多时相遥感影像提取湖泊边界信息的融合算法

为了有效改善遥感影像提取湖泊边界信息的可靠性和精度,减少人为误差,提出了一种利用多时相遥感影像提取边界信息的加权平均融合算法以及误差的域法修正处理方法.结果表明,该方法能有效融合各时相影像信息,提高湖泊边界信息提取的可靠性,并且对融合时相变化较大的湖泊边界都有一定的普适性.通过融合算法提取的呼伦湖面积为1928.35km2,修正后的面积为1929.85km2.通过利用地统计学理论对算法的验证及误差分析,得出相对误差空间变异拟合模型的块金方差与基台值之比都小于25%,具有很强的空间相关性,修正后的数据空间相关性要优于融合数据,空间变程也得到了有效地降低,显示修正后的数据对半方差函数理论模型的拟合程度更好.     

Spatial distribution and behavior of dissolved selenium speciation in the South China Sea and Malacca Straits during spring inter-monsoon period

Selenium(Se) has been recognized as a key trace element that is associated with growth of primary producers in oceans. During March and May 2018, surface water(67 samples) was collected and measured by HG-ICP-MS to investigate the distribution and behavior of selenite [Se(IV)], selenate [Se(VI)] and dissolved organic selenides(DOSe) concentrations in the Zhujiang River Estuary(ZRE), South China Sea(SCS) and Malacca Straits(MS). It showed that Se(IV)(0.14–3.44 nmol/L) was the dominant chemical species in the ZRE, related to intensive manufacture in the watershed; while the major species shifted to DOSe(0.05–0.79 nmol/L) in the MS, associated with the wide coverage of peatland and intensive agriculture activities in the Malaysian Peninsula. The SCS was identified as the northern and southern sections(NSCS and SSCS) based on the variations of surface circulation.The insignificant variation of Se(IV) in the NSCS and SSCS was obtained in March, potentially resulting from the high chemical activity and related preferential assimilation by phytoplankton communities. Contrastively, the lower DOSe concentrations in the SSCS likely resulted from higher primary production and utilization during March. During May, the concentration of Se(IV) remained low in the NSCS and SSCS, while DOSe concentrations increased notably in the SSCS, likely due to the impact of terrestrial inputs from surface current reversal and subsequent accumulation. On a global scale, DOSe is the dominant Se species in tropical oceans, while Se(IV) and Se(VI) are major fractions in high-latitude oceans, resulting from changes in predominated phytoplankton and related biological assimilation.     

南大洋海-气CO_2通量研究进展

南大洋是全球最重要的CO2汇区之一。准确估算南大洋及其各海区的海-气CO2通量,是全球碳循环研究的重要内容,其对预测和评估未来南大洋在全球变暖日益加剧的背景下发挥的作用有重要意义。但由于南大洋广阔的海域,恶劣的气候条件、自身复杂的水文物理及地球化学过程等原因,目前对南大洋的CO2通量的评估不一而足,存在较大差异和不确定性。本文讨论了南大洋海-气CO2通量的估算方法和各个海域海-气CO2通量研究的最新进展,并分析了南大洋海-气CO2通量的控制及影响因素。目前对南大洋的年吸收量估计为大约在0.1-0.6PgCyr-1,同时,所有的研究都表明,其存在极大的年度变化性。并且,由于各个海区受到生物、物理和水文等各方面的影响,表层海水CO2分压(pCO2)表现出极大的时空变异性。     

季风指数及其年际变化Ⅱ.南海夏季风分量动能强度指数及其年际变化

计算了各年南海夏季风建立前后流场的场相似度、场比幅、季风分量动能强度指数和突变度.指出按变差度最大或相似度绝对值最小及其变化最陡以及比幅最小,可客观定量地定出季风来临的预兆日期,在大多年份该日期比用天气气候学方法得到的季风来临(爆发)日期要早些,且两者有较好正相关.绝大多数年份季风建立时有环流突变发生,但也有少数年份呈调和变化或二次突变.季风分量动能强度指数能够反映各年南海夏季风建立后的强度.最后分析指出,南海850hPa夏季风的前兆日期,突变度和强度指数都有明显的年际和年代际变化.     

