共查询到20条相似文献，搜索用时 46 毫秒
1.
We present a mechanical method to horizontally section soft bottom sediment cores to minimize the vertical post-sampling redistribution
of motile infaunal macroinvertebrates. A clear acrylic core tube for a standard Kajak-Brinkhurst corer was modified by cutting
a series of horizontal slits into the side of the core tube to allow the insertion of sectioning plates for physically sealing
each section immediately after core retrieval. The modification is simple, inexpensive and easily adapted to any open barrel
gravity corer. 相似文献
2.
A. F. Lotter I. Renberg H. Hansson R. Stöckli M. Sturm 《Aquatic Sciences - Research Across Boundaries》1997,59(4):295-303
A new coring device is presented which allows the recovery of loose watery surface sediments and the water/sediment interface
byin situ freezing, resulting in well preserved samples. The instrument consists of a tripod with adjustable legs, a hydraulic system,
an insulated thermos (with two electrical pumps), and a wedge-shaped freeze box. Alcohol chilled with dry ice is the freezing
agent. The corer can be deployed from a boat or a raft and permits recovery of undisturbed surface sediment sections up to
100 cm long in deep waters. The corer is particularly useful for sampling varved sediments. 相似文献
3.
K. Kelts U. Briegel K. Ghilardi K. Hsu 《Aquatic Sciences - Research Across Boundaries》1986,48(1):104-115
Various methods are available for coring in lakes. We have developed an integrated coring system based on a modified Kullenberg poston-corer principle which is particularly useful for multiple coring in deep lakes. The selection of sites is guided by concurrent high-resolution (3.5 kHz) continuous seismic profiling. The system is modular for simple transport, and includes a very reliable tripweight gravity corer which uses the same plastic liners as the piston corer. Piston-core lengths are variable in 2, 4, or 5 m sections up to 16 m. This system has been successfully deployed in glacially deepened perialpine lakes (Lakes Zürich, Zug, Greifensee, Lucerne, Walensee, Constance, Murten, Neuchâtel, Geneva, Thun, Brienz, Maggiore, Lugano, Iseo, Garda, d'Annecy, Bourget and Ammersee), deep rift lakes of Africa (Turkana, Albert, Edward, Kiwu), Lake Ohrid (Jugoslavia), Lake Van (Turkey), Qinghai Lake (China), and in very shallow hypersaline lakes Urmia (Iran) and Great Salt Lake (USA). Following numerous requests, this paper describes the system concept and constructional features that have been refined over the last 12 years. Development has stressed increasing simplification and increased reliability. 相似文献
4.
Wayne S. Gardner Mark J. McCarthy Stephen A. Carini Afonso C. Souza Hou Lijun Karen S. McNeal Mary Keith Puckett Jack Pennington 《Continental Shelf Research》2009,29(18):2207-2213
Settled particles of fresh, labile organic matter may be a significant source of oxygen demand and nutrient regeneration in seasonally-hypoxic regions caused by nutrient inputs into stratified coastal zones. Studying the dynamics of this material requires sediment sampling methods that include flocculent organic materials and overlying water (OLW) at or above the sediment–water interface (SWI). A new coring device (“HYPOX” corer) was evaluated for examining nitrogen- (N) and oxygen-dynamics at the SWI and OLW in the northern Gulf of Mexico (NGOMEX). The HYPOX corer consists of a “Coring Head” with a check-valve, a weighted “Drive Unit,” and a “Lander,” constructed from inexpensive components. The corer collected undisturbed sediment cores and OLW from sediments at NGOMEX sampling sites with underlying substrates ranging from sand to dense clay. The HYPOX corer could be deployed in weather conditions similar to those needed for a multi-bottle rosette water-sampling system with 20 L bottles. As an example of corer applicability to NGOMEX issues, NH4+ cycling rates were examined at hypoxic and control sites by isotope dilution experiments. The objective was to determine if N-dynamics in OLW were different from those in the water column. “Ammonium demand,” as reflected by potential NH4+ uptake rates, was higher in OLW than in waters collected from a meter or more above the bottom at both sites, but the pattern was more pronounced at the hypoxia site. By contrast, NH4+ regeneration rates were low in all samples. These preliminary results suggest that heterotrophic activity and oxygen consumption in OLW in the hypoxic region may be regulated by the availability of NH4+, or other reduced N compounds, rather than by the lack of sufficient labile organic carbon. 相似文献
5.
