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The application of Structure-from-Motion (SfM) and Multi-View-Stereo matching with aerial images can be successfully used for deriving dense point clouds to analyse changes in the mountain environment, which is characterized by changes due to the action of natural process. The comparison of multiple datasets requires to setup a stable reference system, task that is generally implemented by means of ground control points (GCPs). On the other hand, their positioning may be sometimes difficult in mountains. To cope with this drawback an approach termed as Multitemporal SfM (MSfM) is presented: multiple blocks are oriented together within a unique SfM project, where GCPs are used in only one epoch for establishing the absolute datum. Accurate coregistration between different epochs depends on the automatic extraction of tie points in stable areas. To verify the application of MSfM in real cases, this paper presents three case studies where different types of photogrammetric data are adopted, including images from drones and manned aircrafts. Applications to glacier and mountain river erosion are entailed. [ABSTRACT FROM AUTHOR]

This study analyzed the challenges and benefits of the identification and promotion of a long-distance cycleway in high mountain areas with the aim of promoting Alpine eco- and geo-tourism. We also investigated the role of e-biking in discovering local geodiversity and geoheritage in a sustainable way. In particular, we focused on the path from Bormio to the Forni Glacier (Upper Valtellina, Italy), analyzed within the framework of the "E-bike" Interreg project. We performed a detailed analysis to select the points of environmental–geological interest (POIs), with a focus on geoheritage sites to increase the knowledge of the natural heritage of the area. Since these sites are widespread in the study area, within the frame of the "E-bike" project, we selected only the most exemplary ones, covering a wide spectrum of attractions, from a moving geosite (i.e., landslide) to a paradigmatic example of the effects of climate change (glacier). The "E-bike" path represents in its entirety a great opportunity to visit mountain and high-mountain landscapes, even for inexperienced mountain bikers, and to enjoy places rich in naturalistic and cultural values. Our interdisciplinary approach allows visitors to identify the sites of interest and export the structure of the project in different environmental and human contexts. [ABSTRACT FROM AUTHOR]

Megadunes are peculiar features formed by the interaction between the atmosphere and cryosphere and are known to be present only on the East Antarctic Plateau and other planets (Mars and Pluto). In this study, we have analysed the glaciological dynamic of megadunes, their spectral properties and morphology on two sample areas of the East Antarctic Plateau where in the past international field activities were carried out (EAIIST, East Antarctic International Ice Sheet Traverse; It-ITASE, Italian International Trans-Antarctic Scientific Expedition). Using satellite images spanning 7 years, we analysed the spatial and temporal variability in megadune surface characteristics, i.e. near-infrared (NIR) albedo, thermal brightness temperature (BT) and slope along the prevailing wind direction (SPWD), useful for mapping them. These parameters allowed us to characterize and perform an automated detection of the glazed surfaces, and we determined the influence of the SPWD by evaluating different combinations of these parameters. The inclusion of the SPWD significantly increased the accuracy of the method, doubling it in certain analysed scenes. Using remote and field observations, for the first time we surveyed all the components of upwind migration (absolute, sedimentological and ice flow), finding an absolute value of about 10 m a -1. The analysis shows that the migration is driven by the snow accumulation on the crest and trough prograding upwind on the previous windward flanks characterized by glazed surface. Our results present significant implications for the surface mass balance estimation, paleo-climate reconstruction using ice cores, and the measurements using optical and radar images/data in the megadune areas. [ABSTRACT FROM AUTHOR]

This work presents the high-resolution high-accuracy orthophoto map and the Digital Surface Model of Forni Glacier (Italian Alps). These represent the status of the glacier tongue in mid-August 2022 when surveys were carried out with a DJI Phantom 4 RTK drone. The processing was carried out in Leica Infinity, and a 3 cm orthomosaic and a 20 cm Digital Surface Model were generated and made available for analysis of the current status of the glacier, which shows signs of downwasting, with the occurrence of collapsing areas and a rapidly changing proglacial landscape. This work can also be used as a reference to investigate the glacier evolution, also in light of climate change. Accuracy requirements of the deliverables were ensured by combining Post Processed Kinematic and Structure from Motion integrated with bundle block adjustment, and using Ground Control Points and Check Points, to guarantee redundancy and evaluate the geolocation accuracy and precision. [ABSTRACT FROM AUTHOR]

