Blocky regularization schemes for Full‐Waveform Inversion★     

Antoine Guitton 《Geophysical Prospecting》2012,60(5):870-884

With ill‐posed inverse problems such as Full‐Waveform Inversion, regularization schemes are needed to constrain the solution. Whereas many regularization schemes end up smoothing the model, an undesirable effect with FWI where high‐resolution maps are sought, blocky regularization does not: it identifies and preserves strong velocity contrasts leading to step‐like functions. These models might be needed for imaging with wave‐equation based techniques such as Reverse Time Migration or for reservoir characterization. Enforcing blockiness in the model space amounts to enforcing a sparse representation of discontinuities in the model. Sparseness can be obtained using the ?¹ norm or Cauchy function which are related to long‐tailed probability density functions. Detecting these discontinuities with vertical and horizontal gradient operators helps constraining the model in both directions. Blocky regularization can also help recovering higher wavenumbers that the data used for inversion would allow, thus helping controlling the cost of FWI. While the Cauchy function yields blockier models, both ?¹ and Cauchy attenuate illumination and inversion artifacts.  相似文献   

Mud bank colonization by opportunistic mangroves: A case study from French Guiana using lidar data     

Christophe Proisy  Nicolas Gratiot  Edward J. Anthony  Antoine Gardel  François Fromard  Patrick Heuret 《Continental Shelf Research》2009

Mud bank colonization by mangroves on the Amazon-influenced coast of French Guiana was studied using light detection and ranging (lidar) data which provide unique information on canopy geometry an sub-canopy topography. The role of topography was assessed through analysis of vegetation characteristics derived from these data. Measurements and analyses of mangrove expansion rates over space and time led to the identification of two distinct colonization processes. The first involves regular step-by-step mangrove expansion to the northwest of the experimental site. The second is qualified as ‘opportunistic’ since it involves a clear relationship between specific ecological characteristics of pioneer Avicennia and mud cracks affecting the mud bank surface and for which probabilities of occurrence were computed from terrain elevations. It is argued from an original analysis of the latter relationship that mud cracks cannot be solely viewed as water stress features that reflect desiccation potentially harmful to plant growth. Indeed, our results tend to demonstrate that they significantly enhance the propensity for mangroves to anchor and take root, thus leading to the colonization of tens of hectares in a few days. The limits and potential of lidar data are discussed with reference to the study of muddy coasts. Finally, the findings of the study are reconsidered within the context of a better understanding of both topography and vegetation characteristics on mangrove-fringed muddy coasts.  相似文献   

Late Permian to Middle Triassic correlations and palaeogeographical reconstructions in south-western European basins: New sedimentological data from Minorca (Balearic Islands, Spain)     

Bastien Linol  Antoine Bercovici  Sylvie Bourquin  Jos Bienvenido Diez  Jos Lpez-Gmez  Jean Broutin  Marc Durand  Uxue Villanueva-Amadoz 《Sedimentary Geology》2009,220(1-2):77-94

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Ricker‐compliant deconvolution          下载免费PDF全文

Jon Claerbout  Antoine Guitton 《Geophysical Prospecting》2015,63(3):615-625

Ricker‐compliant deconvolution spikes at the center lobe of the Ricker wavelet. It enables deconvolution to preserve and enhance seismogram polarities. Expressing the phase spectrum as a function of lag, it works by suppressing the phase at small lags. A by‐product of this decon is a pseudo‐unitary (very clean) debubble filter where bubbles are lifted off the data while onset waveforms (usually Ricker) are untouched.  相似文献   

Multiple-point geostatistical simulation using enriched pattern databases     

Rezaee  Hassan  Marcotte  Denis  Tahmasebi  Pejman  Saucier  Antoine 《Stochastic Environmental Research and Risk Assessment (SERRA)》2015,29(3):893-913

Stochastic Environmental Research and Risk Assessment - This study presents a new approach of generating a set of alternative training images (ATI) to use in patch-based multiple-point simulation....  相似文献   

