一种低信噪比下PN码的快速捕获技术

直扩系统中,为了硬件实现的简便,PN码的捕获一般都采用串行搜索的方法.但当PN码很长时,由于搜索相位点很多,串行搜索法将使捕获时间过长.并且当信噪比较低时,会有较高的虚警概率.这些都会使系统的捕获性能降低.提出一种基于匹配滤波器的快速捕获算法,改善了在极低信噪比下的性能.降低了平均捕获时间.     

Yukon River Basin long‐term (1977–2006) hydrologic and climatic analysis

In this study, long‐term discharge data and climate records, such as temperature and precipitation during 1977–2006, have been used to define basin climatic and hydrologic regimes and changes. Discharge analyses at four key gauging stations (Eagle, Stevens Village, Nenana, and Pilot Station) in the Yukon River Basin show that the runoff in the cold season (November to April) is low with small variations, whereas it is high (28 500–177 000 ft³/s; 810–5000 m³/s) with high fluctuations in the warm season (May to October). The Stevens Village Station is in the upper basin and has similar changes with the flow near basin outlet. Flow increases in May (61 074 ft³/s; 1729 m³/s) and September (23 325 ft³/s; 660 m³/s); and decreases in July (35 174 ft³/s; 996 m³/s) and August (6809 ft³/s; 193 m³/s). Discharge in May at the Pilot Station (near the basin outlet) shows a positive trend (177 000 ft³/s; 5010 m³/s). Daily flow analyses show high fluctuation during the warm season and very low flow during the cold season; the 10‐year average analyses of daily flow at Pilot Station show a small increase in the peak and its timing shifted to a little earlier date. The annual flow, average of 227 900 ft³/s (6450 m³/s) with high inter‐annual fluctuations, has increased by 18 200 ft³/s (or 8%; 520 m³/s) during 1977–2006. From 1977 to 2006, basin air temperature in June has increased by 3.9 °F (2.2 °C) and decreased by 10.5 °F (5.8 °C) in January. A strong and positive correlation exists between air temperature in April and discharge in May, whereas a strong and negative correlation relates August temperature and September discharge. Negative trend during 1977–2006 is observed for precipitation in June (0.6 in.; 15 mm) with a confidence over 93%. Precipitation in August and September has strong and positive correlations with discharge in September and October at basin outlet; the precipitation in other months has weak correlation with the discharge. The mean annual precipitation during 1977–2006 increased by 1.1 in. (or 8%; 28 mm), which contributes to the annual flow increase during the study period. Copyright © 2012 John Wiley & Sons, Ltd.     

青藏高原西南部塔若错湖泊沉积物记录的近300年来气候环境变化

以青藏高原西南部塔若错的34cm浅湖芯为研究对象,对其沉积物样品进行总有机碳、无机碳、总氮、微量元素、正构烷烃含量及碳氮比等多项指标的分析测定。采用过剩210Pb和137Cs计年法对该湖芯进行了定年和沉积速率研究,获得了近300年的连续湖泊沉积环境序列。在明确了各指标气候环境指示意义的前提下,综合对比分析湖芯中各项气候环境指标,并结合定年结果重建了塔若错湖区近300年来的气候环境变化。结果表明：塔若错湖区气候环境变化可分为3个明显阶段：早期为1705～1778年,该地区气候环境温暖湿润,湖区植被广泛发育;中期为1778～1860年,湖区处于小冰期末次阶段,气候环境寒冷而湿润,植被发育受阻;后期为1860年至今,为小冰期结束后偏暖干化时期。其中,后期又可分为3个亚阶段：1860～1924年,湖区气候环境稍暖且干旱,植被稍有发育;1924～1969年,湖区气候环境呈现偏冷干特点,植被发育暂缓;1969年至今,湖区气候回暖,环境干旱化有所缓解,植被开始逐渐发育。在气候冷暖变化上,该湖芯记录与古里雅冰芯记录和青海湖湖泊沉积记录都有较好的可对比性,只是在起讫年代上存在一些差异。     

Multi‐scale Decomposition of Co‐seismic Deformation from High Resolution DEMs: a Case Study of the 2004 Mid‐Niigata Earthquake

