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Continuous monitoring of bed shear stress in large river systems may serve to better estimate alluvial sediment transport to the coastal ocean.Here we explore the possibility of using a horizontally deployed acoustic Doppler current profiler(ADCP) to monitor bed shear stress,applying a prescribed boundary layer model,previously used for discharge estimation.The model parameters include the local roughness length and a dip correction factor to account for sidewall effects.Both these parameters depend on river stage and on the position in the cross-section, and were estimated from shipborne ADCP data.We applied the calibrated boundary layer model to obtain bed shear stress estimates over the measuring range of the HADCP.To validate the results,co-located coupled ADCPs were used to infer bed shear stress,both from Reynolds stress profiles and from mean velocity profiles. From HADCP data collected over a period of 1.5 years,a time series of width profiles of bed shear stress was obtained for a tidal reach of the Mahakam River,East Kalimantan,Indonesia.A smaller dataset covering 25 hours was used for comparison with results from the coupled ADCPs.The bed shear stress estimates derived from Reynolds stress profiles appeared to be strongly affected by local effects causing upflow and downflow,which are not included in the boundary layer model used to derive bed shear stress with the horizontal ADCP.Bed shear stresses from the coupled ADCP are representative of a much more localized flow,while those derived with the horizontal ADCP resemble the net effect of the flow over larger scales.Bed shear stresses obtained from mean velocity profiles from the coupled ADCPs show a good agreement between the two methods,and highlight the robustness of the method to uncertainty in the estimates of the roughness length. 相似文献
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华北北部古生代大陆地壳增生过程中的岩浆作用与成矿效应 总被引：13，自引：7，他引：6
包括前寒武纪克拉通与显生宙造山带两大构造单元的华北北部,古生代时期板块构造体制下古亚洲洋的裂解-扩展-消亡与汇聚大陆边缘的俯冲-碰撞-伸展循环构成了其大陆地壳增生与再造演化的基本图景,并形成了一系列记录这些因果演变连续过程的岩浆侵入与喷发事件。这些物质记录无疑是研究汇聚大陆边缘壳-幔作用和物质交换、大陆地壳演化与大规模成矿作用耦合关系的绝佳窗口。本文在系统总结最近几年积累的年代学和岩石地球化学资料的基础上,以一些带有特定过程印记的标志性岩浆事件为纲领,表征这些古生代岩浆作用形成过程中的地球动力学演变,揭示其所记录的华北北部大陆地壳的多阶段增生与再造演化机制,并初步探讨了有利地球动力学过程制约下的岩浆行为引起的成矿物质聚集效应。 相似文献
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Industrial pollution at Bagnoli (Naples, Italy): benthic foraminifera as a tool in integrated programs of environmental characterisation 总被引：1，自引：1，他引：0
Romano E Bergamin L Finoia MG Carboni MG Ausili A Gabellini M 《Marine pollution bulletin》2008,56(3):439-457
In the 20th century an important industrial plant operated on the coastal area of Bagnoli. After its closing, an integrated study of environmental characterisation aimed at restoration started. The survey conducted was based on chemical and sedimentological analyses integrated with benthic foraminifera analyses. Statistical analysis of the data shows sectors with a distinct type and degree of pollution. Particularly, pollution linked to the silty sediment fraction, mainly due to Pb and Zn, was recognised in front of the southern sector of the plant. The study of benthic foraminifera provides evidence for a pollution-tolerant character in some species like Haynesina germanica and Quinqueloculina parvula. In addition, two species among the 113 recognised show high percentages of abnormal specimens. These percentages show a statistical correlation with some pollutants (PAHs, Mn, Pb and Zn). In addition, Energy Dispersive Spectrometry shows small amounts of Fe ions included in deformed tests of Miliolinella subrotunda. Because the number of these deformations is positively correlated to the concentration of PAHs, Mn and Zn, the inability of some specimens to exclude the foreign elements from the crystalline reticulum of the test could be attributed to the potential toxic effect of these pollutants. 相似文献
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Hugh Eva Silvia Carboni Frédéric Achard Nicolas Stach Laurent Durieux Jean-François Faure Danilo Mollicone 《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(2):191-197
