1,720,990 research outputs found
Scansione dello spazio di copertura e dimensionamento di massima dell’antenna
No full textRAPPORTO TECNICO PROG. LOTHA
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
Polarimetric Avionic Weather Radar for Increasing Flight Safety and Efficiency
No full textCurrent avionic weather radars cannot give accurate information about the weather hazards. Pilots avoid the potentially dangerous area with a greater detour, but only thirty percent of “red echo” radar returns represent actually a threat. These detours involve a longer trajectory and a greater impact on the environment. Instead, a polarimetric radar, which can discriminate for instance between rain and hail, can enhance pilot situational awareness and support trajectory optimization. In the framework of KLEAN project funded by CLEANSKY Joint Technology Initiative, a customized knowledge-based Electronic Flight Bag (EFB) was developed. This EFB, other than being capable to show the map, the flight trajectory and information about surrounding environment, it also implements a polarimetric radar data processor aimed to the assessment of the risk level of the phenomena encountered en route
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
Analysis of X-band weather polarimetric radar simulator for avionic purposes
No full textThe improvement of the essential aircraft equipment used by pilots has a very important role in safety enhancement. In this context polarimetric weather Doppler radars could offer a valuable aid in improving detection and classification of hydrometeors, helping pilots to take the more efficient trajectory, balancing risk level and unnecessary detours. In this work an analysis of a polarimetric radar signal simulator developed by the RaSS team is presented
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
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
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