several algorithms for BW removal have been proposed in the literature. In this paper, we propose new methods to face the problem that require low computational and memory resources and thus well comply with a wearable device implementation
Fusion of Multispectral and SAR images by Intensity Modulation
No full textThis paper presents a novel multi-sensor image fusion algorithm, which extends pan-sharpening of multispectral (MS) data through intensity modulation to the integration of MS and SAR imagery. The method relies on SAR texture, extracted by ratioing the despeckled SAR image to its lowpass approximation. SAR texture is used to modulate the generalized intensity (GI) of the MS image, which is given by a linear transform extending Intensity-Hue-Saturation (IHS) transform to an arbitrary number of bands. Before modulation, the GI is enhanced by injection of highpass details extracted from the available Pan image by means of the "à-trous" wavelet decomposition. The texture-modulated pan-sharpened GI replaces the GI calculated from the resampled original MS data; then the inverse transform is applied to obtain the fusion product. Experimental results are presented on Landsat-7/ETM+ and ERS-2 images of an urban area. The results demonstrate accurate spectral preservation on vegetated regions, bare soil, and also on textured areas (buildings and road network) where SAR texture information enhances the fusion product, which can be usefully applied for both visual analysis and classification purposes
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
Global simulation of tropospheric water vapor measurements through the Normalized Differential Spectral Attenuation (NDSA) approach: setup, scintillation model and performance evaluation
No full textNDSA (Normalized Differential Spectral Absorption) was recently proposed as a differential attenuation measurement method to estimate the total content of water vapor (IWV, Integrated Water Vapor) along a tropospheric propagation path between two Low Earth Orbit (LEO) satellites during a relative set/rise (occultation) event. The NDSA approach is based on the simultaneous estimate of the total attenuations at two relatively close frequencies and of a "spectral sensitivity parameter" that can be directly converted into IWV through empirical relationships that can be previously derived based on statistical regressions between spectral sensitivity and IWV simulated through real radiosonde data and a propagation model. In this paper we present the error performance in the IWV profile retrievals in the troposphere (up to 14 km) on the basis of an entire day of occultation events in a ECMWF-model simulated atmosphere. For the first time, we present results of simulations of NDSA measurements made in the millimeter band (in addition to the Ku/K bands analysed in previous works), specifically at 179 and 182 GHz. © 2009 SPIE
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
Capabilities and potential of an avionic polarimetric weather radar simulator
No full textIn this paper, the potential of an avionic polarimetric weather radar is shown. The simulator used for such a purpose is a statistical simulator capable of reproducing complex signals as those gathered by an onboard radar, along with polarimetric and Doppler observables. The simulator, developed in the framework of the CleanSky European program, can be an useful tool to evaluate the radar prototypes that in a near future will be mounted on real aircrafts to enhance pilots' environmental awareness, which is declared as a major CleanSky objective
Contributing towards sustainable aviation through an electronic flight bag for processing signals from avionic polarimetric weather radars
No full textDuring the KLEAN project (funded by the EU through the CLEANSKY Joint Technology
Initiative), we developed a customized knowledge-based Electronic Flight Bag (EFB). The
device, besides performing standard operations such as showing flight-related map,
trajectory and environmental information, also implements decisions and optimization
schemes based on the information provided by a polarimetric radar signal processor with
the precise purpose to assess the risk level related to weather phenomena showing up on
the selected route. Indeed, current avionic weather radars are not able to provide accurate
information about the weather hazards, with the result that pilots simply avoid the potentially
dangerous areas with a greater detour. While only 30% of “red echo” returns represent a
real threat, detours involve a longer trajectory and a greater impact on the environment and
fuel consumption. We show how the joint use of customized EFB and polarimetric radar can
improve pilots’ situational awareness and supports trajectory optimization
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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