排序方式： 共有34条查询结果，搜索用时 312 毫秒
11.
Zhi Zhang Hossein Ghaffarian Bruce MacVicar Lise Vaudor Aurélie Antonio Kristell Michel Hervé Piégay 《地球表面变化过程与地形》2021,46(4):822-836
Wood flux (piece number per time interval) is a key parameter for understanding wood budgeting, determining the controlling factors, and managing flood risk in a river basin. Quantitative wood flux data is critically needed to improve the understanding of wood dynamics and estimate wood discharge in rivers. In this study, the streamside videography technique was applied to detect wood passage and measure instantaneous rates of wood transport. The goal was to better understand how wood flux responds to flood and wind events and then predict wood flux. In total, one exceptional wind and seven flood events were monitored on the Ain River, France, and around 24,000 wood pieces were detected visually. It is confirmed that, in general, there is a threshold of wood motion in the river equal to 60% of bankfull discharge. However, in a flood following a windy day, no obvious threshold for wood motion was observed, which confirms that wind is important for the preparation of wood for transport between floods. In two multi-peak floods, around two-thirds of the total amount of wood was delivered on the first peak, which confirms the importance of the time between floods for predicting wood fluxes. Moreover, we found an empirical relation between wood frequency and wood discharge, which is used to estimate the total wood amount produced by each of the floods. The data set is then used to develop a random forest regression model to predict wood frequency as a function of three input variables that are derived from the flow hydrograph. The model calculates the total wood volume either during day or night based on the video monitoring technique for the first time, which expands its utility for wood budgeting in a watershed. A one-to-one link is then established between the fraction of detected pieces of wood and the dimensionless parameter “passing time × frame rate ”, which provides a general guideline for the design of monitoring stations. 相似文献
12.
Maria Norman Anna Rutgersson Lise Lotte Sørensen Erik Sahlée 《Boundary-Layer Meteorology》2012,144(3):379-400
The most direct method for flux estimation uses eddy covariance, which is also the most commonly used method for land-based measurements of surface fluxes. Moving platforms are frequently used to make measurements over the sea, in which case motion can disturb the measurements. An alternative method for flux estimation should be considered if the effects of platform motion cannot be properly corrected for. Three methods for estimating CO2 fluxes are studied here: the eddy-covariance, the inertial-dissipation, and the cospectral-peak methods. High-frequency measurements made at the land-based Östergarnsholm marine station in the Baltic Sea and measurements made from a ship during the Galathea 3 expedition are used. The Kolmogorov constant for CO2, used in the inertial-dissipation method, is estimated to be 0.68 and is determined using direct flux measurements made at the Östergarnsholm site. The cospectral-peak method, originally developed for neutral stratification, is modified to be applicable in all stratifications. With these modifications, the CO2 fluxes estimated using the three methods agree well. Using data from the Östergarnsholm site, the mean absolute error between the eddy-covariance and inertial-dissipation methods is 0.25 μmol m?2 s?1. The corresponding mean absolute error between the eddy-covariance and cospectral-peak methods is 0.26 μmol m?2 s?1, while between the inertial-dissipation and cospectral-peak methods it is 0.14 μmol m?2 s?1. 相似文献
13.
Summer algal blooms in a coastal ecosystem: the role of atmospheric deposition versus entrainment fluxes 总被引：2，自引：1，他引：2
Jacob Carstensen Lise Marie Frohn Charlotte Bay Hasager Bo G. Gustafsson 《Estuarine, Coastal and Shelf Science》2005,62(4):595-608
The nitrogen inputs from atmospheric deposition and bottom water entrainment to the surface layer were modelled in the summer period (May–September) over a 11-year period (1989–1999) and compared to investigate the significance of these fluxes for generating blooms in the Kattegat. In the summer periods the average atmospheric deposition was 2.81 mg N m−2 d−1 compared to average entrainment fluxes of 5.42 mg N m−2 d−1, 1.21 mg N m−2 d−1 and 1.15 mg N m−2 d−1 for the northern, central and southern part of the Kattegat, respectively. Atmospheric nitrogen deposition alone could not sustain biomass increases associated with observed blooms and entrainment fluxes dominated the high nitrogen inputs to the surface layer. The potential for a bloom through growth was typically obtained after several days of high nitrogen inputs from entrainment in the frontal area of the northern Kattegat and to some extent from atmospheric deposition. The modelled nitrogen input in this area could account directly for 30% of the observed blooms in the Northern sub-basin, and through advective transport 24% and 19% of the observed blooms in the central and southern Kattegat. The direct nitrogen inputs through atmospheric deposition and entrainment to the central and southern sub-basins were small and could not be linked to any bloom observation. 相似文献
14.
Sebastin F. Snchez Begoa García-Lorenzo Knud Jahnke Evencio Mediavilla Jos Ignacio Gonzlez-Serrano Lise Christensen Lutz Wisotzki 《New Astronomy Reviews》2006,49(10-12):501
We have developed a new technique to decouple the spectra of the host and the nucleus of type I AGNs using integral field spectroscopy data. The technique is a simple extension of methods widely tested in 2D imaging. We present here the results from applying the technique to data taken with INTEGRAL at the 4.2 m William Herschel Telescope on the Seyfert 1 radio-galaxy 3C 120. We obtained, for the first time, a clean spectrum of the host galaxy, without contamination from the nuclear source. 相似文献
15.
