Producing time series of river water height by means of satellite radar altimetry—a comparative study     

Emmanuel Roux  Joecila Santos da Silva  Augusto Cesar Vieira Getirana  Marie-Paule Bonnet  Stéphane Calmant  Jean-Michel Martinez 《水文科学杂志》2013,58(1):104-120

Abstract

Satellite radar altimetry is complementary to in situ limnimetric surveys as a means of estimating the water height of large rivers, lakes and flood plains. Production of water height time series by satellite radar altimetry technology requires first the selection of radar ground target locations corresponding to water body surfaces under study, i.e. the definition of “virtual limnimetric stations”. We propose to investigate qualitative and quantitative differences between three representative virtual station creation methodologies: (a) a fully manual method, (b) a semi-automatic method based on a land cover characterization that allows the water body surface under study to be located; and (c) an original fully automatic procedure that exploits a digital elevation model and an estimation of the river width. The results yielded by these three methods are comparable: maximum absolute magnitudes of water height differences being 0.46, 0.26 and 0.15 m for, respectively, 95, 90 and 80% of the water height values obtained. Moreover, more than 67% and 92% of time series jointly produced by the methods present root mean square differences lower than 20 and 50 cm, respectively. The results show that the fully automatic method developed herein provides as reliable results as the fully manual one. This opens the way to use of satellite radar altimetry for the generation of water height time series on a large scale, and considerably extends the applicability of satellite radar altimetry in hydrology.

Citation Roux, E., Santos da Silva, J., Vieira Getirana, A. C., Bonnet, M.-P., Calmant, S., Martinez, J.-M. & Seyler, F. (2010) Producing time series of river water height by means of satellite radar altimetry—comparative study. Hydrol. Sci. J. 55(1), 104–120.  相似文献   

Out‐of‐plane behaviour of a full scale stone masonry façade. Part 1: specimen and ground motion selection     

Alexandre A. Costa  António Arêde  Alfredo Campos Costa  Andrea Penna  Aníbal Costa 《地震工程与结构动力学》2013,42(14):2081-2095

The out‐of‐plane response of walls in existing stone masonry buildings is one of the major causes of vulnerability commonly observed in post‐earthquake damage surveys. In this context, a shaking table (ST) test campaign was carried out on a full‐scale masonry façade mainly focusing on the characterization of its out‐of‐plane overturning behaviour. The structure tested on the ST is a partial reproduction of an existing building from Azores, damaged during the 9 July 1998 Faial earthquake. The definition of the tested specimen as well as the selection of the input ground motion is reported in this paper. A specific emphasis is given to the definition of the time‐history to be applied during the tests because it was felt as an essential and crucial part of the work to obtain the desired overturning behaviour. The accelerogram to be imposed was selected from a large set of accelerograms (74) by means of a step‐by‐step procedure on the basis of several numerical analyses resorting to the rocking response of rigid blocks. A companion paper (Part 2) focuses on the ST test results and detailed data interpretation. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Temporal evolution of lead isotope ratios in sediments of the Central Portuguese Margin: A fingerprint of human activities     

Mário Mil-Homens  Miguel Caetano  Ana M. Costa  Susana Lebreiro  Thomas Richter  Henko de Stigter  Maria A. Trancoso  Pedro Brito 《Marine pollution bulletin》2013

Stable Pb isotope ratios (²⁰⁶Pb/²⁰⁷Pb, ²⁰⁸Pb/²⁰⁶Pb), ²¹⁰Pb, Pb, Al, Ca, Fe, Mn and Si concentrations were measured in 7 sediment cores from the west coast of the Iberian Peninsula to assess the Pb contamination throughout the last 200 years. Independently of their locations, all cores are characterized by increasing Pb/Al rends not related to grain-size changes. Conversely, decreasing trends of ²⁰⁶Pb/²⁰⁷Pb were found towards the present. This tendency suggest a change in Pb sources reflecting an increased proportion derived from anthropogenic activities. The highest anthropogenic Pb inventories for sediments younger than 1950s were found in the two shallowest cores of Cascais and Lisboa submarine canyons, reflecting the proximity of the Tagus estuary. Lead isotope signatures also help demonstrate that sediments contaminated with Pb are not constrained to estuarine–coastal areas and upper parts of submarine canyons, but are also to transferred to a lesser extent to deeper parts of the Portuguese Margin.  相似文献   

