Techniques for measuring aerosol attenuation using the Central Laser Facility at the Pierre Auger Observatory

The Pierre Auger Observatory in Malargüe, Argentina, is designed to study the properties of ultra-high energy cosmic rays with energies above 10(18) eV. It is a hybrid facility that employs a Fluorescence Detector to perform nearly calorimetric measurements of Extensive Air Shower energies. To obtain reliable calorimetric information from the FD, the atmospheric conditions at the observatory need to be continuously monitored during data acquisition. In particular, light attenuation due to aerosols is an important atmospheric correction. The aerosol concentration is highly variable, so that the aerosol attenuation needs to be evaluated hourly. We use light from the Central Laser Facility, located near the center of the observatory site, having an optical signature comparable to that of the highest energy showers detected by the FD. This paper presents two procedures developed to retrieve the aerosol attenuation of fluorescence light from CLF laser shots. Cross checks between the two methods demonstrate that results from both analyses are compatible, and that the uncertainties are well understood. The measurements of the aerosol attenuation provided by the two procedures are currently used at the Pierre Auger Observatory to reconstruct air shower data

Ultrahigh energy neutrinos at the Pierre Auger observatory

The observation of ultrahigh energy neutrinos (UHEνs) has become a priority in experimental astroparticle physics. UHEνs can be detected with a variety of techniques. In particular, neutrinos can interact in the atmosphere (downward-going ν) or in the Earth crust (Earth-skimming ν), producing air showers that can be observed with arrays of detectors at the ground. With the surface detector array of the Pierre Auger Observatory we can detect these types of cascades. The distinguishing signature for neutrino events is the presence of very inclined showers produced close to the ground (i.e., after having traversed a large amount of atmosphere). In this work we review the procedure and criteria established to search for UHEνs in the data collected with the ground array of the Pierre Auger Observatory. This includes Earth-skimming as well as downward-going neutrinos. No neutrino candidates have been found, which allows us to place competitive limits to the diffuse flux of UHEνs in the EeV range and above.P. Abreu ... K. B. Barber ... J. A. Bellido ... R. W. Clay ... M. J. Cooper ... B. R. Dawson ... T. A. Harrison ... A. E. Herve ... V. C. Holmes ... J. Sorokin ... P. Wahrlich ... B. J. Whelan ... et al

Suivi et modélisation à haute résolution des flux hydriques d’une toiture végétalisée

