1,721,147 research outputs found
Displacement field of the Italian area from permanent GPS stations
No full textA network of nine permanent GPS stations, six of them located in Italy (Cagliari, Matera, Medicina, Noto, Padova and Torino), the other three in Central Europe (Graz, Zimmervald and Wettzell) was been analyzed four times from October 1996 till 1998. After the GPS data processing, a rigorous statistical analysis based on the F (Fisher) test applied on the detected coordinate differences showed significant displacement at Matera, Medicina and Noto. The mean velocities computed for these sites with respect to Wettzell are (0.6 ± 0.3) cm/yr for Matera, (0.7 ± 0.2) cm/yr for Medicina and (0.6 ± 0.3) cm/yr for Noto. GPS velocities agree with those derived by VLBI and ITRF96 solutions, provided error ellipses are taken into account. The deformation analysis of the last time span shows a suspicious horizontal jump at Padova of (1.0 ± 0.1) cm corresponding to an antenna changing within the same period. This fact shows, in spite of the care used in permanent GPS installation, how the results of the deformation analysis may be strongly conditioned by site problems
UAV photogrammetry and ground surveys as a mapping tool for quickly monitoring shoreline and beach changes
Full text linkThe aim of this work is to evaluate UAV photogrammetric and GNSS techniques to investigate coastal zone morphological changes due to both natural and anthropogenic factors. Monitoring morphological beach change and coastline evolution trends is necessary to plan ecient maintenance work, sand refill and engineering structures to avoid coastal drift. The test area is located on the Northern Adriatic coast, a few kilometres from Ravenna (Italy). Three multi-temporal UAV surveys were performed using UAVs supported by GCPs, and Post Processed Kinematic (PPK) surveys were carried out to produce three-dimensional models to be used for comparison and validation. The statistical method based on Crossover Error Analysis was used to assess the empirical accuracy of the PPK surveys. GNSS surveys were then adopted to evaluate the accuracy of the 2019 photogrammetric DTMs. A multi-temporal analysis was carried out by gathering LiDAR dataset (2013) provided by the "Ministero dell'Ambiente e della Tutela del Territorio e del Mare" (MATTM), 1:5000 Regional Technical Cartography (CTR, 1998; DBTR 2013), and 1:5000 AGEA orthophotos (2008, 2011). The digitization of shoreline position on multi-temporal orthophotos and maps, together with DTM comparison, permitted historical coastal changes to be highlighted
Methodological aspects for the survey of the architectural heritage: a few examples in the fortified island of Malta.
No full textAspetti metodologici per il rilievo del patrimonio architettonico: alcuni esempi nell’isola fortificata di Malta.
No full textEstimation of apparent thermal inertia of roofing materials from aerial thermal imagery
Full text linkThe rapid expansion of urban areas and soil sealing is enhancing the Urban Heat Island (UHI) phenomenon, especially during heat waves. The different thermal inertia of the building materials compared to natural surfaces is one of the major driving factors of UHI. The present contribution aims to test a methodology for mapping the Apparent Thermal Inertia (ATI)—a proxy that can be derived from remote sensing data—of roofing surfaces at the scale of an entire city and with a high spatial resolution. Day and night aerial thermal images with the resolution of 0.5 m were acquired over two test areas in Bologna (Italy), together with satellite multispectral data. Statistics on the buildings in the test areas are computed considering different classes of roofing materials (e.g. bituminous sheath, clay tiles, metal sheet, gravel tiles). Observed median ATI values for each class range from 0.03 to 0.09 K-1 with interquartile ranges between 0.02 and 0.14 K-1, so the intra-class variability in some cases appears higher than the variability among different material classes, proving the importance of ATI mapping for UHI investigations
Sea Tide Analysis Derived by PPP Kinematic GPS Data Acquired at David-Drygalski Floating Ice Tongue (Antarctica)
Full text linkOne of the most important ice-stream of the Victoria Land (VL) is the David Glacier, which produces 100 km long floating sea-ward ice tongues in the Ross Sea, the Drygalski Ice Tongue (DIT). The ice-tongue slides down into the sea increasing its velocity rates and together with ice-stream movement sometime produce characteristic ice-quakes. This paper shows the effects of the sea tidal variation on both horizontal and vertical components of movement at a portion of DIT. Ocean tide is usually modelled by a series of harmonic coefficients (amplitude and phase), which are estimated through several systems of measurement. For the study area, these data are made available by the Antarctic Tide Gauge (ATG) database. Moreover, tidal data recorded by a multiparameter underwater tide gauge, which was installed at Mario Zucchelli Station (MZS), the Italian Antarctic Base, in February 2006, are being processed again. The kinematic Precise Point Positioning (PPP) processing was adopted for the analysis of 24 days of acquisition performed with a GPS receiver located in the initial part of DIT, about 46 km seaward from the Ice Fault David Cauldron. The analysis of harmonic tidal components has shown that PPP solutions show correct values of diurnal and semi-diurnal tidal components and therefore can provide valuable information in the coastal area covered by ice tongues
