132 research outputs found

    Lake and River Ice Investigations in Northern Manitoba Using Airborne SAR Imagery

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    Multichannel airborne SAR data were collected over northern Manitoba in April 1989 and January 1990. During the week of the SAR flights, several reconnaissance helicopter flights were undertaken, and ground calibration sites were visited to collect ice, snow, and water data. A total of six SAR image passes were flown in April 1989 and seven in January 1990, in order to collect a data set with numerous incidence angle, frequency, polarization, and look direction combinations. The data have been qualitatively assessed, with specific emphasis on C-band horizontally polarized imagery - the proposed SAR configuration for Radarsat. Results of the analysis have shown that airborne SAR can be used to identify various freshwater ice features, such as juxtaposition ice, refrozen slush, river ice runs, and lake ice. Open water leads were also successfully identified. A careful interpretation of the airborne SAR imagery in conjunction with the ground truth data has shown that the unusually bright returns characterizing the Burntwood River and the west portion of Split Lake were caused by a layer of refrozen slush that was generated during the initial formation of the ice cover. Although the results reported here focused exclusively on a qualitative analysis of C-HH data, preliminary analysis of the digital data suggests that changes in frequency and polarization produce measurable differences and can be used to develop classification algorithms for freshwater ice.Key words: synthetic aperture radar, fresh water iceMots clés: radar à antenne synthétique, glace d’eau douc

    Le QuĂ©bec rĂ©cemment frappĂ© par les crues extrĂȘmes : une manifestation des changements climatiques?

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    Les printemps 2017 et 2019 auront frappĂ© l’imaginaire collectif en raison de l’ampleur des crues ayant touchĂ© de nombreuses riviĂšres du QuĂ©bec et des dommages qui leur sont associĂ©s. En 2019, prĂšs de 6700 rĂ©sidences localisĂ©es dans 51 municipalitĂ©s et distribuĂ©es dans presque toutes les principales rĂ©gions du QuĂ©bec ont Ă©tĂ© inondĂ©es, sans compter les nombreuses autres rĂ©sidences qui se sont retrouvĂ©es isolĂ©es en raison de routes submergĂ©es et de glissements de terrain. Le bilan en 2017 Ă©tait similaire, avec 5371 maisons inondĂ©es dans 261 municipalitĂ©s et 4066 personnes Ă©vacuĂ©es. Les dĂ©bits dans plusieurs riviĂšres ont excĂ©dĂ© les valeurs mesurĂ©es depuis que les stations de jaugeage ont Ă©tĂ© installĂ©es. À titre d’exemple, en 2019, le dĂ©bit journalier dans la riviĂšre Rouge Ă  la hauteur du Barrage de la Chute-Bell, oĂč Hydro-QuĂ©bec a craint pour la stabilitĂ© de l’ouvrage, a atteint 975 m3/s, la plus forte valeur jamais enregistrĂ©e depuis 1964. Une analyse statistique rĂ©vĂšle qu’un tel dĂ©bit a une chance d’ĂȘtre dĂ©passĂ© en moyenne une fois tous les 175 ans. Il s’agit d’un Ă©vĂ©nement exceptionnel. Pourtant, un autre Ă©vĂ©nement extrĂȘme se produisait au mĂȘme endroit en 1998, cette fois-ci avec un dĂ©bit maximal journalier de 914 m3/s. Deux crues printaniĂšres majeures en 20 ans : est-ce la consĂ©quence des changements climatiques ? Cet article propose une genĂšse des Ă©vĂ©nements hydrologiques extrĂȘmes, puis prĂ©sente des projections climatiques aux horizons 2050 et 2080 pour diffĂ©rentes riviĂšres au Sud et au Nord du fleuve Saint-Laurent. Puis, est exposĂ©e la dĂ©marche gĂ©nĂ©rale employĂ©e pour caractĂ©riser le rĂ©gime hydrologique des bassins versants en climat futur

