Un inventaire des aérophotographies du massif du Mont Blanc

National audienceLe massif du Mont Blanc, espace frontalier entre trois pays alpins, constitue un laboratoire scientifique de premier ordre pour étudier plusieurs des problématiques de recherche du laboratoire EDYTEM, notamment en ce qui concerne les domaines glaciaires et périglaciaires. Dans ce contexte, un inventaire des aérophotographies couvrant le massif et disséminées au sein de plusieurs organismes a été effectué. Près de 5000 photogrammes pris au cours de 92 missions ont ainsi été identifiés, assurant une couverture homogène et à haute résolution temporelle du massif depuis la fin des années 1930. Cet inventaire a donné lieu à une première réflexion sur la constitution d'une base de données de ces documents pour faciliter les recherches documentaires futures

Optimization and Performance of Bifacial Solar Modules: A Global Perspective

With the rapidly growing interest in bifacial photovoltaics (PV), a worldwide map of their potential performance can help assess and accelerate the global deployment of this emerging technology. However, the existing literature only highlights optimized bifacial PV for a few geographic locations or develops worldwide performance maps for very specific configurations, such as the vertical installation. It is still difficult to translate these location- and configuration-specific conclusions to a general optimized performance of this technology. In this paper, we present a global study and optimization of bifacial solar modules using a rigorous and comprehensive modeling framework. Our results demonstrate that with a low albedo of 0.25, the bifacial gain of ground-mounted bifacial modules is less than 10% worldwide. However, increasing the albedo to 0.5 and elevating modules 1 m above the ground can boost the bifacial gain to 30%. Moreover, we derive a set of empirical design rules, which optimize bifacial solar modules across the world, that provide the groundwork for rapid assessment of the location-specific performance. We find that ground-mounted, vertical, east-west-facing bifacial modules will outperform their south-north-facing, optimally tilted counterparts by up to 15% below the latitude of 30 degrees, for an albedo of 0.5. The relative energy output is the reverse of this in latitudes above 30 degrees. A detailed and systematic comparison with experimental data from Asia, Europe, and North America validates the model presented in this paper. An online simulation tool (https://nanohub.org/tools/pub) based on the model developed in this paper is also available for a user to predict and optimize bifacial modules in any arbitrary location across the globe

Thermal and dynamic behaviour of supraglacial clasts and the origin of sorting in supraglacial debris covers

The transition zone from a discontinuous to a continuous debris cover is an extensive part of many glacier ablation zones. Although responsible for the highest specific melt rates of debris-covered glaciers, transition zones have received little research and are poorly understood. Here we consider the interactions between emergent clasts and melting ice surfaces at Glacier d'Estelette and Miage Glacier (Italian Alps). Debris-ice interactions are complex because dispersed heterogenous debris both enhances and retards melt rate in the same locality, depending on the distribution of clast sizes. Observations reveal that thermal and dynamic clast interactions with the glacier surface increase the transport rate of coarse clasts, and initiate vertical sorting at the point when a continuous debris layer forms. This happens because, in summer, clasts exceeding the critical thickness for melt slide over the glacier surface. In contrast finer thermally-embedded material is transported at ice surface velocity and become covered by coarser material from upslope. Once established, debris-cover texture allows sorting to develop as the cover thickens downglacier. A two-layer temperature profile results, in which a coarse, drier clast layer of low thermal conductivity overlies a finer-grained, moist layer of higher thermal conductivity. Transition-zone processes establish inverse grading at the initiation of a debris cover, allowing subsequent sorting to operate as the cover thickens downstream. The processes by which this occurs are unknown, but analogy with periglacial active layers suggests convection within a frost-susceptible lower fine layer and eluviation of fines supplied by aeolian deposition and in-situ clast distintegratio

Spatial heterogeneity in the paraglacial response to post-Little Ice Age deglaciation of four headwater cirques in the Western Alps

International audienceThis paper aims to understand how the paraglacial response to recent glacier retreat varies between four cirques in the Western Alps. Post‐Little Ice Age glacier retreat has created extensive forelands where a variety of gravitational and fluvial process operate on both till‐floored and rock‐floored cirques. These processes may affect transitions from subglacial to proglacial landsystems, by reworking sediment and reorganising drainage. Landsystems achieve a state of preservation once no more adjustment is possible due to buffering by channel network evolution, channel armouring, and sediment exhaustion. We find no consistent trajectory of change across all studied sites: paraglacial responses differ from the classical valley–glacier model, involving variable slope‐channel coupling. Proglacial drainage networks on till surfaces have become more integrated by reducing their low‐order bifurcation ratios, unlike streams locked into rock channels. Reasons for diverse and site‐specific behaviour include cirque floor width, gradient, and surface materials (bedrock, fine till, and/or blocky till). At some cirques, these restrict the downstream diffusion of a paraglacial “signal” of fluvial‐transported sediment. At others, increased sediment flux originated from the erosion of terminal moraines. A high proportion of glacial material generally remains within the glacier foreland, due to proglacial basin sediment traps, inefficiency of fluvial networks, armouring of floors by coarse tills, and rock‐controlled channels. The millennial‐timescale preservation potential of most recent primary glacial deposits and within‐cirque paraglacial landforms appears to be hig

