1,721,344 research outputs found
GPS cinematico per il monitoraggio della topografia dell'area di Dome C (Antartide)
No full textNell’ambito del progetto denominato EPICA (European Project for Ice Core in Antartica), durante la campagna di ricerche in Antartide del 1995/1996, fu istituita e misurata per la prima volta una rete GPS statica finalizzata al controllo delle deformazioni superficiali di un’area del Plateau Antartico a forma di duomo, denominata Dome C, considerata idonea alla realizzazione di un carotaggio profondo per studi paleoclimatici. Il rilievo in modalità statica è stato ripetuto nella campagna antartica dell'anno 1998/1999 ed in entrambe sono stai tacquisiti anche numerosi profili cinematici che elaborati in post-processamento hanno consentito la ricostruzione della superficie topografica relativi ai due periodi di misura a corredo delle informazioni sulle deformazioni locali ricavate dall'analisi delle misure statiche. Nel lavoro vengono discusse le procedure relative al confronto dei DTM per la stima dell'accumulo nevoso sul duomo e delle problematiche annesse, sempre in riferimento all'ambiente particolare in cui è condotta la sperimentazione
Performance of Atlas GNSS Global Correction Service for High-Accuracy Positioning
Full text linkIn the last decade, a number of correction services for global navigation satellite systems (GNSS) precise positioning have been developed, mainly for offshore applications, based on a precise point positioning (PPP) real-time processing. These allow receiving corrections without the need for an internet connection or reference benchmarks around the survey area. In the paper, we tested the Atlas correction service implemented in a Stonex S900A machine (Monza, Italy), with the purpose to verify its performances under optimal operational conditions and in the practical case of a land survey on several benchmarks along the Adriatic coast. The data analysis focused on: accuracy with respect to the reference frame, repeatability of the coordinates considering short and long acquisition periods, time to initialize the survey, and reliability of the formal errors provided by the instrument. The system confirmed the declared performances in most cases and is shown to be a viable alternative to other GNSS techniques also for land surveys where no obstacles affect the sky visibility
Applicazioni della Fotogrammetria in campo Biostereometrico con tecniche analitiche e digitali.
No full textReliability of Real-Time Kinematic (RTK) Positioning for Low-Cost Drones’ Navigation across Global Navigation Satellite System (GNSS) Critical Environments
Full text linkUAVs are nowadays used for several surveying activities, some of which imply flying close to tall walls, in and out of tunnels, under bridges, and so forth. In these applications, RTK GNSS positioning delivers results with very variable quality. It allows for centimetric-level kinematic navigation in real time in ideal conditions, but limitations in sky visibility or strong multipath effects negatively impact the positioning quality. This paper aims at assessing the RTK positioning limitations for lightweight and low-cost drones carrying cheap GNSS modules when used to fly in some meaningful critical operational conditions. Three demanding scenarios have been set up simulating the trajectories of drones in tasks such as infrastructure (i.e., building or bridges) inspection. Different outage durations, flight dynamics, and obstacle sizes have been considered in this work to have a complete overview of the positioning quality. The performed tests have allowed us to define practical recommendations to safely fly drones in potentially critical environments just by considering common software and standard GNSS parameters
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
Study on GPS PPP precision for short observation sessions
No full textPrecise point positioning is increasingly being used in geodetic applications that in many cases are based on static 24-hour RINEX files. Since there are many applications where sub-centimeter position accuracy is not required and users wish to use a single receiver and not be dependent on differential correction, we will evaluate PPP performance for static positioning with 12-, 6-, 3-, 1- and Â1⁄2-h observations. We have, therefore, considered a dataset for the year 2013 from 14 European GNSS stations. The data were analyzed using GIPSY-OASIS II software package and evaluated in terms of repeatability of the coordinates and of coherence with the formal error indicated for each PPP solution. Particular attention was paid to solutions showing large discrepancies in coordinates. The test shows that PPP precision for the 24-h files is below 5Â mm, but decreases slightly for the 12-, 6- and 3-h observation sets. For the 1-h and the Â1⁄2-h RINEX files, precision is within 5 and 10Â cm, respectively. The analysis is completed with a discussion on the impact of the ambiguity resolution that shows how it significantly improves only the easting component and moreover has a higher influence on the formal error rather than on the solutions. Lastly, the study contains an investigation into the reliability of the formal error associated with the PPP solutions. We show that the formal error can be used to identify incorrect solutions, but is not suitable to represent the real accuracy. For that reason, we propose to use the formal error given for the float solutions even for the ones with fixed ambiguities
Analysis of nestin protein in the aqueous humor as biomarker of open angle glaucoma
No full textPrimary open angle glaucoma (POAG) is a progressive optic nerve degeneration, leading to irreversible visual damage. Alterations of the aqueous humor (AH), the biological fluid filling both the anterior and the posterior chambers of the eye, play a pathogenic role in POAG. AH protein composition is altered during glaucoma progression. Nestin protein was found to be differentially expressed in the AH of glaucomatous patients compared to unaffected matched controls. Methods: Nestin was analyzed by an open quartz crystal microbalance (QCM) in the AH of 21 glaucomatous patients compared to nine unaffected controls. The surface of the electrode used in the QCM was coated with an analyte-specific recognition layer. Results: Positive nestin values were recorded in the AH collected from POAG patients; negative values of nestin detection were obtained by analyzing the AH collected from non-POAG glaucomatous patients and unaffected controls. Conclusion: The present study proposes and validates a new clinically applicable approach to analyze biological markers in AH for POAG diagnosis
Impact of Multiconstellation on Relative Static GNSS Positioning
Full text linkUntil a few years ago, a precise survey was only possible using global positioning system (GPS) and Global'naja Navigacionnaja Sputnikovaja Sistema (GLONASS) constellations, but the result was not guaranteed under conditions of poor sky visibility, as in urban canyons. Currently, the number of Global Navigation Satellite System (GNSS) satellites in orbit has strongly increased thanks to the great evolution of the Galileo and the Beidou constellations. In this paper, we investigate the impact of using different constellations and their combinations, in static positioning with the classical differencing approach. For this purpose, two distinct baselines of different lengths (10 and 60 km) were processed using commercial software over a period of one year (2018.24-2019.24). Data were acquired by permanent stations belonging to the European Permanent Network (EPN) network providing 24-h observing sessions. Two datasets were tested, one consisting of 24-h Receiver Independent Exchange Format (RINEX) files and the other considering only 2-h sessions of data acquisition. In both cases, a one-year-long time span has been considered. The baselines were processed considering each of the four GNSS constellations and a series of combinations, for a total of eight solutions. Results have been evaluated looking at the accuracy and repeatability of the coordinates, together with the main constellation parameters. During the analyzed period the number of contemporary visible satellites of the BeiDou constellation was still too poor over the considered area, and therefore this constellation did not provide comparable precisions in respect to the others. Positioning precision provided by the Galileo constellation has shown to be very close to those given by GPS or GLONASS, with a significant difference only on the height component, especially in the case of processing 2-h data. As for 24-h observing sessions, the use of multiconstellation observables actually leads to small improvements in precision with respect to the use of GPS data only, mainly appreciable considering the vertical component. The GPS-Galileo combination gives quite the same performances of the GPS-GLONASS one, but it can potentially take advantage of the integrity message provided by the European constellation
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