Decomposing co-seismic deformation is an immediate need for researchers who are interested in earthquake inversion analysis and geo-hazard mapping. However, conventional InSAR or digital elevation models (DEMs) imagery analyses only provide the displacement in the Line-of-Sight (LOS) direction or elevation changes. The 2004 Mid-Niigata earthquake in Japan provides lessons on how to decompose co-seismic deformation from two sets of DEMs. If three adjacent points undergo a rigid-body-translation movement, their co-seismic deformation can be decomposed by solving simultaneous equations. Although this method has been successfully used to discuss tectonic deformations, the algorithm needed improvement and a more rigorous algorithm, including a new definition of nominal plane, DEMs comparability improvement and matrix condition check is provided. Even with these procedures, the obtained decomposed displacement often showed remarkable scatter prompting the use of the moving average method, which was used to determine both tectonic and localized displacement characteristics. A cut-off window and a pair of band-pass windows were selected according to the regional geology and construction activities to ease the tectonic and localized displacement calculations, respectively. The displacement field of the tectonic scale shows two major clusters of large lateral components, and coincidently major visible landslides were found mostly within them. The localized displacement helps to reveal hidden landslides in the target area. As far as the Kizawa hamlet is concerned, the obtained vectors show down-slope movements, which are consistent with the observed traces of dislocations that were found in the Kizawa tunnel and irrigation wells. The method proposed has great potential to be applied to understanding post-earthquake rehabilitation in other areas.     

成都经济区不同地貌景观区土壤有机碳分布特征及储量估算

利用四川省成都经济区多目标区域地球化学调查获得的土壤有机碳含量数据,探讨了成都经济区不同地貌景观区土壤有机碳的分布特征。山区表层土壤有机碳含量(SOC)最高(22 g/kg左右),较平原区、丘陵区高一倍以上,丘陵区最低(9.49 g/kg)。成都平原区和东部丘陵区深层土壤碳含量相差不大,且均低于研究区深层土壤碳含量均值(6.99 g/kg)。利用指数模型对单位土壤平均碳量(USCATOC)、有机碳储量(USCATOC,h)、有机碳丰度指数(R)进行了估算。结果表明:各地貌单元土壤碳含量、单位土壤平均碳量、有机碳储量、有机碳丰度指数(R)分布具有山区高于平原区、丘陵区最低的一致性特征。龙门山区、西南山区面积约占全区的42%,土壤有机碳储量约占全区的59%;成都平原区、丘陵区面积占58%,土壤有机碳储量约占全区的41%。单位土壤平均碳量、有机碳储量在不同地貌单元中分布的差异主要与不同地貌单元的土壤有机碳含量有关,此外还可能与成土母质、植被发育情况、土地利用方式有关。     

泥炭沉积与气候变化的泥炭记录

气候变化是影响全球泥炭沼泽分布和演化的最重要的因子之一,而泥炭地由于自身的特点成为过去气候变化的良好地质档案。在介绍泥炭沉积过程及不同类型的泥炭沼泽的发育特点基础上,从过去气候变化的常用泥炭记录和泥炭地碳记录等方面总结了国际上针对泥炭地反演气候变化研究的若干重要进展,重点剖析了泥炭腐殖化度、植物残体、有壳变形虫、生物标志化合物、同位素和孢粉等泥炭地过去气候变化重建的代用指标的适用范围和优缺点,同时也分析了泥炭地碳累积和碳循环等热点研究问题。最后从泥炭地作为过去气候变化的记录档案、泥炭地对现在气候变化的响应与反馈及在泥炭地进行现场气候变化监测与实验等方面对泥炭地与气候变化研究进行了展望。     

火山活动的气候影响及其冰芯记录研究进展

系统地总结了不同时间尺度内火山活动影响气候的机理,回顾了不同区域冰芯记录火山喷发物质沉积信号的研究历史,阐述了不同气候模式对火山活动影响气候的数值模拟结果,并指出了相关研究中存在的不确定性.结果表明:火山活动通过释放大量的火山物质气溶胶影响气候波动,在年际至年代际时间尺度上,这种影响是显著的;然而,在更长的时间尺度上这种影响是否仍然存在,尚需更多研究的证实.冰芯中火山喷发物质沉积记录为研究历史时期火山活动及其气候影响提供了必要的参考资料,相关的气候模式利用该沉积记录较好地模拟了火山活动对区域乃至全球尺度气候的影响,为我们认识火山活动影响气候变化的机理提供了重要的理论支持,同时也为研究未来火山活动对气候的可能影响提供了参照.但是,冰芯中火山喷发物质沉积记录研究及数值模式模拟结果中尚存在诸多的问题和不确定性.     