Remaking South Beach: metropolitan gayborhood trajectories under homonormative entrepreneurialism     

Juan Miguel Kanai  Kai Kenttamaa-Squires 《Urban geography》2013,34(3):385-402

This paper contributes to research on metropolitan gayborhood trajectories and homonormative urban entrepreneurialism by assessing a South Florida case study. We probe allegations of gay men being displaced from South Beach and the opposing narrative of a sexually diverse city with undiminished appeal. To that end, we present expert informant interviews, participant observation, media archives, and census data showing that the remade gayborhood coexists and competes with other, more affordable LGBT nodes. While socioeconomic, demographic and cultural characteristics differentiate these clusters, exploratory spatial data analysis indicates that the majority of metropolitan same-sex households reside elsewhere. We acknowledge Miami Beach’s recent pro-equality efforts, yet argue that homonormative politics conditions them. Public–private actions adopt corporate formats, prioritizing tourist-oriented initiatives and spectacular events that promote nonthreatening, market-friendly forms of sexual dissidence. The conclusion discusses implications for queer community-building in metropolitan regions fragmented by socio-spatial inequality and competitive city-marketing catering to heterogeneous yet exclusive global audiences.  相似文献   

LAND SUBSIDENCE IN THE LOS BANOS–KETTLEMAN CITY AREA,CALIFORNIA: PAST AND FUTURE OCCURRENCE     

Hakan Başağaoğlu  Miguel A. Mariño  Tudor M. Botzan 《自然地理学》2013,34(1):67-82

Land subsidence in the western San Joaquin Valley has been studied and monitored for almost six decades. Especially in the 1950s and 1960s, land subsidence had tremendous negative environmental and socioeconomic implications. The rate of land subsidence in the Los Banos–Kettleman City area, however, has decreased during the last three decades as a result of a decrease in groundwater withdrawal, following the importation of surface water to the Valley in late 1960s. The land subsidence in the Valley potentially could be a serious issue if the existing surface water supplies cannot meet increasing water demands during future critical drought periods. In this respect, this paper proposes a preliminary analysis to predict magnitudes of subsidence for the period 2000 to 2040, based on historical occurrences. In this study, extrapolation from earlier subsidence is based on: (1) knowledge of recent post-drought records at extensometers, (2) assumption of a single time porosity scenario, and (3) the premise that pumpage from the confined aquifer gradually will decrease as a result of progressive water quality degradation. Predicted magnitudes of land subsidence in the Los Banos–Kettleman City area are expected to be in the range 0.5 to 4.0 m for the next 4 to 5 decades under the scenario considered in this paper. [Key words: subsidence, groundwater extraction, aquitard, inelastic compaction, active porosity, Los Banos-Kettleman City, California.]  相似文献   

Chironomid assemblages in cores from multiple water depths reflect oxygen-driven changes in a deep French lake over the last 150 years     

Victor Frossard  Laurent Millet  Valérie Verneaux  Jean-Philippe Jenny  Fabien Arnaud  Michel Magny  Jérôme Poulenard  Marie-Elodie Perga 《Journal of Paleolimnology》2013,50(3):257-273