In the current global warming phase, relict glacial areas are one of the most threatened ecosystems in the world. They are "cold-spots" of biodiversity and of great interest both from the ecological and conservation point of view. We investigated the biological communities (plants and arthropods) hosted by one of the southernmost European glaciers: Calderone Glacier, the last preserved glacier of the Apennines mountain chain (Italy). We analyzed supraglacial debris and the nearby moraine and we found a rather diverse and peculiar biodiversity, which includes also new species. Some arthropods, such as the springtail Desoria calderonis, are particularly sensitive to the presence of ice at microtopographic level. Among plants, only Arabis alpina caucasica is able to grow on the supraglacial debris, perhaps because of factors related to the seed germination and seedling survival on this habitat type. Calderone glacier, with its particular biogeographic location, is probably currently acting as one of the last refugia for rare and endemic cryophilic species within the Mediterranean Region during the ongoing warm period. [ABSTRACT FROM AUTHOR]

The use of special concentrically braced frames has increased since the 1994 Northridge and 1995 Hyogoken-Nanbu Earthquakes. However, past performance suggests limited ductility and energy dissipation in braced frame systems due to buckling of conventional braces. In order to address this limitation, three- and six-story concentrically braced frames with superelastic shape memory alloy (SMA) braces are studied to evaluate their seismic performance in comparison to traditional systems. SMAs are unique metallic alloys that have the ability to undergo large deformations while reverting back to their original undeformed shape providing recentering capabilities to the braced frame. Detailed analytical models of the frames with SMA braces are developed and two suites of ground motions are used to evaluate the structures with respect to interstory drift and residual drift. The results suggest that the SMA braces are effective in limiting interstory drifts and residual drifts during an earthquake, in part, due to the recentering nature of superelastic SMAs. DOI: 10.1061/(ASCE)0733-9445(2007)133:6(862) CE Database subject headings: Steel structures; Nonlinear analysis; Seismic analysis; Earthquake resistant structures; Innovation; Bracing.

Two uniaxial rate dependent constitutive models capable of reproducing the superelastic effect of SMAs and able to take into account the different elastic properties between austenite and martensite are compared. It is observed that the advantages of the presented models are the simplicity, the possibility of implementing a robust solution algorithm and the ability to reproduce experimental data obtained at different frequency levels of excitation.

Superelastic NiTi shape memory alloy (SMA) wires and bars are examined in order to determine their damping and recentering capability for applications in the structural control of buildings subjected to earthquake loadings. Results show that larger diameter bars perform well and the unique properties of SMAs help in reducing vibration response of a structure during seismic events.

The Irtysh River is the main water resource of Eastern Kazakhstan and its upper basin is severely affected by spring floods each year, primarily as a result of snowmelt. Knowledge of the large‐scale processes that influence the timing of these snow‐induced floods is currently lacking, but critical for the management of water resources in the area. In this study, we evaluated the variability in winter–spring snow cover in five major sub‐basins of the Upper Irtysh basin between 2000 and 2017 as a possible explanatory factor of spring flood events, assessing the time of peak snow cover depletion rate and snow cover disappearance from the moderate‐resolution imaging spectroradiometer (MODIS) MOD10A2 data set. We found that on average, peak snow cover retreat occurs between 22 March and 14 April depending on the basin, with large interannual variations but no clear trend over the MODIS period, while our comparative analysis of longer‐term snow cover extent from the National Oceanic and Atmospheric Administration Climate Data Record data set suggests a shift to earlier snow cover disappearance since the 1970s. In contrast, the annual peak snow cover depletion rate displays a weak increasing trend over the study period and exceeded 5,900 km2/day in 2017. The timing of snow disappearance in spring shows significant correlations of up to 0.82 for the largest basin with winter indices of the Arctic Oscillation (AO) over the region. The primary driver is the impact of the large‐scale pressure anomalies upon the mean spring (MAM) air temperatures and resultant timing of snow cover disappearance, particularly at elevations 500–2,000 m above sea level. This suggests a lagged effect of this atmospheric circulation pattern in spring snow cover retreat. The winter AO index could therefore be incorporated into long‐term runoff forecasts for the Irtysh. Our approach is easily transferable to other similar catchments and could support flood management strategies in Kazakhstan and other countries. [ABSTRACT FROM AUTHOR]

