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1.
Very high-frequency marine multichannel seismic reflection data generated by small-volume air- or waterguns allow detailed, high-resolution studies of sedimentary structures of the order of one to few metres wavelength. The high-frequency content, however, requires (1) a very exact knowledge of the source and receiver positions, and (2) the development of data processing methods which take this exact geometry into account. Static corrections are crucial for the quality of very high-frequency stacked data because static shifts caused by variations of the source and streamer depths are of the order of half to one dominant wavelength, so that they can lead to destructive interference during stacking of CDP sorted traces. As common surface-consistent residual static correction methods developed for land seismic data require fixed shot and receiver locations two simple and fast techniques have been developed for marine seismic data with moving sources and receivers to correct such static shifts. The first method – called CDP static correction method – is based on a simultaneous recording of Parasound sediment echosounder and multichannel seismic reflection data. It compares the depth information derived from the first arrivals of both data sets to calculate static correction time shifts for each seismic channel relative to the Parasound water depths. The second method – called average static correction method – utilises the fact that the streamer depth is mainly controlled by bird units, which keep the streamer in a predefined depth at certain increments but do not prevent the streamer from being slightly buoyant in-between. In case of calm weather conditions these streamer bendings mainly contribute to the overall static time shifts, whereas depth variations of the source are negligible. Hence, mean static correction time shifts are calculated for each channel by averaging the depth values determined at each geophone group position for several subsequent shots. Application of both methods to data of a high-resolution seismic survey of channel-levee systems on the Bengal Fan shows that the quality of the stacked section can be improved significantly compared to stacking results achieved without preceding static corrections. The optimised records show sedimentary features in great detail, that are not visible without static corrections. Limitations only result from the sea floor topography. The CDP static correction method generally provides more coherent reflections than the average static correction method but can only be applied in areas with rather flat sea floor, where no diffraction hyperbolae occur. In contrast, the average static correction method can also be used in regions with rough morphology, but the coherency of reflections is slightly reduced compared to the results of the CDP static correction method. 相似文献
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Nathaniel G. Plant Kacey L. Edwards James M. Kaihatu Jayaram Veeramony Larry Hsu K. Todd Holland 《Coastal Engineering》2009
Nearshore wave and flow model results are shown to exhibit a strong sensitivity to the resolution of the input bathymetry. In this analysis, bathymetric resolution was varied by applying smoothing filters to high-resolution survey data to produce a number of bathymetric grid surfaces. We demonstrate that the sensitivity of model-predicted wave height and flow to variations in bathymetric resolution had different characteristics. Wave height predictions were most sensitive to resolution of cross-shore variability associated with the structure of nearshore sandbars. Flow predictions were most sensitive to the resolution of intermediate scale alongshore variability associated with the prominent sandbar rhythmicity. Flow sensitivity increased in cases where a sandbar was closer to shore and shallower. Perhaps the most surprising implication of these results is that the interpolation and smoothing of bathymetric data could be optimized differently for the wave and flow models. We show that errors between observed and modeled flow and wave heights are well predicted by comparing model simulation results using progressively filtered bathymetry to results from the highest resolution simulation. The damage done by over smoothing or inadequate sampling can therefore be estimated using model simulations. We conclude that the ability to quantify prediction errors will be useful for supporting future data assimilation efforts that require this information. 相似文献
