Improving resolution and accuracy of mean sea surface from kinematic GPS,Vanuatu subduction zone     

Marie-Noëlle Bouin  Valérie Ballu  Stéphane Calmant  Bernard Pelletier 《Journal of Geodesy》2009,83(11):1017-1030

Satellite altimetry provides an ocean mean sea surface (MSS) map with global coverage and overall excellent precision. However, in some areas, like the Vanuatu archipelago, the coverage and resolution of this tool are not sufficient to correctly map the short scale undulations of the sea surface, due to numerous islands and to strong lithospheric and mantle heterogeneities. New applications such as seafloor geodesy may require local mean surface representation with improved resolution in specific areas. We used sea surface height collected with kinematic GPS during three different cruises in 2004, 2006 and 2007 to reconstruct a homogeneous sea surface map around Santo Island, Vanuatu. We assess the accuracy of this GPS-derived local sea surface to 6–19 cm and evaluate the quality of existing altimetry and gravity-derived MSSs on the Vanuatu archipelago. Observed short scale undulations are interpreted as due to local geodynamics.  相似文献   

Correlation and dating of Quaternary alluvial-fan surfaces using scarp diffusion     

Leslie Hsu  Jon D. Pelletier 《Geomorphology》2004,60(3-4):319-335

Great interest has recently been focused on dating and interpreting alluvial-fan surfaces. As a complement to the radiometric methods often used for surface-exposure dating, this paper illustrates a rapid method for correlating and dating fan surfaces using the cross-sectional shape of gullies incised into fan surfaces. The method applies a linear hillslope-diffusion model to invert for the diffusivity age, κt (m²), using an elevation profile or gradient (slope) profile. Gullies near the distal end of fan surfaces are assumed to form quickly following fan entrenchment. Scarps adjacent to these gullies provide a measure of age. The method is illustrated on fan surfaces with ages of approximately 10 ka to 1.2 Ma in the arid southwestern United States. Two areas of focus are Death Valley, California, and the Ajo Mountains piedmont, Arizona. Gully-profile morphology is measured in two ways: by photometrically derived gradient (slope) profiles and by ground-surveyed elevation profiles. The κt values determined using ground-surveyed profiles are more consistent than those determined using photo-derived κt values. However, the mean κt values of both methods are comparable. The photometric method provides an efficient way to quantitatively and objectively correlate and relatively-date alluvial-fan surfaces. The κt values for each surface are determined to approximately 30–50% accuracy.  相似文献   

Water organisation at the solid–aqueous solution interfaceOrganisation de l'eau à l'interface solide–solution aqueuse     

Laurent J. Michot  Frédéric Villiéras  Michèle François  Isabelle Bihannic  Manuel Pelletier  Jean-Maurice Cases 《Comptes Rendus Geoscience》2002,334(9):611-631

The aim of this review is to examine the present knowledge about water structure close to an interface or confined in porous spaces. First, the structure of liquid water is briefly described. Though its understanding remains incomplete, it appears that it is largely dominated by the hydrogen bond network and its dynamical evolution. The presence of any ‘foreign’ substance in water perturbs such a structure by changing at least locally the hydrogen bond network. For this reason, the presence of a solid interface significantly modifies the structure of the first adsorbed layers. Whatever the support, it is now clearly evidenced that structural perturbations are limited to distances lower than 10–15 Å from the interface. The nature, energetic heterogeneity and hydrophilicility/hydrophobicity of the solid surface influence the arrangement of water molecules. This surface organisation must definitely be considered when studying adsorption phenomena at the solid–aqueous solution interface. The relevance of such problems to geosciences is illustrated by a few situations in which water structure plays a prominent role. To cite this article: L.J. Michot et al., C. R. Geoscience 334 (2002) 611–631.  相似文献   

Possibilities of soil spectroscopy for the classification of contaminated areas in river floodplains     

Lammert Kooistra  Ron Wehrens  Lutgarde MC Buydens  Rob S. E. W. Leuven  Piet H Nienhuis 《International Journal of Applied Earth Observation and Geoinformation》2001,3(4):337