The ongoing glacier shrinkage in the Alps requires frequent updates of glacier outlines to provide an accurate database for monitoring, modelling purposes (e.g. determination of run-off, mass balance, or future glacier extent), and other applications. With the launch of the first Sentinel-2 (S2) satellite in 2015, it became possible to create a consistent, Alpine-wide glacier inventory with an unprecedented spatial resolution of 10 m. The first S2 images from August 2015 already provided excellent mapping conditions for most glacierized regions in the Alps and were used as a base for the compilation of a new Alpine-wide glacier inventory in a collaborative team effort. In all countries, glacier outlines from the latest national inventories have been used as a guide to compile an update consistent with the respective previous interpretation. The automated mapping of clean glacier ice was straightforward using the band ratio method, but the numerous debris-covered glaciers required intense manual editing. Cloud cover over many glaciers in Italy required also including S2 scenes from 2016. The outline uncertainty was determined with digitizing of 14 glaciers several times by all participants. Topographic information for all glaciers was obtained from the ALOS AW3D30 digital elevation model (DEM). Overall, we derived a total glacier area of 1806±60 km 2 when considering 4395 glaciers >0.01 km 2. This is 14 % (-1.2 % a -1) less than the 2100 km 2 derived from Landsat in 2003 and indicates an unabated continuation of glacier shrinkage in the Alps since the mid-1980s. It is a lower-bound estimate, as due to the higher spatial resolution of S2 many small glaciers were additionally mapped or increased in size compared to 2003. Median elevations peak around 3000 m a.s.l., with a high variability that depends on location and aspect. The uncertainty assessment revealed locally strong differences in interpretation of debris-covered glaciers, resulting in limitations for change assessment when using glacier extents digitized by different analysts. The inventory is available at 10.1594/PANGAEA.909133 (Paul et al., 2019). [ABSTRACT FROM AUTHOR]

The on-going glacier shrinkage in the Alps requires frequent updates of glacier outlines to provide an accurate database for monitoring or modeling purposes (e.g. determination of run-off, mass balance, or future glacier extent) and other applications. With the launch of the first Sentinel-2 (S2) satellite in 2015, it became possible to create a consistent, Alpine-wide glacier inventory with an unprecedented spatial resolution of 10 m. Fortunately, already the first S2 images acquired in August 2015 provided excellent mapping conditions for most of the glacierised regions in the Alps. We have used this opportunity to compile a new Alpine-wide glacier inventory in a collaborative team effort. In all countries, glacier outlines from the latest national inventories have been used as a guide to compile a consistent update. However, cloud cover over many glaciers in Italy required including also S2 scenes from 2016. Whereas the automated mapping of clean glacier ice was straightforward using the band ratio method, the numerous debris-covered glaciers required in-tense manual editing. The uncertainty in the outlines was determined with a multiple digitising experiment of 14 glaciers by all participants. Topographic information for all glaciers was derived from the ALOS AW3D30 DEM. Overall, we derived a total glacier area of 1806 ± 60 km² when considering 4394 glaciers > 0.01 km². This is 14 % (−1.2 %/a) less than the 2100 km² derived from Landsat scenes acquired in 2003 and indicating an unabated continuation of glacier shrinkage in the Alps since the mid-1980s. Due to the higher spatial resolution of S2 many small glaciers were additionally mapped in the new inventory or increased in size compared to 2003. An artificial reduction to the former extents would thus result in an even higher overall area loss. Still, the uncertainty assessment revealed locally considerable differences in interpretation of debris-covered glaciers, resulting in limitations for change assessment when using glacier extents digitised by different analysts. [ABSTRACT FROM AUTHOR]

This study presents a map reporting valuable information on the cryosphere of the Central Karakoram National Park (CKNP, the largest protected area of Pakistan and the highest park in the world). All the information is provided considering the CKNP as a whole, and in detail by dividing it into five basins (i.e. Shigar, Hunza, Shyok, Upper Indus, and Gilgit). The glacier inventory reports 608 ice bodies covering 3680 km2 (∼35% of the CKNP area), with a total glacier volume of ca. 532 km3. In addition, we modeled the meltwater from glacier ice ablation over the period 23 July to 9 August 2011. The total melt amount is ca. 1.5 km3. Finally, we considered glacial lakes (202 water-bodies, covering 4 km2). For these latter glacier features, we also analyzed their potentially dangerous conditions and two lakes were found having such conditions. [ABSTRACT FROM AUTHOR]

