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1.
基于小波变换的瞬时谱分析方法，克服了传统傅立叶时频转换时的时窗问题，提高了地震资料频域内的分辨能力。通过谱分析方法的比较，介绍了瞬时谱分析方法比传统傅立叶变换的改进效果，以及利用瞬时谱分析方法在分频数据体低频部分识别富气层下方的低频阴影来综合预测储层的横向展布特征和含气性异常的检测。研究实例表明低频阴影检测技术可以作为一种储层预测和油气检测的有效辅助方法。 相似文献
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对云及其阴影的识别是遥感图像处理中的一项基础性工作,在高分辨率遥感影像中,云及其阴影在图像中的分布是有规律的,利用两者在平坦区域高分辨率卫星影像上具有相似性的特征对其进行识别与匹配,可以比较简单地利用图像域值分割方法得到更好的识别与匹配结果.采用面向对象的思路提取云及其阴影的轮廓,在分析图像分割误差原因的基础上,考虑影像上云与其阴影的空间拓扑关系,应用改进的分数Hausdorff距离的图像匹配方法(MPHD),通过云及其阴影的局部相似的匹配,从而很好地识别出云及与其匹配的阴影,同时还可计算出匹配两者在投影平面上的距离.提出的云及其阴影的识别与匹配算法,为计算云高和应用遥感图像处理云及其云阴影的掩模提供科学依据. 相似文献
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Jochem I. Jongma Emmanuelle Driesschaert Thierry Fichefet Hugues Goosse Hans Renssen 《Ocean Modelling》2009,26(1-2):104-113
Melting icebergs are a mobile source of fresh water as well as a sink of latent heat. In most global climate models, the spatio-temporal redistribution of fresh water and latent heat fluxes related to icebergs is parameterized by an instantaneous more or less arbitrary flux distribution over some parts of the oceans. It is uncertain if such a parameterization provides a realistic representation of the role of icebergs in the coupled climate system. However, icebergs could have a significant climate role, in particular during past abrupt climate change events which have been associated with armada’s of icebergs. We therefore present the interactive coupling of a global climate model to a dynamic thermodynamic iceberg model, leading to a more plausible spatio-temporal redistribution of fresh water and heat fluxes. We show first that our model is able to reproduce a reasonable iceberg distribution in both hemispheres when compared to recent data. Second, in a series of sensitivity experiments we explore cooling and freshening effects of dynamical icebergs on the upper Southern Ocean and we compare these dynamic iceberg results to the effects of an equivalent parameterized iceberg flux.In our model without interactive icebergs, the parameterized fluxes are distributed homogeneously South of 55°S, whereas dynamic icebergs are found to be concentrated closer to shore except for a plume of icebergs floating North–East from the tip of the Antarctic Peninsula. Compared to homogeneous fluxes, the dynamic icebergs lead to a 10% greater net production of Antarctic bottom water (AABW). This increased bottom water production involves open ocean convection, which is enhanced by a less efficient stratification of the ocean when comparing to a homogeneous flux distribution.Icebergs facilitate the formation of sea-ice. In the sensitivity experiments, both the fresh water and the cooling flux lead to a significant increase in sea-ice area of 12% and 6%, respectively, directly affecting the highly coupled and interactive air/sea/ice system. The consequences are most pronounced along the sea-ice edge, where this sea-ice facilitation has the greatest potential to affect ocean stratification, for example by heat insulation and wind shielding, which further amplifies the cooling and freshening of the surface waters. 相似文献
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《Ocean Modelling》2010,35(3-4):111-124
Icebergs are an important part of the fresh-water cycle and, until now, have not been explicitly represented in Intergovernmental Panel on Climate Change (IPCC) class coupled global circulation models (CGCMs) of the climate system. In this study we examine the impact of introducing interactive icebergs in a next-generation CGCM designed for 21st Century climate predictions. The frozen fresh-water discharge from land is used as calving to create icebergs in the coupled system which are then free to evolve and interact with the sea-ice and ocean components. Icebergs are fully prognostic, represented as point particles and evolve according to momentum and mass balance equations. About 100,000 individual particles are present at any time in the simulations but represent many more icebergs through a clustering approach. The various finite sizes of icebergs, which are prescribed by a statistical distribution at the calving points, lead to a finite life-time of icebergs ranging from weeks, for the smallest icebergs (60 m length), up to years for the largest (2.2 km length). The resulting melt water distribution seen by the ocean enhances deep-water formation, in particular on the continental shelves, relative to the model without icebergs. 相似文献
