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1.
With the development of high-resolution multibeam echosounder systems (MBES) for surveying shallow-water areas a new tool is available to monitor rapid changes in seabed morphology as, e.g., caused by the dumping of dredge spoil in coastal waters. In this study, four data sets of repeated bathymetric surveys with a MBES were processed and analyzed. The data were collected in a 1.94-km2 dumping site in the outer Weser Estuary (German Bight). Between June and December 1998, 2.6 million m3 of dredged sediment were deposited there. The bathymetric maps generated in the course of this study reveal features such as subaqueous dunes, scour holes, and mounds of dumped dredge spoil. The mean water depth decreased by about 1 m during the dumping period. Furthermore, difference grids showing changes in sediment volume allowed a calculation of the sediment budget for the monitored area. After a time period of only 5 months, 0.5 million m3 of the originally dumped 2.6 million m3 of dredge spoil had already been removed from the dumping site. 相似文献
2.
Dimitrios Eleftherakis Laurent Berger Naig Le Bouffant Anne Pacault Jean-Marie Augustin Xavier Lurton 《Marine Geophysical Researches》2018,39(1-2):55-73
The calibration of multibeam echosounders for backscatter measurements can be conducted efficiently and accurately using data from surveys over a reference natural area, implying appropriate measurements of the local absolute values of backscatter. Such a shallow area (20-m mean depth) has been defined and qualified in the Bay of Brest (France), and chosen as a reference area for multibeam systems operating at 200 and 300 kHz. The absolute reflectivity over the area was measured using a calibrated single-beam fishery echosounder (Simrad EK60) tilted at incidence angles varying between 0° and 60° with a step of 3°. This reference backscatter level is then compared to the average backscatter values obtained by a multibeam echosounder (here a Kongsberg EM 2040-D) at a close frequency and measured as a function of angle; the difference gives the angular bias applicable to the multibeam system for recorded level calibration. The method is validated by checking the single- and multibeam data obtained on other areas with sediment types different from the reference area. 相似文献
3.
Marc Roche Koen Degrendele Christophe Vrignaud Sophie Loyer Tim Le Bas Jean-Marie Augustin Xavier Lurton 《Marine Geophysical Researches》2018,39(1-2):89-104
The increased use of backscatter measurements in time series for environmental monitoring necessitates the comparability of individual results. With the current lack of pre-calibrated multibeam echosounder systems for absolute backscatter measurement, a pragmatic solution is the use of natural reference areas for ensuring regular assessment of the backscatter measurement repeatability. This method mainly relies on the assumption of a sufficiently stable reference area regarding its backscatter signature. The aptitude of a natural area to provide a stable and uniform backscatter response must be carefully considered and demonstrated by a sufficiently long time-series of measurements. Furthermore, this approach requires a strict control of the acquisition and processing parameters. If all these conditions are met, stability check and relative calibration of a system are possible by comparison with the averaged backscatter values for the area. Based on a common multibeam echosounder and sampling campaign completed by available bathymetric and backscatter time series, the suitability as a backscatter reference area of three different candidates was evaluated. Two among them, Carré Renard and Kwinte, prove to be excellent choices, while the third one, Western Solent, lacks sufficient data over time, but remains a valuable candidate. The case studies and the available backscatter data on these areas prove the applicability of this method. The expansion of the number of commonly used reference areas and the growth of the number of multibeam echosounder controlled thereon could greatly contribute to the further development of quantitative applications based on multibeam echosounder backscatter measurements. 相似文献
4.
The sediment backscatter strength measured by multibeam echosounders is a key feature for seafloor mapping either qualitative (image mosaics) or quantitative (extraction of classifying features). An important phenomenon, often underestimated, is the dependence of the backscatter level on the azimuth angle imposed by the survey line directions: strong level differences at varying azimuth can be observed in case of organized roughness of the seabed, usually caused by tide currents over sandy sediments. This paper presents a number of experimental results obtained from shallow-water cruises using a 300-kHz multibeam echosounder and specially dedicated to the study of this azimuthal effect, with a specific configuration of the survey strategy involving a systematic coverage of reference areas following “compass rose” patterns. The results show for some areas a very strong dependence of the backscatter level, up to about 10-dB differences at intermediate oblique angles, although the presence of these ripples cannot be observed directly—neither from the bathymetry data nor from the sonar image, due to the insufficient resolution capability of the sonar. An elementary modeling of backscattering from rippled interfaces explains and comforts these observations. The consequences of this backscatter dependence upon survey azimuth on the current strategies of backscatter data acquisition and exploitation are discussed. 相似文献
5.
