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251.
Journal of Geographical Sciences - Water depths and flow velocities decisively influence the damage caused by flash floods. Geographic Information System (GIS) is a powerful and useful tool,... 相似文献
252.
Performance of intertidal topography video monitoring of a meso-tidal reflective beach in South Portugal 总被引:2,自引:1,他引:1
Michalis Ioannis Vousdoukas Pedro Manuel Ferreira Luis Pedro Almeida Guillaume Dodet Fotis Psaros Umberto Andriolo Rui Taborda Ana Nobre Silva Antonio Ruano Óscar Manuel Ferreira 《Ocean Dynamics》2011,61(10):1521-1540
This study discusses site-specific system optimization efforts related to the capability of a coastal video station to monitor
intertidal topography. The system consists of two video cameras connected to a PC, and is operating at the meso-tidal, reflective
Faro Beach (Algarve coast, S. Portugal). Measurements from the period February 4, 2009 to May 30, 2010 are discussed in this
study. Shoreline detection was based on the processing of variance images, considering pixel intensity thresholds for feature
extraction, provided by a specially trained artificial neural network (ANN). The obtained shoreline data return rate was 83%,
with an average horizontal cross-shore root mean square error (RMSE) of 1.06 m. Several empirical parameterizations and ANN
models were tested to estimate the elevations of shoreline contours, using wave and tidal data. Using a manually validated
shoreline set, the lowest RMSE (0.18 m) for the vertical elevation was obtained using an ANN while empirical parameterizations
based on the tidal elevation and wave run-up height resulted in an RMSE of 0.26 m. These errors were reduced to 0.22 m after
applying 3-D data filtering and interpolation of the topographic information generated for each tidal cycle. Average beach-face
slope tan(β) RMSE were around 0.02. Tests for a 5-month period of fully automated operation applying the ANN model resulted in an optimal,
average, vertical elevation RMSE of 0.22 m, obtained using a one tidal cycle time window and a time-varying beach-face slope.
The findings indicate that the use of an ANN in such systems has considerable potential, especially for sites where long-term
field data allow efficient training. 相似文献
253.
Elisa Villa Heather Stoll Pedro Farias Luna Adrados R. Lawrence Edwards Hai Cheng 《Quaternary Research》2013,79(1):1-5
Cemented calcareous breccias appear in the Picos de Europa (Cantabrian Mountains, Spain) resting on glacially abraded surfaces and covered by moraines. U/Th dating of the calcite coating the clasts was successful in two samples, the oldest one indicating that the breccias accumulated during or prior to Marine Isotope Stage (MIS) 11, and the youngest indicating later cementation during MIS 8. The former introduces a limit for the age of the glaciation preceding the breccias, which cannot correspond to an event younger than MIS 12. This is the oldest absolute age so far obtained for intercalated glacial/interglacial deposits of the Iberian Peninsula. 相似文献
254.
Abstract The first numerical age determinations from radiocarbon dating establish the chronology of glacial events in Redes Natural Park (Cantabrian Mountain, NW Spain). A core drilled in an ice-dammed deposit provided a minimum age of 28 990 ± 230 years BP for the maximum glacial expansion (phase I). Another core from a cirque bottom-fill provided organic sediment with 20 640 ± 300 years BP, a minimum age for the first glacial retreat (phase II). Radiometric dating of proglacial deposits interpreted as synchronous with the last glacial maximum phase in neighbouring Cornelia basin (Picos de Europa), yield ages of 40 480 ± 820 years BP. The chronological data presented in this work are consistent with the model of glacier evolution established in the Pyrénées, with a glacial maximum phase for the last glacial period older than 18 ka. © 2002 Éditions scientifiques et médicales Elsevier SAS. AU rights reserved. 相似文献
255.
