Développement d’une nouvelle méthode de régionalisation basée sur le concept de « régime des débits naturels » : la méthode éco-géographique

Nous proposons une nouvelle méthode de régionalisation des débits fondée sur le concept de « régime des débits naturels » introduit en écologie aquatique : l’approche éco-géographique. Elle se distingue de deux approches de régionalisation existantes (approches hydrologique et écologique) sur les trois points suivants : le choix des variables hydrologiques, l’échelle d’analyse et la finalité de la régionalisation. En ce qui concerne le choix des variables hydrologiques, la nouvelle méthode est fondée sur le choix des caractéristiques des débits et non sur les variables hydrologiques. Ces caractéristiques des débits sont définies au moyen de l’analyse en composantes principales appliquée sur les variables hydrologiques. Contrairement aux autres approches, l’approche éco-géographique tient compte de toutes les caractéristiques des débits dans la régionalisation conformément au concept de « régime des débits naturels ». Quant à l’échelle d’analyse, à l’instar de l’approche écologique, la nouvelle méthode s’applique aussi à toutes les échelles d’analyse (annuelle, mensuelle et journalière) mais en les considérant séparément afin de tenir compte de toutes les caractéristiques de débits dans la régionalisation. Enfin, la finalité de la nouvelle méthode est de pouvoir déterminer les facteurs de variabilité spatiale des caractéristiques de débits (et non des variables hydrologiques) au moyen de l’analyse canonique des corrélations, notamment afin d’assurer une gestion durable des ressources hydriques dans un contexte de changement de l’environnement. Nous avons appliqué cette nouvelle méthode aux débits moyens annuels au Québec.Flow regionalization has been the subject of numerous hydrologic studies. However, despite the development of regionalization methods, there are still differences in the approaches used amongst hydrologists on the one hand, and between hydrologists and experts in other fields (aquatic ecology and physical geography) on the other hand. Those differences relate to five aspects of the regionalization process: the choice of hydrologic variables, station grouping methods to produce homogeneous hydrologic regions, the choice of appropriate statistical laws to estimate quantiles for non-gauged or partially-gauged sites, the scale of flow analysis, and the ultimate purpose of the regionalization exercise. Depending on the choice of hydrologic variables, the scale of analysis and their ultimate purpose, regionalization studies may thus be divided according to two distinct approaches: the hydrologic approach and the ecologic approach.The ultimate purpose of the hydrologic approach is to estimate flows at non-gauged or partially-gauged sites. For this reason, it has been primarily concerned with methods that allow the grouping of stations into homogeneous hydrologic regions and with the choice of statistical laws to estimate quantiles for non-gauged or partially-gauged sites. However, despite its undeniable interest from a practical point of view, this approach does not address the concerns of ecologists and geographers for three reasons: 1) the choice of hydrologic variables used for regionalization is not based on a scientific concept (this choice is arbitrary, and the variables selected do not constrain all the flow characteristics); 2) the ultimate purpose of the regionalization exercise is limited to estimating flows and is of limited interest to geographers and ecologists; 3) regionalization is performed at a daily scale, without taking into account other scales.To make up for these limitations, ecologists have recently proposed regionalization based on the “natural flow regime” concept (the ecologic approach), which allows all fundamental flow characteristics (magnitude, frequency, duration, timing of occurrence and variability) to be taken into account. The rationale for considering all flow characteristics is that each characteristic has an effect on the behaviour of river ecosystems. Hence, regionalization based on the ecologic approach relies on a large number of hydrologic variables that define the fundamental flow characteristics. Rather than being arbitrary, the choice of variable is based on this new paradigm. Regionalization using the ecologic approach considers all time scales, and its ultimate purpose is to account for differences in the structure and biological composition of aquatic ecosystems.However, one of the limitations of studies based on this approach is that, no matter how numerous they are, the variables used for regionalization do not constrain all flow characteristics, as required by the natural flow regime concept, so that application of this concept is incomplete. In addition, simultaneous analysis of all time scales does not allow consideration of all flow characteristics. To overcome these limitations, we propose a new regionalization approach based on the natural flow regime concept, an “ecogeographic” approach that differs from the ecologic approach in three ways. First, the proposed method is based on the use of flow characteristics rather than hydrologic variables. The reason for this is that there are an infinite number of hydrologic variables to define the five fundamental characteristics, making it impossible to account for all of them in the regionalization process. In contrast, since the number of fundamental flow characteristics is limited, they can all be taken into account, consistent with the “natural flow regime” requirements. Second, the ultimate purpose of the proposed regionalization method is to identify the physiographic and climatic factors that explain the spatial variability of these fundamental characteristics. To achieve this goal, it is necessary to analyze the different time scales (daily, monthly, annual) separately given the fact that it is impossible to constrain the effect of these various physiographic and climatic factors at all time scales. Indeed, some factors may show an effect at some time scales and not at others. This ultimate purpose addresses the concerns of geographers interested in explaining the spatial variability of such phenomena, among other things. Finally, separate analysis of the various time scales makes it possible to define all flow characteristics linked to a given time scale. As such, application of the “natural flow regime” concept to regionalization is complete.Application of the ecogeographical method involves four separate steps: 1) the definition of the flow characteristics for the hydrologic series of interest; 2) the determination of minor and major characteristics using principal component analysis, where a “major” flow characteristic is defined as one which meets the following criterion: TVE ≥ (100% / N), where N is the total number of characteristics that define the analyzed hydrologic series and TVE is the total variance explained; 3) the grouping of stations in homogeneous hydrologic regions based on factorial scores. Homogeneous hydrologic regions are divided in two types based on the presence or absence of stations: effective homogeneous regions contain stations whereas fictive homogenous regions do not; 4) the determination of the factors that affect the spatial variability of flow characteristics. This is achieved using canonical correlation analysis, an approach that we have applied to average annual flows in Quebec watersheds