Green roofs are multifunctional type of Nature-Based Solutions that provide different ecosystem services among which the reduction and detention of the urban drainage outflow are the most important from the aspects of hydrology and stormwater management. As for various scientific fields, the issue of scales also appears as rather important scientific question in case of hydrology, and thus in case of green roofs. The idea behind it is to find a proper way of treating spatio-temporal variabilities of different processes involved in green roofs at larger scales, without masking heterogeneity characteristic for smaller scales. This is rather important for green roof designers, since the homogenization (averaging) in both space and time domain can impact the results of modeling significantly, providing unreliable insight into the hydrological performances of green roofs. This way, predictions of hydrological responses at larger urban (sub)catchment scales are also affected, which prevents from meeting regulation rules adopted by local authorities in charge of stormwater management.In order to improve reliability of hydrological predictions, various thorough investigations were performed on Green Wave, a green roof of the Bienvenüe building located close to Ecole des Ponts ParisTech, in suburban area of Paris. Firstly, different physical properties of the Green Wave substrate were measured in laboratory (specimen scale). The laboratory investigation of the hydraulic properties of the unsaturated / saturated Green Wave substrate, were carried out by means of the newly developed apparatus and the innovative methodology for determination of the hydraulic conductivity function.Furthermore, on the specimen scale, spatial variability of the soil density field obtained using X-ray CT scanner is analyzed using Universal Multifractals, a theoretical framework convenient for characterizing both spatial and temporal variabilities of different geophysical fields. As a result of the investigation, new methodology and analytical functions for describing different soil properties such as the grain / pore size distribution, water retention curve and the hydraulic conductivity function, are derived. The obtained analytical functions proved to be able to interpret rather well the experimentally determined properties of the Green Wave substrate, and other soil types taken from the literature.On the green roof scale, in-situ conditions were investigated using detailed monitoring system installed on Green Wave, where three main water balance components are measured: rainfall rate, water content indicator and drained discharge. Results showed that based on the multifractal analysis of temporal variabilities of three mentioned components, where the indicator of water content is measured by means of the network of TDR sensors distributed along the roof slope, it is possible to go beyond the standard investigation of the rainfall-runoff ration and to analyze the impact of roof inclination on the lateral water movement within the substrate. The mentioned analysis showed that the roof inclination does not affect the peak outflow, allowing development of a new one-dimensional analytical hydrological model.The proposed model is based on a cascade of non-linear reservoirs, where the leakage from each reservoir is described by means of the analytical function of hydraulic conductivity, also developed in this work. The model was proved as an adequate alternative for numerical solving of Richards equation in terms of accuracy and reliability, but also as a significant improvement from the aspect of computational efficiency. As such, it can be further used to efficiently treat spatial heterogeneity of green roofs at the scale of a single roof and larger, allowing reliable investigation of hydrological impacts of this type of Nature-Based Solutions on the urban catchment scale.Les toitures végétalisées représentent un type de solutions fondées sur la nature. Dans ce contexte, l’objectif de ces travaux de thèse est de trouver un moyen approprié de traiter les variabilités spatio-temporelles des différents processus hydrologiques mis en jeu à travers les échelles, sans masquer l'hétérogénéité caractérisant les échelles les plus fines. Ceci est important pour les concepteurs, car l'homogénéisation (dans l’espace et le temps) de ces processus dans un modèle peut avoir un impact significatif sur ses simulations, et produire des résultats peu fiables concernant les performances hydrologiques des toitures végétalisées. Afin d'améliorer la fiabilité des estimations réalisées à l’aide d’une modélisation hydrologique, diverses investigations ont été réalisées sur la Vague Verte de Champs-sur-Marne, une toiture végétalisée d’un hectare située à proximité de l'Ecole des Ponts ParisTech, en banlieue parisienne. Tout d'abord, différentes caractéristiques physiques du substrat ont été mesurées en laboratoire à l’échelle d'échantillons. La quantification des propriétés hydrauliques du substrat insaturé / saturé - et plus particulièrement la détermination de la fonction de conductivité hydraulique - a été réalisée au moyen d’une méthodologie et d'un appareil nouvellement développés à cette occasion. A l'échelle de l'échantillon, la variabilité spatiale du champ constitué par la densité du sol a été appréhendée à l'aide d'un microtomographe à rayons X. Les résultats ont ensuite été analysés dans le cadre des multifractals universels, particulièrement adapté pour caractériser les variabilités spatiales et temporelles de champs géophysiques complexes. Ces travaux ont permis de faire émerger de nouvelles méthodes et fonctions analytiques pour décrire les différentes propriétés du sol telles que la distribution granulométrique (ainsi que celle des pores), la courbe de rétention d'eau et la fonction de conductivité hydraulique. Ces nouvelles fonctions se sont avérées assez proches de celles issues des travaux effectués en laboratoire que ce soit pour le substrat de la vague verte, comme pour d'autres types de sols issus de la littérature. Á l'échelle de la vague verte, le comportement hydrologique de la structure a été étudié à l'aide du suivi expérimental continu des trois principales composantes du bilan hydrique : la précipitation, la teneur en eau (à l’aide d’un réseau de sondes TDR répartis le long de la pente) et le débit en sortie d’ouvrage. Ces mesures analysées à l’aide d'une nouvelle analyse multifractale conduite sur la variabilité temporelle de trois composantes, ont montré qu’il est possible d'aller au-delà dune simple quantification du coefficient de ruissellement et d'analyser l'impact de l'inclinaison du toit sur le mouvement latéral de l'eau à l'intérieur du substrat. Il en ressort que l'inclinaison du toit n'affecte pas le transfert de l’eau dans le substrat, permettant ainsi le développement d'un nouveau modèle hydrologique analytique unidimensionnel. Le modèle proposé repose sur une cascade de réservoirs non linéaires, où la sortie de chaque réservoir est décrite au moyen d’une fonction analytique de la conductivité hydraulique (également développée lors de ces travaux). Le modèle s'avère représenter une alternative intéressante pour la résolution numérique de l'équation de Richards en termes de précision et de fiabilité. Cette méthode entraine également une amélioration significative du temps de calcul. Ce modèle peut être utilisé pour tenir compte efficacement de l'hétérogénéité spatiale des toitures végétalisée à l'échelle du toit. Il doit aussi permettre de tenir compte de cette variabilité dans un bassin versant urbain et d’évaluer ainsi leur impact hydrologique à cette échell

