Search results for "Earth sciences"
showing 10 items of 2281 documents
Shallow vent architecture during hybrid explosive-effusive activity at Cordón Caulle (Chile, 2011-12): Evidence from direct observations and pyroclas…
2013
International audience; In June 2011, an eruption of rhyolite magma began at the Puyehue-Cordón Caulle volcanic complex, southern Chile. By January 2012, explosive activity had declined from sustained pyroclastic (Plinian to sub-Plinian) fountaining to mixed gas and ash jetting punctuated by Vulcanian blasts. This explosive activity was accompanied by synchronous effusion of obsidian lava in a hybrid explosive-effusive eruption. Fortuitous climatic conditions permitted ground-based observation and video recording of transient vent dynamics as well as real-time collection of proximal juvenile ash as it sedimented from the active plume. The main eruptive vent complex and site of lava effusion…
The Permeability Evolution of Tuffisites and Implications for Outgassing Through Dense Rhyolitic Magma
2019
There is growing evidence that outgassing through transient fracture networks exerts an important control on conduit processes and explosive‐effusive activity during silicic eruptions. Indeed, the first modern observations of rhyolitic eruptions have revealed that degassed lava effusion may depend upon outgassing during simultaneous pyroclastic venting. The outgassing is thought to occur as gas and pyroclastic debris are discharged through shallow fracture networks within otherwise low‐permeability, conduit‐plugging lava domes. However, this discharge is only transient, as these fractures become clogged and eventually blocked by the accumulation and sintering of hot, melt‐rich pyroclastic d…
Shallow system rejuvenation and magma discharge trends at Piton de la Fournaise volcano (La Réunion Island)
2017
International audience; Basaltic magma chambers are often characterized by emptying and refilling cycles that influence their evolution in space and time, and the associated eruptive activity. During April 2007, the largest historical eruption of Piton de la Fournaise (Île de La Réunion, France) drained the shallow plumbing system (>240×106 m3>240×106 m3) and resulted in collapse of the 1-km-wide summit crater. Following these major events, Piton de la Fournaise entered a seven-year long period of near-continuous deflation interrupted, in June 2014, by a new phase of significant inflation. By integrating multiple datasets (lava discharge rates, deformation, seismicity, gas flux, gas composi…
Sedimentation close to the active Medlicott Wadia Thrust (Western Himalaya): how to estimate climatic base level changes and tectonics.
2017
16 pages; International audience; The Medlicott-Wadia Thrust (MWT) is one of the major active out-of-sequence thrusts in the Himalaya. Studies on Quaternary terraces in its vicinity have been performed using sedimentological, geomorphic and geochronological methods. We focus on the Riasi zone, south of the Pir Panjal range, in the Jammu and Kashmir region of India. The sedimentary units of Quaternary landforms have been mapped as a function of their location with respect to the thrust faults, their relative chronology, and their lithology. Three aggrading sedimentary units, five thin units above strath surfaces at the footwall of the fault system, and seven thin units above strath surfaces …
The imprint of subduction fluids on subducted MORB-derived melts (Sierra del Convento Mélange, Cuba)
2011
International audience; Major and trace element signatures and Sr-Nd-Pb isotope data for muscovite (Ms)-bearing amphibolite blocks and associated muscovite-bearing trondhjemite and quartz-muscovite rocks from the Sierra del Convento melange (eastern Cuba) indicate that Proto-Caribbean oceanic crust underwent wet partial melting processes during Mesozoic subduction and after accretion to the upper plate. Trace element normalized patterns of Ms-bearing amphibolites are enriched in light rare earth elements (LREE) and large-ion lithophile elements (LILE) and evidence variable trace element transfer from the Proto-Caribbean subducting slab to the mantle wedge. Ms-bearing trondhjemites show LREE…
Radiometric calibration of SeaWIFS in the near infrared
2005
The radiometric calibration of the Sea-Viewing Wide-Field-of-View Sensor (SeaWiFS) in the near infrared (band 8, centered on 865 nm) is evaluated by use of ground-based radiometer measurements of solar extinction and sky radiance in the Sun's principal plane at two sites, one located 13 km off Venice, Italy, and the other on the west coast of Lanai Island, Hawaii. The aerosol optical thickness determined from solar extinction is used in an iterative scheme to retrieve the pseudo aerosol phase function, i.e., the product of single-scattering albedo and phase function, in which sky radiance is corrected for multiple scattering effects. No assumption about the aerosol model is required. The ae…
Mapping land surface emissivity from NDVI: Application to European, African, and South American areas
1996
Thermal infrared emissivity is an important parameter both for surface characterization and for atmospheric correction methods. Mapping the emissivity from satellite data is therefore a very important question to solve. The main problem is the coupling of the temperature and emissivity effects in the thermal radiances. Several methods have been developed to obtain surface emissivity from satellite data. In this way we propose a theoretical model that relates the emissivity to the NDVI (normalized difference vegetation index) of a given surface and explains the experimental behavior observed by van de Griend and Owe. We can use it to obtain the emissivity in any thermal channel, but in this …
Quantifying vegetation biophysical variables from the Sentinel-3/FLEX tandem mission: Evaluation of the synergy of OLCI and FLORIS data sources
2020
The ESA’s forthcoming FLuorescence EXplorer (FLEX) mission is dedicated to the global monitoring of the vegetation’s chlorophyll fluorescence by means of an imaging spectrometer, FLORIS. In order to properly interpret the fluorescence signal in relation to photosynthetic activity, essential vegetation variables need to be retrieved concomitantly. FLEX will fly in tandem with Sentinel-3 (S3), which conveys the Ocean and Land Colour Instrument (OLCI) that is designed to characterize the atmosphere and the terrestrial vegetation at a spatial resolution of 300 m. In this work we present the retrieval models of four essential biophysical variables: (1) Leaf Area Index (LAI), (2) leaf chlorophyll…
Hybrid inversion of radiative transfer models based on high spatial resolution satellite reflectance data improves fractional vegetation cover retrie…
2021
In forest landscapes affected by fire, the estimation of fractional vegetation cover (FVC) from remote sensing data using radiative transfer models (RTMs) enables to evaluate the ecological impact of such disturbance across plant communities at different spatio-temporal scales. Even though, when landscapes are highly heterogeneous, the fine-scale ground spatial variation might not be properly captured if FVC products are provided at moderate or coarse spatial scales, as typical of most of operational Earth observing satellite missions. The objective of this study was to evaluate the potential of a RTM inversion approach for estimating FVC from satellite reflectance data at high spatial reso…
Validation of SMAP surface soil moisture products with core validation sites
2017
Abstract The NASA Soil Moisture Active Passive (SMAP) mission has utilized a set of core validation sites as the primary methodology in assessing the soil moisture retrieval algorithm performance. Those sites provide well-calibrated in situ soil moisture measurements within SMAP product grid pixels for diverse conditions and locations. The estimation of the average soil moisture within the SMAP product grid pixels based on in situ measurements is more reliable when location specific calibration of the sensors has been performed and there is adequate replication over the spatial domain, with an up-scaling function based on analysis using independent estimates of the soil moisture distributio…