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黄河三角洲前沿的陆地由于受地面沉降的影响,使地面高程不断发生变化.在水深测量中,深度基准面是根据陆地水准点高程确定的,陆地水准点高程的变化影响深度基准面的确定,从而影响水深测量的准确性.又由于黄河海港附近有一无潮点,其附近的潮汐性质变化大,在黄河三角洲前沿大范围水深测量中,根据测区潮位变化设立足够的验潮站及统一各个验潮站的水尺零点到同一个深度基准面上,是保证水深测量结果可靠的关键.通过黄河三角洲前沿陆地高程的变化和验潮获得的资料,介绍了黄河三角洲前沿深度基准面的变化和潮位变化情况. 相似文献
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Gridding heterogeneous bathymetric data sets with stacked continuous curvature splines in tension 总被引：3，自引：0，他引：3
Gridding heterogeneous bathymetric data sets for the compilation of Digital bathymetric models (DBMs), poses specific problems
when there are extreme variations in source data density. This requires gridding routines capable of subsampling high-resolution
source data while preserving as much as possible of the small details, at the same time as interpolating in areas with sparse
data without generating gridding artifacts. A frequently used gridding method generalizes bicubic spline interpolation and
is known as continuous curvature splines in tension. This method is further enhanced in this article in order to specifically
handle heterogeneous bathymetric source data. Our method constructs the final grid through stacking several surfaces of different
resolutions, each generated using the splines in tension algorithm. With this approach, the gridding resolution is locally
adjusted to the density of the source data set: Areas with high-resolution data are gridded at higher resolution than areas
with sparse source data. In comparison with some of the most widely used gridding methods, our approach yields superior DBMs
based on heterogeneous bathymetric data sets with regard to preserving small bathymetric details in the high-resolution source
data, while minimizing interpolation artifacts in the sparsely data constrained regions. Common problems such as artifacts
from ship tracklines are suppressed. Even if our stacked continuous curvature splines in tension gridding algorithm has been
specifically designed to construct DBMs from heterogeneous bathymetric source data, it may be used to compile regular grids
from other geoscientific measurements. 相似文献
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B. Gjevik D. Hareide B. K. Lynge A. Ommundsen J. H. Skailand H. B. Urheim 《Marine Geodesy》2006,29(1):1-17
A system for displaying tidal currents in an electronic chart display and information system (ECDIS) has been developed and implemented in compliance with the standards of the International Hydrographic Organization (IHO). The tidal current fields can be displayed in real time on the electronic navigational chart and several options and functions for updating and zooming have been designed. The current fields are calculated from a data base with the harmonic constants for the four major tidal constituents. The harmonic constants are obtained from a high resolution numerical model with horizontal grid resolution of 100 m. The model is validated by comparing with sea level and current measurements. The depth matrix for the central part of the model domain was calculated from data from multibeam bathymetric surveys. An application example of the implementation is given for Trondheimsleia, a part of the main sailing route along the western coast of Norway. 相似文献
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W. S. D. Wilcock D. R. Toomey G. M. Purdy S. C. Solomon 《Marine Geophysical Researches》1993,15(1):1-12
We present a gridded Sea Beam bathymetric map of a 5100 km2 area between 9° and 10° N on the East Pacific Rise (included as a color separate accompanying this issue). The raw bathymetric data are renavigated using a technique for calculating smooth adjustments to navigation that incorporates absolute constraints from satellite fixes and acoustically-located explosive shots, and relative constraints from the misfit of bathymetric data at ship track crossovers. We describe a back-projection technique for gridding the bathymetric data that incorporates an approximation for the power distribution within a narrow-beam echo sounding system and accounts for the variable uncertainties associated with multi-beam data. The nodal separation of the resulting map is ~ 80 m in both latitude and longitude, and the sampling of grid points within a 60 × 85 km2 region is in excess of 99%. A formal analysis of variance is applied to the gridded bathymetric data. For each grid point, the difference between the variance of data from within a track versus data from between tracks provides an upper bound on the magnitude of bathymetric misfits arising from navigational errors. The renavigation results in an 88% reduction in this quantity. We also examine the effects of renavigation on the misfit of magnetic and gravity data at crossovers and compare our results with other bathymetric surveys. A striking feature of the final bathymetric map is the sinuous regional shape of the rise axis. In plan view, the local trend of morphology sometimes varies by up to 15° and the distances separating changes in morphological trend are about 10–20 km. In cross section the slopes of the rise flanks are notably asymmetric and show some correlation with the offset of the axial magmatic system as detected by seismic methods. 相似文献