During the past decades, large amounts of diffuse contaminated soil material have been deposited in the floodplains of the river Rhine in the Netherlands. The dynamic character of this river causes a large spatial variability in the contamination level of its floodplain soils. Characterisation of the spatial variability exclusively based on soil sampling and analysis is often insufficient and expensive. Hyperspectral images can provide additional spatial information for a proper characterisation of the contamination situation of river floodplains. This paper describes the possible application of soil spectroscopy to estimate metal concentration levels in river floodplains. Soil reflectance spectra in the visible-near infrared region (VNIR) were measured in the laboratory for soil samples taken from two river floodplains along the river Waal, the main tributary of the river Rhine in the Netherlands. A multivariate calibration procedure using partial least squares (PLS) regression was applied to establish a relationship between reflectance spectra in the visible-near infrared (VNIR) region and spectrally active soil characteristics (organic matter and clay content) that are intercorrelated with concentration levels of Cd and Zn. Results of the analysis of two river floodplains are summarised and the influence of scale-level and sub soil material on the prediction capability is discussed.  相似文献   

A New Octahedrite from South Africa     

MATTHIAS F. COMERFORD  ROBERT H. MC CORKELL  SAMUEL W. TISHLER 《Meteoritics & planetary science》1968,4(1):7-21

Abstract Examination of an iron meteorite found in South Africa discloses it to be a coarse octahedrite containing 6.90 weight-percent nickel. The meteorite body contains several inclusions of troilite, or troilite plus graphite, and at least one of pure graphite veined with kamacite. Kamacite, cohenite, and phosphides are the other major constituents of the structure.  相似文献   

Hydrologic evaluation of spatially disaggregated global ensemble rainfall forecasts          下载免费PDF全文

E. Gaborit  F. Anctil  V. Fortin  G. Pelletier 《水文研究》2014,28(17):4682-4693

A statistic–stochastic multi‐fractal downscaling technique was evaluated from a hydrologic point of view. Ensemble hydrologic forecasts with a time step of 3 h were performed for original and disaggregated ensemble rainfall forecasts issued by the Canadian Global Ensemble Prediction System in its 2009 operational version. This hydro‐meteorological operational forecasting chain was conducted using the hydrological model SWMM5. The model was implemented on a small 6‐km² urban catchment located in the Québec City region. The hydrological evaluation was based on the comparison of forecasted flows to the observed ones, calculating several deterministic and probabilistic scores, and drawing rank histograms and reliability diagrams. Disaggregated products led to a better representation of the ensemble members' dispersion. This disaggregation technique represents an interesting way of bridging the gap between the meteorological models' resolution and the high degree of spatial precision sometimes required by hydrological models in their precipitation representation. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Controls on valley spacing in landscapes subject to rapid base‐level fall          下载免费PDF全文

Luke A. McGuire  Jon D. Pelletier 《地球表面变化过程与地形》2016,41(4):460-472

What controls the architecture of drainage networks is a fundamental question in geomorphology. Recent work has elucidated the mechanisms of drainage network development in steadily uplifting landscapes, but the controls on drainage‐network morphology in transient landscapes are relatively unknown. In this paper we exploit natural experiments in drainage network development in incised Plio‐Quaternary alluvial fan surfaces in order to understand and quantify drainage network development in highly transient landscapes, i.e. initially unincised low‐relief surfaces that experience a pulse of rapid base‐level drop followed by relative base‐level stasis. Parallel drainage networks formed on incised alluvial‐fan surfaces tend to have a drainage spacing that is approximately proportional to the magnitude of the base‐level drop. Numerical experiments suggest that this observed relationship between the magnitude of base‐level drop and mean drainage spacing is the result of feedbacks among the depth of valley incision, mass wasting and nonlinear increases in the rate of colluvial sediment transport with slope gradient on steep valley side slopes that lead to increasingly wide valleys in cases of larger base‐level drop. We identify a threshold magnitude of base‐level drop above which side slopes lengthen sufficiently to promote increases in contributing area and fluvial incision rates that lead to branching and encourage drainage networks to transition from systems of first‐order valleys to systems of higher‐order, branching valleys. The headward growth of these branching tributaries prevents the development of adjacent, ephemeral drainages and promotes a higher mean valley spacing relative to cases in which tributaries do not form. Model results offer additional insights into the response of initially unincised landscapes to rapid base‐level drop and provide a preliminary basis for understanding how varying amounts of base‐level change influence valley network morphology. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Mapping and detection of land use change in a coal mining area using object-based image analysis     

Wenming Pei  Suping Yao  Joseph F. Knight  Shaochun Dong  Keith Pelletier  Lian P. Rampi  Yan Wang  Jim Klassen 《Environmental Earth Sciences》2017,76(3):125