Sea Tide Influence on Ice Flow of David Drygalski’s Ice Tongue Inferred from Geodetic GNSS Observations and SAR Offset Tracking Analysis
Full text linkDavid Glacier and Drygalski Ice Tongue are massive glaciers in Victoria Land, Antarctica. The ice from the East Antarctic Ice Sheet is drained through the former, and then discharged into the western Ross Sea through the latter. David Drygalski is the largest outlet glacier in Northern Victoria Land, floating kilometers out to sea. The floating and grounded part of the David Glacier are the main focus of this article. During the XXI Italian Antarctic Expedition (2005-2006), within the framework of the National Antarctic Research Programme (PNRA), two GNSS stations were installed at different points: the first close to the grounding line of David Glacier, and the second approximately 40 km downstream of the first one. Simultaneous data logging was performed by both GNSS stations for 24 days. In the latest data processing, the kinematic PPP technique was adopted to evaluate the dominant diurnal components and the very small semi-diurnal variations in ice motion induced by the ocean tide and the mean ice flow rates of both GNSS stations. Comparison of the GNSS time series with predicted ocean tide calculated from harmonic coefficients of the nearest tide gauge stations, installed at Cape Roberts and Mario Zucchelli Station, highlight different local response of the glacier to ocean tide, with a minor amplitude of vertical motion at a point partially anchored at the bedrock close to the grounding line. During low tide, the velocity of the ice flow reaches its daily maximum, in accordance with the direction of seawater outflow from the fjord into the ocean, while the greatest daily tidal excursion generates an increase in the horizontal ice flow velocity. With the aim to extend the analysis in spatial terms, five COSMO-SkyMED Stripmap scenes were processed. The comparison of the co-registered offset tracking rates, obtained from SAR images, with the GNSS estimation shows good agreement
Digital orthophoto as a tool for the restoration of monuments
No full textFor the restoration of monuments it is now becoming normal practice to carry out a preliminary study of the monument before starting any kind of work. The metric survey is one of the main operations required. For this reason, photogrammetry applications already have a large bibliography. In particular, digital photogrammetry is currently an effective system, providing different solutions of both the vector and raster type. For an 18th-century gate in the Malta fortification walls, many tests were carried out in order to establish a suitable procedure for the creation of digital orthophotos. A photographic metric product, showing maximum detail without subjective interpretation of the object and the conditions of the material, could be very interesting in supporting any restoration work. The use of automatic procedures is also particularly suitable where large-scale surveys have to be carried out on very large objects with homogeneous characteristics, as is the case with the Malta fortification Walls. The advantages of digital over manual processing lie in the possibility of measuring a very large number of points without fatigue and with a high level of productivity. Digital orthophotos require a digital surface model as input, but the production of a high-fidelity reconstruction of surfaces by automatic measurement of points in close range photogrammetry still remains an open problem. Particular difficulties are caused for instance by object details that are not imaged or with strong shadows, or by complete failure of the image matching algorithms. Discontinuities in the surface, very common in architectonic objects, complicate the generation of models and surfaces. Within this work, several tests using commercial software were carried out, to define the best parameters for the automatic generation of DSM (Digital Surface Model) related to the monument being studied. The initial tests are based on the different dimension of the search window and the consequences of this choice on the accuracy and reliability of the matching procedure. Further tests are related to the number of points needed to start the matching procedure: firstly, points have been entered following a regular grid, then a greater number of points from the analytical plotting have been entered. The results are compared, also taking in account practical and economic considerations. Finally, different aspects for the creation of representative surfaces of the object have been analysed due to the non planarity of the object, presence of linear discontinuities and noticeable overhangs. The above-mentioned tests lead to several general considerations regarding strategies for creating orthophotos as a suitable qualitative and quantitative tool for the restoration of a monument
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