High resolution monitoring and modelling of hydrologicial fluxes in a green roof

Les toitures végétalisées représentent un type de solutions fondées sur la nature. Dans ce contexte, l’objectif de ces travaux de thèse est de trouver un moyen approprié de traiter les variabilités spatio-temporelles des différents processus hydrologiques mis en jeu à travers les échelles, sans masquer l'hétérogénéité caractérisant les échelles les plus fines. Ceci est important pour les concepteurs, car l'homogénéisation (dans l’espace et le temps) de ces processus dans un modèle peut avoir un impact significatif sur ses simulations, et produire des résultats peu fiables concernant les performances hydrologiques des toitures végétalisées. Afin d'améliorer la fiabilité des estimations réalisées à l’aide d’une modélisation hydrologique, diverses investigations ont été réalisées sur la Vague Verte de Champs-sur-Marne, une toiture végétalisée d’un hectare située à proximité de l'Ecole des Ponts ParisTech, en banlieue parisienne. Tout d'abord, différentes caractéristiques physiques du substrat ont été mesurées en laboratoire à l’échelle d'échantillons. La quantification des propriétés hydrauliques du substrat insaturé / saturé - et plus particulièrement la détermination de la fonction de conductivité hydraulique - a été réalisée au moyen d’une méthodologie et d'un appareil nouvellement développés à cette occasion. A l'échelle de l'échantillon, la variabilité spatiale du champ constitué par la densité du sol a été appréhendée à l'aide d'un microtomographe à rayons X. Les résultats ont ensuite été analysés dans le cadre des multifractals universels, particulièrement adapté pour caractériser les variabilités spatiales et temporelles de champs géophysiques complexes. Ces travaux ont permis de faire émerger de nouvelles méthodes et fonctions analytiques pour décrire les différentes propriétés du sol telles que la distribution granulométrique (ainsi que celle des pores), la courbe de rétention d'eau et la fonction de conductivité hydraulique. Ces nouvelles fonctions se sont avérées assez proches de celles issues des travaux effectués en laboratoire que ce soit pour le substrat de la vague verte, comme pour d'autres types de sols issus de la littérature. Á l'échelle de la vague verte, le comportement hydrologique de la structure a été étudié à l'aide du suivi expérimental continu des trois principales composantes du bilan hydrique : la précipitation, la teneur en eau (à l’aide d’un réseau de sondes TDR répartis le long de la pente) et le débit en sortie d’ouvrage. Ces mesures analysées à l’aide d'une nouvelle analyse multifractale conduite sur la variabilité temporelle de trois composantes, ont montré qu’il est possible d'aller au-delà dune simple quantification du coefficient de ruissellement et d'analyser l'impact de l'inclinaison du toit sur le mouvement latéral de l'eau à l'intérieur du substrat. Il en ressort que l'inclinaison du toit n'affecte pas le transfert de l’eau dans le substrat, permettant ainsi le développement d'un nouveau modèle hydrologique analytique unidimensionnel. Le modèle proposé repose sur une cascade de réservoirs non linéaires, où la sortie de chaque réservoir est décrite au moyen d’une fonction analytique de la conductivité hydraulique (également développée lors de ces travaux). Le modèle s'avère représenter une alternative intéressante pour la résolution numérique de l'équation de Richards en termes de précision et de fiabilité. Cette méthode entraine également une amélioration significative du temps de calcul. Ce modèle peut être utilisé pour tenir compte efficacement de l'hétérogénéité spatiale des toitures végétalisée à l'échelle du toit. Il doit aussi permettre de tenir compte de cette variabilité dans un bassin versant urbain et d’évaluer ainsi leur impact hydrologique à cette échelleGreen roofs are multifunctional type of Nature-Based Solutions that provide different ecosystem services among which the reduction and detention of the urban drainage outflow are the most important from the aspects of hydrology and stormwater management. As for various scientific fields, the issue of scales also appears as rather important scientific question in case of hydrology, and thus in case of green roofs. The idea behind it is to find a proper way of treating spatio-temporal variabilities of different processes involved in green roofs at larger scales, without masking heterogeneity characteristic for smaller scales. This is rather important for green roof designers, since the homogenization (averaging) in both space and time domain can impact the results of modeling significantly, providing unreliable insight into the hydrological performances of green roofs. This way, predictions of hydrological responses at larger urban (sub)catchment scales are also affected, which prevents from meeting regulation rules adopted by local authorities in charge of stormwater management.In order to improve reliability of hydrological predictions, various thorough investigations were performed on Green Wave, a green roof of the Bienvenüe building located close to Ecole des Ponts ParisTech, in suburban area of Paris. Firstly, different physical properties of the Green Wave substrate were measured in laboratory (specimen scale). The laboratory investigation of the hydraulic properties of the unsaturated / saturated Green Wave substrate, were carried out by means of the newly developed apparatus and the innovative methodology for determination of the hydraulic conductivity function.Furthermore, on the specimen scale, spatial variability of the soil density field obtained using X-ray CT scanner is analyzed using Universal Multifractals, a theoretical framework convenient for characterizing both spatial and temporal variabilities of different geophysical fields. As a result of the investigation, new methodology and analytical functions for describing different soil properties such as the grain / pore size distribution, water retention curve and the hydraulic conductivity function, are derived. The obtained analytical functions proved to be able to interpret rather well the experimentally determined properties of the Green Wave substrate, and other soil types taken from the literature.On the green roof scale, in-situ conditions were investigated using detailed monitoring system installed on Green Wave, where three main water balance components are measured: rainfall rate, water content indicator and drained discharge. Results showed that based on the multifractal analysis of temporal variabilities of three mentioned components, where the indicator of water content is measured by means of the network of TDR sensors distributed along the roof slope, it is possible to go beyond the standard investigation of the rainfall-runoff ration and to analyze the impact of roof inclination on the lateral water movement within the substrate. The mentioned analysis showed that the roof inclination does not affect the peak outflow, allowing development of a new one-dimensional analytical hydrological model.The proposed model is based on a cascade of non-linear reservoirs, where the leakage from each reservoir is described by means of the analytical function of hydraulic conductivity, also developed in this work. The model was proved as an adequate alternative for numerical solving of Richards equation in terms of accuracy and reliability, but also as a significant improvement from the aspect of computational efficiency. As such, it can be further used to efficiently treat spatial heterogeneity of green roofs at the scale of a single roof and larger, allowing reliable investigation of hydrological impacts of this type of Nature-Based Solutions on the urban catchment scale

