1,721,014 research outputs found
Unmanned Aerial Systems and DSM matching for rock glacier monitoring
No full textAmong other techniques, aerial and terrestrial photogrammetry have long been used to control the displacements of landslides and glaciers as well as for the detection of terrain morphological changes. Unmanned Aerial Systems (UAS) are today an efficient tool to perform data acquisition in rough or difficult terrain, both safely and quickly, avoiding hazards and risks for the operators while at the same time containing the survey costs. Since 2012 ARPAVdA (the Regional Environmental Protection Agency of Aosta Valley, Italy) periodically surveys with UAS photogrammetry the Gran Sometta rock glacier, the Agency main monitoring site for the climate change impacts on high-mountain areas and related infrastructures.
A Digital Surface Model (DSM) and an orthophoto of the rock glacier are produced after each survey flight. In order to accurately georeference them in a stable reference system, a Global Navigation Satellite System (GNSS) campaign is carried out at each epoch, to update the coordinates of signalised Ground Control Points (GCPs), since they partly lay in unstable (moving) areas. In late August 2015 a survey flight has been executed with a senseFly eBee RTK, with differential corrections sent from a ground reference station. The block has been adjusted without GCP using, as control information, only the projection centres coordinates encoded in the images. The RMS of the differences found on twelve Check Points were about 4 cm in horizontal and 7 cm in elevation, i.e. practically the same accuracy found using GCP. Differences between the DSMs produced at the same epoch with block orientation performed with GCP and with GNSS-determined projection centres were also investigated.
To evaluate the rock glacier displacement fields between two epochs, corresponding features were at first manually identified on the orthophotos by a trained operator. To avoid the manual time-consuming procedure and increase the density of displacement information, two automatic procedures, the former using Least Squares Matching (LSM) and the latter a proprietary implementation of Semi-Global Matching (SGM) have been implemented. Both techniques were applied to pairs of orthophotos as well as to pairs of DSMs at different epochs. A discussion of the characteristics of the implemented methods is provided and the results of the comparison of the two methods with manual measurements are illustrated. Overall, results using DSM matching provided higher completeness of the displacement field than orthophoto matching, especially if long-term (year-to-year) comparisons are considered. At the same time, SGM in both cases produced less mismatches and more smooth and reliable displacement fields than LSM
Ambient Seismic Noise and Microseismicity Monitoring of Periglacial Bodies: A Case Study on the Gran Sometta Rock Glacier (NW Italian Alps)
Full text linkAmbient seismic noise and microseismicity analyses are increasingly applied for the monitoring of landslides and natural hazards. These methodologies can offer a valuable monitoring tool also for glacial and periglacial bodies, to understand the internal processes driven by external modifications in air temperature and rainfall/snowfall regimes and to forecast possible melting-related hazards in the light of climate change adaptation. We applied the methods to an almost continuous year of data recorded by a network of four passive seismic stations deployed in the frontal portion of the Gran Sometta rock glacier (Aosta Valley, NW Italian Alps). The spectral analysis of ambient seismic noise revealed frequency peaks related to stratigraphic resonances inside the rock glacier. Although the resonance frequency related to the bedrock interface was constant over time, a second higher resonance frequency was identified as the effect of variations in the active layer thickness driven by external air temperature modifications at the daily and seasonal scales. Ambient seismic noise cross-correlation highlighted coherent shear wave velocity modifications inside the periglacial body. The microseismicity dataset extracted from the continuous ambient noise recordings was analyzed and clustered to further investigate the ongoing internal processes and gain insight into their source mechanism and location. The first cluster of events was found to be likely related to the basal movements of the rock glacier and to falls and slides of the debris material. The second cluster was possibly related to shallow ice and rock fracturing processes. The validation of the seismic results through simple models of the rock glacier physical and mechanical layering, the internal thermal regime and the surface displacements allowed for a comprehensive understanding of the rock glacier's reaction to the external conditions
Detecting climatic treelines in the Italian Alps: the influence of geomorphological factors and human impacts.