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Physical evidence on the dimensions of icebergs released from the mouth of Hudson Strait into the northwest Atlantic during the last Heinrich event (H-0) is presented. Side-scan sonar imagery shows scour marks up to 700 m wide and longer than 28 km. These scour marks were carved by gigantic icebergs (megabergs) with keel drafts possibly as great as 660 m capable of scouring trenches 20 to 25 m deep into the seabed. These icebergs were likely calved from the grounding margin of a thick (possibly as thick as 640 m) rapidly-flowing glacial margin during the H-0 Heinrich event (11 ka BP). Along with the relatively few megabergs released were large numbers of smaller icebergs that calved from the ice margin at the same time and were also produced from break-up of the megabergs. Scouring of the seabed by the large and smaller icebergs happened at the same time, with megabergs scouring only in the deep waters of Hatton Basin, and the smaller bergs scouring only on the eastern, shallow margin of the Basin at the continental shelf break. 相似文献
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在高斯白噪声背景下,匹配滤波器作为线性调频信号的最优检测器,在水声信号处理中被广泛应用。 当发射信号为线性调频信号时,由水下目标径向速度引起的多普勒频移会造成回波和样本之间失配, 使匹配滤波器的检测性能下降,增加了目标速度估计的难度。 利用分数阶傅里叶变换对于线性调频信号的聚焦特性,提出了应用分数阶傅里叶变换的水下运动目标线性调频回波检测算法,完成对目标速度的估计, 推导目标运动速度与分数阶傅里叶变换阶数之间的关系,并对测量结果进行误差分析。 仿真测试表明,该算法可有效地估计混响背景下的目标径向速度,且具有良好的估计性能。 相似文献
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通过迭代CFAR算法，本文发展了一种针对分块SAR图像的冰山检测方法。考虑到滑动窗口运算负担大、计算效率低，首先对SAR图像进行分块，以提取分块内的亮目标冰山。利用高斯模型表征后向散射系数的统计分布，冰山检测阈值可简单地表达为均值和方差的线性组合，将分块内像素逐个比对阈值以检测冰山。考虑到同一场景中尺寸变化大的冰山影响检测精度，以识别的冰山像素做种子执行区域生长，从而提取大尺寸的冰山。针对单个分块迭代上述处理，以降低高斯模型表征分块统计分布的误差，提高冰山检测精度。利用2013年11月22日和29日获取自极地海域的两景RADARSAT-2图像开展验证试验。结果表明，数量多、尺寸变化大并嵌入在海冰等极地常见情形下的冰山，能被文中方法有效识别，选取区域内正确率高达85%以上，且具有良好的运行效率。 相似文献
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Tad Murty 《Marine Geodesy》2013,36(4):331-332
Optimal interpolation in the spatial domain is limited by computer storage requirements and the computational effort to invert the autocovariance matrix. The procedure can be simplified by use of the fast Fourier transform (FFT), where matrix inversion is replaced by a quotient of power spectral density (PSD) functions in the spectral domain. Such a methodology is developed and utilized to estimate an altimetric mean sea surface from a single 35‐day cycle of ERS‐1. ERS‐1 radial orbit error is first reduced by minimizing dual crossover residuals with TOPEXIPoseidon through solution for a sinusoidal correction for each ascending and descending arc along with the relative altimeter bias. A regular grid for ascending (descending) arcs is then formed by use of the equator‐crossing longitudes and the along‐track displacement. Gaps in the altimeter data set are filled by use of a reference model. PSDs derived from the data and reference surface enable computation of the least‐Squares estimator in the spectral domain, from which the optimally interpolated surface heights for ascending (descending) arcs are derived by the inverse Fourier operator. The resolution is bounded across track by the Nyquist frequencies, which for the 35‐day repeat period correspond to 1.44° longitudinal spacings or 160 km. For consistency, the along‐track resolution is reduced to a comparable level. The combination of the ascending and descending sea surface heights yields a surface up to the isotropic frequency that corresponds to surface spherical harmonics of degree and order 250. Comparisons show that the model performs almost as well as the Ohio State University model present on the TOPEXIPoseidon CD‐ROMs. 相似文献
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This paper describes a new framework for detection and tracking of underwater pipeline,which includes software system and hardware system.It is designed for vision system of AUV based on monocular CCD camera.First,the real-time data flow from image capture card is pre-processed and pipeline features are extracted for navigation.The region saturation degree is advanced to remove false edge point group after Sobel operation.An appropriate way is proposed to clear the disturbance around the peak point in the process of Hough transform.Second,the continuity of pipeline layout is taken into account to improve the efficiency of line extraction.Once the line information has been obtained,the reference zone is predicted by Kalman filter.It denotes the possible appearance position of the pipeline in the image.Kalman filter is used to estimate this position in next frame so that the information of pipeline of each frame can be known in advance.Results obtained on real optic vision data in tank experiment are displayed and discussed.They show that the proposed system can detect and track the underwater pipeline online,and is effective and feasible. 相似文献
