Generalyzed variance-covariance propagation law formulae and application to explicit least-squares adjustments     

Luc M. A. Jeudy 《Journal of Geodesy》1988,62(2):113-124

Standard formulae overlook the contribution of a number of terms in the derivation of variance-covariance matrices for parameters in nonlinear least squares adjustment. In a large class of nonlinear mathematical models, these terms can contribute to an important error in the estimation of parameter variances. Improved formulae are derived. A numerical example is given and the use of our improved formula in the case of least-squares adjustment in the explicit case (L=F(X)) is fully documented.  相似文献   

The precession phase of hydrological variability in the Western Pacific Warm Pool during the past 400 ka     

Kazuyo Tachikawa  Olivier Cartapanis  Laurence Vidal  Luc Beaufort  Tatiana Barlyaeva  Edouard Bard 《Quaternary Science Reviews》2011,30(25-26):3716-3727

The low-latitude hydrological cycle is a key climate parameter on different timescales, as it contributes to various feedback processes. Modelling studies suggest that the interhemispheric insolation contrast is the major factor controlling the cycle, although the influence of glacial conditions and the phase relationships relative to insolation forcing remain undetermined. In this work, we studied precipitation variability over Papua New Guinea (PNG, 3°S) for the past 400 ka using terrigenous fractions transported by the Sepik River to the Western Pacific Warm Pool (WPWP). A multi-decadal to centennial resolution of the elemental content was obtained using X-ray fluorescence scanning of a marine sediment core using an age model based on ¹⁴C dates and benthic foraminiferal δ¹⁸O. Indicators of the coarse river particulate fraction (bulk and CaCO₃-free basis Ti concentrations, the log intensity ratios of Ti/K and Ti/Ca) displayed a dominant 23 ka periodicity without a clear glacial–interglacial trend. Our precipitation records showed a tight relationship with local summer insolation (3°S, January) with time-dependent lag of 0 to 4 ka. They were generally in anti-phase for U–Th dated Chinese speleothem δ¹⁸O records. Based on an analogy to modern climate, we propose that precipitation over PNG was primarily determined by interhemispheric insolation contrast, and the contribution of austral fall/winter precipitation added second-order variability that formed the lags. For the last four climate cycles, the WPWP hydrological cycle was closely associated with the eastern Asian monsoon, and the influence of glacial conditions on the low-latitude hydrological cycle was estimated to be limited.  相似文献   

Water quality changes in the dunes of the western Belgian coastal plain due to artificial recharge of tertiary treated wastewater     

Alexander Vandenbohede  Emmanuel Van Houtte  Luc Lebbe 《Applied Geochemistry》2009

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Textural Characterization Using Gy’s Heterogeneity Functions     

Luc Barbanson  Stanislas Sizaret  Olivier Rozembaum  Jean Louis Rouet 《Mathematical Geosciences》2009,41(8):855-868

A solid can be regarded as a set of contiguous elementary units. The distribution within the solid of any properties, measurable within each elementary unit, can be characterized using two parameters. These parameters are built using the constitution and distribution heterogeneities of Gy. The former account for the granularity of the elementary units, whereas the latter assess the spatial distribution of the property. A texture which definition involves several properties can be described using a diagram where both parameters work as variables. Potential applications encompass (i) the textural classification of soils, ore, breccia, and concrete and (ii) the monitoring of textural transformation during process like dolomitization, metamorphism, weathering, deformation, or annealing.  相似文献   

Eyes of the landscape – Value,conservation and management of European ponds     

Naomi Ewald  Thomas Kalettka  Luc Brendonck 《Limnologica》2012,42(4):251-253

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A practical review of geostatistical processing applied to geophysical data: methods and applications     

Matthieu Bourges  Jean‐Luc Mari  Nicolas Jeannée 《Geophysical Prospecting》2012,60(3):400-412

Nowadays, geostatistics is commonly applied for numerous gridding or modelling tasks. However, it is still under used and unknown for classical geophysical applications. This paper highlights the main geostatistical methods relevant for geophysical issues, for instance to improve the quality of seismic data such as velocity cubes or interpreted horizons. These methods are then illustrated through four examples. The first example, based on a gravity survey presents how a geostatistical interpolation can be used to filter out a global trend, in order to better define real anomalies. In the second case study, dedicated to refraction surveying, geostatistical filtering is used to filter out acquisition artefacts and identify the main geological structures. The third one is an example of porosity being integrated geostatistically with a seismic acoustic impedance map. The last example deals with geostatistical time to depth conversion; the interest of performing geostatistical simulations is finally discussed.  相似文献   

An integrated approach for investigating geomorphic response to extreme events: methodological framework and application to the October 2011 flood in the Magra River catchment,Italy          下载免费PDF全文

Massimo Rinaldi  William Amponsah  Marco Benvenuti  Marco Borga  Francesco Comiti  Ana Lucía  Lorenzo Marchi  Laura Nardi  Margherita Righini  Nicola Surian 《地球表面变化过程与地形》2016,41(6):835-846