A global systematic sampling scheme has been developed by the UN FAO and the EC TREES project to estimate rates of deforestation at global or continental levels at intervals of 5 to 10 years. This global scheme can be intensified to produce results at the national level. In this paper, using surrogate observations, we compare the deforestation estimates derived from these two levels of sampling intensities (one, the global, for the Brazilian Amazon the other, national, for French Guiana) to estimates derived from the official inventories. We also report the precisions that are achieved due to sampling errors and, in the case of French Guiana, compare such precision with the official inventory precision.We extract nine sample data sets from the official wall-to-wall deforestation map derived from satellite interpretations produced for the Brazilian Amazon for the year 2002 to 2003. This global sampling scheme estimate gives 2.81 million ha of deforestation (mean from nine simulated replicates) with a standard error of 0.10 million ha. This compares with the full population estimate from the wall-to-wall interpretations of 2.73 million ha deforested, which is within one standard error of our sampling test estimate. The relative difference between the mean estimate from sampling approach and the full population estimate is 3.1%, and the standard error represents 4.0% of the full population estimate.This global sampling is then intensified to a territorial level with a case study over French Guiana to estimate deforestation between the years 1990 and 2006. For the historical reference period, 1990, Landsat-5 Thematic Mapper data were used. A coverage of SPOT-HRV imagery at 20 m × 20 m resolution acquired at the Cayenne receiving station in French Guiana was used for year 2006.Our estimates from the intensified global sampling scheme over French Guiana are compared with those produced by the national authority to report on deforestation rates under the Kyoto protocol rules for its overseas department. The latter estimates come from a sample of nearly 17,000 plots analyzed from same spatial imagery acquired between year 1990 and year 2006. This sampling scheme is derived from the traditional forest inventory methods carried out by IFN (Inventaire Forestier National). Our intensified global sampling scheme leads to an estimate of 96,650 ha deforested between 1990 and 2006, which is within the 95% confidence interval of the IFN sampling scheme, which gives an estimate of 91,722 ha, representing a relative difference from the IFN of 5.4%.These results demonstrate that the intensification of the global sampling scheme can provide forest area change estimates close to those achieved by official forest inventories (<6%), with precisions of between 4% and 7%, although we only estimate errors from sampling, not from the use of surrogate data.Such methods could be used by developing countries to demonstrate that they are fulfilling requirements for reducing emissions from deforestation in the framework of an REDD (Reducing Emissions from Deforestation in Developing Countries) mechanism under discussion within the United Nations Framework Convention on Climate Change (UNFCCC). Monitoring systems at national levels in tropical countries can also benefit from pan-tropical and regional observations, to ensure consistency between different national monitoring systems. 相似文献
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M. Gabriella Carboni Luisa Bergamin Daniela Esu Emanuela Pisegna Cerone Vladimiro Verrubbi 《Quaternary Research》2010,74(2):265-128
Foraminifera and molluscs from the 90 m deep ENEA borehole (Versilian plain, central Italy) were studied for paleoenvironmental purposes. Palaeontological analyses, integrated with U/Th and radiocarbon data, helped to recognize late Quaternary sea-level changes and supplied results on tectonic mobility of the area. The study highlighted four sedimentary phases. The first phase consists of a shore environment attributed to MIS 7.1. A hiatus corresponding to MIS 6 is hypothesized at the top of this interval. Recognition of the paleo-shoreline of MIS 7.1 at − 72.8 m signifies a vertical displacement due to the extensional tectonics of the Apennine orogenesis. The second phase consists of a transgressive succession with evidence of warm temperatures, which was interpreted as part of the transgression leading to the MIS 5.5 highstand. The third phase includes sub-aerial and lacustrine deposits. Radiocarbon dates and palaeoecological reconstruction led us to attribute this interval to MIS 4, MIS 3 and MIS 2. The fourth phase begins with a lagoon environment attributable to Holocene sea-level rise and ends with marsh episodes, signifying the progradation of the alluvial plain. This reconstruction confirms the hypothesis of tectonic stability for the Versilian area during the Holocene. 相似文献
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T Sancelme J Goetze S Jaquemet MG Meekan A Flam AM Watts 《African Journal of Marine Science》2020,42(1):95-107
