Intercalibration of benthic flux chambers I. Accuracy of flux measurements and influence of chamber hydrodynamics

The hydrodynamic properties and the capability to measure sediment-water solute fluxes, at assumed steady state conditions, were compared for three radically different benthic chamber designs: the “Microcosm”, the “Mississippi” and the “Göteborg” chambers. The hydrodynamic properties were characterized by mounting a PVC bottom in each chamber and measuring mixing time, diffusive boundary layer thickness (DBL thickness) shear velocity (u∗), and total pressure created by the water mixing. The Microcosm had the most even distribution of DBL thickness and u∗, but the highest differential pressure at high water mixing rates. The Mississippi chamber had low differential pressures at high u∗. The Göteborg chamber was in between the two others regarding these properties. DBL thickness and u∗ were found to correlate according to the following empirical formula: DBL=76.18(u∗)−0.933. Multiple flux incubations with replicates of each of the chamber types were carried out on homogenized, macrofauna-free sediments in four tanks. The degree of homogeneity was determined by calculating solute fluxes (of oxygen, silicate, phosphate and ammonium) from porewater profiles and by sampling for porosity, organic carbon and meiofauna. All these results, except meiofauna, indicated that there were no significant horizontal variations within the sediment in any of the parallel incubation experiments. The statistical evaluations also suggested that the occasional variations in meiofauna abundance did not have any influence on the measured solute fluxes. Forty-three microelectrode profiles of oxygen in the DBL and porewater were evaluated with four different procedures to calculate diffusive fluxes. The procedure presented by Berg, Risgaard-Petersen and Rysgaard, 1989 [Limnol. Oceanogr. 43, 1500] was found to be superior because of its ability to fit measured profiles accurately, and because it takes into consideration vertical zonation with different oxygen consumption rates in the sediment. During the flux incubations, the mixing in the chambers was replicated ranging from slow mixing to just noticeable sediment resuspension. In the “hydrodynamic characterizations” these mixing rates corresponded to average DBL thickness from 120 to 550 μm, to u∗ from 0.12 to 0.68 cm/s, and to differential pressures from 0-3 Pa. Although not directly transferable, since the incubations were done on a “real” sediment with a rougher surface while in the characterizations a PVC plate simulated the sediments surface, these data give ideas about the prevailing hydrodynamic condition in the chambers during the incubations. The variations in water mixing did not generate statistically significant differences between the chamber types for any of the measured fluxes of oxygen or nutrients. Consequently it can be concluded that, for these non-permeable sediments and so long as appropriate water mixing (within the ranges given above) is maintained, the type of stirring mechanism and chamber design used were not critical for the magnitude of the measured fluxes. The average measured oxygen flux was 11.2 ± 2.7 (from 40 incubations), while the diffusive flux calculated (from 43 profiles using the Berg et al., 1989 [Limnol. Oceanogr. 43, 1500] procedure) was 11.1 ± 3.0 mmol m⁻² day⁻¹. This strongly suggests that accurate oxygen flux measurements were obtained with the three types of benthic chambers used and that the oxygen uptake is diffusive.     

ASHTECH LOCUS GPS接收机测边精度及基线处理软件的检验

本文研究ＡＳＨＴＥＣＨ ＬＯＣＵＳ ＧＰＳ接收机测边精度,同时给出一种检验其基线处理软件的有效方法。在不需要标准基线场的情况下这种方法不失为一种检测ＧＰＳ接收机精度的好途径。     

