1,720,961 research outputs found
Global Navigation Satellite Systems as Signals of Opportunity for Environmental Applications: Reflectometry and Scintillation
Full text linkL'abstract è presente nell'allegato / the abstract is in the attachmen
Detecting Phase Scintillation at High Latitudes Using Ionospheric Scintillation Monitoring Records and Machine Learning Techniques
Full text linkIn this paper, we present a bagged tree model able to detect phase scintillation at high latitudes with 95% accuracy, 5% scintillation miss-detection and 5% scintillation false alarm. The input to the model is a series of 3 minutes of the Total Electron Content (TEC), 3 minutes of the change in TEC (dTEC), and the satellite elevation. These values are extracted from Ionospheric Scintillation Monitoring Records (ISMR) logged by Ionospheric Scintillation Monitoring (ISM) receivers. We compare the performance of this model to Support Vector Machine (SVM) models, k-Nearest Neighbors (k-NN) models, and also to other decision tree models. Furthermore, we assess the ability of the TEC and dTEC features to detect scintillation independently of the scintillation indexes. For this, we compare the above decision trees, kNN and SVM models to the same models but trained using scintillation indexes as additional inputs. Moreover, we show the results of testing the proposed model using a novel data set. Finally, we compare the accuracy of the machine learning model to the performance of a detector based on the phase scintillation index σ φ threshold
Data from GNSS-Based Passive Radar to Support Flood Monitoring Operations
Full text linkSignals transmitted by Global Navigation Satellite Systems can be exploited as signals of opportunity for remote sensing applications. Satellites can be seen as spread sources of electromagnetic radiation, whose signals reflected back from ground can be processed to detect and monitor geophysical properties of the Earth’s surface. In the past years, several experiments of GNSS-based passive radars have been demonstrated successfully, mainly from piloted aircraft. Then, the proliferation of small UAVs enabled new applications where GNSS-based passive radars can provide useful geospatial information for environmental monitoring. Thanks to the availability of commercial Radio Frequency front ends and the enhanced processing capabilities of embedded platforms, it is possible to develop GNSS-based passive radars at moderated cost. These can be mounted on Unmanned Aerial Vehicles, and be used to support the sensing of environmental parameters. This paper presents the results of an experimental campaign based on the use of a UAV for GNSS reflectometry, tailored to the detection of the presence of water on ground after floods. The work is part of wider project, which intends to develop solutions to support rescuers and decision makers to manage operations after natural disasters, through the integration and modelling of geospatial data coming from multiple sources
Monitoring the Effects of the October 10-11 Solar Storm at Mid-Latitudes Using a GNSS SDR Receiver
Full text linkThe October 10–11, 2024, geomagnetic storm, one of the most intense of solar cycle 25, significantly impacted ionospheric conditions at mid-latitudes. In this study, we analyze the effects of this storm on Global Navigation Satellite System (GNSS) signals using a Software-Defined Radio (SDR)-based receiver at a location in North Italy. The storm, triggered by multiple solar flares and Earth-directed coronal mass ejections (CMEs), induced strong ionospheric disturbances, affecting GNSS signal propagation beyond equatorial and high-latitude regions. To investigate these effects, we recorded GNSS signals on L1 and L2 bands throughout the storm period, along with GNSS observation data from a nearby geodetic station. Our
analysis focuses on ionospheric irregularities using the Rate of TEC Index (ROTI) and scintillation indices. ROTI values revealed a significant increase in ionospheric turbulence during the storm’s main phase, coinciding with a Kp index of 9 and a Dst minimum of -335 nT. The recorded IQ samples were processed by using a software receiver, showing moderate amplitude scintillation on multiple GNSS satellites.
Furthermore, we show the effectiveness of the Software Defined Radio approach, to capture capture and reconstruct ionospheric disturbances with high fidelity for advanced post-processing of the events. The approach is validated by re-playing the recorded GNSS signals and processing the reproduced scenario by means of a commercial GNSS receiver and successfully reproducing scintillation indices
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
On estimating the phase scintillation index using TEC provided by ISM and IGS professional GNSS receivers and machine learning
Full text linkAmplitude and phase scintillation indexes (S4 and sigma_phii) provided by Ionospheric Scintillation Monitoring (ISM) receivers are the most used GNSS-based indicators of the signal fluctuations induced by the presence of ionospheric irregularities. These indexes are available only from ISM receivers which are not as abundant as other types of professional GNSS receivers, resulting in limited geographic distribution. This makes the scintillation indexes measurements rare and sparse compared to other types of ionospheric measurements available from GNSS receivers. Total Electron Content (TEC), on the other hand, is an ionospheric parameter available from a wide range of multi-frequency GNSS receivers. Many efforts have worked on establishing scintillation indicators based on TEC, and geodetic receiver in general, introducing various metrics, including the Rate of TEC change (ROT) and ROT Index (ROTI)
Scintillation Climatology from a Software Defined Radio Receiver over Antarctica
Full text linkSoftware-Defined Radio (SDR) Global Navigation Satellite System (GNSS) receivers for operational Ionospheric Scintillation Monitoring (ISM) have faced challenges and were deemed failures by many research projects. The need for a highly stable oscillator and a robust real-time signal-tracking capability have been the main challenges.
The Istituto Nazionale di Geofisica e Vulcanologia (INGV) led a project called DemoGRAPE (Demonstrator of GNSS Research and Application for Polar Environment) to deploy an SDR GNSS Receiver in SANAE IV Antarctica station, which has been continuously operating since January 2016. The SDR receiver was designed by the Navigation Signal Analysis and Simulation (NavSAS) group in collaboration with the Joint Research Centre (JRC) of the European Commission. The system deploys the SDR in parallel to a Septentrio PolaRxS ISM receiver. The two receivers are fed by the same receiving antenna (i.e., they share the same field of view and, hence, cross the same portion of the ionosphere) such that they receive quasi-identical signals except for the independent effects of their front-ends. The SDR produces as output a log file, equivalent to the ISM record produced by PolaRxS, that contains the amplitude and phase scintillation indexes. In addition to this, the SDR system records the raw digital samples of the GNSS signal when the internal algorithm of the receiver detects scintillation presence. These data can be used to replicate the scintillation event in the laboratory and perform dedicated post-processing of the raw signal itself.
The system has been in operation for over seven years now, spanning more than half a solar cycle. It has recorded several geomagnetic storm events as well as abundant data in quiet conditions. To the best of our knowledge, this is the longest dataset of this nature (co-located PolaRxS and SDR receivers). We compare the performance of the two receivers by analyzing the scintillation climatology maps obtainable from both receivers\u27 data. Here, the climatology is obtained using the well-established Ground Based Scintillation Climatology (GBSC) technique from the data provided by the two different receivers.
The study shows that the SDR climatology maps under disturbed geomagnetic conditions are equivalent to those obtained from the PolaRxS receiver. Under quiet conditions, the SDR shows more scintillation events than the PolaRxS. Carefully inspecting the differences in the scintillation occurrence between the two receivers, they seem not to happen randomly but mainly concentrated along the expected (climatological) position of the auroral oval. This means that the SDR application for space weather monitoring could be possible and that the SDR could be utilizable as an informative tool by the ionospheric scintillation community
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
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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