Tourists and hikers visiting glaciers all year round face hazards such as sudden terminus collapses, typical of such a dynamically evolving environment. In this study, we analyzed the potential of different survey techniques to analyze hazards of the Forni Glacier, an important geosite located in Stelvio Park (Italian Alps). We carried out surveys in the 2016 ablation season and compared point clouds generated from an unmanned aerial vehicle (UAV) survey, closerange photogrammetry and terrestrial laser scanning (TLS). To investigate the evolution of glacier hazards and evaluate the glacier thinning rate, we also used UAV data collected in 2014 and a digital elevation model (DEM) created from an aerial photogrammetric survey of 2007. We found that the integration between terrestrial and UAV photogrammetry is ideal for mapping hazards related to the glacier collapse, while TLS is affected by occlusions and is logistically complex in glacial terrain. Photogrammetric techniques can therefore replace TLS for glacier studies and UAV-based DEMs hold potential for becoming a standard tool in the investigation of glacier thickness changes. Based on our data sets, an increase in the size of collapses was found over the study period, and the glacier thinning rates went from 4.55±l0.24ma-1 between 2007 and 2014 to 5.20±1.11ma-1 between 2014 and 2016. [ABSTRACT FROM AUTHOR]

Over the last decades, the expansion of supraglacial debris on worldwide mountain glaciers has been reported. Nevertheless, works dealing with the detection and mapping of supraglacial debris and detailed analyses aimed at identifying the temporal and spatial trends affecting glacier debris cover are still limited. In this study, we used different remote sensing sources to detect and map the supraglacial debris cover, to analyze its evolution, and to assess the potential of different remote-sensed image data. We performed our analyses on the glaciers of Ortles-Cevedale Group (Stelvio Park, Italy), one of the most representative glacierized sectors of the European Alps. High-resolution airborne orthophotos (pixel size 0.5 m × 0.5 m) acquired during the summer season in the years 2003, 2007, and 2012 permitted to map in detail, with an error lower than ±5%, the supraglacial debris cover through a maximum likelihood classification. Our findings suggest that over the period 2003–2012, supraglacial debris cover increased from 16.7% to 30.1% of the total glacier area. On Forni Glacier we extended these quantification thanks to the availability of UAV (Unmanned Aerial Vehicle) orthophotos from 2014 and 2015 (pixel size 0.15 m × 0.15 m): this detailed analysis permitted to confirm debris is increasing on the glacier melting surface (+20.4%) and confirms the requirement of high-resolution data in debris mapping on Alpine glaciers. Finally, we also checked the suitability of medium-resolution Landsat ETM+ data and Sentinel 2 data to map debris in a typical Alpine glaciation scenario where small ice bodies (<0.5 km2) are the majority. The results we obtained suggest that medium-resolution data are not suitable for a detailed description and evaluation of supraglacial debris cover in the Alpine scenario, nevertheless Sentinel 2 proved to be appropriate for a preliminary mapping of the main debris features. [ABSTRACT FROM AUTHOR]

Tourists and hikers visiting glaciers all year round face hazards such as the rapid formation of collapses at the terminus, typical of such a dynamically evolving environment. In this study, we analysed potential hazards of the Forni glacier, an important geo-site located in Stelvio Park (Italian Alps), by describing local surface features and evaluating the glacier melting rate. The analyses were based on point clouds and digital elevation models (DEMs) from two separate surveys of the glacier tongue carried out in 2014 and 2016 with Unmanned Aerial Vehicles (UAVs), terrestrial photogrammetry (only in 2016) and a DEM obtained in 2007 from an aerial survey. On the area covered by the 2016 survey, average glacier thinning rates of -4.15 ma-1 were found in 2007-2016, while the mean thickness change of the glacier tongue in 2014-2016 was -10.40 ± 2.60 m. UAV-based DEMs were thus found to be sufficiently accurate with respect to the rates of glacier down-wasting, while terrestrial photogrammetry allowed the reconstruction of the glacier terminus, presenting several vertical and sub-vertical surfaces whose modelling was difficult to obtain from airborne UAV images. The integration of UAV and terrestrial photogrammetry provided a detailed and accurate 3D model of the glacier tongue, which we used to identify hazard areas. [ABSTRACT FROM AUTHOR]