Object-based image analysis was used to map land use in the Panxie coal mining area, East China, where long-term underground coal mines have been exploited since the 1980s. A rule-based classification approach was developed for a Pleiades image to identify the desired land use classes, and the same rule-based classification strategies, after the threshold values had been modified slightly, were applied to the Landsat series images. Five land use classes were successfully captured with overall accuracies of between 80 and 94%. The classification approach was validated for its flexibility and robustness. Multitemporal classification results indicated that land use changed considerably in the Panxie coal mining area from 1989 to 2013. The urban, coal and coal gangue, and water areas increased rapidly in line with the growth in mine production. Urban areas increased from 9.38 to 20.92% and showed a tendency to increase around the coal mines. From 1989 to 2013 the coal and coal gangue area increased by 40-fold, from 0.02 to 0.58%. Similarly, the water area increased from 2.77 to 7.84% over this time period, mainly attributable to the spread of waterlogged areas. The waterlogged areas increased to about 2900 ha in 2013, which was about 80 times more than their area in 1989. In contrast, the area of cultivated land was negatively related to the increase in mine production and decreased from 73.11 to 57.25%. The results of this study provide a valuable basis for sustainable land management and environmental planning in the Panxie coal mining area.  相似文献   

Climate change triggered sedimentation and progressive tectonic uplift in a coupled piedmont–axial system: Cuyama Valley,California, USA     

Stephen B. DeLong  Jon D. Pelletier  Lee J. Arnold 《地球表面变化过程与地形》2008,33(7):1033-1046

Channels on the north‐facing piedmont of the Sierra Madre range in Cuyama Valley, California have alternated between three process regimes during the late Quaternary: (1) vertical incision into piedmont alluvium and older sedimentary deposits; (2) lateral erosion; and (3) sediment accumulation. The state of the piedmont system at a given time has been controlled by upstream sediment flux, regional tectonic uplift and incision of the axial Cuyama River. To better understand the timing and to attempt to interpret causes of past geomorphological processes on the Sierra Madre piedmont, we mapped the surficial geology and dated alluvial deposits using radiocarbon, cosmogenic and optical dating methods. Four primary episodes of sedimentation have occurred since ca. 100 ka, culminating in the most recent period of extensive piedmont sedimentation between 30 and 20 ka. Fill terraces in Cuyama Valley formed by piedmont sediment accumulation followed by vertical incision and lateral erosion are fairly planar and often mantle strath bedrock surfaces. Their vertical spatial arrangement is a record of progressive regional tectonic uplift and concomitant axial Cuyama River channel incision migrating up tributary piedmont channels. Subparallel longitudinal terrace profiles which have a linear age–elevation relationship indicate that multiple episodes of climatically controlled sedimentation overprints ～1 m kyr^?1 of regional uplift affecting the Cuyama River and its tributaries. Sedimentation was probably a result of increased precipitation that caused saturation landsliding in steep catchments. It is possible that increased precipitation during the Last Glacial Maximum was caused by both continental‐scale circulation pattern reorganization and increased Pacific storm frequency and intensity caused by ‘early warming’ of nearby Pacific Ocean surface waters. Older episodes of piedmont sedimentation are difficult to correlate with specific climate regimes, but may correlate with previous periods of increased precipitation. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Evaluating suitability of a tephra dispersal model as part of a risk assessment framework     

Gordon N. Keating  Jon D. Pelletier  Greg A. Valentine  William Statham 《Journal of Volcanology and Geothermal Research》2008

In volcanic risk assessment it is necessary to determine the appropriate level of sophistication for a given predictive model within the contexts of multiple sources of uncertainty and coupling between models. A component of volcanic risk assessment for the proposed radioactive waste repository at Yucca Mountain (Nevada, USA) involves prediction of dispersal of contaminated tephra during violent Strombolian eruptions and the subsequent transport of that tephra toward a hypothetical individual via surface processes. We test the suitability of a simplified model for volcanic plume transport and fallout tephra deposition (ASHPLUME) coupled to a surface sediment-transport model (FAR) that calculates the redistribution of tephra, and in light of inherent uncertainties in the system. The study focuses on two simplifying assumptions in the ASHPLUME model: 1) constant eruptive column height and 2) constant wind speed and direction during an eruption. Variations in tephra dispersal resulting from unsteady column height and wind conditions produced variations up to a factor of two in the concentration of tephra in sediment transported to the control population. However, the effects of watershed geometry and terrain, which control local remobilization of tephra, overprint sensitivities to eruption parameters. Because the combination of models used here shows limited sensitivity to the actual details of ash fall, a simple fall model suffices to estimate tephra mass delivered to the hypothetical individual.  相似文献