Low-density geochemical mapping in Hungary

Guidelines for a low-density geochemical survey were described in 1990 by the Western European Geological Surveys. A low-density geochemical survey of Hungary was carried out in 1991–1995. The results are useful for future surveys and for the IGCP 360 project ‘Global Geochemical Baseline’. In regions with well-developed drainage systems in Hungary, 196 catchment basins of approx. 400 km² were delineated and flood-plain deposits sampled at their outlets. The samples were taken from 0 to 10 cm and from 50 to 60 cm depths. Samples were analysed by ICP-AES and AAS techniques in two laboratories. A Geochemical Atlas of Hungary is in preparation that will show the distribution of 25 elements in the two sampled layers. Maps for the lower layer represent regional geochemical baseline values and a geochemical subdivision of the country (maps showing the distribution of element associations) was made on the basis of factor variables. Maps constructed from the data of the upper sampling level show us the present state of contamination of the surface. The results of this survey have contributed to the establishment of guidance values for soils prepared by the Hungarian Ministry of the Environment in 1995. Safe levels were established for As, Cd, Cr, Cu, Hg, Pb and Zn and regional environmental loads plotted. Differences between the median values of the two levels are generally small. However, the concentrations of certain elements like P, Pb and S are significantly greater in the upper layer reflecting contamination from agriculture. In certain regions, the rate of sedimentation was fairly fast such that the environmental effects of ore mining in Transylvania and southern Slovakia as well as those of heavy industry in northern Hungary can be observed in samples from the lower level. The main factor controlling the geochemical pattern in Hungary is the predominance of young (Pleistocene or Miocene) clastic sediments at the surface. Approx. 90% of the surface is covered by these young sediments. This kind of survey has the disadvantage of not providing enough contrast to differentiate geologically dissimilar areas but it has the advantage to provide regional surface background geochemical data and it helps to outline areas of possible surface contamination. Based on the results of this survey we conclude that it would be much better to sample smaller, but geologically homogeneous areas in mountainous terrain to obtain data characteristic of the geochemical background of lithologic units. This approach would mean a sampling density of a few tens of km²/sample for hilly areas, and a few hundred km²/sample for lowland areas.     

上海崇明岛表层土壤重金属元素分布特征与环境地球化学基线值研究

对上海崇明岛地区表层土壤中重金属元素的分布特征进行了研究,结果表明崇明岛表层土壤未受人为污染。运用标准化方法计算了崇明岛地区表层土壤中重金属元素镉、铬、铜、铅、锌、砷的环境地球化学基线值,建立了元素镉、铬、铜、铅、锌、砷的环境地球化学基线模型,确定其环境地球化学基线值分别为0.19、71.97、31.32、24.79、86.43、8.34μg/g。与上海市土壤背景值进行了对比检验,结果显示,标准化方法能有效计算土壤中元素的环境地球化学基线,获得的基线符合其定义和实际意义,为区域经济发展规划和环境评价提供了实用的基础地球化学信息。     

深度衰减效应对大型地下洞室群强震响应的影响分析

介绍了大型地下洞室群强震反应分析所需要输入地震波的选用原则,重点考虑了场地的深度衰减效应,同时提出了一种假设来确定地震危险性分析提供的峰值加速度的所在位置。选用了两组攀枝花实测地震记录,同时利用三角级数叠加法综合考虑了深度衰减效应,合成了一组人工地震动,使用ABAQUS软件对某水电站大型地下洞室群进行了二维非线性强震动力时程数值计算分析。结果表明：生成的地震波能较好地模拟地下洞室群的地震响应,深度衰减对地震响应结果有明显影响,不同频谱的地震波相对位移-时程差距较大,但频谱参数的影响还有待于深入研究。研究成果对大型地下洞室群地震动输入问题研究具有一定的指导意义。     

一次多回击负地闪放电过程的甚高频辐射和传输特征分析

利用短基线时间差甚高频(VHF)辐射源定位系统对一次多回击负地闪放电过程进行详细研究发现, 负地闪的预击穿、梯级先导、直窜先导及回击后云内放电过程伴随有较强烈的VHF辐射。结合同步观测的闪电快、慢电场变化资料, 分析VHF辐射源时空发展特征发现, 预击穿阶段辐射源在云中的放电通道为双向发展, 平均速度均在104 m s-1量级, 预击穿下行分支直接转化为梯级先导, 并产生多个分支通道同时向地面发展, 先导平均速度在105 m s-1量级。继后回击之前先导过程均产生多个分支通道, 直窜先导平均速度在105～106 m s-1量级, 新开辟的梯级先导速度在105 m s-1量级。闪击间及地闪后期云内放电活动较为复杂, 主要表现为辐射源从闪电起始区域发展, 进一步延伸云内闪电通道。地闪后期多次负极性K变化过程(Kitagawa and Kobayashi, 1958)主要表现为负极性流光沿之前的正极性电离通道快速发展, 平均速度在106 m s-1量级。     