Using ArcticDEM to analyse the dimensions and dynamics of debris-covered glaciers in Kamchatka, Russia

On the Kamchatka Peninsula, a number of glaciers are covered by thick volcanic debris, which makes their margins difficult to delineate from satellite imagery. Fortunately, high resolution, multi-temporal digital surface models (DSMs) covering the entire peninsula have recently become freely available (i.e., ArcticDEM). We use these DSMs to analyse the dimensions and dynamics of debris-covered glaciers in the northern Kluchevskoy Volcanic Group, central Kamchatka. This approach demonstrates that between 2012 and 2016, some of the region’s glaciers advanced despite regional and local climate warming. These glacial advances are part of a long-term trend, presumed to reflect the role of extensive supraglacial debris in limiting ice ablation, though there is also evidence for local ice melt due to supraglacial lava/debris flows. Glacier surface velocities during the period 2012–2015 were typically 5–140 m yr−1. Velocities for the major outlets of the region’s central icefield were typically higher than for other extensively debris-covered glaciers globally, likely reflecting the influence of ice supply from the high altitude Ushkovsky caldera. In all, we find ArcticDEM useful for analysing debris-covered glaciers in Kamchatka, providing important information on flow dynamics and terminus change that is difficult to derive from satellite imagery

Stability monitoring of high Alpine infrastructure by terrestrial laser scanning

International audienceRock mass movements are dominant in the morphodynamics of high Alpine rock slopes and are at the origin of significant risks for people who attend these areas and for infrastructures that are built on (e.g. huts, cable cars). These risks are increasing because of permafrost degradation and glacier retreat as consequences of the global warming. These two factors may affect slope stability by changing mechanical properties of the interstitial ice and modifying the mechanical constraints in these rock slopes. The monitoring of rock slopes is thus an essential element for risk management. Our study focuses on two particularly active areas of the Western Alps: the lower Arête des Cosmiques (3613 m a.s.l., Mont Blanc massif, France) on which is located the very popular Refuge des Cosmiques, and the Col des Gentianes (2894 m a.s.l., Valais, Switzerland) where is located a cable car station. Discussed on the basis of geophysical and glaciological data, the evolutions monitored by terrestrial laser scanning probably result from the combination between permafrost activity/degradation and glacier shrinkage

Reducing Interanalyst Variability in Photovoltaic Degradation Rate Assessments

The economic return on investment of a commercial photovoltaic system depends greatly on its performance over the long term and, hence, its degradation rate. Many methods have been proposed for assessing system degradation rates from outdoor performance data. However, comparing reported values from one analyst and research group to another requires a common baseline of performance; consistency between methods and analysts can be a challenge. An interlaboratory study was conducted involving different volunteer analysts reporting on the same photovoltaic performance data using different methodologies. Initial variability of the reported degradation rates was so high that analysts could not come to a consensus whether a system degraded or not. More consistent values are received when written guidance is provided to each analyst. Further improvements in analyst variance was accomplished by using the free open-source software RdTools, allowing a reduction in variance between analysts by more than two orders of magnitude over the first round, where multiple analysis methods are allowed. This article highlights many pitfalls in conducting 'routine' degradation analysis, and it addresses some of the factors that must be considered when comparing degradation results reported by different analysts or methods

Concurrent versus simultaneous use of alcohol and non-medical use of prescription drugs: is simultaneous use worse for mental, social, and health issues?

Abstract This study investigated the difference between concurrent and simultaneous use of alcohol and non-medical use of prescription drugs (NMUPD) in relation to mental, social, and health issues. The 544 study participants of the Swiss ongoing Cohort Study on Substance Use Risk Factors (C-SURF) had a combined use of alcohol with NMUPD during the previous 12 months. Alcohol-related problems (i.e., dependence and consequences), as well as mental, social, and health concerns (i.e., depression, general mental/physical health, and social/health consequences), were assessed. The simultaneous use of alcohol and NMUPD proved to be a greater risk factor for mental, social, and health issues than concurrent use. This study adds information regarding simultaneous polydrug use, which results in distinct effects compared to concurrent use, including important social, psychosocial, and health-related consequences