No full textTreelines are widely studied worldwide in relation to climate changes because they are hypothesized to be sensitive climate proxies. However, forest treeline expansion toward higher altitudes may be influenced both by a warming climate and by other factors, such as surface morphology and, in the European Alps, the decline in alpine farming. Our results from five valleys in the inner and peripheral regions of the Alps show that present-day treeline altitudes mostly depend on anthropogenic and orographicgeomorphologic factors. Climatic treelines are limited to steep and inaccessible slopes, and occur at higher altitudes and farther from mountain peaks in the inner regions than in the peripheral regions of the mountain range. Looking for sites in which to study treeline responses to climate change, we recommend investigating the inner regions of the Alps where treelines are farther from human disturbances and from geomorphologic constraints, potentially resulting in freer upward shifts under warmer temperature conditions. We also found that, in the valleys selected, human disturbance is mainly concentrated about 165 m below non-climatic treelines, suggesting a homogeneous influence on treelines, regardless of geographic position
Detection of Large Woody Debris in Braided-Rivers RGB-UAV Dataset: A Comparative Study
No full textLarge woody debris (LWD), a key indicator of riparian vegetation disturbance and river corridor dynamic, plays a crucial role in habitat complexity, geomorphic dynamics and river management. Accurate mapping and monitoring of LWDs are therefore essential for river process analysis and ecosystem assessment, particularly in highly dynamic braided river systems. However, mapping and monitoring LWD remains challenging due to its variable morphology, spectral similarity, and dynamics of braided river. Advancements in artificial intelligence (AI) and unmanned aerial vehicle (UAV) remote sensing offer promising opportunities for addressing these applied geoscience challenges. In this study, we evaluate different AI techniques for the accurate detection of LWD in braided rivers. Specifically, using RGB-UAV imagery, we test two DL models, U-Net and DeepLabv3+, and compare them to other classifiers to identify the most accurate and transferable approach. The results indicate that the DeepLabv3+ method effectively captures the actual spatial distribution of LWD, and two-class classifications were more efficient than multi-class ones. Furthermore, the DL model demonstrated strong transferability when applied to a different spatiotemporal area, highlighting its utility for applied geoscience investigations and river management
HISTORY, GEOMETRY, STRUCTURE: INTERDISCIPLINARY ANALYSIS OF A HISTORICAL BRIDGE
Full text linkIn this paper, an integrated analysis of the geometric and photogrammetric surveys on a 19th century bridge is proposed as an instrument for the comprehension of the historical evolution of its structural disorders, of its present conservation status and as a reliable base to define future interventions. The studied 20 arches brick masonry bridge in Northern Italy, that reaches the length of nearly 600 meters, constitutes a very interesting case study, not only for the technical and structural issues related to its restoration and use (with increased traffic loads) but also for its geometry, that has strict connections with the design methods that lead its construction, based on proportions, and whose changes in time embody the present symptoms of possible structural illnesses. Moreover, the bridge shows many decay phenomena, whose treatment will require a large part of the restoration resources. For this reason, a precise quantification of the affected surfaces, also in the curved parts, is important for the definition of conservative interventions. To this aim, possible methods of mapping and measuring the decay phenomena starting from the photogrammetric survey are also discussed
Winter snow deficit was a harbinger of summer 2022 socio-hydrologic drought in the Po Basin, Italy
No full textAbstract Snow in mountainous regions is a key water resource from local to continental scales. However, the link between increasingly frequent snow droughts and socio-hydrologic impacts from headwaters to lowlands is not fully understood. To untangle this relationship, here we combine snow and climate reanalyses with a range of data of terrestrial water storage, streamflow, and emergency water-use restrictions for the archetypal 2022 snow drought in the Po basin (Italy). We find that a persistent high-pressure ridge during winter 2021–2022 translated into a −88% anomaly in peak snow water equivalent, intraseasonal snowmelt, and earlier melt-out dates. Compounded by reduced summer precipitation and importantly increased temperatures, this snow deficit led to the lowest terrestrial water storage on record in summer 2022. Emergency water-use restrictions were concurrent with the peak in snowmelt deficit in early summer, rather than the peak in precipitation deficit in mid-winter. This study highlights the contribution of snowmelt deficit in driving the 2022 socio-hydrologic drought in the Po Basin
Towards an interdisciplinary characterization of the Rutor glacier (Aosta Valley)
No full textThe Rutor Glacier is located in the upper part of La Thuile valley, Italy (46.637° N, 7.016° E, area 7.5 km2, length 3.8 km, elevation between 2600-3420 m). It is one of the ten biggest glaciers in Italian Alps. Its basin is bound to the south-west by French/Italian border and the accumulation area is open to the western (Atlantic) fluxes. Three shallow firn cores (3-4 m long), representative of the previous winter season, were collected in June 2015, 2016, and 2017 on the top of the glacier. Samples were divided into two aliquots for physical analyses at the EuroCold laboratory of the University of Milano-Bicocca and for chemical analyses at the Institute of Polar Sciences and Ca’ Foscari University of Venice. The optical characterization has been carried out at EuroCold with the SPES method, which provides the extinction cross-section and optical thickness of single particles, as well as the relative concentration of particles in each sample. These physical quantities were related to the stratigraphic data and compared to the chemical analyses. The particle-by-particle approach and the simultaneous measurement of two optical parameters allow sample characterization beyond the measurement of their particle size distribution. Moreover, from the two-dimensional distribution, absorbing particles can be isolated in each sample; samples exhibiting contamination or melting and refreezing are easily recognized. The chemical analyses were devoted to the quantification of inorganic and organic species. We focused on the high-temporal resolution quantification of heavy metals, crustal elements, and Levoglucosan as biomass burning tracer, and on the year-averaged quantification of a set of organic contaminants (PFASs and their precursors, PAHs, PBDEs, PCBs, PCDD/Fs), providing the first comprehensive environmental quality study of the Rutor Glacier. The integration of the chemical results with the physical properties of the particles and future back-trajectory studies will be introductory for the determination of the contamination sources that affect the Rutor Glacier during winters. Moreover, the quantification of the organic pollutants in the ice will provide preliminary indications on their potential release in the environment under a global warming scenario
Seasonal and annual dynamics of frozen ground in a mountain permafrost site in the Italian Alps detected by Spectral Induced Polarization
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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
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