一种PSInSAR干涉测量公共主影像选择新方法

在PSInSAR干涉测量技术中,主影像的选择直接影响后续的形变相位提取及沉降信息解算。在综合考虑空间垂直基线、时间基线和多普勒中心频率对影像去相干影响的基础上,将三因素的相干性测度映射到三维空间,构成三个质点,通过对三质点的质心的研究来衡量三因素对影像相干性的综合影响,构建一种新的主影像选择模型。以2003~2009年北京地区28景ENVISAT ASAR影像为试验数据,分别采用该模型及综合最大相关系数模型进行主影像选择,并进行实际干涉处理,以生成干涉图及相干系数均值,对两种方法主影像选取结果进行定量评价。结果表明,与直接以去相干因素的相干测度乘积构建的综合相关系数模型相比,该方法选取的主影像更为合理,与其他辅影像总体干涉性更好。     

Surface displacement estimation using multi-temporal SAR Interferometry in a seismically active region of the Himalaya

The Indian subcontinent is one of the most earthquake-prone regions of the world. The Himalayas are well known for high seismic activity, and the ongoing northwards drift of the Indian plate makes the Himalaya geodynamically active. During the last three decades, several major earthquakes occurred at the plate interiors and boundaries in this subcontinent causing massive losses. Therefore, one of the major challenges in seismology has been to estimate long recurrence period of large earthquakes where most of the classical Probabilistic Seismic Hazard Approaches fail due to short catalogues used in the prediction models. Therefore, during the past few decades, the Himalayan region has been studied extensively in terms of the present ongoing displacements. In this context the present study has been carried out to estimate the surface displacement in a seismically active region of the Himalaya, in between Ganga and Yamuna Tear, using multi-temporal Synthetic Aperture Radar (SAR) Interferometry. A displacement rate of 6.2–8.2 mm/yr in N14°E direction of the Indian plate towards the Tibetan plate has been obtained. It has been noted that the estimated convergence rate using Differential SAR Interferometry technique is relatively low in comparison with those obtained from previous classical studies. The reported low convergence rate may be due to the occurrence of silent/quite earthquakes, aseismic slip, differential movement of Delhi Hardwar ridge, etc. Therefore, in view of the contemporary seismicity and conspicuous displacements, a study of long-term observations of this surface movement has been recommended in future through a time-series SAR Interferometry analysis.     

超短基线定位系统在深拖探测中的应用

作为水下探测设备的载体,深拖系统可长时间大范围的进行海洋调查,其水下位置的准确与否,将直接关系到探测资料的可用度。该文从深拖水下导航定位的关键技术问题出发,总结了适用于深拖系统的水下定位方法,重点介绍了具备高稳定度、高精度等诸多优点的超短基线声学定位系统。结合实例,阐述了超短基线定位工作原理、误差分析及数据处理方法,在拖曳系统匀速直线运动状态下,基于抗差自适应卡尔曼滤波算法对超短基线定位数据进行了处理,滤除了定位数据中的跳点,得到了较平滑且与原始数据相吻合的滤波数据。     

基于三维移动变形平台的GPS/BDS中长基线解算性能分析

针对中长基线解算测站间的大气误差无法通过双差完全消除、影响模糊度的固定与精度的问题,在得到宽巷模糊度后,利用Kalman滤波算法对L1、B1基频模糊度进行估计,并使用LAMBDA算法确定基频模糊度。以三维移动变形平台中长基线实测数据为例,解算GPS、BDS、GPS/BDS系统3种模式下的数条中长基线。总体而言,GPS/BDS组合系统较单GPS、BDS系统精度有所提升,GPS/BDS组合系统各基线固定率、正确率优于82.08%、81.53%,X、Y、Z、3D方向的精度可达15.4 mm、15.9 mm、20.1 mm、30.0 mm;20.8 km、46.6 km基线三维移动变形中误差分别优于18.8 mm、22.5 mm,相对中误差分别优于1/71.9、1/60.1。