Heinz Ambühl 《Aquatic Sciences - Research Across Boundaries》1969,31(1):132-140
Summary A new method is described for taking sediment sample cores of a diameter of 112 millimeters from deep lakes. The rather large
core diameter requires a mechanism which closes the lower end of the core before retraction so that the core can be raised
without loss of the sample. The apparatus is set on to a cutting table on which the core, still in the tube, is separated
from the closing mechanism without disturbance by means of a blade. The bottom end of the tube is then secured and the corer
can be re-used with a new core tube.
相似文献
6.
Mick S. Filmer Christian Hirt Will E. Featherstone 《Studia Geophysica et Geodaetica》2013,57(1):47-66
Gravity-based heights require gravity values at levelled benchmarks (BMs), which sometimes have to be predicted from surrounding observations. We use the Earth Gravitational Model 2008 (EGM2008) and the Australian National Gravity Database (ANGD) as examples of model and terrestrial observed data respectively to predict gravity at Australian National Levelling Network (ANLN) BMs. The aim is to quantify errors that may propagate into the predicted BM gravity values and then into gravimetric height corrections (HCs). Our results indicate that an approximate ±1 arc-min horizontal position error of the BMs causes maximum errors in EGM2008 BM gravity of ~22 mGal (~55 mm in the HC at ~2200 m elevation) and ~18 mGal for ANGD BM gravity because the values are not computed at the true location of the BM. We use RTM (residual terrain modelling) techniques to show that ~50% of EGM2008 BM gravity error in a moderately mountainous region can be accounted for by signal omission. Non-representative sampling of ANGD gravity in this region may cause errors of up to 50 mGals (~120 mm for the Helmert orthometric correction at ~2200 m elevation). For modelled gravity at BMs to be viable, levelling networks need horizontal BM positions accurate to a few metres, while RTM techniques can be used to reduce signal omission error. Unrepresentative gravity sampling in mountains can be remedied by denser and more representative re-surveys, and/or gravity can be forward modelled into regions of sparser gravity. 相似文献
7.
利用二维全隐欧拉格式对重力波在可压、非等温大气中的非线性传播过程进行了数值模拟和分析.分析结果表明，从对流层顶激发的重力波能稳定地经平流层传到中层顶，从而将能量和动量从一个区域带到另一个区域；在向上传播过程中，重力波经历了发展、位温翻转、对流直至最终破碎的演变；重力波的破碎是对流和小尺度波动的重要的源，对流不稳定和翻转是非线性现象的一个基本特征.计算还显示，扰动源的大小直接影响着重力波的非线性传播过程，当扰动源足够小时，重力波能稳定传播，而大振幅扰动可以加速重力波的破碎. 相似文献
8.
Z. FAJKLEWICZ 《Geophysical Prospecting》1983,31(5):748-765
Microgravity can be used for predicting rock bursts. For the first time gravity anomalies related to rock bursts have been recorded. The methodology developed has lead to the first successful predictions. The depth of the rock-burst focus might be determined on the basis of analytical downward continuation of related gravity anomalies: the focus is treated as a singular point of the gravity potential and its derivatives. The rock-burst gravity anomalies might be explained on the basis of the assumed dilatancy process that causes the rock burst. The mean density change of the rock mass threatened with rock bursts can be estimated from the corresponding rock-burst gravity anomalies. 相似文献
9.
