256 research outputs found
Variations de hauteur de la calotte antarctique par altimétrie radar par satellite : amincissement dynamique, vidanges de lacs sous-glaciaires et autres curiosités
La calotte polaire Antarctique est une région immense et peu accessible, mais partie intégrante du système climatique planétaire. Pour mieux comprendre son fonctionnement et prévoir ses réactions face à un climat qui évolue, les mesures satellites sont des outils précieux. Nous exploitons l'un de ces capteurs satellites : l'altimètre radar d'Envisat. Cet instrument permet de mesurer la hauteur de la surface de la calotte et, par des mesures répétées dans le temps, son évolution temporelle. Nous explorons les changements de volume de la calotte sur une période entre 2002 et 2010. Cette période est très courte en regard de certains phénomènes agissant sur la calotte mais permet néanmoins de détecter d'importants changements, dus à des excès de précipitations ou à une accélération de l'écoulement de la glace. Par ailleurs, la densité spatiale et temporelle de l'échantillonnage d'Envisat permet d'observer des événements rapides (quelques mois) et localisés (quelques kilomètres) tels que des vidanges de lacs sous-glaciaires. Ces phénomènes sont encore mal connus et l'altimétrie est un des principaux outils aptes à les observer. La manière dont l'onde radar est réfléchie et rétrodiffusée par la surface de la calotte est un problème complexe, principalement parce que le manteau neigeux est lui-même changeant et complexe. Nous évoquons l'état de l'art de la compréhension des phénomènes impliqués. Nous terminons ces travaux par une ouverture sur les techniques qui permettront d'avancer dans la compréhension des calottes polaires : nouveaux altimètres, séries de données plus longues, fusion de jeux de données provenant de capteurs différents et complémentarité avec les données in situ.The Antarctic Ice Sheet is a vast and remote hostile land. It is nonetheless an important part of the planetary climate system. Space-borne instruments are among the best tools to study the evolution of the ice sheet. In this work, we use data from one of these space sensors: the Envisat radar altimeter. This instrument provided us repeated measurements of the ice sheet surface elevation every 35 days during 8 years. From this dataset, we investigated volume change of the ice sheet between 2002 and 2010. This period is relatively short compared to the typical duration of ice sheet response (thousands of years after an ice age) but the data show some evolution, either extreme precipitation events or accelerated flow and associated thinning. The high space and time resolution also allowed us to observe rapid and local events such as subglacial lake drainages. These were only recently discovered in Antarctica and altimetry is one of the best suited tools to study them. The reflection and backscatter of the radar wave by the snowpack is still a complex problem that has to be further investigated. The own behavior of the snowpack must be better understood. We present the state of the art of the understanding of the radar/snowpack interaction. We conclude with an outlook on future techniques that will enhance our understanding of the ice sheet process and ice sheet evolution: new altimeters, longer time series, multi-sensor studies and additional in situ calibration
Fine insight on high temperature hydrogen attack initiation and morphology on case studies
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Young Adults’ Knowledge and Attitudes Regarding “Music” and “Loud Music” Across Countries: Applications of Social Representations Theory
Exposure to loud music, especially by young people, has significantly increased in recent years as a result of (a) advancements in technology in terms of personal music players and smart mobile phones, and (b) streaming of music through these devices. The World Health Organization (WHO) estimates that some 1.1 billion teenagers and young adults are at risk of developing hearing loss due to exposure to recreational noise such as music. It is suggested that knowledge and attitude of young adults toward music has bearing upon their music listening habits and thereby influences who is at risk of developing music induced hearing loss. Hence, researchers from various fields have tried to understand the knowledge and attitude of young adults regarding loud music. However, there is some criticism of attitude studies as there is little relation between expressed attitude and behavior. Some recent studies have explored the social representations of music and loud music using the Social Representations Theory (SRT). It has been suggested that social representation is more fundamental than attitude (or in other words social representation informs attitude), hence, it has a better relation to behavior. The current paper: (1) provides an overview of studies on knowledge and attitude of young adults toward loud music, (2) discusses the limitations of attitude theories and introduces SRT, and (3) provides a summary of social representation studies on “music” and “loud music” in young adults from different countries
Rapid dynamic activation of a marine-based Arctic ice cap
We use satellite observations to document rapid acceleration and ice loss from a formerly slow-flowing, marine-based sector of Austfonna, the largest ice cap in the Eurasian Arctic. During the past two decades, the sector ice discharge has increased 45-fold, the velocity regime has switched from predominantly slow (~ 101 m/yr) to fast (~ 103 m/yr) flow, and rates of ice thinning have exceeded 25 m/yr. At the time of widespread dynamic activation, parts of the terminus may have been near floatation. Subsequently, the imbalance has propagated 50 km inland to within 8 km of the ice cap summit. Our observations demonstrate the ability of slow-flowing ice to mobilize and quickly transmit the dynamic imbalance inland; a process that we show has initiated rapid ice loss to the ocean and redistribution of ice mass to locations more susceptible to melt, yet which remains poorly understood.This work was supported by the UK Natural Environment Research Council.This article was originally published in Geophysical Research Letters (M McMillan, A Shepherd, N Gourmelen, A Dehecq, A Leeson, A Ridout, T Flament, A Hogg, L Gilbert, T Benham, M van den Broeke, JA Dowdeswell, X Fettweis, B Noël, T Strozzi, Geophysical Research Letters 2014, 41, 8902–8909)
ESA's Space-based Doppler Wind Lidar Mission Aeolus - First Wind and Aerosol Product Assessment Results
The European Space Agency (ESA) wind mission,
Aeolus, hosts the first space-based Doppler Wind
Lidar (DWL) world-wide. The primary mission
objective is to demonstrate the DWL technique for
measuring wind profiles from space, intended for
assimilation in Numerical Weather Prediction
(NWP) models. The wind observations will also be
used to advance atmospheric dynamics research
and for evaluation of climate models. Mission spinoff products are profiles of cloud and aerosol
optical properties. Aeolus was launched on 22
August 2018, and the Atmospheric LAser Doppler
INstrument (Aladin) instrument switch-on was
completed with first high energy output in wind
mode on 4 September 2018. The on-ground
data processing facility worked excellent, allowing
L2 product output in near-real-time from the start
of the mission. First results from the wind profile
product (L2B) assessment show that the winds are
of very high quality, with random errors in the free
Troposphere within (cloud/aerosol backscatter
winds: 2.1 m/s) and larger (molecular backscatter
winds: 4.3 m/s) than the requirements (2.5 m/s), but
still allowing significant positive impact in first
preliminary NWP impact experiments. The higher
than expected random errors at the time of writing
are amongst others due to a lower instrument outand input photon budget than designed. The
instrument calibration is working well, and some of
the data processing steps are currently being
refined to allow to fully correct instrument
alignment related drifts and elevated detector dark
currents causing biases in the first data product
version. The optical properties spin-off product
(L2A) is being compared e.g. to NWP model
clouds, air quality model forecasts, and collocated
ground-based observations. Features including
optically thick and thin particle and hydrometeor
layers are clearly identified and are being validated
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