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基于Hough变换原理的海冰厚度识别方法 总被引：1，自引：1，他引：0
作为主要海冰参数之一的海冰厚度对海冰灾害评估和极地船舶与冰区海洋工程结构设计具有重要意义。采用船侧视频图像对海冰厚度进行自动识别是提取海冰参数的重要方式。本文采用基于Hough变换的机器视觉方法对海冰翻转过程中的表面轮廓线进行识别,从而自动获取海冰厚度参数。根据海冰图像特征制定了图像边缘识别?近似线段识别?海冰轮廓线段组识别的计算流程。在线段组识别过程中,根据海冰的几何特征建立了由夹角、长度及间距参数相关联的3个识别参数所组成的判断条件。为验证方法的可靠性,将该方法用于“雪龙”号第八次北极科考的走航实测数据中,结果表明,3个识别参数均具有最优阈值。当低于最优值时提高阈值可增加有效识别率;而高于最优值时提高阈值则会导致误判率增大,采用最优阈值可使冰厚识别率达到90%以上。因此,采用基于Hough变换的冰厚识别方法可实现对海冰厚度的实时监测。 相似文献
13.
J.N. Schwarz M.P. Schodlok 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1727-1741
Icebergs that calve from the Antarctic ice shelves and drift in the Southern Ocean melt to deliver fresh water, dust and minerogenic particles to the surface ocean along the iceberg's path. Each of these components may have an effect on growth conditions for phytoplankton, as might the mechanical effects of the iceberg keel disturbing the water. Although anecdotal and small-scale surveys suggest that drifting icebergs increase local primary production, no large-scale studies have been reported. An analysis of satellite and automated iceberg tracking data from the Weddell Sea, covering the months October to March, from 1999 to 2004, showed that the probability of increased surface phytoplankton biomass was up to one-third higher in the wake of a tracked iceberg compared to background biomass fluctuations. Only during the month of February were the effects of icebergs on surface biomass likely to be negative, whereas background biomass fluctuations were likely to be negative during March. These results confirm icebergs as a factor affecting phytoplankton in the Southern Ocean and highlight the need for detailed process studies so that responses to future changes in the Antarctic ice sheets may be predicted. 相似文献
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Canada׳s Department of Fisheries and Oceans (DFO) conducts annual surveys in the Labrador Sea along the repeat hydrography line AR7W. The occupation of the AR7W line in May 2013 was followed by the experiment aimed at resolving the imprint of melting drifting icebergs on the upper layer thermohaline characteristics in the Labrador Sea. We present high-resolution observations around two icebergs conducted with the towed undulating platform Moving Vessel Profiler (MVP). The first iceberg drifted in relatively warm water of Atlantic origin (~2.5–3.1 °C) off Greenland, while the second iceberg was on the Labrador shelf in cold water below 0 °C. Both icebergs had a lengthscale of O(100 m). In both cases surface buoyant plumes fed by melt water and attached to the iceberg were observed. The plumes were evident in the anomalous thermohaline characteristics of the seawater. Their density anomalies were sufficiently strong to produce visible frontal structures, which imply a development of the intrinsic dynamics associated with a plume. The first plume formed over a time interval of ~10 h, while the second plume formed over several days and extended for more than 1 km (tenfold the iceberg׳s size). Strong vertical displacements of the pycnocline were observed near the second iceberg. They are interpreted as the internal wave wake. This interpretation is based on the temporal scale of these oscillations (local buoyancy frequency), as well as on the spatial orientation of these waves with respect to the iceberg drift relative to the pycnocline. The observed internal waves partially overlapped with the plume and affected its structure. The saline seawater splashing by swell contributed to the surface melting of the icebergs. Scaling analysis of the second plume suggests that it could be in the “rotational” dynamic regime with recirculating anticyclonic flow. 相似文献
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Kay I. Ohshima Toshiyuki Kawamura Takatoshi Takizawa Shuki Ushio 《Journal of Oceanography》1994,50(3):365-372
