1,720,989 research outputs found
Using deformation for reservoir monitoring and characterization: InSAR surveillance of CO2 injection at the Krechba field, Algeria
No full textObserving crustal deformation and atmospheric signals from COSMO-SKYMED and GPS data
No full textThe combined use of InSAR and GPS allows for the full exploitation of the complementary aspects of the two
techniques by overcoming the limitations inherent in the use of each technique alone. Additionally, GPS-based
estimates of tropospheric delays may contribute in obtaining better corrections of the wet tropospheric path delay in InSAR signals. This will enhance the coherence and will allow the application of InSAR in a wider range of
applications.
We have compared the InSAR and GPS data at Bologna (urbanized area) and Medicina (agricultural area), in
northeastern Italy, where two permanent GPS stations of the University of Bologna are operational since mid
1999 and 1996 respectively. The InSAR data used are the COSMO-SkyMed (CSK) images made available by
the Italian Space Agency (ASI) in the framework of the research contract AO-1140. The Permanent Scatterers
(PS) technique was applied to a number of repeated CSK strip map SAR images acquired over a 40x40 square
km area encompassing the two towns mentioned above. The results of this work demonstrate on the one hand the
CSK capabilities to operate in a repeated interferometric survey mode for measuring ground deformation with
millimeter accuracy in different environments. On the other, the comparison of the differential height between the two stations derived with the GPS and the InSAR data, using both acquisition geometries, is satisfactory.
Elevation, ground deformation and atmospheric artifacts were estimated in correspondence of the identified PS
and compared with the GPS measurements carried out at the same acquisition time by the permanent stations at
Bologna and Medicina. The comparison of the differential height between the two stations shows the sensitivity
of the GPS height solution to the length of the observation interval. The vertical dispersion achieved by GPS is
higher than that achieved by PS InSAR, as expected; however, a similar linear trend appears in the results of both techniques.
The comparison of differential tropospheric delays has been carried out. Two GPS solutions derived with different
session length and data acquisition rate were considered. The InSAR results were those relevant to two PS located
at a very close distance from the GPS stations. These are representative of the majority of PSs identified around
the two stations. A similar behavior is present in the results achieved by both GPS and PS-InSAR techniques,
despite of expected differences due to the almost instantaneous nature of the PS-InSAR estimates compared to the GPS 5-min averaged results
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 of GPS and InSAR time series for detecting and understanding crustal deformation and atmospheric signals
No full textNowadays a wealth of information is available from different space geodetic techniques to address different study areas in the fields of geodesy and geophysics. The GNSS and InSAR techniques play a key role in the determination of crustal deformation with high precision and resolution which is a fundamental contribution towards the interpretation of geodynamic processes at different spatial and temporal scales. Dense GNSS networks allow determining the total water vapor content of the atmosphere thus contributing to short-term weather forecast. InSAR determined atmospheric artifacts can be compared with the GNSS estimates aiming at a higher coherence between the two techniques. The integration of GNSS and INSAR into a multi-technique approach for monitoring the Earth system will significantly contribute to the detection and understanding of both natural and anthropogenic fingerprints in climate variability and changes. GNSS coordinate time series often suffer from undesired signals of different nature which may impair the reliable estimation of the long-period trend and that should be therefore corrected in the original data series. We have adapted the STARS methodology, first proposed by Rodionov (2004), to the detection of discontinuities in the GPS time series of EUREF stations located in and around the city of Bologna in Italy. Jumps were identified due to changes in the reference system, to the magnitude 5.9 earthquake that on May 20th 2012 struck a vast area of the Po Plain, to increasing multipath effects in conjunction with the year 2000 solar maximum, to local water table variations and to instrumentation maintenance/changes. After correcting the GPS time series for the identified jumps, over the time period 2010-2011, comparisons were performed for the up and east coordinates with the results derived from a PS-InSAR analysis of COSMO SkyMed images made available by the Italian Space Agency (ASI). Differential tropospheric delays derived by both the GPS and PS-InSAR analysis were also compared
Subsidence monitoring update for Emilia-Romagna region (Italy) by integrated use of InSAR and GNSS data
Full text linkVariations 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
SAR monitoring of progressive and seasonal ground deformation using the permanent scatterers technique
No full textAppropriate 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
Seasonal modulation in the horizontal components of GPS station positions
No full textThe combination of different techniques such as InSAR and GPS is characterized by the added value of taking
advantage of their complementary strengths and of minimizing their respective weaknesses, thus allowing for the full exploitation of the complementary aspects by overcoming the limitations inherent in the use of each technique alone. Another important aspect of the GPS/InSAR integration regards the fact that today’s application of interferometric SAR techniques is limited by the knowledge of the wet tropospheric path delay in microwave observations. GPS-based estimates of tropospheric delays may help in obtaining better corrections which will enhance the coherence and will allow the application of InSAR in a wider range of applications.
The area selected for the InSAR/GPS comparison/integration is in northeastern Italy and includes the town of Bologna, and two nearby sites Medicina (agricultural area) and Loiano (a small city on the Apennines) where a small network of permanent GPS stations is operated by the University of Bologna. The InSAR data used are the COSMO-SkyMed (CSK) images made available by the Italian Space Agency (ASI) in the framework of the research contract AO-1140.
The Permanent Scatterers (PS) technique will be applied to a number of repeated CSK strip map SAR images
acquired over a 40x40 square km area encompassing the towns mentioned above. Ultimately this work will contribute demonstrating the CSK capabilities to operate in a repeated interferometric survey mode for measuring
ground deformation with millimeter accuracy in different environments. A PS is a target whose radar signature is
stable with time. Such targets can be identified by means of multiple SAR observations and they can be exploited
for jointly estimating their relative motion and the atmospheric artifacts on a grid that can be quite dense in space but not in time (depending on the SAR revisiting time interval). On the contrary the GPS can provide very frequent time measurements in correspondence of a few measuring points. Elevation, ground deformation and atmospheric artifacts estimated in correspondence of the identified PS will be compared with independent measurements carried out at the same acquisition time by permanent GPS stations in the area of Bologna, Medicina and Loiano. The comparison of these independent measurements is itself a cross-validation of the obtained results. The value of cross-validation of different and compatible techniques is to provide reliable vertical crustal motion determinations in space and time. Urban areas such as that of Bologna will be examined to evaluate CSK capabilities to measure extended subsidence (or up-swelling) and single building deformation
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