Manuela Morales Demarco Pedro Oyhantçabal Karl-Jochen Stein Siegfried Siegesmund 《Environmental Earth Sciences》2013,69(4):1361-1395
Slates are internationally known as roof and façade-cladding material since prehistoric times. The methods required to mine and manufacture these dimensional stones are relatively simple in comparison to those utilized in granitic dimensional stones. This has led to a worldwide rentable commercialization of slate in the last centuries and also to the development of characteristic cultural landscapes. In Uruguay several slates are mined and used in architecture, especially as façade cladding and floor slabs. The most important slates regarding their production and utilization are the dolomitic slates. These dolomitic slates are associated with the Neoproterozoic thrust and fold belt of the Dom Feliciano belt. Representative samples have been geochemically and petrographically characterized, as well as petrophysically and petromechanically analyzed. The petrophysical and petromechanical properties were investigated in a very systematic way with respect to the new European standards, showing values comparable to those registered for internationally known slates. Detailed structural and deposit analysis were carried out in Uruguay in order to evaluate the dolomitic slate deposits. The slates are linked to calc-silicate strata in a greenschist facies volcano-sedimentary sequence and the deposits are located in the limb of a regional fold, where bedding and cleavage are parallel. The main lithotype is a layered and fine-grained dolomitic slate with a quite diverse palette of colors: light and dark green, gray, dark gray, reddish and black. The mined slate is split into slabs 0.5–2 cm thick. In the past, the average production in Uruguay was around 4,000 tons/year and a historical maximum of 13,000 tons was reached in 1993 (Oyhantçabal et al. in Z dt Ges Geowiss 158(3):417–428, 2007). The oscillations in the regional demand were the cause of several flourishing and decay cycles in the activity, but our investigation shows a considerable volume of indicated resources and therefore a very good potential. 相似文献
256.
Pedro Del Río Antonio Casas Juan J. Villalaín Tania Mochales Ruth Soto Belén Oliva-Urcia 《Studia Geophysica et Geodaetica》2013,57(3):442-459
Outstanding potential field anomalies (gravimetric and magnetic) in the Cameros Basin (N Spain) follow a WNW-ESE trend, parallel to the geological structures resulting from Mesozoic extension and Tertiary basin inversion. The positive Bouguer gravity anomaly (15 mGal) is interpreted as the result of a strong contrast between the density of Tertiary rocks of the foreland basin and the Paleozoic and Mesozoic rocks, combined with crustal thickening in the Iberian Chain with respect to the Ebro Basin. The dipolar magnetic anomaly, slightly shifted to the south with respect to the relative maximum of the Bouguer anomaly, can be interpreted as related to volcanic rocks within the basement, which are linked to Triassic rifting as witnessed by outcrops of basalts along the basin margins. An exhaustive analysis of rock properties (density, magnetic susceptibility and remanence) and basin geometry from other sources (seismic reflection profiles) allow to constrain variations in crustal thickness and the location of large-scale basement faults. 相似文献
257.
Pedro H. A. Medeiros Andreas Güntner Till Francke George L. Mamede José Carlos de Araújo 《水文科学杂志》2013,58(4):636-648
Abstract Rainfall–runoff induced soil erosion causes important environmental degradation by reducing soil fertility and impacting on water availability as a consequence of sediment deposition in surface reservoirs used for water supply, particularly in semi-arid areas. However, erosion models developed on experimental plots cannot be directly applied to estimate sediment yield at the catchment scale, since sediment redistribution is also controlled by the transport conditions along the landscape. In particular, representation of landscape connectivity relating to sediment transfer from upslope areas to the river network is required. In this study, the WASA-SED model is used to assess the spatial and temporal patterns of water and sediment connectivity for a semi-arid meso-scale catchment (933 km2) in Brazil. It is shown how spatial and temporal patterns of sediment connectivity within the catchment change as a function of landscape and event characteristics. This explains the nonlinear catchment response in terms of sediment yield at the outlet. Citation Medeiros, P. H. A., Güntner, A., Francke, T., Mamede, G. L. & de Araújo, J. C. (2010) Modelling spatio-temporal patterns of sediment yield and connectivity in a semi-arid catchment with the WASA-SED model. Hydrol. Sci. J. 55(4), 636–648. 相似文献
258.
Pedro Machado David Luz Thomas Widemann Emmanuel Lellouch Olivier Witasse 《Icarus》2012,221(1):248-261
The most significant aspect of the general circulation of the atmosphere of Venus is its retrograde super-rotation. A complete characterization of this dynamical phenomenon is crucial for understanding its driving mechanisms. Here we report on ground-based Doppler velocimetry measurements of the zonal winds, based on high resolution spectra from the UV–Visual Echelle Spectrograph (UVES) instrument at ESO’s Very Large Telescope. Under the assumption of predominantly zonal flow, this method allows the simultaneous direct measurement of the zonal velocity across a range of latitudes and local times in the day side. The technique, based on long slit spectroscopy combined with the high spatial resolution provided by the VLT, has provided the first ground-based characterization of the latitudinal profile of zonal wind in the atmosphere of Venus, the first zonal wind field map in the visible, as well as new constraints on wind variations with local time. We measured mean zonal wind amplitudes between 106 ± 21 and 127 ± 14 m/s at latitudes between 18°N and 34°S, with the zonal wind being approximately uniform in 2.6°-wide latitude bands (0.3 arcsec at disk center). The zonal wind profile retrieved is consistent with previous spacecraft measurements based on cloud tracking, but with non-negligible variability in local time (longitude) and in latitude. Near 50° the presence of moderate jets is apparent in both hemispheres, with the southern jet being stronger by ~10 m/s. Small scale wind variations with local time are also present at low and mid-latitudes. 相似文献
259.