    Economic Evaluation of Conservation Concepts for Municipal Water Systems

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    Five concepts for conservation of municipal water supply are analyzed from an economic efficiency perspectice. They include: 1) seasonal pricing (for reduction of peak period water use), 2) dual water systems (separate high quality drinking water and untreated outdoor irrigation systems), 3) imported water transmission facility capacity optimization, 4) flow restricting devices, and 5) short-term rationing concepts. Optimization models, including generalized model generators, were developed for analysis of the first three concepts and demonstrated by applications to cities in Utah. The flow restricting device and short-term rationsing concept analyses applied approaches taken from the literature to example sites in Utah. The final chapter is a comparison of results and summary of conditions which favor each approach to conservation. Conclusions include: Seasonal pricing was demonstarted to reduce peak period water use but is not justified in Salt Lake City because the added cost of metering exceeds the additional benefits. Dual water systems are potentially an important concept for matching various qualities of water with appropriate uses and producing net economic benefits. Determination of capacity of an imported water facility is dominated more by the decision maker\u27s attitude toward risk than by pricing policy. Flow restricting devices produce economic benefits only if the change in quality of service is ignored. Price elasticity is much lower during a drought than during normal conditions

    Flood monitoring over the Mackenzie River Basin using passive microwave data.

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    Abstract Flooding over the Mackenzie River Basin, which is situated in northwestern Canada, is a complex and rapid process. This process is mainly controlled by the occurrence of ice jams. Flood forecasting is of very important in mitigating social and economic damage. This study investigates the potential of a rating curve model for flood forecasting. The proposed approach is based on the use of a Water Surface Fraction derived from SSM/I passive microwave images and discharge observations. The rating curve model is based on an existing correlation between flooded areas and measured discharge. However, a time lag can be observed between these two variables. Thus, the rating curve model has been modified by the introduction of a lag term that could vary depending on the flooding intensity and the features of the basin. Hence, the lag term is computed dynamically using a cross-correlation function between Water Surface Fraction values which are derived from SSM/I observations and the discharge vectors. The rating curve model is based on two empirical parameters that depend on the site features, which vary in both space and time. To overcome this dependency, the rating curve model was linked to a Kalman filter in order to dynamically estimate the empirical parameters according to the forecasting errors encountered at each time step. With the Kalman filter, the dynamic rating curve model continuously readjusts its parameters to satisfy the non-stationary behavior of hydrological processes. The model is thus sufficiently flexible and adapted to various conditions. Simulations were carried out over the Mackenzie River Basin (1.8 million km 2 ) during the summers of 1998 and 1999. NOAA-AVHRR images were used to validate the forecast WSF values. The predicted flooded areas agree well with those derived from the NOAA-AVHRR images. Further simulations were carried out from 1992 to 2000 using the rating curve model to predict discharge at a downstream location. Even though an interannual variability of the water surface fractions was observed over the PAD area, the modified model was sufficiently flexible to be readjusted and to reproduce satisfactory results. This implies that a combination of passive microwave data and discharge observations presents an interesting potential in flood and discharge prediction.

    Hydrodynamic modelling and the dispersion of water fecal contaminants in current and future climates

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    10 p.International audienceDuring precipitation events in regions with combined sewers, overflows can occur upstream of drinking water treatment plants. The purpose of the research was to model the transport and propagation of pathogens and pharmaceuticals in the RiviĂšre Des Prairies during flood and low flow events. The water quality is quantified in terms of the behaviour of the river, the interactions of contaminants with the environment and the impacts of climate change. Hydrosim was used for hydrodynamic modeling; Dispersim was used to model the dispersion of contaminants. The impact of climate change was represented by the change of flow in the river. To do so, simulations were performed using Hydrotel, a hydrologic model applied to the Ottawa River. Thus, the impact of dispersion and diffusion of contaminants on the water quality were analyzed to determine the potential impact on raw water quality. Water quality will be affected by lower flows and heavy rains, which will change the frequency distributions of fecal contaminants upon which microbial risk models are based

    L'adaptation de la gestion des barrages aux changements climatiques

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    La gestion des barrages implique la prise en compte de nombreuses contraintes afin de veiller Ă  l’équilibre de l’ensemble du territoire. Les changements climatiques, avec leurs multiples impacts sur les plans d’eau, exercent une pression sur cet Ă©quilibre et accentuent, dans certains cas, les conflits dĂ©jĂ  prĂ©sents. Dans ce contexte, le projet « Acclimatons-nous » rĂ©pond Ă  la fois au besoin d’une gestion adaptĂ©e et intĂ©grĂ©e de trois barrages dans le sud du QuĂ©bec (Jules-Allard, North Hatley et Montjoie) et au besoin de gestion des risques rĂ©siduels, liĂ©s aux impacts des changements climatiques, qui ne peuvent ĂȘtre internalisĂ©s dans les plans de gestion des barrages. Le projet, de type « living lab », fournit aux communautĂ©s locales les informations scientifiques et les outils de gouvernance leur permettant de renforcer, Ă  court et long termes, leur capacitĂ© d’adaptation aux changements climatiques