A high‐magnitude flash flood, which took place on 25 October 2011 in the Magra River catchment (1717 km²), central‐northern Italy, is used to illustrate some aspects of the geomorphic response to the flood. An overall methodological framework is described for using interlinked observations and analyses of the geomorphic impacts of an extreme event. The following methods and analyses were carried out: (i) hydrological and hydraulic analysis of the event; (ii) sediment delivery by event landslide mapping; (iii) identification and estimation of wood recruitment, deposition, and budgeting; (iv) interpretation of morphological processes by analysing fluvial deposits; (v) remote sensing and geographic information system (GIS) analysis of channel width changes. In response to the high‐magnitude hydrological event, a large number of landslides occurred, consisting of earth flows, soil slips, and translational slides, and a large quantity of wood was recruited, in most part deriving from floodplain erosion caused by bank retreat and channel widening. The most important impact of the flood event within the valley floor was an impressive widening of the overall channel bed and the reactivation of wide portions of the pre‐event floodplain. Along the investigated (unconfined or partly confined) streams (total investigated length of 93.5 km), the channel width after the flood was up to about 20 times the channel width before the event. The study has shown that a synergic use of different methods and types of evidence provides fundamental information for characterizing and understanding the geomorphic effects of intense flood events. The prediction of geomorphic response to a flood event is still challenging and many limitations exist; however a robust geomorphological analysis can contribute to the identification of the most critical reaches. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Morphology and distribution of dolines on ultramafic rocks from airborne LiDAR data: the case of southern Grande Terre in New Caledonia (SW Pacific)   总被引：1，自引：0，他引：1       下载免费PDF全文

Julie Jeanpert  Pierre Genthon  Pierre Maurizot  Jean‐Luc Folio  Myriam Vendé‐Leclerc  Jeremy Sérino  Jean‐Lambert Join  Marion Iseppi 《地球表面变化过程与地形》2016,41(13):1854-1868

Dolines are closed geomorphological depressions which are surface manifestations of karstic systems. Usually developed on limestones, they also typify the morphology of the New Caledonian landscape, particularly on the southern massif of the main island (known as Massif du Sud). The specificity of dolines here lies in their development on ultramafic rocks. They are evidences of subsidence, suffosion and collapse phenomena resulting from dissolution weathering of peridotites. However, extensive underground drainage systems are still not yet recognized. Semi‐automatic mapping of dolines is carried out on a 148 km² area of the Massif du Sud from a high accuracy LiDAR digital elevation model. In this area 8601 dolines ranging from 1 m² to 2 km² are identified and morphologically characterized with precision. Most are small, shallow and round‐shaped, yet more complex shapes are locally observed. Size distribution analysis allows the setting of a threshold of 20 000 m² above which surface processes rather than chemical weathering control doline evolution. Doline density analysis reveals high concentrations on flat areas where ferricrete overlies the complete weathering profile, especially in the case of elevated rainy watersheds. Dolines are aligned and elongated along a north 135° ± 5° major fracture direction, which is inherited from the obduction of the Pacific Plate upper mantle in the Late Eocene. Finally, we propose a pioneering morphometric typology of dolines that provides important clues as to pseudokarstic activity. We define collapse, bowl‐shaped and flat bottom dolines. Collapse and bowl‐shaped dolines are assumed to denote active pseudokarst. They may widen and deepen, or eventually be filled by sediments. They are distinguished from flat bottom dolines that are partially to completely filled, which suggests that they are associated with paleo‐pseudokarsts. However the groundwater flow paths associated with the genesis and evolution of dolines must be clarified, thus collapse and bowl‐shaped dolines should be hydrologically monitored. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Cyclic macro‐element for soil–structure interaction: material and geometrical non‐linearities     

Ccile Cremer  Alain Pecker  Luc Davenne 《国际地质力学数值与分析法杂志》2001,25(13):1257-1284

This paper presents a non‐linear soil–structure interaction (SSI) macro‐element for shallow foundation on cohesive soil. The element describes the behaviour in the near field of the foundation under cyclic loading, reproducing the material non‐linearities of the soil under the foundation (yielding) as well as the geometrical non‐linearities (uplift) at the soil–structure interface. The overall behaviour in the soil and at the interface is reduced to its action on the foundation. The macro‐element consists of a non‐linear joint element, expressed in generalised variables, i.e. in forces applied to the foundation and in the corresponding displacements. Failure is described by the interaction diagram of the ultimate bearing capacity of the foundation under combined loads. Mechanisms of yielding and uplift are modelled through a global, coupled plasticity–uplift model. The cyclic model is dedicated to modelling the dynamic response of structures subjected to seismic action. Thus, it is especially suited to combined loading developed during this kind of motion. Comparisons of cyclic results obtained from the macro‐element and from a FE modelization are shown in order to demonstrate the relevance of the proposed model and its predictive ability. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Thin Threads of Solar Filaments   总被引：1，自引：0，他引：1  

Yong?LinEmail author  Oddbj?rn?Engvold  Luc?Rouppe?van?der?Voort  Jun?Elin?Wiik  Thomas?E.?Berger 《Solar physics》2005,226(2):239-254

High-resolution images obtained in H with the new Swedish Solar Telescope at La Palma, Spain, have been used for studies of fine-scale threads in solar filaments. The widths of the thin threads are 0.3 arcsec. The fact that the width of the thinnest threads is comparable to the diffraction limit of the telescope of about 0.14 arcsec, at the wavelength of H, suggests that even thinner threads may exist. Assuming that the threads represent thin magnetic strings, we conclude that only a small fraction of these are filled with observable absorbing plasma, at a given time. The absorbing plasma is continuously flowing along the thread structures at velocities 15± 10 kms^–1, which suggests that the flows must be field-aligned. In one case where a bundle of thin threads appears to be rooted in the nearby photosphere, we find that the individual threads connects with intergranular, dark lanes in the photosphere. We do not find signs of typical network fields at the roots of the fine threads, as normally evidenced by bright points in associated G-band images. It is suggested that filament threads are rooted in relatively weak magnetic fields.  相似文献