Airborne Laser Sensing of Scottish Coastal Waters     

Grigorii Kokhanenko  Geoff Ludbrook  Ivan Penner  Vitalii Shamanaev 《Marine Geodesy》2001,24(4):195-207

An Nd:YAG-based airborne lidar system has been used to measure the optical properties of littoral waters off the northwest Scottish coast. The small-scale structure of subsurface scattering layers was also investigated. Methods of solving the Lidar Sensing Equation in the single scattering approximation are described and the values of the derived extinction indices presented. The extinction index averaged over a series of five flights to the northeast of the Gulf Stream was ε= 0.224 m -1 with a standard deviation of 0.212 m -1 . Further, it was demonstrated that, in coastal waters, optical inhomogeneities with dimensions between 50 m and 200 km obey the power law Sp ε ~ k -P with the parameter P close to two. In turbid or transparent areas, the water extinction index can change by several tenths of a percent with respect to the surrounding water mass. This suggests that the observed nonmonotonic behavior of the power spectra of the water extinction index fluctuations is caused by the outer scale of turbulence, in particular, by the bottom depth at the measurement site.  相似文献   

Post-Clovis survival of American Mastodon in the southern Great Lakes Region of North America     

Neal Woodman  Nancy Beavan Athfield   《Quaternary Research》2009,72(3):359-363

The end of the Pleistocene in North America was marked by a wave of extinctions of large mammals, with the last known appearances of many species falling between ca. 11,000–10,000 ¹⁴C yr BP. Temporally, this period overlaps with the Clovis Paleoindian cultural complex (11,190–10,530 ¹⁴C yr BP) and with sudden climatic changes that define the beginning of the Younger Dryas chronozone (ca. 11,000–10,000 ¹⁴C yr BP), both of which have been considered as potential proximal causes of this extinction event. Radiocarbon dating of enamel and filtered bone collagen from an extinct American Mastodon (Mammut americanum) from northern Indiana, USA, by accelerator mass spectrometer yielded direct dates of 10,055 ± 40 ¹⁴C yr BP and 10,032 ± 40 ¹⁴C yr BP, indicating that the animal survived beyond the Clovis time period and into the late Younger Dryas. Although the late survival of this species in mid-continental North America does not remove either humans or climatic change as contributing causes for the late Pleistocene extinctions, neither Clovis hunters nor the climatic perturbations initiating the Younger Dryas chronozone were immediately responsible for driving mastodons to extinction.  相似文献   

上海市大气颗粒物与能见度的关系   总被引：6，自引：0，他引：6       下载免费PDF全文

姚剑  王广华  林俊  范雪波  耿彦红  位楠楠  单健  李燕  刘卫 《气象与环境学报》2010,26(4):17-21

大气能见度成为当前区域大气环境研究的重要指标,不同粒径的颗粒物对能见度的影响有着显著的区别。本研究在线连续监测了上海市嘉定区2008年11月—2009年1月不同粒径大气颗粒物质量浓度和粒子数浓度的日变化,同步收集了相同区域空气水平能见度的数据。比较不同粒径大气颗粒物质量浓度与空气水平能见度和颗粒物消光系数的相关性,结果表明：中值粒径为0.4 μm和0.65 μm的大气颗粒物对上海嘉定空气水平能见度的影响最显著;中值粒径为0.17 μm、0.26 μm、0.40 μm和0.65 μm的大气颗粒物对颗粒物的消光系数影响较大。该相关系数的分布趋势与各种组分(SO42-、NO3-、NH4+、OC和EC)的粒径分布十分一致,证明了这五种组分是影响大气颗粒物消光系数的重要原因。  相似文献   

沙尘天气的定量化指数及其应用   总被引：7，自引：0，他引：7  

张冬斌尚可政  王式功杨德保 赵燕宁 《干旱气象》2003,21(3):58-62

按照《地面气象观测规范》规定,能见度VV与风速V是对沙尘天气进行分级的重要指标。我们利用能见度和风速构造沙尘指数,用以衡量沙尘现象的强弱,并通过它对时间和空间的累积来分析某一地区的沙尘天气发生状况。结果表明：所构造的指数能够代表我国沙尘天气多发区的沙尘天气状况。对上游沙区的沙尘指数与下游邻近城市空气污染指数所作的相关分析显示：二者间存在较为密切的关系。因此．利用上游沙区的沙尘指数作为下游邻近城市空气污染预报的重要因子。  相似文献   

Comparison of taxonomic diversity,strontium isotope and sea-level patterns     

Edward G. Purdy 《International Journal of Earth Sciences》2008,97(3):651-664

Sepkoski’s compendium of 28,730 marine genera was analyzed with a view toward comparing taxonomic diversity, strontium isotope stratigraphy and sea-level changes. The fossil record analyses discriminated between origination, extinction and pass through genera and collectively delineated changes in number of genera with time at the largely stratigraphic stage level. With notable exceptions of the Cretaceous and Tertiary, taxonomic diversity generally paralleled both strontium isotope stratigraphy and sea-level changes. Sampling bias was suggested in the Tertiary where an increase in genera numbers toward the Recent opposed the downward trends of both strontium isotope and sea level curves. The removal of all Recent genera from the Sepkoski database confirmed the bias in producing complimentary downward trends in all curves. Regression analysis of taxonomic diversity with respect to sea level extent and time duration explained 82% of the variability of the remaining data. Sea-level fluctuations are not always accompanied by significant changes in taxonomic diversity but strontium isotope analyses offers the potential of constraining the extent to which the magnitude of changes are associated with time duration.  相似文献   

Interstellar polarization and extinction toward the Recurrent Nova T CrB     

《New Astronomy》2022

  相似文献