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Adjustments to satellite constrained navigation are required to match SeaBeam bathymetric data at track crossings due to errors in dead reckoning and inaccuracies in satellite fixes. By shifting one of the SeaBeam swaths involved in a track crossing relative to the other and calculating the sum of the squares of the differences in bathymetry within the area of overlapping coverage, we map a two-dimensional error surface whose minimum corresponds to the best estimate of the correction to navigation required at the crossing point. Estimates of the covariance of this correction are derived from the error surface. We employ the curve fitting technique of Tarantola and Valette (1982) to invert for a smooth correction function to a starting model of the position of the ship as a function of time. This technique incorporates formal errors assigned to dead reckoning, satellite fixes, and the shifts required to match bathymetric swaths at crossing points in a simultaneous inversion for the correction function for all tracks within the study area.In a test of the method in a study area on the southern Mid-Atlantic Ridge, a data set involving two cruises, 30 days of SeaBeam data, and 753 track crossings, we found that crossing SeaBeam swaths can potentially resolve the relative position of the ship on the two tracks to within 30 to 70 m. The inversion procedure yielded a much better constrained navigation function and much improved match of bathymetry. The final model of the navigation fit crossing shifts about as well as satellite data (with respect to their assigned data errors) with the RMS value of the crossing shifts decreasing from 1200 m in the original satellite-constrained navigation to 200 m in the final solution. However, the potential resolution of position using SeaBeam swaths was not fully achieved in the solution because there are systematic bathymetric artifacts in SeaBeam data, multiple local minima in the error surfaces in highly lineated topography, inadequate dead reckoning data, occasional bad satellite fixes, and limitations on the short period corrections allowed in the model. 相似文献
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对运用小排列高分辨多道地震系统获取的岱山岛大桥附近海域高精度的地震数据进行了综合分析和处理,查明了调查区域的工程地质条件,并对两个桥址方案进行了地质条件的对比。采用的地震系统参数:拖缆为24道,道间距为2 m,偏移距为46 m,枪容积为10 in3,频带范围为1~1 000Hz。结果表明:(1)采用了统一方法和流程对岱山岛大桥工程中所获得的地震数据进行分析、处理,保证了两种选址方案调查结果的一致性。(2)舟山本岛-岱西桥位(方案Ⅰ)和舟山本岛-双合山桥位(方案Ⅱ)海底地形平缓,不存在海底滑坡体等不良地质现象,调查区域虽分别有6条和5条断裂,但所有断层的上覆第四系均未发生错断,断裂均为非活动性断裂,两个方案桥位线均具有建桥的良好工程地质条件。(3)与单道地震相比,小排列高分辨多道地震系统能得到更为丰富的地层反射地震数据,而该系统比传统的多道反射地震方法具有作业方便、经济的优势,可见,该调查方法适用于近岸区域浅水工程环境的地质调查工作,是一种方便、实用和经济的地质调查手段。 相似文献
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传统的湖泊、海岸带测深主要是基于船载多波束系统或者机载激光雷达测深系统,但这些方式测量成本较高。因此提出了一种仅利用卫星观测数据,实现高分辨率动态水域地形图的获取方法,该方法基于ICESat-2单光子激光点云和Landsat图像数据的全球地表水数据集(GSWD),对所获取的高精度激光沿轨轮廓线与多年期湖泊水域边界等高线进行融合匹配。以美国最大的水库米德湖为实验区域,生成高程范围约为34 m的地形图结果,覆盖面积超过307 km~2,水平分辨率为30 m;在与机载激光雷达数据等现场实测结果的对比中,所绘制地形图均方根误差约为2 m。研究方法有望为水位波动较大或水质相对较好的内陆水体(例如湖泊)和沿海地区(例如潮间带)提供一种新的水陆交界区域地形图获取方法。 相似文献
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The sea surface heights (SSHs) observed by the TOPEX altimeter are compared with tide gauge data at Chichijima in Ogasawara (Bonin) Islands and hydrographic data taken around the islands, in order to quantitatively verify the altimeter observations and oceanic tide corrections by three tide models proposed by Cartwright and Ray (1991), Rayet al. (1994), and Maet al. (1994). First, performance of the new tide models is assessed by comparing tidal variations consisting of diurnal and semi-diurnal constituents with the tide gauge data at Chichijima. The tide model proposed by Rayet al. gives the smallest root-mean-squared (rms) difference of 2.61 cm. Errors in amplitude and phase in each tide model are evaluated by spectral analysis. The TOPEX SSHs corrected by the tide models are compared with sea level data at Chichijima. A long-term variation of a period of about 1 year is found in the residual between the SSHs and the Chichijima sea levels. This variation is also found in the difference between the dynamic height anomalies calculated from hydrographic data around the island and the Chichijima sea levels. By subtracting the long-term variation, the rms difference between the TOPEX SSHs and the Chichijima sea levels is reduced to about 4 cm and the slope of the regression line is improved to unity. The residual shows variations related to aliasing caused by incompleteness of the ocean tide correction with the repeat cycle of the altimeter observation. 相似文献
