共查询到20条相似文献，搜索用时 31 毫秒
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Some errors and noises are often present in multibeam swath bathymetric data. Echo detection error (EDE) is one of the main errors. It causes the depth error to become bigger in outer beams and looks like sound refraction. But depth errors due to EDEs have a trumpet-shaped appearance, instead of a curved appearance that is caused by the sound refraction errors. EDEs, including systematic acoustic signal detection errors and internal noises, cannot be removed during the correction of sound refraction. It causes depth inconsistencies between adjacent swaths and degrades precision of outer beams. Sometimes, the bathymetric errors caused by EDEs do not even meet the requirements of IHO (International Hydrographic Organization). Therefore, a post-processing method is presented to minimize the EDEs by filtering outliers and compressing outer beams of multibeam bathymetric data. The outliers caused by internal noises are removed by an automatic filter algorithm first. Then the outer beams are compressed to reduce systematic acoustic signal detection errors according to their depths, the calculated depth line and standard deviations (SDs). The automatic filter process is important for calculating the depth line. The selection of inner beams to calculate the average SD of beam depths is crucial to achieving compressing goals. The quality of final bathymetric data in outer beams can be improved by these steps. The method is verified by a field test. 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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Seafloor massive sulphides are deep sea mineral deposits currently being examined as a potential mining resource. Conventional sonar bathymetry products gathered by sea surface platforms do not achieve adequate spatial resolution to detect these resources. High-resolution beamforming methods (such as multiple signal classification and estimation of signal parameters via rotational invariance techniques) improve the resolution of sonar bathymetry. We perform a quantitative review of these high-resolution methods using a novel simulator, showing results in the absence of platform motion for a single ping cycle. It was found that high-resolution methods achieved greater bathymetric accuracy and higher resolution than conventional beamforming and that these methods may be adequate for this style of marine exploration. These methods were also robust in the presence of unwanted persistent signals and low signal to noise ratios. 相似文献
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Simulations of estuarine bathymetric change over decadal timescales require methods for idealization and reduction of forcing data and boundary conditions. Continuous simulations are hampered by computational and data limitations and results are rarely evaluated with observed bathymetric change data. Bathymetric change data for Suisun Bay, California span the 1867–1990 period with five bathymetric surveys during that period. The four periods of bathymetric change were modeled using a coupled hydrodynamic-sediment transport model operated at the tidal-timescale. The efficacy of idealization techniques was investigated by discontinuously simulating the four periods. The 1867–1887 period, used for calibration of wave energy and sediment parameters, was modeled with an average error of 37% while the remaining periods were modeled with error ranging from 23% to 121%. Variation in post-calibration performance is attributed to temporally variable sediment parameters and lack of bathymetric and configuration data for portions of Suisun Bay and the Delta. Modifying seaward sediment delivery and bed composition resulted in large performance increases for post-calibration periods suggesting that continuous simulation with constant parameters is unrealistic. Idealization techniques which accelerate morphological change should therefore be used with caution in estuaries where parameters may change on sub-decadal timescales. This study highlights the utility and shortcomings of estuarine geomorphic models for estimating past changes in forcing mechanisms such as sediment supply and bed composition. The results further stress the inherent difficulty of simulating estuarine changes over decadal timescales due to changes in configuration, benthic composition, and anthropogenic forcing such as dredging and channelization. 相似文献
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A new method for weakening the combined effect of residual errors on multibeam bathymetric data 总被引：2，自引：0，他引：2
Jianhu Zhao Jun Yan Hongmei Zhang Yuqing Zhang Aixue Wang 《Marine Geophysical Researches》2014,35(4):379-394
Multibeam bathymetric system (MBS) has been widely applied in the marine surveying for providing high-resolution seabed topography. However, some factors degrade the precision of bathymetry, including the sound velocity, the vessel attitude, the misalignment angle of the transducer and so on. Although these factors have been corrected strictly in bathymetric data processing, the final bathymetric result is still affected by their residual errors. In deep water, the result usually cannot meet the requirements of high-precision seabed topography. The combined effect of these residual errors is systematic, and it’s difficult to separate and weaken the effect using traditional single-error correction methods. Therefore, the paper puts forward a new method for weakening the effect of residual errors based on the frequency-spectrum characteristics of seabed topography and multibeam bathymetric data. Four steps, namely the separation of the low-frequency and the high-frequency part of bathymetric data, the reconstruction of the trend of actual seabed topography, the merging of the actual trend and the extracted microtopography, and the accuracy evaluation, are involved in the method. Experiment results prove that the proposed method could weaken the combined effect of residual errors on multibeam bathymetric data and efficiently improve the accuracy of the final post-processing results. We suggest that the method should be widely applied to MBS data processing in deep water. 相似文献