East Asia winter monsoon variations on a millennial time‐scale before the last glacial–interglacial cycle

Grain size and magnetic susceptibility measurements on samples from a typical loess–palaeosol sequence on the central Chinese Loess Plateau are used to reconstruct the Pleistocene East Asian monsoon climate. The coarse‐grained fraction, i.e. the weight percentage > 30 μm of the bulk grain‐size distribution, is used as a sensitive proxy index of the East Asia winter monsoon strength. On the basis of an absolute time‐scale, time‐series variations of this proxy show that winter monsoon strengths varied on millennial time‐scales during the periods 145–165, 240–280, 320–350, 390–440, 600–640, 860–890, 900–930 and 1330–1400 kyr BP. The wavelength of these climatic oscillations varied between 1.89 and 4.0 kyr, as is shown by spectral analysis using the multitaper method. Although numerical simulation experiments show that high frequencies also can arise from measurement errors in the grain‐size analysis, the frequencies prove to be sufficiently stable when the spectral analysis is repeated with a different number of tapers. For the time being, we do not correlate these climatic oscillations with palaeoclimatic records in the North Atlantic deep‐sea sediments because both time‐scales need to be further improved. Our data, however, certainly demonstrate that millennial‐scale East Asian winter monsoon variations in the last 1.4 million years can be detected from terrestrial loess records. Copyright © 1999 John Wiley & Sons, Ltd.     

Understanding hydrological processes of glacierized catchments in the western Himalayas by a multi-year tracer-based hydrograph separation analysis

Snow and glacier melt are significant contributors to streamflow in Himalayan catchments, and their increasing contributions serve as key indicators of climate change. Consequently, the quantification of these streamflow components holds significant importance for effective water resource management. In this study, we utilized the spatio-temporal variability of isotopic signatures in stream water, rainfall, winter fresh snow, snowpack, glaciers, springs, and wells, in conjunction with hydrometeorological observations and Snow Cover Area (SCA) data, to identify water sources and develop a conceptual understanding of streamflow dynamics in three catchments (Lidder, Sindh, and Vishow) within the western Himalayas. The following results were obtained: (a) endmember contributions to the streamflow exhibit significant spatial and seasonal variability across the three catchments during 2018–2020; (b) snowmelt dominates streamflow, with average contributions across the entire catchment varying: 59% ± 9%, 55% ± 4%, 56% ± 6%, and 55% ± 9% in Lidder, 43% ± 6%, 38% ± 6%, 32% ± 4%, and 33% ± 5% in Sindh and 45% ± 8%, 40% ± 6%, 39% ± 6%, and 32% ± 5% in Vishow during spring, summer, autumn, and winter seasons, respectively; (c) glacier melt contributions can reach ~30% to streamflow near the source regions during peak summer; (d) The primary uncertainties in streamflow components are attributed to the spatiotemporal variability of tracer signatures of winter fresh snow/snowpack (±1.9% to ±20%); (e)regarding future streamflow components, if the glacier contribution were to disappear completely, the annual average streamflow in Lidder and Sindh could decrease up to ~20%. The depletion of the cryosphere in the region has led to a rapid increase in runoff (1980–1900), but it has also resulted in a significant streamflow reduction due to glacier mass loss and changes in peak streamflow over the past three decades (1990–2020). The findings highlight the significance of environmental isotope analysis, which provides insights into water resources and offers a critical indication of the streamflow response to glacier loss under a changing climate.     