Anne‐Lise Montreuil Joanna E. Bullard Jim H. Chandler Jon Millett 《地球表面变化过程与地形》2013,38(15):1851-1868
Embryo dunes are often ephemeral, but can develop to become established coastal foredunes. In 2001 a patch of embryo dunes 13.11 m2 appeared on a beach in north Lincolnshire, UK and had expanded to over 3600 m2 by 2011. The rate of expansion is linked to storm occurrence, where expansion is slowed during years with a higher incidence of storm surges. From July 2009–October 2010 seasonal changes in dune field topography were determined using terrestrial laser scanning (TLS) data. Vegetation is important in the development of embryo dunes, but can cause errors in TLS data. Tests evaluating the impact of vegetation on the TLS data suggest the minimum elevation value from the TLS point cloud within a 0.05 m grid cell gives a good approximation of the ground surface. Digital elevation models (DEMs) of the dunes constructed using filtered data showed the embryo dunes underwent a classic seasonal cycle of erosion during the winter and accretion during the summer. For example from October 2009 to April 2010 over 375 m3 of sediment was eroded from the dunes whereas during spring and summer 2010 the dune field gained over 600 m3 of sand. The overall magnitude of change in dune height and volume from season to season exceeded the errors associated with the construction of the DEM from the TLS data and the vegetation filtering process, which suggests TLS can be useful for documenting topographic change in vegetated dunes. After 10 years, the patch of embryo dunes is still expanding but has not yet merged with more established foredunes to landward. Aeolian process measurements indicate that, at present, the embryo dunes do not prevent sand from reaching the foredunes, however the rate of foredune progradation has slowed concurrently with the expansion of the embryo dune field. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
16.
We evaluate three categories of variables for explaining the spatial pattern of warming and cooling trends over land: predictions of general circulation models (GCMs) in response to observed forcings; geographical factors like latitude and pressure; and socioeconomic influences on the land surface and data quality. Spatial autocorrelation (SAC) in the observed trend pattern is removed from the residuals by a well-specified explanatory model. Encompassing tests show that none of the three classes of variables account for the contributions of the other two, though 20 of 22 GCMs individually contribute either no significant explanatory power or yield a trend pattern negatively correlated with observations. Non-nested testing rejects the null hypothesis that socioeconomic variables have no explanatory power. We apply a Bayesian Model Averaging (BMA) method to search over all possible linear combinations of explanatory variables and generate posterior coefficient distributions robust to model selection. These results, confirmed by classical encompassing tests, indicate that the geographical variables plus three of the 22 GCMs and three socioeconomic variables provide all the explanatory power in the data set. We conclude that the most valid model of the spatial pattern of trends in land surface temperature records over 1979–2002 requires a combination of the processes represented in some GCMs and certain socioeconomic measures that capture data quality variations and changes to the land surface. 相似文献
17.
Giloy Nathalie Hamdi Yasser Bardet Lise Garnier Emmanuel Duluc Claire-Maire 《Natural Hazards》2019,98(3):869-893
Natural Hazards - As instrumental records often cover only short time periods, historical information is the main source of data in order to extend natural disaster catalogs. This study... 相似文献
18.
Many highly productive marine ecosystems exhibit nitrogen limitation or co-limitation. This article is a status review of research into the exchange of nitrogen between the atmosphere and these ecosystems with a particular focus on reactive nitrogen compounds. A summary of research conducted over the past ten years is presented and a perspective given as to remaining uncertainities and research needs. Looking toward development of coastal management modeling tools, we illustrate the processes that need to be resolved in order to accurately simulate the flux from the atmosphere and provide guidance on the required resolution of such models. 相似文献
19.
Herslund Lise Byskov Jalayer Fatemeh Jean-Baptiste Nathalie J&#;rgensen Gertrud Kabisch Sigrun Kombe Wilbard Lindley Sarah Nyed Patrik Karlsson Pauleit Stephan Printz Andreas Vedeld Trond 《Natural Hazards》2015,82(2):149-172
In this paper, we develop and apply a multi-dimensional vulnerability assessment framework for understanding the impacts of climate change-induced hazards in Sub-Saharan African cities. The research was carried out within the European/African FP7 project CLimate change and Urban Vulnerability in Africa, which investigated climate change-induced risks, assessed vulnerability and proposed policy initiatives in five African cities. Dar es Salaam (Tanzania) was used as a main case with a particular focus on urban flooding. The multi-dimensional assessment covered the physical, institutional, attitudinal and asset factors influencing urban vulnerability. Multiple methods were applied to cover the full range of vulnerabilities and to identify potential response strategies, including: model-based forecasts, spatial analyses, document studies, interviews and stakeholder workshops. We demonstrate the potential of the approach to assessing several dimensions of vulnerability and illustrate the complexity of urban vulnerability at different scales: households (e.g., lacking assets); communities (e.g., situated in low-lying areas, lacking urban services and green areas); and entire cities (e.g., facing encroachment on green and flood-prone land). Scenario modeling suggests that vulnerability will continue to increase strongly due to the expected loss of agricultural land at the urban fringes and loss of green space within the city. However, weak institutional commitment and capacity limit the potential for strategic coordination and action. To better adapt to urban flooding and thereby reduce vulnerability and build resilience, we suggest working across dimensions and scales, integrating climate change issues in city-level plans and strategies and enabling local actions to initiate a ‘learning-by-doing’ process of adaptation.
相似文献20.
Annelise Tran Flavie Goutard Lise Chamaillé Nicolas Baghdadi Danny Lo Seen 《International Journal of Applied Earth Observation and Geoinformation》2010
Recent studies have highlighted the potential role of water in the transmission of avian influenza (AI) viruses and the existence of often interacting variables that determine the survival rate of these viruses in water; the two main variables are temperature and salinity. 相似文献