Gravity change observed in a local gravity network and its implication to seasonal precipitation in Dali county,Yunnan province,China 
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下载免费PDF全文 Xin Zhou Wenke Sun Hui Li Shuhei Okubo Shaoan Sun Lelin Xing Dongzhi Liu Chongyang Shen 《地震科学（英文版）》2014,27(1):79-88
This study investigates data-processing methods and examines the precipitation effect on gravity measurements at the Dali gravity network, established in 2005. High-quality gravity data were collected during four measurement campaigns. To use the gravity data validly, some geophysical corrections must be considered carefully. We first discuss data-processing methods using weighted least-squares adjustment with the constraint of the absolute gravity datum. Results indicate that the gravity precision can be improved if all absolute gravity data are used as constraints and if calibration functions of relative gravimeters are modeled within the observation function. Using this data-processing scheme, the mean point gravity precision is better than 12 μgal. After determining the best data-processing scheme, we then process the gravity data obtained in the four measurement campaigns, and obtain gravity changes in three time periods. Results show that the gravity has a remarkable change of more than 50 μgal in the first time period from Apr–May of 2005 to Aug–Sept of 2007. To interpret the large gravity change, a mean water mass change (0.6 m in height) is assumed in the ETOPO1 topographic model. Calculations of the precipitation effect on gravity show that it can reach the same order of the observed gravity change. It is regarded as a main source of the remarkable gravity change in the Dali gravity network, suggesting that the precipitation effect on gravity measurements must be considered carefully. 相似文献
10.
多网重力数据联合平差和系统误差改正 总被引：1，自引：0，他引：1
华北地区现行的地震重力监测网由于独立联测, 自成体系, 绝对控制点较少, 获得的重力场动态变化图像在绝对控制较弱的地区会产生畸变, 也不能有效的消除仪器标定系统所引起的测量误差。 本文以华北大网作为控制网, 结合绝对重力点进行联合平差计算, 使各省区地震重力监测网平差精度提高了(0~4)×10-8 m/s2, 平差起算基准相统一, 绝对控制较弱的地区畸变减小。 采用相关系数检验法, 对华北地区各省区地震重力监测网2010年二期重力平差计算结果进行检验, 部分重力点位系统误差高达60×10-8 m/s2, 经过系统误差改正后, 重力场动态变化趋于一致。 经过各项改正后, 华北地区2010年重力场动态差分图像对地震前兆具有更好的反映。 相似文献
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14.
Bernhard Heck 《Studia Geophysica et Geodaetica》2011,55(3):441-454
For more than 150 years gravity anomalies have been used for the determination of geoidal heights, height anomalies and the
external gravity field. Due to the fact that precise ellipsoidal heights could not be observed directly, traditionally a free
geodetic boundary-value problem (GBVP) had to be formulated which after linearisation is related to gravity anomalies. Since
nowadays the three-dimensional positions of gravity points can be determined by global navigation satellite systems very precisely,
the modern formulation of the GBVP can be based on gravity disturbances which are related to a fixed GBVP using the known
topographical surface of the Earth as boundary surface. The paper discusses various approaches into the solution of the fixed
GBVP which after linearization corresponds to an oblique-derivative boundary-value problem for the Laplace equation. Among
the analytical solution approaches a Brovar-type solution is worked out in detail, showing many similarities with respect
to the classical solution of the scalar free GBVP. 相似文献
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激光雷达观测得到的密度、温度等数据被广泛应用于大气重力波研究.瑞利激光雷达可以获取激光路径上的大气密度、温度数据.对于大气中的三维波动而言,单条路径上的观测参量能提取得到的波动信息有限.本文首先以单色重力波为例,分析了利用激光雷达直接观测三维波动结构的可行性.激光雷达垂直观测即可得到重力波的垂直波长,当激光雷达以一定的天顶角斜向测量时,所得到的波长包含了重力波的垂直波长以及水平波长信息.因此,利用激光雷达同时以三个方向(垂直、向南(天顶角30°)以及向西(天顶角30°))测量,可以提取得到重力波的垂直波长和水平波长.本文利用中国科学院国家空间科学中心研制的车载532nm瑞利激光雷达的经向系统和纬向系统同时以不同的指向角观测大气重力波,对利用激光雷达获取三维波动结构的方法进行了分析研究.本文给出了北京地区激光雷达观测重力波的诸多案例,分析了30~60km高度范围内北京地区大气重力波的垂直及水平波长信息.并以2017年11月7日观测的准单色重力波为例,结合再分析资料的风场数据,分析了该重力波的水平波长,垂直波长及传播方向等信息. 相似文献
17.
