Real Time Weed Detection using a Boosted Cascade of Simple Features

Weed detection is a crucial issue in precision agriculture. In computer vision, variety of techniques are developed to detect, identify and locate weeds in different cultures. In this article, we present a real-time new weed detection method, through an embedded monocular vision. Our approach is based on the use of a cascade of discriminative classifiers formed by the Haar-like features. The quality of the results determines the validity of our approach, and opens the way to new horizons in weed detection

A Fast and Efficient Shape Descriptor for an Advanced Weed Type Classification Approach

In weed management, the distinction between monocots and dicots species is an important issue. Indeed, the yield is much higher with the application of a selective treatment instead of using a broadcast herbicide overall the parcel. This article presents a fast shape descriptor designed to distinguish between these two families of weeds. The efficiency of the descriptor is evaluated by analyzing data with the pattern recognition process known as the discriminant factor analysis (DFA). Excellent results have been obtained in the differentiation between these two weed specie

A Practical Grid-Based Alternative Method to Advective Particle Tracking

International audienceAdvective particle tracking is a conventional groundwater modeling technique that is widely used as a screening tool but lacks robustness as a reliable method for general applications. In this work, we investigate the suitability of industry-standard, finite-difference, grid-based methods as an alternative to the conventional particle-tracking approach. The presented method is classified as a particular case of the more general forward- or backward-in-time advective-dispersive probabilistic transport approaches. The proposed method is used as a powerful screening tool to accurately delineate and visualize capture zones around abstraction wells or outflow boundaries, the swept zones formed by injection wells or inflow boundaries, and the partitions associated with injection-pumping well doublets or inflowing-outflowing boundary pairs. Moreover, we show that the forward or backward travel times and residence time distributions are robustly simulated and visualized on the computational grid with little computational effort. Two examples are given to illustrate the key advantages of this method in groundwater applications. The first example considers a synthetic pump-and-treat remediation system in an irregularly layered aquifer. The second example involves four doublet wells operating for heat extraction in the Dogger geothermal reservoir in the Paris Basin, a leading European scale project. The presented approach is far more comprehensive as a screening tool than the conventional method, providing a natural intermediate step before processing the more general time-dependent advective-dispersive simulations

Well Rate and Placement for Optimal Groundwater Remediation Design with A Surrogate Model

A new surrogate-assisted optimization formulation for groundwater remediation design was developed. A stationary Eulerian travel time model was used in lieu of a conservative solute transport model. The decision variables of the management model are well locations and their flow rates. The objective function adjusts the residence time distribution between all pairs of injection-production wells in the remediation system. This goal is achieved by using the Lorenz coefficient as an effective metric to rank the relative efficiency of many remediation policies. A discrete adjoint solver was developed to provide the sensitivity of the objective function with respect to changes in decision variables. The quality management model was checked with simple solutions and then applied to hypothetical two- and three-dimensional test problems. The performance of the simulation-optimization approach was evaluated by comparing the initial and optimal remediation designs using an advective-dispersive solute transport simulator. This study shows that optimal designs simultaneously delay solute transport breakthrough at pumping wells and improve the sweep efficiency leading to smaller cleanup times. Well placement optimization in heterogeneous porous media was found to be more important than well rate optimization. Additionally, optimal designs based on two-dimensional models were found to be more optimistic suggesting a direct use of three-dimensional models in a simulation-optimization framework. The computational budget was drastically reduced because the proposed surrogate-based quality management model is generally cheaper than one single solute transport simulation. The introduced model could be used as a fast, but first-order, approximation method to estimate pump-and-treat capital remediation costs. The results show that physically based low-fidelity surrogate models are promising computational approaches to harness the power of quality management models for complex applications with practical relevance

Modelling three dimensional groundwater flow and transport by hexahedral finite elements.

This research work deals with three-dimensional modeling of groundwater flow and solute transport problems in groundwater aquifer systems, with several complexities, heterogeneities and variable conditions as encountered in the field. Finite element methods are used throughout to solve a range of different problems, using in particular the Galerkin weighted residual approach based on trilinear hexahedral elements. Special emphasis is made on transient and non-linear groundwater flow problems with moving interfaces, such as the water table and the freshwater-saltwater sharp interface. A generalized Fast Updating Procedure technique is developed for these situations, which presents a number of advantageous features in comparison to classic computational techniques used to deal with such problems. One of the important contributions is the automatic construction of the generic soils characteristic curves, which are dynamically dependent upon the overall system water status. Several test examples are successfully worked out for validating this technique in different aquifer configurations, and under different initial and boundary conditions. These test cases show that the proposed method is cheap, numerically stable and accurate. Numerical stability is guaranteed through a developed solver, which is obtained by using state of the art methods for robust preconditioning and efficient numerical implementation. The accuracy is demonstrated by comparison against analytical, other numerical approaches, and laboratory experimental solutions. The usefulness of the method is clearly shown by the application of the 3-D sharp interface finite element model 'GEO-SWIM' to the coastal aquifer system of Martil in the north of Morocco. Several efficient runs are made, leading to a calibrated management model for the study area, giving a clear picture of the salinization risk in the aquifer due to saltwater encroachment. Three-dimensional modeling of solute transport problems in groundwater aquifer systems is equally investigated. It is concluded that the standard Galerkin finite element method is computationally intensive, since the obtained system of numerical equations is very large, sparse, none symmetric and usually difficult to solve with standard iterative techniques. Hence, preconditioning is necessary to improve the convergence behavior of ill-conditioned systems. In this work, we propose an M-matrix type of transformation on the general transport matrix which guarantees the existence of the preconditioning schemes, and hence improves the overall solvers performance and robustness. The usefulness of the method is demonstrated by solving several test examples with different complexities, including hypothetical and field applications in Belgium. Different solvers are tested as the minimal residual method and the stabilized biconjugate gradient method, in combination with different preconditioning schemes, as diagonal scaling and incomplete factorization. It is concluded that M-matrix preconditioning is very simple to implement, and proves to be very efficient and robust. An effort is put on packaging the computer programs, by giving modern visual support to many modules. Therefore, several GUI programs are provided as complementary tools to support the developed models, enabling their friendly use, and the possibility for future extensions

