1,720,959 research outputs found
Observing and assessing seasonal non-tidal ocean loading through ocean, continuous GPS and gravity data in the Adriatic area
No full textA combined GPS and Gravity analysis to study the effect of environmental parameters
No full textGeodetic in-situ observations are always effected by environmental parameters like atmosphere, ocean and hydrology. It is often criticised that seasonal effects accounted for global network analysis do not significantly improve the resulting parameters. In a local case study at Medicina, space geodetic (GPS and VLBI) and gravity observations (SCG and FG5) are used together with environmental observations and models to provide significant information both on the seasonal fluctuation as well as on the linear and non-linear long-term trend in height. Models of seasonal height and gravity components have been achieved by accounting for loading and mass effects, by atmosphere, non tidal ocean and the local hydrology. This last component shows to be a major contribution of the seasonal variations not only in terms of loading and mass variations but also for soil consolidation effects induced by water table decrease / increase on the clayey soil in Medicina. The local hydrology is an important component to understand the seasonal effects but it is difficult and / or expensive to get sufficient information at the observation sites. It will be demonstrated that regional and global information on hydrology, the Hydrological Balance and GRACE results used as input can satisfactory replace locally observed environmental data. The experiment carried out in Medicina demonstrates that only the combined reduction of the effect of environmental parameters will improve the overall analysis. Rigorously applied it allows to study linear and non-linear long-term station variations. There is a high probability that the consequent consideration of environmental parameters will have positiv effects on the long-term evolution of the global reference frame
Height seasonal oscillations and long-term trends from a combination of GPS, gravity and InSAR data
No full textA fundamental development of the next coming years shall be the definition and the implementation of a high-accuracy and space-time continuous observation system for monitoring Earth’s surface deformation. The IAG project GGOS (Global Geodetic Observing System) will be the geodetic contribution to such a realization. A detailed knowledge of the crustal deformation is a key element to achieve a thorough comprehension of how the solid Earth responds to deformational forces and for an improved understanding of the seismogenetic cycle. We have studied and applied a combined observational strategy for monitoring and reliably identifying both seasonal and log-term crustal movements, namely height variations/changes. The strategy adopted is based on a multidisciplinary approach that combines the information provided by GPS, InSAR and terrestrial gravimetry. The results of these different techniques are compared and combined in a study on land subsidence in the southeastern Po Plain and the northern Adriatic coast, in Italy
Monitoring Crustal Deformation by Continuous Gravity and GPS Observations
No full textAt Medicina, near Bologna, Italy, a superconducting gravimeter, periodically controlled by absolute gravity observations, is acquiring continuous data series since the beginning of measurements in October 1996. A permanent GPS receiver was also installed at the station and is providing continuous observations since mid 1996. The time series are about 8 years long and they constitute, together with a remarkable ensemble of environmental parameters, a unique data set. The results of the gravity data analysis are interpreted to separate seasonal oscillations from a long-term trend and are compared with the height variations estimated by means of GPS. Noticeable seasonal oscillations are present both in the gravity and GPS time series and they were modeled by accounting for atmospheric, hydrological and non-tidal oceanic effects. Interannual variability is observed. A mean seasonal model derived by stacking of the observations is computed both for the gravity and GPS data series and it is compared with that obtained from the models. A moderate long-term trend has been identified in gravity, which is confirmed by the GPS height variations
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Vertical Crustal Movements and Sea-level Changes in the Northern Adriatic
No full textThe Department of Physics of the University of Bologna (UNIBO), the Consorzio Venezia Nuova, sole agent of the Magistrato alle Acque di Venezia for the managemente of the Venice lagoon environment (MAV), the Italian National Agency for Environmental Protection and Technical Services (APAT), have recently started joint projects to determine and study vertical crustal movements and sea-level fluctuations in the northern Adriatic area where the natural subsidence has been enhanced by anthropogenic components during last century. The combination of the permanent GPS stations belonging to UNIBO and of those of the MAV and APAT constitutes a basic network for the study of land subsidence in the northern Adriatic. We have studied and applied a combined observational strategy for monitoring and reliably identifying both seasonal and log-term crustal movements, namely height variations/changes. The strategy adopted is based on a multidisciplinary approach that combines the information provided by GPS, InSAR and terrestrial and space gravimetry. The results of these different techniques are compared and combined in a study on land subsidence in the southeastern Po Plain and the northern Adriatic coast, in Italy. The sea-level time series of the Marina di Ravenna, Venice and Trieste tide gauge stations are compared to the Topex/Poseidon satellite altimetry sea-level elevation and to the GPS height and InSAR long-term trends at the same stations
Monitoring natural and anthropogenic subsidence in the northern Adriatic area by space and terrestrial techniques
No full textAt local to regional scales, land-surface deformations (subsidence or uplift) can be driven by numerous effects, e.g. natural and/or anthropogenic fluid withdrawal, river and coastal erosion and deposition, and landslides. These deformations are in conjunction with deformations caused by loading effects due to atmospheric pressure variations, continental water storage variations and oceanic circulation, as well as by solid Earth tides. It is well known that the northern Adriatic area, including the eastern Po Plain, is affected by natural long-term subsidence. This has been greatly enhanced, during the second half of last century, by anthropogenic factors such as the over-pumping of water and gas from the underground reservoirs. Induced subsidence rates, with peaks up to 60-70 mm/yr, were recorded in the 1970’s in the Ravenna area on the Adriatic coast. The adoption of groundwater control policies since the beginning of the1980’s has resulted in a noticeable decrease in the subsidence rates during the last two decades. Vertical crustal movements can be monitored to high accuracy by space geodetic techniques such as GPS and InSAR, the combination of the two allows us to measure space and time-continuous deformation. The GRACE mission data can be used to study, among other phenomena, continental water variation, including groundwater. High accuracy terrestrial gravity data such as those collected continuously by superconducting gravimeters and episodically by absolute gravimeters are also valuable for monitoring both secular and seasonal water-level variations in aquifers. We present a network encompassing northeastern Italy, which extends from the Apennines to the southeastern Po Plain and, along the Adriatic coast, to the Venice area and Trieste. Our initial results have primarily concentrated on parameterizing the land subsidence by comparing and combining GPS, terrestrial gravity, local environmental parameters and InSAR, We update the time-series and extend the analysis to include GRACE gravity field observations in an effort to better understand the process of subsidence
Variations on the Author
Get PDF“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
Get PDFWe 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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