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An adaptive noise cancelling (ANC) technique involving a joint-process deterministic least-squares lattice filter was applied to the Sea Beam bathymetric survey system data. The filtering scheme used in Sea Beam adversely affects the underlying acoustic return and may also lead to bathymetric artifacts. The authors investigate a possible remedy for this sidelobe interference problem offered by ANC coupled with signal preservation, provided both amplitude and phase information. The joint-process deterministic least-squares lattice is the adaptive filter of choice because of its superior transit response in the presence of power discontinuities. A REVGEN (reverberation generator) simulation (R.P. Goddard, 1985) of the Sea Beam system provided support for the proposed filtering technique. A complex data acquisition system was designed and built to record the in-phase and quadrature component of Sea Beam returns. Initial ANC processing of these recorded Sea Beam data provided satisfactory sidelobe interference cancellation with no noticeable degradation of the actual bottom returns 相似文献
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Analyzing Uncertainty in Multibeam Bathymetric Data and the Impact on Derived Seafloor Attributes 总被引：2，自引：0，他引：2
Multibeam bathymetric data provide critical information for the modeling of seabed geology and benthic biodiversity. The accuracy of these models depends on the accuracy of the bathymetric data, which contain uncertainties that are stochastic at individual soundings but exhibit a distinct spatial distribution with increasing magnitude from nadir to the outer beams. A restricted spatial randomness method that simulates both the stochastic and spatial characteristics of the data uncertainty performed better than a complete spatial randomness method in analyzing the impact of bathymetric data uncertainty on derived seafloor attributes. 相似文献
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在典型的实验海区，使用双频测深仪和箱式取样器，对海底进行同步探测，获取双频测深仪不同底质类型数据。比较了式取样器海底底质样品，归纳出海底基岩、沙、粘土的双频测深仪水深数据和双频测深仪海底模拟记录图象特征，该特征可为双频测深仪识别海底底质类型提供先验认识。 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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The phase difference principle is widely applied nowadays to sonar systems used for sea floor bathymetry. The apparent angle of a target point is obtained from the phase difference measured between two close receiving arrays. Here we study the influence of the phase difference estimation errors caused by the physical structure of the backscattered signals. It is shown that, under certain current conditions, beyond the commonly considered effects of additive external noise and baseline decorrelation, the processing may be affected by the shifting footprint effect: this is due to the fact that the two interferometer receivers get simultaneous echo contributions coming from slightly shifted seabed parts, which results in a degradation of the signal coherence and, hence, of the phase difference measurement. This geometrical effect is described analytically and checked with numerical simulations, both for square- and sine-shaped signal envelopes, its relative influence depends on the geometrical configuration and receiver spacing; it may be prevalent in practical cases associated with bathymetric sonars. The cases of square and smooth signal envelopes are both considered. The measurements close to nadir, which are known to be especially difficult with interferometry systems, are addressed in particular 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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Pierre Cervenka Ute Christina Herzfeld Christian De Moustier 《Marine Geophysical Researches》1994,16(6):407-425
When isobath maps of the seafloor are constructed with a bathymetric sidescan sonar system the position of each sounding is derived from estimates of range and elevation. The location of each pixel forming the acoustic backscatter image is calculated from the same estimates. The accuracy of the resulting maps depends on the acoustic array geometry, on the performances of the acoustic signal processing, and on knowledge of other parameters including: the platform's navigation, the sonar transducer's attitude, and the sound rays' trajectory between the sonar and the seafloor. The relative importance of these factors in the estimation of target location is assesed. The effects of the platform motions (e.g. roll, pitch, yaw, sway, surge and heave) and of the uncertainties in the elevation angle measurements are analyzed in detail. The variances associated with the representation (orientation and depth) of a plane, rectangular patch of the seafloor are evaluated, depending on the geometry of the patch. The inverse problem is addressed. Its solution gives the lateral dimensions of the spatial filter that must be applied to the bathymetric data to obtain specified accuracies of the slopes and depths. The uncertainty in the estimate of elevation angle, mostly due to the acoustic noise, is found to bring the main error contribution in across-track slope estimates. It can also be critical for along-track slope estimates, overshadowing error contributions due to the platform's attitude. Numerical examples are presented.On leave at the Naval Research Laboratory, Code 7420, Washington D.C. 20375-5350, U.S.A. 相似文献
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洋中脊热液活动多产生于不同扩张速率洋中脊的局部高地形区域,基于达西流体充填的孔隙?弹性热力学模型可以直观、有效地模拟出洋壳内部热液对流的形态、温度结构和喷发位置等信息。数值模拟结果和所得解析模型表明:不同规模的洋底地形起伏会对洋壳内部的热液对流形态产生不同程度的影响,高地形规模越大,起伏程度越大,下伏热液羽向地形高点的偏移就越明显。通过结合东太平洋海隆9°17′N热液区和大西洋洋中脊Lucky Strike热液区实际的跨轴水深分布,也可获得与二者实际喷发位置相吻合的模拟结果。地形起伏相关的洋中脊热液喷发模型揭示洋底低地形及其下伏渗透性洋壳表现为主要的海水充注区域,而高地形由于上覆压力的减小,使其成为汇集热液释放和喷发的主要区域。 相似文献
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