Assessment of Climate Change Impacts on Water Resources in the Somme River Basin (France)

International audienceModelling the impacts of climate change on water resources in the Somme watershed in northern France is investigated with a multimodel ensemble to probe the sensitivity of hydrologic response to uncertainties in climate projections provided by general circulation models. At the Somme watershed scale, the average decrease in predicted recharge from seven climate models is -18.7%. However, significant disparities appear between simulation results for different climate models. These variations are bounded between -30.4% for the most pessimistic model and-5.6% for the most optimistic model. Moreover, seasonal gaps are markedly important. For all climate models, the impacts on groundwater levels would be greater on plateaus than in humid valleys. The water level changes would be on the order of -10m on the plateaus for five climate models and between 0.2m and 0.5m in humid valleys. The impacts of two other climate models on water levels are rather low. In addition, the monthly average discharge of the Somme River and its tributaries is predicted to decrease by 2065. The seven-model average shows that the low outlet flow rate to the Somme basin would be reduced by 23% but with disparities between models. The decrease would be more severe in the Avre basin, with the minimal discharge reduced by 32%. This study is a first step towards addressing uncertainties in climate models such that an adaptive watershed management strategy could be devised for water resource managers

Generalized Mixed-Cell Mass Balance Solute Transport Modeling in Pore-Scale Disordered Networks: A New Semi-Analytical Approach

International audienceAccurately predicting (non-reactive or reactive) solute transport migration, at multiple scales, in subsurface aquifers is identified among urgent societal and scientific challenges in water resources engineering and environmental pollution [1]. In particular, pore-scale models are essential tools to bridge the gap between the pore and REV scales at which observable macroscopic behavior of solute transport processes become apparent. While challenges do persist in this field, we derive cutting-edge pore scale semi-analytical formulation for solute transport modelling in disordered networks. Continuous concentration profiles along pore throats are calculated analytically, a posteriori, from time-dependent numerically simulated concentrations in neighboring pores. A double Laplace transform method is applied to governing advection-diffusion equations in network elements by enforcing mass flux continuity along their interfaces. We show that these solutions involve a time-dependent convolution product kernels or interpolating functions expressed as convergent exponentially decreasing series of locally embedded pore-throat geometrical and flow properties. Explicit dependence of interpolating kernels on the local Péclet numbers leads to a generalized numerical scheme for accurate simulation of solute transport processes in pore networks. Indeed, widely used numerical schemes in the literature [2-7] are equivalent to the asymptotic (long-time) form of our general scheme for extremely small or high Péclet numbers. Therefore, we demonstrate for the first-time that previously adopted numerical schemes for mass balance in pore networks [2-7] may overlook pore scale dynamics for a full range of intermediate Péclet numbers occurring in subsurface aquifers. These findings are illustrated by analysis of simulated concentration distributions in a benchmark pore network extracted from Berea sandstone three-dimensional pore space image. Our findings [8] provide additional insights into the understanding of pore-scale solute transport processes to further improve the predictive capability of existing mixed-cell mass balance network models

Iléus biliaire: une cause rare d’occlusion intestinale, à propos d’un cas

L’iléus biliaire est une complication rare de la lithiase vésiculaire secondaire à une fistule cholécysto-duodénale avec passage d’un macrocalcul dans l’intestin grêle. L’occlusion est provoquée par le blocage du calcul au niveau de l’iléon. Nous rapportons le cas d’une patiente de 75 ans, présentant des vomissements avec des douleurs abdominales diffuses. L’IRM abdominal a objectivé une aérobilie importante, une vésicule biliaire atrophique associée à une occlusion grêlique terminale sur obstacle intraluminal. La laparotomie a objectivé la présence d’une fistule cholécystoduodénale, une vésicule biliaire scléro-atrophique avec la présence d’un calcul obstruant la lumière au niveau du grêle distal (à 1 mètre de la valvule de Bauhin); une enterolithotomie a été réalisé avec une cholécystectomie et fermeture du trajet fistuleux en un seul temps opératoire; les suites postopératoires ont été simples

A benchmark study on problems related to CO₂ storage in geologic formations:SSummary and discussion of the results

International audienceThis paper summarises the results of a benchmark study that compares a number of mathematical and numerical models applied to specific problems in the context of carbon dioxide (CO2) storage in geologic formations. The processes modelled comprise advective multi-phase flow, compositional effects due to dissolution of CO2 into the ambient brine and non-isothermal effects due to temperature gradients and the Joule–Thompson effect. The problems deal with leakage through a leaky well, methane recovery enhanced by CO2 injection and a reservoir-scale injection scenario into a heterogeneous formation. We give a description of the benchmark problems then briefly introduce the participating codes and finally present and discuss the results of the benchmark study