新疆伊犁晚全新世风成沙-古土壤序列磁化率特征及气候变化

选择新疆伊犁河谷塔克尔莫乎尔沙漠古风成沙-古土壤沉积剖面为研究对象,通过73块样品的磁化率及其与TOC、CaCO3、Fe2O3和粒度组成的相关分析,并以OSL测年为时间标尺,讨论剖面沉积的磁化率变化机制及其古气候意义。结果表明:剖面低频磁化率（χlf）与16～250 μm百分含量为正相关,即低频磁化率χlf变化主要受粗组分含量变化的影响。其中,古风成沙χlf值多高于古土壤,这与我国季风区沙漠沉积的磁化率变化特征相反。根据剖面磁化率及各种环境指标综合分析,研究区3.7 kaBP以来的气候变化可划分为5个阶段:3.71～3.06 kaBP凉湿、3.06～2.78 kaBP冷干、2.78～2.10 kaBP凉湿、2.10～0.50 kaBP冷湿、0.50～0.00 kaBP温干。晚全新世气候变化与周边地区古气候记录有较好的一致性,并与同期北大西洋表层海温变化事件呈现很好的遥相关,总体上表现为相对暖干、凉湿的典型西风气候变化模式。     

Facies analysis and palaeoclimatic significance of ironstones formed during the Eocene greenhouse

Lower and middle Eocene ironstone sequences of the Naqb and Qazzun formations from the north‐east Bahariya Depression, Western Desert, Egypt, represent a proxy for early Palaeogene climate and sea‐level changes. These sequences represent the only Palaeogene economic ooidal ironstone record of the Southern Tethys. These ironstone sequences rest unconformably on three structurally controlled Cenomanian palaeohighs (for example, the Gedida, Harra and Ghorabi mines) and formed on the inner ramp of a carbonate platform. These palaeohighs were exposed and subjected to subaerial lateritic weathering from the Cenomanian to early Eocene. The lower and middle Eocene ironstone sequences consist of quiet water ironstone facies overlain by higher energy ironstone facies. The distribution of low‐energy ironstone facies is controlled by depositional relief. These deposits consist of lagoonal, burrow‐mottled mud‐ironstone and laterally equivalent tidal flat, stromatolitic ironstones. The agitated water ironstone facies consist of shallow subtidal–intertidal nummulitic–ooidal–oncoidal and back‐barrier storm‐generated fossiliferous ironstones. The formation of these marginal marine sequences was associated with major marine transgressive–regressive megacycles that separated by subaerial exposure and lateritic weathering. The formation of lateritic palaeosols with their characteristic dissolution and reprecipitation features, such as colloform texture and alveolar voids, implies periods of humid and warm climate followed major marine regressions. The formation of the lower to middle Eocene ironstone succession and the associated lateritic palaeosols can be linked to the early Palaeogene global warming and eustatic sea‐level changes. The reworking of the middle Eocene palaeosol and the deposition of the upper Eocene phosphate‐rich glauconitic sandstones of the overlying Hamra Formation may record the initial stages of the palaeoclimatic transition from greenhouse to icehouse conditions.     

1980—2019年中国西北地区降雪和融雪时空变化特征北大核心CSCDCSSCI

西北地区降雪和融雪特征的长期变化对于融雪洪水过程的准确模拟具有重要意义。本研究基于1961—1979年站点观测的日降水和气温等数据,首先对比了湿球温度法、KS方法和双临界气温法计算的降雪量,确定了精度最高的双临界气温方案,进而计算了1980—2019年的日雪雨比,最后分析了雪雨比、降雪开始日期和融雪开始日期的变化规律。结果包括:①春季平均气温呈显著上升趋势,随海拔上升升温速率减小,青藏高原地区、东南部半干旱区、半湿润区春季气温上升速率略低于北疆、南疆、河西走廊及内蒙古西部,春季雪雨比在海拔1000 m以上呈显著下降趋势,在青藏高原地区、东南部半干旱区、半湿润区呈显著下降趋势;秋季平均气温显著上升,随海拔上升升温速率增大,空间上在青藏高原地区上升速率最快,秋季雪雨比在不同海拔和部分气候分区都呈不显著下降趋势;冬季平均气温在海拔2000 m以上呈现显著升温,且随着海拔的升高升温速率加快,空间上在青藏高原地区、东南部半干旱区、半湿润区呈现显著升温,降雪量在1000~2000 m呈现显著增加趋势,空间上在北疆地区呈现显著增加趋势。②降雪开始日期随着温度的升高在所有区域都没有显著的推迟,每一年的降雪开始日期在不同高程带和不同气候区之间的差别没有变化,仍为30~40d。③融雪开始日期在所有海拔区间和气候分区都呈现出显著的提前趋势,每一年的融雪开始的日期在不同高程带和不同气候区的差别仍为25~30d。降雪和融雪特征的变化说明气候变化可能已经对融雪洪水的特征产生了明显的影响。