We sampled modern chironomids at multiple water depths in Lake Annecy, France, before reconstructing changes in chironomid assemblages at sub-decadal resolution in sediment cores spanning the last 150 years. The lake is a large, deep (z_max = 65 m), subalpine waterbody that has recently returned to an oligotrophic state. Comparison between the water-depth distributions of living chironomid larvae and subfossil head capsules (HC) along three surface-sediment transects indicated spatial differences in the influence of external forcings on HC deposition (e.g. tributary effects). The transect with the lowest littoral influence and the best-preserved, depth-specific chironomid community characteristics was used for paleolimnological reconstructions at various water depths. At the beginning of the twentieth century, oxygen-rich conditions prevailed in the lake, as inferred from M. contracta-type and Procladius sp. at deep-water sites (i.e. cores from 56 to 65 m) and Paracladius sp. and H. grimshawi-type in the core from 30 m depth. Over time, chironomid assemblages in cores from all three water depths converged toward the dominance of S. coracina-type, indicating enhanced hypoxia. The initial change in chironomid assemblages from the deep-water cores occurred in the 1930s, at the same time that an increase in lake trophic state is inferred from an increase in total organic carbon (TOC) concentration in the sediment. In the 1950s, an assemblage change in the core from 30 m water depth reflects the rapid expansion of the hypoxic layer into the shallower region of the lake. Lake Annecy recovered its oligotrophic state in the 1990s. Chironomid assemblages, however, still indicate hypoxic conditions, suggesting that modern chironomid assemblages in Lake Annecy are decoupled from the lake trophic state. Recent increases in both TOC and the hydrogen index indicate that changes in pelagic functioning have had a strong indirect influence on the composition of the chironomid assemblage. Finally, the dramatic decrease in HC accumulation rate over time suggests that hypoxic conditions are maintained through a feedback loop, wherein the accumulation of (un-consumed) organic matter and subsequent bacterial respiration prevent chironomid re-colonization. We recommend study of sediment cores from multiple water depths, as opposed to investigation of only a single core from the deepest part of the lake, to assess the details of past ecological changes in large deep lakes.  相似文献   

Floods control the influence of environmental gradients on the diversity of zooplankton communities in a neotropical floodplain     

Nadson Ressyé Simões  Juliana Déo Dias  Clarice Maria Leal  Louizi de Souza Magalhães Braghin  Fábio Amodêo Lansac-Tôha  Cláudia Costa Bonecker 《Aquatic Sciences - Research Across Boundaries》2013,75(4):607-617

Floodplains show a high biodiversity due to their spatial heterogeneity and temporal variability, which are governed by environmental dynamics resulting from the flood pulse. We evaluated the importance of this driving force, the flood pulse, in the structuring of environmental gradients that influence species diversity in a neotropical floodplain. Gamma (γ) and alpha (α) zooplankton diversities were higher in the year with a typical flood pulse (2010), indicating that flood dynamics contributed to high diversity component values. We found significant relationships between α- and β-diversity and local environmental gradients, indicating that in years with a flood pulse, environmental filters might be the dominant mechanisms that structure the zooplankton community. Additive partitioning of γ-diversity showed that even in 2000 with atypical flood conditions, zooplankton diversities showed non-random patterns of spatial distribution and temporal variation in the floodplain. Our results indicate that the driving force of a floodplain can determine the spatial distribution of α- and β-diversity of aquatic communities owing to its primary effect on environmental filters. Therefore, if human activities that influence this driving force, such as water regulation, affect those environmental filters, floodplain biodiversity may decline.  相似文献   

Paying as the urban areas grow – implementing and managing urban development charges using a GIS application     

Jorge Baptista e Silva  Raquel Faria de Deus  José António Tenedório 《International journal of geographical information science》2013,27(9):1689-1705

Urban development charges (UDC) are considered relevant taxation instruments that can improve the economic sustainability of urban areas and the financial health of the respective local governments. The economic formulation and justification based on the ‘direct benefit principle,’ the ‘accountability principle,’ and the ‘proportionality principle’ requires a methodology that can be supported by a geographic information system (GIS) application. This article presents the research output of a real case study – the municipality of Aljezur, Portugal – and the fundamentals of the GIS tool that was designed. This GIS-based methodology comprises a multi-annual infrastructure capital plan and an accurate zoning map for spatial differentiation of values combining municipal-wide and site-specific approaches, following ‘pay as the urban areas grow’ perspective applied to urban development and new buildings. It requires data integration of the urban planning process with infrastructure and urban growth data in order to manage and monitor the computation of this charge over time, thereby increasing the accuracy, the objectivity and the clarity of the process. The results obtained show that this UDC-GIS application seems well adapted to small municipalities. Its possible replication and use in other contexts require adaptations derived from different urban and taxation policy options and from different legal, organizational, technological, and informational local systems.  相似文献   