Measurement and characterization of space-time variability of thermo-hydric fluxes in Blue Green Solutions

International audienc

Water retention and transfer properties of a Green roof volcanic substrate

The water retention curve and the hydraulic conductivity function of a volcanic coarse granular material used as a substrate in an urban green roof in the Paris area was carried out on a newly developed device, in which low suctions were controlled. In the same cell, a hanging column system was used for controlling smaller suctions (up to 32 kPa) and the axis translation technique for larger suctions (up to 50 kPa). Water exchanges were monitored in connected tubes by using a high accuracy differential pressure transducer. The step changes in suction were also used to determine the hydraulic conductivity function by means of Gardner’s method, accounting for the impedance effects due to the high air entry value ceramic porous disk with Kunze and Kirkham’s method. van Genuchten and Brooks and Corey models were used for the water retention curve, but the hydraulic conductivity functions derived from these expressions appeared to lead to a significant under-estimation, confirming the need of operational and simple device for the experimental determination of the hydraulic conductivity function

Measurements of the water balance components of a large green roof in the greater Paris area

International audienceThe Blue Green Wave of Champs-sur-Marne (France) represents the largest green roof (1 ha) of the greater Paris area. The Hydrology, Meteorology and Complexity lab of École des Ponts ParisTech has chosen to convert this architectural building into a full-scale monitoring site devoted to studying the performance of green infrastructures in storm-water management. For this purpose, the relevant components of the water balance during a rainfall event have been monitored: rainfall, water content in the substrate, and the discharge flowing out of the infrastructure. Data provided by adapted measurement sensors were collected during 78 d between February and May 2018. The related raw data and a Python program transforming them into hydrological quantities and providing some preliminary elements of analysis have been made available. These measurements are useful to better understand the hydrological processes (infiltration and retention) conducting green roof performance and their spatial variability due to substrate heterogeneity. The data set is available here

Toward quantitative indicators to assess the cooling effect of Blue Green Solutions by combining experimental and modelling approaches

International audienc

Analysis of green roof's water balance components using Universal Multifractal (UM) framework

International audienc

Investigation of retention and transfer properties of green roofs: the Green Wave of Champs-sur-Marne (France)

International audienceOne of the main performances of green roofs is to reduce and/or delay urban runoff during the strong rainfall events.The substrate retention capacity and transfer properties is often described by the water retention and hydraulicconductivity curves. This work presents comparison between measured and different theoretical characteristicscurves, as well as determination of more reliable fractal based substrate model.Firstly, samples of organic volcanic substrate from wavy-form green roof of Champs-sur-Marne (France), calledthe Green Wave, were taken for detailed laboratory investigation. In order to simultaneously determine waterretention and hydraulic conductivity curves of this unconventional substrate, special device based on tensiometryand axis translation technique has been designed (Stanic et al, 2018). Then different (semi-)empirical and fractalbased theoretical curves were compared with results obtained in laboratory in order to determine the model thatrealistically describes green roof substrate’s characteristics curves. Models based on (multi-)fractal theory areproved to be able to describe characteristics curves by calibrating several physically based parameters. It wasshown that these models are able to fit better with water retention and hydraulic conductivity curves of the greenroof substrate than the common (semi-)empirical models.At the end we discuss why this kind of approach is very helpful for giving insight into the accuracy of theoreticalcurves in general, regarding both substrate characteristics curves. Also it gives an idea about the most realistictheoretical model, which is a very useful indicator for users and developers of rainfall-runoff models in widercontext. Indeed, taking into account the most accurate option to describe substrate characteristics curves will resultin more reliable runoff estimations