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Meredith R.W. Stanic S.J. Goodman R.R. Kennedy E.T. Pace N.G. 《Oceanic Engineering, IEEE Journal of》2004,29(2):524-533
Dynamic ocean processes produce small thermal variations that induce spatial and temporal variability in the ocean's index of refraction and in the spatial scale along an acoustic propagation path. This paper reports measurements and analysis of thermal microstructure effects on ping-to-ping amplitude and phase variability of shallow-water direct-path acoustic propagation in the 20-200 kHz frequency range. These measurements were conducted during a joint experiment conducted by the Naval Research Laboratory and the North Atlantic Treaty Organization Supreme Allied Commander Atlantic (SACLANT) Undersea Research Centre, La Spezia, Italy, in 8 m of water off American Beach, located between Pisa and Livorno, Italy. Experimental observations are compared with predictions for isotropic and anisotropic turbulence, as well as for sea-surface swell. Measured phase and log-amplitude variances coincide with predictions and are relatively insensitive to weak water-column stability. The sea-surface swell dominates phase variances for this data and turbulence dominates log-amplitude variances. These results provide a reasonable lower limit on high-frequency ping-to-ping amplitude and on phase variability produced by benign shallow-water thermal fluctuations. 相似文献
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CHOI Jinyong JUN Kicheon CHOI Youngkwang CHO Kyoungho KWON Jae-Il PARK Jinsoon PARK Kwangsoon 《海洋学报(英文版)》2015,34(12):11-18
The Maenggol Channel and Uldolmok Strait, located on the south-west coast of Korea, have notably strong and complex currents due to tidal effects and to local geological factors. In these areas, electric power has been generated using strong tidal currents, the speed of which is more than 3 m/s during spring tides. The region also provides a shortcut for navigation. These tidal conditions are therefore sometimes useful, but may also cause terrible accidents or severe economic damage, in the absence of accurate information regarding ocean conditions. In April 2014, the passenger ferry MV Sewol capsized in the Maenggol Channel, with 295 passengers killed and 9 still missing. While this was unquestionably a man-made disaster, strong currents were one of the contributing causes. It was also difficult to conduct scuba diving rescue operations given strong current speeds, and accurate prediction of the time when the tide would turn was thus critically needed. In this research, we used the high-resolution coastal circulation forecasting system of KOOS (Korea Operational Oceanographic System) for analysis and simulation of strong tidal currents in such areas with many small islands, using measurements and modeling from this research area. For accurate prediction of tidal currents, small grid size-modeling was needed, and in this study, we identified a suitable grid size that offers efficiency as well as accuracy. 相似文献
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闽江感潮河段潮汐-洪水相互作用数值模拟 总被引：1，自引：0，他引：1
本文分析了闽江感潮河段洪水、潮汐特征,利用高精度GIS数据建立了基于非结构三角网的高分辨率洪-潮耦合模型,在闽江口重点区域的网格分辨率达到50~100m。选取竹岐断面作为径流边界并基于"2006.6.6"洪水过程设计了3组数值实验,模拟结果表明:相比于只考虑洪水或者潮汐,在耦合洪水和潮汐后,各代表站的模拟值与实测值更为吻合;在30年一遇洪水的作用下,闽江感潮河段各断面的原有潮汐特征都不同程度地被洪水信号所影响,其中,文山里和解放大桥站表现出明显的洪水特征,而峡南、白岩潭和琯头站则表现出洪、潮混合特征;从峡南到琯头对应河段在高潮时段流速减小而低潮时段则流速增大,说明该河段存在很明显的洪-潮相互作用。 相似文献
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SEDIS IV型短周期自浮式海底地震仪数据校正方法 总被引：6，自引：0，他引：6
利用15台SEDISIV型短周期自浮式海底地震仪在南海中、北部地壳深部结构调查中所获得的资料,探讨了海底地震仪数据校正的方法和校正后的效果,结果表明:使用该地震仪所获得的原始资料经过放炮时间、炮点坐标数据局部化、海底地震仪位置误差以及记录时间漂移4方面的校正后,数据更趋合理,误差显著降低。放炮时间的校正消除了时钟漂移和时间延迟的误差;炮点坐标数据局部化处理消除了炮点位置整体趋势性偏移的现象;试错法进行位置误差和记录时间的精细校正时,时间漂移的校正量值约为几个到十几个毫秒,位置校正的量值仅在几米到数百米之间,实测数据所绘曲线的形态和位置都与理论曲线十分吻合,可见校正后误差显著降低。 相似文献
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声速误差是多波束水深地形测量主要误差源之一,通常采用现场声速剖面测量的方式加以改正,但在深远海多波束水深地形测量时,现场获取全深度的声速剖面并非易事。针对这一问题,利用东南印度洋海洋调查工作中采集到的17个站位的CTD数据,将所有站位声速剖面拓展到全深度,采用经验正交函数分析法(Empirical Orthogonal Functions,EOF)构建调查区声速剖面场,可获得声速剖面场内任意一点的声速值。然后通过EOF重构声速剖面场获得的声速值对测区内多波束水深地形数据进行改正,并与实测声速剖面对多波束水深地形数据的改正结果进行对比,结果表明,5000 m水深范围内2种声速改正结果相差很小,EOF重构法对深水多波束的声速改正满足水深测量的要求。 相似文献