UV Capabilities to Probe the Formation of Planetary Systems: From the ISM to Planets     

Ana I. Gómez De Castro  Alain Lecavelier  Miguel D'Avillez  Jeffrey L. Linsky  José Cernicharo 《Astrophysics and Space Science》2006,303(1-4):33-52

Planetary systems are angular momentum reservoirs generated during star formation. Solutions to three of the most important problems in contemporary astrophysics are needed to understand the entire process of planetary system formation: The physics of the ISM. Stars form from dense molecular clouds that contain ∼ 30% of the total interstellar medium (ISM) mass. The structure, properties and lifetimes of molecular clouds are determined by the overall dynamics and evolution of a very complex system – the ISM. Understanding the physics of the ISM is of prime importance not only for Galactic but also for extragalactic and cosmological studies. Most of the ISM volume (∼ 65%) is filled with diffuse gas at temperatures between 3000 and 300 000 K, representing about 50% of the ISM mass. The physics of accretion and outflow. Powerful outflows are known to regulate angular momentum transport during star formation, the so-called accretion–outflow engine. Elementary physical considerations show that, to be efficient, the acceleration region for the outflows must be located close to the star (within 1 AU) where the gravitational field is strong. According to recent numerical simulations, this is also the region where terrestrial planets could form after 1 Myr. One should keep in mind that today the only evidence for life in the Universe comes from a planet located in this inner disk region (at 1 AU) from its parent star. The temperature of the accretion–outflow engine is between 3000 and 10 ⁷ K. After 1 Myr, during the classical T Tauri stage, extinction is small and the engine becomes naked and can be observed at ultraviolet wavelengths. The physics of planet formation. Observations of volatiles released by dust, planetesimals and comets provide an extremely powerful tool for determining the relative abundances of the vaporizing species and for studying the photochemical and physical processes acting in the inner parts of young planetary systems. This region is illuminated by the strong UV radiation field produced by the star and the accretion–outflow engine. Absorption spectroscopy provides the most sensitive tool for determining the properties of the circumstellar gas as well as the characteristics of the atmospheres of the inner planets transiting the stellar disk. UV radiation also pumps the electronic transitions of the most abundant molecules (H ₂, CO, etc.) that are observed in the UV.Here we argue that access to the UV spectral range is essential for making progress in this field, since the resonance lines of the most abundant atoms and ions at temperatures between 3000 and 300 000 K, together with the electronic transitions of the most abundant molecules (H ₂, CO, OH, CS, S ₂, CO ₂ ⁺, C ₂, O ₂, O₃, etc.) are at UV wavelengths. A powerful UV-optical instrument would provide an efficient mean for measuring the abundance of ozone in the atmosphere of the thousands of transiting planets expected to be detected by the next space missions (GAIA, Corot, Kepler, etc.). Thus, a follow-up UV mission would be optimal for identifying Earth-like candidates.  相似文献   

On the effect of overshooting as predicted by the modelling of the pre-main-sequence evolution of a 2 M_⊙ star     

João P. Marques  Mário J. P. F. G. Monteiro  João Fernandes 《Monthly notices of the Royal Astronomical Society》2006,371(1):293-302

We discuss the effects of convective overshooting in the pre-main-sequence (PMS) evolution of intermediate-mass stars, by analysing in detail the early evolution towards the main sequence of a  2 M_⊙  stellar model. These effects can be extremely important in the end of the PMS, when the abundances in CNO elements approach the equilibrium in the centre. We provide a possible physical explanation on why a moderate amount of overshooting produces, as the star approaches the zero-age main-sequence, an extra loop in the evolutionary tracks on the Hertzsprung–Russell diagram.
An interesting feature is that there is a very well defined amount of overshooting (for a given stellar mass and chemical composition) beyond which a loop is produced. For smaller amounts of overshooting such a loop does not take place and the evolutionary tracks are similar to those found in the literature. The amount of overshooting needed to produce the loop decreases with stellar mass.
We discuss the underlining physical reasons for the behaviour predicted by the evolution models and argue that it provides a crucial observational test for convective overshooting in the core of intermediate-mass stars.  相似文献