High-resolution mapping of large gas emitting mud volcanoes on the Egyptian continental margin (Nile Deep Sea Fan) by AUV surveys 总被引：4，自引：1，他引：3
S. Dupré G. Buffet J. Mascle J.-P. Foucher S. Gauger A. Boetius C. Marfia 《Marine Geophysical Researches》2008,29(4):275-290
Two highly active mud volcanoes located in 990–1,265 m water depths were mapped on the northern Egyptian continental slope
during the BIONIL expedition of R/V Meteor in October 2006. High-resolution swath bathymetry and backscatter imagery were
acquired with an autonomous underwater vehicle (AUV)-mounted multibeam echosounder, operating at a frequency of 200 kHz. Data
allowed for the construction of ~1 m pixel bathymetry and backscatter maps. The newly produced maps provide details of the
seabed morphology and texture, and insights into the formation of the two mud volcanoes. They also contain key indicators
on the distribution of seepage and its tectonic control. The acquisition of high-resolution seafloor bathymetry and acoustic
imagery maps with an AUV-mounted multibeam echosounder fills the gap in spatial scale between conventional multibeam data
collected from a surface vessel and in situ video observations made from a manned submersible or a remotely operating vehicle. 相似文献
6.
The impact of dredge spoil disposal on asymmetrical large-scale dunes has been studied at a disposal site in a shallow subtidal area of the outer Weser Estuary (German Bight, southeastern North Sea). Between June and December 1998, this site was used for the disposal of ~3×106 m3 dredge spoil. Repeated bathymetric surveys with a multibeam echosounder system reveal that the artificial supply of sediment provoked significant morphological changes in the dune field, including the infill of dune troughs and even the complete burial of individual dunes. However, even completely buried dunes began to regenerate within a few months. In addition, slow migration of the dunes toward the open sea was observed, indicating net seaward sediment transport in the survey area. Since the dumped sediment does not appear to have a persistent effect on the bedforms and, in all likelihood, will be exported from the estuarine system on medium- to long-term timescales, the investigated area constitutes a suitable disposal site. 相似文献
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Obtaining absolute seafloor backscatter measurements from hydrographic multibeam echosounders is yet to be achieved. We propose a low-cost experiment to calibrate the various acquisition modes of a 30-kHz Kongsberg EM 302 multibeam echosounder in a range of water depths. We use a 38-kHz Simrad EK60 calibrated fisheries split-beam echosounder mounted at 45° angle on the vessel’s hull as a reference for the calibration. The processing to extract seafloor backscatter from the EK60 requires bottom detection, ray tracing and motion compensation to obtain acceptable geo-referenced backscatter measurements from this non-hydrographic system. Our experiment was run in Cook Strait, New Zealand, on well-known seafloor patches in shallow, mid, and deep-water depths. Despite acquisition issues due to weather, our results demonstrate the strong potential of such an approach to obtain system’s absolute calibration which is required for quantitative use of backscatter strength data. 相似文献
9.
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
10.
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
11.
多波束测量过程中，受到多种因素的影响，不可避免地存在各种误差，其中系统某个部件出现故障也不少见，如换能器、行波管、大功率微波开关或表层声速仪等器件功能不正常，引起多波束每 ping (一个发射接收周期） 数据中部分固定波束号的测深结果发生系统性偏移，以 2003 年东海调查 SeaBat900X 数据为例，其在垂直航向正投影平面上出现类似“W”字型的系统误差。本文基于该批次数据，系统分析了该类型系统偏差成因及外观表现，针对性提出基于等均值-方差拟合模型的改正方法，首先对异常区域和正常区域分别拟合地形趋势线，统计其均值和方差；然后以正常区域为基准，对异常区域内数据进行压缩和移动；最后通过面积差法，对数据中存在的折射残差进行消除，从而有效去除“W”型残差。文中实测数据验证了本文算法的有效性和可行性，对多波束其他类型的测深系统偏差处理具有一定的参考意义。 相似文献
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13.
Precise Multibeam Acoustic Bathymetry 总被引：7，自引：0，他引：7
The maximum error in ocean depth measurement as specified by the International Hydrographic Organization is 1% for depth greater than 30m. Current acoustic multibeam bathymetric systems used for depth measurement are subject to errors from various sources which may significantly exceed this limit. The lack of sound speed profiles may be one significant source of error. Because of the limited ability of sound speed profile measurement, depth values are usually estimated using an assumed profile. If actual sound speed profiles are known, depth estimate errors can be corrected using ray-tracing methods. For depth measurements, the calculation of the location at which a sound pulse impinges on the sea bottom varies with the variation of the sound speed profile. We demonstrate that this location is almost unchanged for a family of sound speed profiles with the same surface value and the same area under them. Based on this observation, we can construct a simple constant-gradient equivalent sound speed profile to correct errors. Compared with ray-tracing methods, the equivalent sound speed profile method is more efficient. If a vertical depth is known (or independently measured), then depth correction for a multibeam system can be accomplished without knowledge of the actual sound speed profile. This leads to a new type of precise acoustic multibeam bathymetric system. 相似文献
14.