    The Lyot Project Direct Imaging Survey of Substellar Companions: Statistical Analysis and Information from Nondetections

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    The Lyot project used an optimized Lyot coronagraph with Extreme Adaptive Optics at the 3.63m Advanced Electro-Optical System telescope (AEOS) to observe 86 stars from 2004 to 2007. In this paper we give an overview of the survey results and a statistical analysis of the observed nondetections around 58 of our targets to place constraints on the population of substellar companions to nearby stars. The observations did not detect any companion in the substellar regime. Since null results can be as important as detections, we analyzed each observation to determine the characteristics of the companions that can be ruled out. For this purpose we use a Monte Carlo approach to produce artificial companions, and determine their detectability by comparison with the sensitivity curve for each star. All the non-detection results are combined using a Bayesian approach and we provide upper limits on the population of giant exoplanets and brown dwarfs for this sample of stars. Our nondetections confirm the rarity of brown dwarfs around solar-like stars and we constrain the frequency of massive substellar companions (M>40Mjup) at orbital separation between and 10 and 50 AU to be <20%.Comment: 32 pages, 11 figures, 2 tables. Published in the Astrophysical Journa

    Exoplanet phase curves: observations and theory

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    Phase curves are the best technique to probe the three dimensional structure of exoplanets' atmospheres. In this chapter we first review current exoplanets phase curve observations and the particular challenges they face. We then describe the different physical mechanisms shaping the atmospheric phase curves of highly irradiated tidally locked exoplanets. Finally, we discuss the potential for future missions to further advance our understanding of these new worlds.Comment: Fig.5 has been updated. Table 1 and corresponding figures have been updated with new values for WASP-103b and WASP-18b. Contains a table sumarizing phase curve observation

    Effects of the oral endothelin-receptor antagonist bosentan on echocardiographic and doppler measures in patients with pulmonary arterial hypertension

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    OBJECTIVES The purpose of this study was to investigate the effects of bosentan (125 or 250 mg twice daily) on echocardiographic and Doppler variables in 85 patients with World Health Organization class III or IV pulmonary arterial hypertension (PAH). BACKGROUND Bosentan, an orally active dual endothelin-receptor antagonist, improves symptoms, exercise capacity, and hemodynamics in patients with PAH. METHODS Patients had primary pulmonary hypertension (84%) or PAH associated with connective tissue disease. Of these, 29 patients received placebo and 56 received bosentan (1:2 randomization). Six-minute walk tests and echocardiograms were performed at baseline and after 16 weeks of treatment. RESULTS Baseline characteristics were similar in the placebo and bosentan groups, and echocardiographic and Doppler findings were consistent with marked abnormalities of right ventricular (RV) and left ventricular (LV) structure and function that were due to PAH. The treatment effect on 6-min walking distance was 37 m in favor of bosentan (p = 0.036). Treatment effects of bosentan compared with placebo on other parameters were as follows: Doppler-derived cardiac index = + 0.4 l/min/m2(p = 0.007), LV early diastolic filling velocity = + 10.5 cm/s (p = 0.003), LV end-diastolic area = + 4.2 cm2(p = 0.003), LV systolic eccentricity index = -0.12 (p = 0.047), RV end-systolic area = -2.3 cm2(p = 0.057), RV:LV diastolic areas ratio = -0.64 (p = 0.007), Doppler RV index = -0.06 (p = 0.03), and percentage of patients with an improvement in pericardial effusion score = 17% (p = 0.05). CONCLUSIONS Bosentan improves RV systolic function and LV early diastolic filling and leads to a decrease in RV dilation and an increase in LV size in patients with PAH

    A chemical survey of exoplanets with ARIEL

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    Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 ÎŒm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio
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