《Journal of Geodynamics》2010,49(3-5):348-353
In this study, the loading gravity effect of air mass changes calculated with the three-dimension (3D) meteorological data from the European Centre for Medium-range Weather Forecasts (ECMWF) are removed from superconducting gravimeter (SG) observations. The global hydrological gravity effect is computed and removed with hydrological data from the Global Land Data Assimilation System (GLDAS). Otherwise, the gravity influences induced by a theoretical self-consistent ocean pole tide and variations in length of day (LOD) are considered in the calculation. After removing the influences mentioned previously and also considering the long term trend in the data, a very nice linear relationship between the theoretical gravity pole tide and observed gravity residual (containing the observed gravity pole tide) for each of the selected 9 GGP stations we considered can be obtained. Therefore, the gravimetric factor of the gravity pole tide can be estimated with a simple linear regression. The results show that no clear phase lag is found between the theoretical gravity pole tide and observed gravity residuals from the nine SG stations. 相似文献
18.
本文利用澳大利亚北领地West Arnhem Land 地区实测重力异常数据并联合DEM(9")和SRTM3(3")地形高程数据,使用移去-恢复技术和Stokes积分方法计算了该地区两条剖面的重力梯度及其功率谱密度,使用FFT方法解算了整个地区的重力梯度值,结果证明了联合重力异常数据和高分辨率地形高程数据能有效地提高重力梯度的解算精度;功率谱密度的计算结果与国外成熟的重力梯度功率谱密度模型相吻合,表明高于0.3 Hz频率范围的功率谱密度可看做噪声,为重力梯度数据处理中噪声的辨别和剔除提供了借鉴,另外对重力梯度辅助导航基准图的构建以及重力梯度测量系统的标定提供了有益的探索. 相似文献
19.
基于标准大气定律和大气圆柱体分布模型,本文引进了大气重力格林函数,用离散格积方法求得了大气对重力场观测的影响,对台站高程、周围地形和地表温度变化等因素的影响问题进行了讨论．结果说明台站近区气压变化是大气重力信号的主要贡献者,考虑大气质量负荷引起的弹性地球形变效应后,对距台站0．5°的区域积分获得的大气重力导纳值为-0．3603μGal／hPa,占全球大气变化引起的总信号的90％以上,这一理论模型结果与超导重力仪实测结果相吻合,并能较有效地用于消除重力观测中的气压干扰成分． 相似文献
20.
Pierre Keating 《Geophysical Prospecting》1995,43(4):569-580
Gravity data are often acquired over long periods of time using different instruments and various survey techniques, resulting in data sets of non-uniform accuracy. As station locations are inhomogeneously distributed, gravity values are interpolated on to a regular grid to allow further processing, such as computing horizontal or vertical gradients. Some interpolation techniques can estimate the interpolation error. Although estimation of the error due to interpolation is of importance, it is more useful to estimate the maximum gravity anomaly that may have gone undetected by a survey. This is equivalent to the determination of the maximum mass whose gravity anomaly will be undetected at any station location, given the data accuracy at each station. Assuming that the maximum density contrast present in the survey area is known or can be reasonably assumed from a knowledge of the geology, the proposed procedure is as follows: at every grid node, the maximum mass whose gravity anomaly does not disturb any of the surrounding observed gravity values by more than their accuracies is determined. A finite vertical cylinder is used as the mass model in the computations. The resulting map gives the maximum detection error and, as such, it is a worst-case scenario. Moreover, the map can be used to optimize future gravity surveys: new stations should be located at, or near, map maxima. The technique is applied to a set of gravity observations obtained from different surveys made over a period of more than 40 years in the Abitibi Greenstone Belt in eastern Canada. 相似文献