Coastal populations of maritime countries in eastern Africa rely on fish as a primary source of protein, but baseline information on the abundance of fish communities on these coastlines is often lacking. We used baited remote underwater video stations to compare the abundance and diversity of reef fishes targeted by fishing at two sites in southern Mozambique, one at Lighthouse Reef within the Bazaruto Archipelago National Park and the other to the south at San Sebastian Reef on the San Sebastian Peninsula. Fish that are known targets of fisheries (mostly small-scale and artisanal) had an abundance that was almost three-times greater at San Sebastian Reef (80.22 ind. h–1 [SE 18.00]) than at Lighthouse Reef (29.70 ind. h–1 [SE 8.91]). Similarly, there was greater mean species richness at San Sebastian Reef (38.74 species h–1 [SE 2.79]) than at Lighthouse Reef (25.37 species h–1 [SE 3.66]). The main drivers of targeted fish abundance were habitat and depth, with shallow (<15 m) and mixed reef areas having the greatest abundance and richness. More sampling was done over sand habitat at Lighthouse Reef, which likely led to the lower abundance and species richness observed at this site; however, that finding could also be attributable to the fact that protection is provided to only a section of available coral reef habitat in a small area. Nevertheless, fish community structure was comparable between the sites, with similar proportions of carnivores (78–81%), herbivores (12–14%) and omnivores (7–8%). Our findings highlight the variation in species abundance and assemblages of coral-reef fish targeted by fishing in Mozambique and emphasise the importance of localised environmental variables as a driver of these patterns. To ensure maximum protection of Lighthouse Reef fish communities, we recommend an extension of the no-take zone to include the entire reef complex. 相似文献
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Aerosol remote sensing over land: A comparison of satellite retrievals using different algorithms and instruments 总被引：2，自引：0，他引：2
A.A. Kokhanovsky F.-M. Breon A. Cacciari E. Carboni D. Diner W. Di Nicolantonio R.G. Grainger W.M.F. Grey R. Hller K.-H. Lee Z. Li P.R.J. North A.M. Sayer G.E. Thomas W. von Hoyningen-Huene 《Atmospheric Research》2007,85(3-4):372-394
An inter-comparison study of the aerosol optical thickness (AOT) at 0.55 μm retrieved using different satellite instruments and algorithms based on the analysis of backscattered solar light is presented for a single scene over central Europe on October 13th, 2005. For the first time comparisons have been performed for as many as six instruments on multiple satellite platforms. Ten different algorithms are briefly discussed and inter-compared. It was found that on the scale of a single pixel there can be large differences in AOT retrieved over land using different retrieval techniques and instruments. However, these differences are not as pronounced for the average AOT over land. For instance, the average AOT at 0.55 μm for the area 7–12E, 49–53N was equal to 0.14 for MISR, NASA MODIS and POLDER algorithms. It is smaller by 0.01 for the ESA MERIS aerosol product and larger by 0.04 for the MERIS BAER algorithm. AOT as derived using AATSR gives on average larger values as compared to all other instruments, while SCIAMACHY retrievals underestimate the aerosol loading. These discrepancies are explained by uncertainties in a priori assumptions used in the different algorithms and differences in the sensor characteristics. Validation against AERONET shows that MERIS provides the most accurate AOT retrievals for this scene. 相似文献
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A detailed simulation of vertical showers in atmosphere produced by primary gammas and protons, in the energy range 1–100 TeV, has been performed by means of the FLUKA Monte Carlo code, with the aim of studying the time structure of the shower front at different detector heights. It turns out that the time delay distribution can be fitted using few parameters coincident with the distribution central moments. Such parameters exhibit a smooth behaviour as a function of energy. These results can be used both for detector design and for the interpretation of the existing measurements. Differences in the time structure between gamma and proton induced showers are found and explained in terms of the nonrelativistic comonent of extensive air showers. 相似文献
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