Ricardo Sánchez-Murillo Germain Esquivel-Hernández José L. Corrales-Salazar Laura Castro-Chacón Ana M. Durán-Quesada Manuel Guerrero-Hernández Valeria Delgado Javier Barberena Katia Montenegro-Rayo Heyddy Calderón Carlos Chevez Tania Peña-Paz Saúl García-Santos Pedro Ortiz-Roque Yaneth Alvarado-Callejas Laura Benegas Antonio Hernández-Antonio Marcela Matamoros-Ortega Lucia Ortega Stefan Terzer-Wassmuth 《水文研究》2020,34(11):2660-2675
Numerous socio-economic activities depend on the seasonal rainfall and groundwater recharge cycle across the Central American Isthmus. Population growth and unregulated land use changes resulted in extensive surface water pollution and a large dependency on groundwater resources. This work combines stable isotope variations in rainfall, surface water, and groundwater of Costa Rica, Nicaragua, El Salvador, and Honduras to develop a regionalized rainfall isoscape, isotopic lapse rates, spatial–temporal isotopic variations, and air mass back trajectories determining potential mean recharge elevations, moisture circulation patterns, and surface water–groundwater interactions. Intra-seasonal rainfall modes resulted in two isotopically depleted incursions (W-shaped isotopic pattern) during the wet season and two enriched pulses during the mid-summer drought and the months of the strongest trade winds. Notable isotopic sub-cloud fractionation and near-surface secondary evaporation were identified as common denominators within the Central American Dry Corridor. Groundwater and surface water isotope ratios depicted the strong orographic separation into the Caribbean and Pacific domains, mainly induced by the governing moisture transport from the Caribbean Sea, complex rainfall producing systems across the N-S mountain range, and the subsequent mixing with local evapotranspiration, and, to a lesser degree, the eastern Pacific Ocean fluxes. Groundwater recharge was characterized by (a) depleted recharge in highland areas (72.3%), (b) rapid recharge via preferential flow paths (13.1%), and enriched recharge due to near-surface secondary fractionation (14.6%). Median recharge elevation ranged from 1,104 to 1,979 m a.s.l. These results are intended to enhance forest conservation practices, inform water protection regulations, and facilitate water security and sustainability planning in the Central American Isthmus. 相似文献
260.
Throughfall enrichment and stream nutrient chemistry in small headwater catchments with different land cover in southern Chile 下载免费PDF全文
Land cover changes have a great impact on nitrogen (N) and phosphorous (P) fluxes catchments. In this study, we wanted to compare different land covers: deciduous (D), evergreen (E) (both native forests), and exotic Eucalyptus globulus plantation (EP), affected precipitation, and stream discharge on N and P species concentrations and fluxes, under a low deposition climate in south‐central Chile. For this, we collected bulk precipitation, throughfall, and stream water samples after 41 rainfall events in E and EP, during the period June 2009–March 2011, and 31 rainfall events in D, during the period October 2009–March 2011. The highest canopy enrichment of N and P species for throughfall was observed in deciduous forest, while E. globulus showed the minimum enrichment. Total nitrogen (total‐N) discharge in EP was about 8.6 times higher than that of E and D catchments. Total‐N annual retention was positive only in E and D catchments. However, EP catchment showed a net loss (?4.79 kg N ha/year). The biggest difference was observed in nitrate stream concentrations, which showed low values for E (3.4 ± 1.3 μg/L), while EP and D showed higher nitrate concentrations (84.9 ± 16.7 and 134.7 ± 36.7 μg/L, for EP and D, respectively). Total phosphorous (total‐P) discharge flux was low in EP (0.4 kg P ha/year), and negligible in E and D forests (<0.1 kg P ha/year). Total‐P annual retention was near to 1.0 kg N ha/year (on E and D), while a net loss (?1.5 kg N ha/year) was observed for EP. We attribute the observed differences in nutrient throughfall enrichment due to high multi‐stratified canopies in the native forests. Both deciduous and evergreen native forest‐covered catchments showed the highest retention of total‐N and total‐P, in contrast to Eucalyptus‐covered plantation. 相似文献