Step-like thermohaline structure was observed near icebergs trapped by fast ice in Lützow-Holm Bay, Antarctica. The structure was developed within the draft depth of the icebergs. The typical vertical distance between the succeeding step surfaces is 20–30 m, and the temperature and salinity differences across the step surface are about 0.05–0.06 deg and 0.06–0.10 psu, respectively. The structure appears to be generated by a sea-water/iceberg interaction, and is explainable by a simple model in which an ice wall is placed in the ocean linearly stratified by vertical salinity gradient. 相似文献
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Abstract Geoid heights and vertical deflections derived from satellite radar altimetry contain characteristic signals that may be reproduced and explained by simple models for seamount gravitation acting on the sea surface. Computer algorithms capable of automatic operation and able to detect, approximately locate, and estimate parameters constraining the shape of actual sea‐mounts were written and tested. The computer program which utilized a digital high‐pass filter combined with a roughness sensor was effective in separating the seamount produced geoid undulation/vertical deflection pattern from the remaining data track features, simultaneously detecting and locating along the track such signals. Tests of the algorithm on several SEASAT passes over known bathymetry produced mixed results. Meaningful shape constraints were obtained by matching the geoid anomaly calculated from the seamount model to the actual mean sea level pattern for some seamounts. Results for other seamounts were poor and possible reasons for the failure are discussed. It is concluded that a computerized seamount detection program for radar altimetry data is feasible, but it will have to be more complex than the present one for fully successful operation. 相似文献
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Side-scan sonar and sub-bottom profiling investigations of the Iceland-Faeroe Ridge have revealed the widespread presence
of iceberg plowmarks at water depths between 750 and 860 m. This is well beyond the maximum water depth reported for ice scouring
in the adjacent areas of the North Atlantic. An exceptionally deep iceberg plowmark was found at the southern flank of the
ridge, which could be traced down to 940 m water depth. Supported by published nearby sediment core data, a Saalian (MIS 6)
age of that iceberg plowmark is suggested. Considering a glacial sea level of 120 m below present, the paleo-draft of this
iceberg is estimated to have been at least 820 m. The keel depth of such giant icebergs drifting in the glacial northern North
Atlantic significantly exceeds the draft dimensions of large icebergs seen today in the Antarctic. The most likely source
area for this extreme deep-draft type of iceberg is inferred to be southern Greenland. Plowmark direction, which in our case
indicates iceberg entrainment by the North Atlantic Current, is suggested to be a useful indicator of (sub)surface paleo-circulation
during late Pleistocene iceberg surging and deglaciation episodes. 相似文献
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A series of sub-parallel linear glacial scours are identified on the crest of the Baoshi Seamount in the Northwind Abyssal Plain by compiling new multibeam data acquired during the 9th Chinese Arctic Research Expedition (CHINARE-Arc9) in 2018 and previously published data. The new data reveal scours that developed at water depths of 850–1 030 m with an orientation of about 75°/255°. The maximum water depth occurs in the southernmost scour and is deeper than that from previous investigations, which showed a maximum scouring depth of about 900 m on the seamount. The topographic and geomorphological characteristics suggest that these scours resulted from erosion by the ice shelf extending from the Chukchi margin and/or Laurentide Ice Sheet that grounded on the crest of the seamount and moved in a NE–SW direction. Other possibilities of their genesis include armadas of large icebergs/multi-keel icebergs calved from the Chukchi Shelf or the Laurentide Ice Sheet. The new data provide new constraints for assessing the extent and volume of the ice sheet in the Chukchi area during glacial maxima. 相似文献