The giant clam Tridacna maxima communities of three French Polynesia islands: comparison of their population sizes and structures at early stages of their exploitation     

Gilbert  Antoine; Andrefouet  Serge; Yan  Laurent; Remoissenet  Georges 《ICES Journal of Marine Science》2006,63(9):1573-1589

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The remarkable population size of the endangered clam Tridacna maxima assessed in Fangatau Atoll (Eastern Tuamotu, French Polynesia) using in situ and remote sensing data     

Andrefouet  Serge; Gilbert  Antoine; Yan  Laurent; Remoissenet  Georges; Payri  Claude; Chancerelle  Yannick 《ICES Journal of Marine Science》2005,62(6):1037-1048

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A chronology of the Little Ice Age in the tropical Andes of Bolivia (16°S) and its implications for climate reconstruction     

Antoine Rabatel  Bernard Francou  Philippe Naveau 《Quaternary Research》2008,70(2):198-212

Dating moraines by lichenometry enabled us to reconstruct glacier recession in the Bolivian Andes since the Little Ice Age maximum. On the 15 proglacial margins studied, we identified a system of ten principal moraines that marks the successive positions of glaciers over the last four centuries. Moraines were dated by performing statistical analysis of lichen measurements based on the extreme values theory. Like glaciers in many mid-latitude mountain areas, Bolivian glaciers reached their maximal extent during the second half of the 17th century. This glacier maximum coincides with the Maunder minimum of solar irradiance. By reconstructing the equilibrium-line altitude and changes in mass-balance, we think the glacier maximum may be due to a 20 to 30% increase in precipitation and a 1.1 to 1.2 °C decrease in temperature compared with present conditions. In the early 18th century, glaciers started to retreat at varying rates until the late 19th to early 20th century; this trend was generally associated with decreasing accumulation rates. By contrast, glacier recession in the 20th century was mainly the consequence of an increase in temperature and humidity. These results are consistent with observations made in the study region based on other proxies.  相似文献   

The impact of Dansgaard–Oeschger cycles on the loessic environment and malacofauna of Nussloch (Germany) during the Upper Weichselian   总被引：1，自引：0，他引：1  

Olivier Moine  Denis-Didier Rousseau  Pierre Antoine 《Quaternary Research》2008,70(1):91-104

A loess sequence has been sampled continuously at high resolution in Nussloch (Rhine Valley, Germany) for malacological and grain-size analyses between ca. 34 and 20 ka. Molluscan abundance and richness, percentage in hygrophilous species and grain-size index show cyclical variations related to the lithological loess–gley alternation. Major molluscan abundance maxima were triggered by temperature increases through an enhancement of the reproduction cycle, whereas cyclical richness fluctuations and percentage in hygrophilous species reflect variations in local humidity and changes in the environmental mosaic. Malacological parameters allow the distinction of four environmental phases organised in cyclical successions correlated with most of the loess–gley doublets. The correlation of the grain-size index of the Nussloch loess sequence with the dust content of the GRIP ice core demonstrates the synchronicity of major molluscan abundance maxima and δ¹⁸O increases characterising temperature increases during Dansgaard–Oeschger interstades. A schematic model is proposed to link the North Atlantic Dansgaard–Oeschger climatic oscillations with local environmental changes indicated by both malacofauna and pedostratigraphy. This malacological study of the Nussloch loess sequence thus provides new information about the response of terrestrial loessic palaeoenvironments to millennial-timescale climatic fluctuations during the Upper Weichselian ( marine isotope stage 2 (MIS 2) and end of MIS 3).  相似文献   

On the sensitivity of Antarctic sea ice model biases to atmospheric forcing uncertainties     

Barthélemy  Antoine  Goosse  Hugues  Fichefet  Thierry  Lecomte  Olivier 《Climate Dynamics》2018,51(4):1585-1603

Climate Dynamics - Although atmospheric reanalyses are an extremely valuable tool to study the climate of polar regions, they suffer from large uncertainties in these data-poor areas. In this work,...  相似文献