Computation of the area in the discrete plane: Green’s theorem revisited

International audienceThe detection of the contour of a binary object is a common problem; however, the area of a region, and its moments, can be a significant parameter. In several metrology applications, the area of planar objects must be measured. The area is obtained by counting the pixels inside the contour or using a discrete version of Green's formula. Unfortunately, we obtain the area enclosed by the polygonal line passing through the centers of the pixels along the contour. We present a modified version of Green's theorem in the discrete plane, which allows for the computation of the exact area of a two-dimensional region in the class of polyominoes. Penalties are introduced and associated with each successive pair of Freeman displacements along the contour in an eight-connectivity system. The proposed equation is shown to be true and properties of the equation related to the topology of the regions are presented. The proposed approach is adapted for faster computation than the combinatorial approach proposed in the literature. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.DIGITAL PICTURES; POLYOMINOES; GEOMETR

Deep Underground Neutrino Experiment (DUNE), Far Detector Technical Design Report, Volume I Introduction to DUNE

International audienceThe preponderance of matter over antimatter in the early universe, the dynamics of the supernovae that produced the heavy elements necessary for life, and whether protons eventually decay—these mysteries at the forefront of particle physics and astrophysics are key to understanding the early evolution of our universe, its current state, and its eventual fate. The Deep Underground Neutrino Experiment (DUNE) is an international world-class experiment dedicated to addressing these questions as it searches for leptonic charge-parity symmetry violation, stands ready to capture supernova neutrino bursts, and seeks to observe nucleon decay as a signature of a grand unified theory underlying the standard model. The DUNE far detector technical design report (TDR) describes the DUNE physics program and the technical designs of the single- and dual-phase DUNE liquid argon TPC far detector modules. This TDR is intended to justify the technical choices for the far detector that flow down from the high-level physics goals through requirements at all levels of the Project. Volume I contains an executive summary that introduces the DUNE science program, the far detector and the strategy for its modular designs, and the organization and management of the Project. The remainder of Volume I provides more detail on the science program that drives the choice of detector technologies and on the technologies themselves. It also introduces the designs for the DUNE near detector and the DUNE computing model, for which DUNE is planning design reports. Volume II of this TDR describes DUNE's physics program in detail. Volume III describes the technical coordination required for the far detector design, construction, installation, and integration, and its organizational structure. Volume IV describes the single-phase far detector technology. A planned Volume V will describe the dual-phase technology

Deep Underground Neutrino Experiment (DUNE), Far Detector Technical Design Report, Volume II: DUNE Physics

The preponderance of matter over antimatter in the early universe, the dynamics of the supernovae that produced the heavy elements necessary for life, and whether protons eventually decay -- these mysteries at the forefront of particle physics and astrophysics are key to understanding the early evolution of our universe, its current state, and its eventual fate. DUNE is an international world-class experiment dedicated to addressing these questions as it searches for leptonic charge-parity symmetry violation, stands ready to capture supernova neutrino bursts, and seeks to observe nucleon decay as a signature of a grand unified theory underlying the standard model. The DUNE far detector technical design report (TDR) describes the DUNE physics program and the technical designs of the single- and dual-phase DUNE liquid argon TPC far detector modules. Volume II of this TDR, DUNE Physics, describes the array of identified scientific opportunities and key goals. Crucially, we also report our best current understanding of the capability of DUNE to realize these goals, along with the detailed arguments and investigations on which this understanding is based. This TDR volume documents the scientific basis underlying the conception and design of the LBNF/DUNE experimental configurations. As a result, the description of DUNE's experimental capabilities constitutes the bulk of the document. Key linkages between requirements for successful execution of the physics program and primary specifications of the experimental configurations are drawn and summarized. This document also serves a wider purpose as a statement on the scientific potential of DUNE as a central component within a global program of frontier theoretical and experimental particle physics research. Thus, the presentation also aims to serve as a resource for the particle physics community at large