Structural glaciology yields important details about the evolution of glacier dynamics in response to climate change. The maps provided here document the occurrence and evolution of brittle and ductile structures on the tongue of Forni Glacier, Ortles-Cevedale Group, Central Italian Alps, between 2003 and 2014. Through the remote sensing-based analysis of structures, we found evidence of brittle fractures such as crevasses, faults and ring faults, and ductile structures such as ogives at the base of the icefall in the eastern glacier tongue. Although each of the three glacier tongues have evolved differently, a reduction in flow-related dynamics and an increase in the number of collapse structures occurred over the study period. Analysis of the glacier structural evolution based on the numbers and the locations of different structures, suggest a slowdown of glacier flow on the eastern tongue. The recent evolution of the glacier also suggests that the occurrence of a disintegration scenario is likely to worsen over the next decades. [ABSTRACT FROM PUBLISHER]

The programming speed in a phase change memory (PCM) relies on the kinetics of crystallization in the pulsed regime. To predict the programming speed and retention of a PCM, a careful understanding and modeling of crystallization in the phase change material is essential. In this paper, we study crystallization kinetics directly in PCM devices. From thermal annealing and pulsed-set experiments, we extract the temperature dependence of the crystallization in a wide temperature range between 170^\circC and the melting point (about 620^\circC). Our results indicate two markedly different activation energies below/above 300^\circC, thus providing evidence for a non-Arrhenius crystallization kinetics in PCM. [ABSTRACT FROM PUBLISHER]

The amorphous phase of the chalcogenide material in phase-change memory (PCM) devices is sensitive to temperature-activated crystallization and structural relaxation (SR). The latter leads to a change of device/material properties, such as the mobility band gap, the resistance, and the threshold voltage VT for threshold switching. In this paper, we present a VT drift model based on physical descriptions of the electrical transport, the threshold switching, and the SR. We introduce an analytical formula describing the relation between the drift slopes of resistance and VT via the subthreshold slope STS of the I– V curve. A numerical model predicting the time evolution of VT for different programmed states in the PCM multilevel cell is finally presented and compared with experiments. [ABSTRACT FROM PUBLISHER]

Experimental tests performed on superelastic shape-memory alloys (SMAs) show a significant dependence of the stress-strain relationship on the loading-unloading rate, coupled with a not negligible oscillation of the material temperature. This feature is of particular importance in view of the use of such materials in earthquake engineering, where the loading rate affects the structural response. Motivated by this observation and by the limited number of available works on the modelling of SMAs for seismic applications, the present article addresses a uniaxial constitutive model for representing the system rate-dependent thermo-mechanical behavior of superelastic SMAs. The model is based on a single internal scalar variable, the martensite fraction, for which different rate-independent evolutionary equations in rate form are proposed. Moreover, it takes into account the different elastic properties between austenite and martensite. The whole model is then thermo-mechanically coupled with a thermal balance equation. Hence, it considers mechanical dissipation as well as latent heat and includes temperature as a primary independent variable, which is responsible for the dynamic effects. The article also provides a description for the integration, in time, of the constitutive equation and presents the solution algorithm of the corresponding time-discrete problem. Finally, results from numerical analyses are reported and the ability of the model to simulate experimental data obtained from uniaxial tests performed on superelastic SMA wires and bars at frequency levels of excitation typical of earthquake engineering is assessed. [ABSTRACT FROM AUTHOR]

This paper presents and compares two different uniaxial constitutive models for super-elastic shape-memory alloys (SMAs), suitable to study the dependence of the stress-strain relationship on the loading-unloading rate. The first model is based on the inclusion of a direct viscous term in the evolutionary equation for the martensite fraction and it shows how the material response is bounded between two distinct rate-independent models. The second model is based on a rate-independent evolutionary equation for the martensite fraction coupled with a thermal balance equation. Hence, it considers mechanical dissipation as well as latent heat and includes the temperature as a primary independent variable, which is responsible of the dynamic effects. The ability of both models to reproduce the observed reduction of damping properties through the modification of the hysteresis size is discussed by means of several numerical simulations. Finally, the capacity of the constitutive equations to simulate experimental data from uniaxial tests performed on SMA wires and bars of different size and chemical composition is shown. [ABSTRACT FROM AUTHOR]

