1,720,960 research outputs found
Geophysical Challenges for Future Satellite Gravity Missions: Assessing the Impact of MOCASS Mission
Full text linkThe GRACE/GRACE-FO satellites have observed large scale mass changes, contributing to the mass budget calculation of the hydro-and cryosphere. The scale of the observable mass changes must be in the order of 300 km or bigger to be resolved. Smaller scale glaciers and hydrologic basins significantly contribute to the closure of the water mass balance, but are not detected with the present spatial resolution of the satellite. The challenge of future satellite gravity missions is to fill this gap, providing higher temporal and spatial resolution. We assess the impact of a geodetic satellite mission carrying on board a cold atom interferometric gradiometer (MOCASS: Mass Observation with Cold Atom Sensors in Space) on the resolution of simulated geophysical phenomena, considering mass changes in the hydrosphere and cryosphere. Moreover, we consider mass redistributions due to seamounts and tectonic movements, belonging to the solid earth processes. The MOCASS type satellite is able to recover 50% smaller deglaciation rates over a mountain range as the High Mountains of Asia compared to GRACE, and to detect the mass of 60% of the cumulative number of glaciers, an improvement respect to GRACE which detects less than 20% in the same area. For seamounts a significantly smaller mass eruption could be detected with respect to GRACE, reaching a level of mass detection of a submarine basalt eruption of 1.6 109 m3. This mass corresponds to the eruption of Mount Saint Helens. The simulations demonstrate that a MOCASS type mission would significantly improve the resolution of mass changes respect to existing geodetic satellite missions
Analysis of direct current resistivity data using continuous wavelet transform
No full textWe have developed a new method for the direct current resistivity interpretation, based on the continuous wavelet transform
(CWT) of electric potential-difference data. It exploits the main
properties of the CWT, such as stability versus noise, and does
not require a starting model or other a priori information such as a
model weighting function or constraints. Because the approximate integral equation of the resistivity problem has the same
form as the forward problem for potential fields, the authors analyze geoelectric data (with dipole-dipole configuration) using the
wavelets belonging to the Poisson kernel semigroup. They find
that the CWT analysis of the measured electric potential difference is able to identify buried bodies, defining their depth, position, and extent. Such parameters are estimated with no prior
knowledge of the resistivity contrast between the bodies and
the background. We consider several synthetic models, such as
dikes, compact bodies, and contacts. In general, the depth and
the lateral thickness of the buried bodies are estimated with good
accuracy, using a diagram relating the singular point estimations
to the different values of the dipole separation factor n. Thanks
to the good results obtained from synthetic data, we test the
method with data generated during laboratory experiments. In
two laboratory-scale models, our method displays a better precision compared with smoothness-constrained least-squares inversion in identifying the exact position of the edges of a buried
body. Finally, we find that combining CWT and inversion is
advantageous: after constraining the inverse problem with a priori
information from the CWT analysis, we obtain an improved
inverse model
Seamount growth to be observed in future satellite gravity missions
Full text linkGrowing seamounts bear a hazard to navigation, especially if their summit reaches shallow depths and they reach the ocean surface. A seamount that expands up to the surface and creates an island, is detectable by remote sensing images, but not if the island retracts below the surface. Real time gravity observations detect the mass change independently of the optical detection, the limiting factor being only the noise level of the data acquisition in relation to the signal generated by the mass change. Starting from realistic size-frequency distributions of seamounts, we estimate the expected signals of seamount growth. We develop a method to compare the signal to the spectral noise characteristics of a GRACE-type mission, expandable to a possible mission with improved noise curve. We evaluate the expected gravity changes of seamounts and find that a noise curve of GRACE improved by a factor 10 would be sufficient to detect a realistic sea mount growth with a latency of 1 year. The detection threshold though has a tradeoff with the time resolution, since resolution improves for increased time periods over which the satellite observation can be averaged
Geodetic observations to monitor natural hydraulic overpressure
Full text linkThe pressurization of a channel system occurs naturally through intake of rainfall and river drainage. The consequences of up to 1MPa pressurization include sudden uprise of water level, blockage of channels, increased erosion and possible triggering of seismicity, with associated diversified hazards. We model the expected deformation with the Finite Element Method and analytical approaches, and find that the pressures induce deformation which can be geodetically detected. The careful analysis of GNSS timeseries and tilt observations recovered in N-Italy demonstrates that the signals are observable. The observations of tilt have been made in karstic caves where a GPS station has been colocated on the surface. The uplift of GPS during underground floods is expected to be up to several mm and the titling at the microradians level for the tiltmeters. The results demonstrate that geodetic observations could be used to monitor internal pressure loading of the underground channel system. The research is based on the results described in Grillo et al. 2018 and Braitenberg et al. 2019.
References
Braitenberg C., Pivetta T., Barbolla D.F., Gabrovšek F., Devoti R., Nagy I. (2019) Terrain uplift due to natural hydrologic overpressure in karstic conduits, Scientific Reports, in press.
Grillo B., Braitenberg C., Nagy I., Devoti R., Zuliani D., Fabris P. (2018). Cansiglio Karst-Plateau: 10 years of geodetic-hydrological observations in seismically active northeast Italy. Pure and Applied Geophysics, Volume 175, Issue 5, 1765-1781, doi:10.1007/s00024-018-1860-7
Hydrologic induced deformation : Distinguish surface loading from pressure induced uplift
No full textThe observation of crustal deformation is a means to calculate the strain rates and the stress loading at faults. The strain rate is expected to vary in time during the earthquake cycle, but also due to hydrologic masses and fluxes. Hydrologic mass is an elastic loading of the crust, with a consequent lowering and return to the starting position. The opposite effect occurs in places in which the subsurface waters are constrained to flow in channels with consequent buildup of pressure of the water, which determines a surface uplift and deformation. This latter effect is present in karst areas, and in particular in the classical karst shared between Italy and Slovenia, where crustal deformation is measured with tiltmeters in caves and GPS at the surface
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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