Role of time variant and invariant terms on soil moisture spatio-temporal variability in a subhumid coastal wetland

The knowledge of soil moisture spatio-temporal variability is highly relevant for water resources management. This paper reports an analysis of the spatial–temporal variability of soil moisture data for a small to medium-scale soil-sensors network in a coastal wetland of southwestern Spain. Measurements were taken from five sites located in the Doñana National Park over the time-period of one hydrological year from September 2017 to September 2018. The total area of the soil-sensors network shows an extension about 25 × 3 km. Soil moisture data was separated into time invariant (the temporal mean of the whole period at each site) and time-variant terms (the deviations of soil moisture from the mean, or anomalies). The time-invariant component was generally the main contributor to the total spatial variance of soil moisture and it was mostly controlled by the groundwater levels in the area. Nevertheless, the time variant terms have a huge effect on soil moisture variability in very dry states. Characteristic convex time-dependent patterns for this field site were found between spatially averaged soil moisture and its variability. This information could be used for the up and downscaling of soil moisture from satellite data. Those patterns of relation between spatial mean and variability of soil moisture were only affected by heavy rainfalls giving rise to hysteretic behaviour. This study shows that even though groundwater level is a time-variant variable, it significantly affects soil moisture's time-variant but also time-invariant terms due to the different average groundwater level depths at the different sites.     

Bed material texture in low order streams on the Queen Charlotte Islands,British Columbia

Low order channels comprise a large proportion of the links of every drainage basin, and are often at the centre of land management concerns. They exhibit hydrological and geomorphological characteristics atypical of higher order links. This paper examines the nature and causes of variations in the bed material texture of two streams on the Queen Charlotte Islands, British Columbia. The extant, functional exponential model is found to be inadequate for explaining observed changes in grain size parameters with distance downstream. Recurrent disruption of sediment transport by large organic debris jams, and the sporadic contamination of the fluvial sediment population by colluvial inputs, preclude the development of longitudinal structure. Rather, grain size varies erratically over short distances. A stochastic model best describes the observed variations, and should be adopted as an alternative to the exponential model in low order links. Characteristic variances are controlled by the degree of hillslope-channel coupling, and the extent and characteristics of non-alluvial storage mechanisms.     

不排水抗剪强度非平稳随机场模拟及边坡可靠度分析

边坡可靠度分析中通常假定采用平稳或准平稳随机场表征土体参数的空间变异性,然而大量现场试验数据表明,土体参数如不排水抗剪强度沿土体埋深常呈现明显的非平稳分布特征,即其均值和标准差均随埋深发生变化,因此亟需发展土体参数非平稳随机场模型及其模拟方法。针对目前不能有效单独模拟土体参数趋势分量和随机波动分量的不确定性,提出了一种有效的不排水抗剪强度参数非平稳随机场模型,并给出了土体参数二维非平稳随机场模拟方法计算流程,同时将新提出的模型与现有非平稳随机场模型及平稳随机场模型进行了系统比较。最后通过不排水饱和黏土边坡算例验证了提出模型的有效性,并揭示了不排水抗剪强度非平稳分布特征对边坡可靠度的影响规律。结果表明：提出模型能够有效地单独模拟土体参数趋势分量和随机波动分量的不确定性,考虑土体参数均值和标准差随埋深增加而增大的特性,可为表征土体参数非平稳分布特征提供了一条有效的途径。此外,与采用非平稳随机场模拟土体参数空间变异性相比,采用常用的平稳随机场模型会低估边坡失效概率,从而造成偏危险的边坡工程设计方案。     

考虑砂土抗剪强度空间变异性的盾构开挖面稳定性分析

采用传统研究方法对盾构开挖面稳定性的分析多基于土体是均质、各向同性材料的假设,显然与其本身的非均质性相违背。为此,开展了考虑土体抗剪强度参数的空间变异性对盾构开挖面稳定性的影响研究。在随机场理论的基础上,采用协方差矩阵分解法建立了描述砂土内摩擦角空间变异性的三维随机场模型,借助于数值分析软件平台研究了内摩擦角的变异系数、自相关距离对开挖面失稳模式、极限支护应力的影响规律,并采用概率分析法探讨了极限支护应力特征值的选取。结果表明：砂土内摩擦角的空间变异性对开挖面稳定性有重要的影响;随内摩擦角的变异系数的增大,极限支护应力的概率分布离散性越大;开挖面失稳模式与自相关距离的大小密切相关,当自相关距离与隧道直径比较接近时,开挖面可能出现局部失稳;提出了开挖面极限支护应力特征值的概念,并结合失稳概率给出了其初步确定方法。