In this paper, the seismic performance of a three- and a six-storey steel frame equipped with different bracing configurations is assessed. The bracing systems consist of traditional buckling-restrained steel braces and superelastic Nitinol shape-memory alloy (SMA) braces. Background on the behaviour of SMAs is provided and a state-of-the-art review of the applications of such new materials in earthquake engineering is presented. A uniaxial constitutive model for superelastic SMAs is then implemented into the finite element platform OpenSees and nonlinear dynamic analyses are performed. Finally, the seismic performance of the structures under investigation is judged through the evaluation of several response quantities, to determine the efficacy of the new bracing system in reducing earthquake-induced vibrations. [ABSTRACT FROM AUTHOR]

Snow cover is particularly important in the Alps for tourism and the production of hydroelectric energy. In this study, we investigate the spatiotemporal variability in three snow cover metrics, i.e., the length of season (LOS), start of season (SOS) and end of season (EOS), obtained by gap-filling of MOD10A1 and MYD10A1, daily snow cover products of MODIS (Moderate-resolution Imaging Spectroradiometer). We analyze the period 2000–2019, evaluate snow cover patterns in the greater Alpine region (GAR) as a whole and further subdivide it into four subregions based on geographical and climate divides to investigate the drivers of local variability. We found differences both in space and time, with the northeastern region having generally the highest LOS (74 ± 4 days), compared to the southern regions, which exhibit a much shorter snow duration (48/49 ± 2 days). Spatially, the variability in LOS and the other metrics is clearly related to elevation (r2 = 0.85 for the LOS), while other topographic (slope, aspect and shading) and geographic variables (latitude and longitude) play a less important role at the MODIS scale. A high interannual variability was also observed from 2000 to 2019, as the average LOS in the GAR ranged between 41 and 85 days. As a result of high variability, no significant trends in snow cover metrics were seen over the GAR when considering all grid cells. Considering 500-m elevation bands and subregions, as well as individual grid points, we observed significant negative trends above 3000 m a.s.l., with an average of −17 days per decade. While some trends appeared to be caused by glacierized areas, removing grid cells covered by glaciers leads to an even higher frequency of grid cells with significant trends above 3000 m a.s.l., reaching 100% at 4000 m a.s.l. Trends are however to be considered with caution because of the limited length of the observation period. [ABSTRACT FROM AUTHOR]

The albedo is a fundamental component of the processes that govern the energy budget, and particularly important in the context of climate change. However, a satellite-based high-resolution (30 m) albedo product which can be used in the polar regions up to 82.5° latitude during the summer seasons is lacking. To cover this gap, in this study we calculate satellite-based broadband albedo from Landsat 8 OLI and validate it against broadband albedo measurements from in situ stations located on the Antarctic and Greenland icesheets. The model to derive the albedo from raw satellite data includes an atmospheric and topographic correction and conversion from narrow-band to broadband albedo, and at each step different options were taken into account, in order to provide the best combination of corrections. Results, after being cleaned from anomalous data, show a good agreement with in situ albedo measurements, with a mean absolute error between in situ and satellite albedo of 0.021, a root mean square error of 0.026, a standard deviation of 0.015, a correlation coefficient of 0.995 (p < 0.01) and a bias estimate of −0.005. Considering the structure of the model, it could be applied to data from previous sensors of the Landsat family and help construct a record to analyze albedo variations in the polar regions. [ABSTRACT FROM AUTHOR]

Climate Monitoring Satellite Application Facility (CM SAF) surface solar irradiance (SSI) products were compared with ground-based observations over the Piedmont region (north-western Italy) for the period 1990–2016. These products were SARAH-2.1 (Surface Solar Radiation DataSet—Heliosat version 2.1) and CLARA-A2 (Cloud, Albedo and Surface Radiation dataset version A2). The aim was to contribute to the discussion on the representativeness of satellite SSI data including a focus on high-elevation areas. The comparison between SSI averages shows that for low OCI (orographic complexity index) stations, satellite series have higher values than corresponding ground-based observations, whereas for high OCI stations, SSI values for satellite records are mainly lower than for ground stations. The comparison between SSI anomalies highlights that satellite records have an excellent performance in capturing SSI day-to-day variability of ground-based low OCI stations. In contrast, for high OCI stations, the agreement is much lower, due to the higher uncertainty in both satellite and ground-based records. Finally, if the temporal trends are considered, average low-elevation ground-based SSI observations show a positive trend, whereas satellite records do not highlight significant trends. Focusing on high-elevation stations, the observed trends for ground-based and satellite records are more similar with the only exception of summer. This divergence seems to be due to the relevant role of atmospheric aerosols on SSI trends. [ABSTRACT FROM AUTHOR]