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71.
Erwan Gloaguen Denis Marcotte Michel Chouteau Herv Perroud 《Journal of Applied Geophysics》2005,57(4):242-259
A new radar velocity tomography method is presented based on slowness covariance modeling and cokriging of the slowness field using only measured travel time data. The proposed approach is compared to the classical LSQR algorithm using various synthetic models and a real data set. In each case, the proposed method provides comparable to or better results than LSQR. One advantage of this approach is that it is self-regularized and requires less a priori information. The covariance model also allows stochastic imaging of slowness fields by geostatistical simulations. Stable characteristics and uncertain features of the inverted models can then be easily identified. 相似文献
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Ana Casado Borbála Hortobágyi Erwan Roussel 《International journal of geographical information science》2018,32(12):2427-2446
The geometry of impounded surfaces is a key tool to reservoir storage management and projection. Yet topographic data and bathymetric surveys of average-aged reservoirs may be absent for many regions worldwide. This paper examines the potential of contour line interpolation (TOPO) and Structure from Motion (SfM) photogrammetry to reconstruct the topography of existing reservoirs prior to dam closure. The study centres on the Paso de las Piedras reservoir, Argentina, and assesses the accuracy and reliability of TOPO- and SfM- derived digital elevation models (DEMs) using different grid resolutions. All DEMs were of acceptable quality. However, different interpolation techniques produced different types of error, which increased (or decreased) with increasing (or decreasing) grid resolution as a function of their nature, and relative to the terrain complexity. In terms of DEM reliability to reproduce area–elevation relationships, processing-related disagreements between DEMs were markedly influenced by topography. Even though they produce intrinsic errors, it is concluded that both TOPO and SfM techniques hold great potential to reconstruct the bathymetry of existing reservoirs. For areas exhibiting similar terrain complexity, the implementation of one or another technique will depend ultimately on the need for preserving accurate elevation (TOPO) or topographic detail (SfM). 相似文献
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The prediction of fluid flows within hydrocarbon reservoirs requires the characterization of petrophysical properties. Such characterization is performed on the basis of geostatistics and history-matching; in short, a reservoir model is first randomly drawn, and then sequentially adjusted until it reproduces the available dynamic data. Two main concerns typical of the problem under consideration are the heterogeneity of rocks occurring at all scales and the use of data of distinct resolution levels. Therefore, referring to sequential Gaussian simulation, this paper proposes a new stochastic simulation method able to handle several scales for both continuous or discrete random fields. This method adds flexibility to history-matching as it boils down to the multiscale parameterization of reservoir models. In other words, reservoir models can be updated at either coarse or fine scales, or both. Parameterization adapts to the available data; the coarser the scale targeted, the smaller the number of unknown parameters, and the more efficient the history-matching process. This paper focuses on the use of variational optimization techniques driven by the gradual deformation method to vary reservoir models. Other data assimilation methods and perturbation processes could have been envisioned as well. Last, a numerical application case is presented in order to highlight the advantages of the proposed method for conditioning permeability models to dynamic data. For simplicity, we focus on two-scale processes. The coarse scale describes the variations in the trend while the fine scale characterizes local variations around the trend. The relationships between data resolution and parameterization are investigated. 相似文献
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La présente étude a pour objectif d’analyser la variabilité spatiale multi-échelles de l’équivalent en eau de la neige (EEN). Dans un premier temps, la variabilité spatiale de l’EEN par rapport à la latitude et à la longitude a été analysée. Des indices locaux ont été utilisés pour caractériser les différentes structures spatiales. Par la suite, les structures spatiales homogènes ont été délimitées à l’aide de l’approche de segmentation spatiale multi-résolutions en utilisant des méta-variables physiographiques. La segmentation a été validée à l’aide du test non paramétrique de Kruskal-Wallis appliqué aux données de l’EEN de chaque paire de zones adjacentes. À l’échelle régionale, la segmentation spatiale a permis d’identifier six zones géographiques différenciées par leur position par rapport aux modes de circulations atmosphériques et la disposition du relief. À l’échelle locale, la segmentation spatiale montre le rôle de la pente, de la courbure, etc. dans la variabilité spatiale du couvert nival.
Editeur Z. W. Kundzewicz; Editeur associé E. Gargouri 相似文献
77.
The round-trip travel time measurements made by spacecraft laser altimeters are primarily used to construct topographic maps
of the target body. The accuracy of the calculated bounce point locations of the laser pulses depends on the quality of the
spacecraft trajectory reconstruction. The trajectory constraints from Doppler and range radio tracking data can be supplemented
by altimetric “crossovers”, to greatly improve the reconstruction of the spacecraft trajectory. Crossovers have been used
successfully in the past (e.g., Mars Orbiter Laser Altimeter on Mars Global Surveyor), but only with single-beam altimeters.
The same algorithms can be used with a multi-beam laser altimeter, but we present a method using the unique cross-track topographic
information present in the multi-beam data. Those crossovers are especially adapted to shallow (small angle) intersections,
as the overlapping area is large, reducing the inherent ambiguities of single-beam data in that situation. We call those “swath
crossovers”. They prove particularly useful in the case of polar-orbiting spacecraft over slowly rotating bodies, because
all the non-polar crossovers have small intersection angles. To demonstrate this method, we perform a simplified simulation
based on the Lunar Reconnaissance Orbiter (LRO) and its five-beam Lunar Orbiter Laser Altimeter. We show that swath crossovers
over one lunar month can independently, from geometry alone, recover the imposed orbital perturbations with great accuracy
(5 m horizontal, < 1 m vertical, about one order of magnitude smaller than the imposed perturbations). We also present new
types of constraints that can be derived from the swath crossovers, and designed to be used in a precision orbit determination
setup. In future work, we will use such multi-beam altimetric constraints with data from LRO. 相似文献