The maximum error in ocean depth measurement as specified by the International Hydrographic Organization is 1% for depth greater than 30m. Current acoustic multibeam bathymetric systems used for depth measurement are subject to errors from various sources which may significantly exceed this limit. The lack of sound speed profiles may be one significant source of error. Because of the limited ability of sound speed profile measurement, depth values are usually estimated using an assumed profile. If actual sound speed profiles are known, depth estimate errors can be corrected using ray-tracing methods. For depth measurements, the calculation of the location at which a sound pulse impinges on the sea bottom varies with the variation of the sound speed profile. We demonstrate that this location is almost unchanged for a family of sound speed profiles with the same surface value and the same area under them. Based on this observation, we can construct a simple constant-gradient equivalent sound speed profile to correct errors. Compared with ray-tracing methods, the equivalent sound speed profile method is more efficient. If a vertical depth is known (or independently measured), then depth correction for a multibeam system can be accomplished without knowledge of the actual sound speed profile. This leads to a new type of precise acoustic multibeam bathymetric system. 相似文献
15.
On the Uncertainty of Archive Hydrographic Data Sets 总被引：2，自引：0，他引：2
《Oceanic Engineering, IEEE Journal of》2006,31(2):249-265
As the international hydrographic community continues to address the question of irreducible uncertainty in modern surveys, a similar question must be asked of archived vertical beam echosounder (VBES) and leadline data sets. The Office of Naval Research funded STRATAFORM project surveyed an area of the New Jersey shelf around 39$^circ$ 12' N 72$^circ$ 50' W using an EM1000 multibeam echosounder (MBES). This area is also covered by National Oceanic and Atmospheric Administration surveys from 1936 to 1938 (from early visual indicating fathometers) and 1975–1976 (VBES). The analysis shows that the earlier data are biased in deeper water, most probably because of “hydrographic rounding” or instrument limitations, and may be unrecoverable, but that the VBES data appear approximately unbiased. Estimates of uncertainty for a surface model generated from the archive data are constructed, taking into account measurement, interpolation, and hydrographic uncertainty (addressing the problems of unobserved areas and surface reconstruction stability). Comparison of predicted depths against the MBES data shows that the VBES-derived surface is consistent given the quoted uncertainty and that the uncertainty corresponds with appropriate hydrographic survey standards. However, spatial aliasing of the VBES surface is observed, which may be the limiting factor in the applicability of this data. 相似文献
16.
Alex Rattray Daniel Ierodiaconou Laurie Laurenson Shoaib Burq Marcus Reston 《Estuarine, Coastal and Shelf Science》2009
Information regarding the composition and extent of benthic habitats on the South East Australian continental shelf is limited. In this habitat mapping study, multibeam echosounder (MBES) data are integrated with precisely geo-referenced video ground-truth data to quantify benthic biotic communities at Cape Nelson, Victoria, Australia. Using an automated decision tree classification approach, 5 representative biotic groups defined from video analysis were related to hydro-acoustically derived variables in the Cape Nelson survey area. Using a combination of multibeam bathymetry, backscatter and derivative products produced highest overall accuracy (87%) and kappa statistic (0.83). This study demonstrates that decision tree classifiers are capable of integrating variable data types for mapping distributions of benthic biological assemblages, which are important in maintaining biodiversity and other system services in the marine environment. 相似文献
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19.
We analyze errors in the global bathymetry models of Smith and Sandwell that combine satellite altimetry with acoustic soundings
and shorelines to estimate depths. Versions of these models have been incorporated into Google Earth and the General Bathymetric
Chart of the Oceans (GEBCO). We use Japan Agency for Marine-Earth Science and Technology (JAMSTEC) multibeam surveys not previously
incorporated into the models as “ground truth” to compare against model versions 7.2 through 12.1, defining vertical differences
as “errors.” Overall error statistics improve over time: 50th percentile errors declined from 57 to 55 to 49 m, and 90th percentile
errors declined from 257 to 235 to 219 m, in versions 8.2, 11.1 and 12.1. This improvement is partly due to an increasing
number of soundings incorporated into successive models, and partly to improvements in the satellite gravity model. Inspection
of specific sites reveals that changes in the algorithms used to interpolate across survey gaps with altimetry have affected
some errors. Versions 9.1 through 11.1 show a bias in the scaling from gravity in milliGals to topography in meters that affected
the 15–160 km wavelength band. Regionally averaged (>160 km wavelength) depths have accumulated error over successive versions
9 through 11. These problems have been mitigated in version 12.1, which shows no systematic variation of errors with depth.
Even so, version 12.1 is in some respects not as good as version 8.2, which employed a different algorithm. 相似文献