共查询到20条相似文献，搜索用时 15 毫秒
1.
Three decades of continuous ocean exploration have led us to identify subsurface fluid related processes as a key phenomenon in marine earth science research. The number of seep areas located on the seafloor has been constantly increasing with the use of multi-scale imagery techniques. Due to recent advances in transducer technology and computer processing, multibeam echosounders are now commonly used to detect submarine gas seeps escaping from the seafloor into the water column. A growing number of en-route surveys shows that sites of gas emissions escaping from the seafloor are much more numerous than previously thought. Estimating the temporal variability of the gas flow rate and volumes escaping from the seafloor has thus become a challenge of relevant interest which could be addressed by sea-floor continuous acoustic monitoring. Here, we investigate the feasibility of estimating the volumetric flow rates of gas emissions from horizontal backscattered acoustic signals. Different models based on the acoustic backscattering theory of bubbles are presented. The forward volume backscattering strength and the inversion volumetric flow rate solutions were validated with acoustic measurements from artificial gas flow rates generated in controlled sea-water tank experiments. A sensitivity analysis was carried out to investigate the behavior of the 120-kHz forward solution with respect to model input parameters (horizontal distance between transducer and bubble stream, bubble size distribution and ascent rate). The most sensitive parameter was found to be the distance of the bubble stream which can affect the volume backscattering strength by 20 dB within the horizontal range of 0–200 m. Results were used to derive the detection probability of a bubble stream for a given volume backscattering strength threshold according to different bubble flow rates and horizontal distance. 相似文献
2.
Seafloor acoustic remote sensing with multibeam echo-sounders and bathymetric sidescan sonar systems 总被引：5，自引：0，他引：5
This paper examines the potential for remote classification of seafloor terrains using a combination of quantitative acoustic backscatter measurements and high resolution bathymetry derived from two classes of sonar systems currently used by the marine research community: multibeam echo-sounders and bathymetric sidescans sonar systems. The high-resolution bathymetry is important, not only to determine the topography of the area surveyed, but to provide accurate bottom slope corrections needed to convert the arrival angles of the seafloor echoes received by the sonars into true angles of incidence. An angular dependence of seafloor acoustic backscatter can then be derived for each region surveyed, making it possible to construct maps of acoustic backscattering strength in geographic coordinates over the areas of interest. Such maps, when combined with the high-resolution bathymetric maps normally compiled from the data output by the above sonar systems, could be very effective tools to quantify bottom types on a regional basis, and to develop automatic seafloor classification routines. 相似文献
3.
An ahead-looking probe of some kind, optical or acoustic, is critical when one is attempting seafloor exploration from a mobile platform. A single-frequency, split aperture sonar system can be used for this purpose, but a wideband monopulse sonar offers many advantages. It computes a running estimate of the vertical directional cosine of the source of the echo, and can thus reveal the positions of multiple wave scatterers as long as their echoes can still be time resolved. Theoretical studies of its performance have been made previously, but were directly applicable only to extremely simple seafloor geometries. A new time-domain digital simulation that largely circumvents this limitation has been developed. The simulation also provides a means for testing the theory and optimizing system parameters. The reverberation model does not account for some features of acoustic backscattering such as diffraction, but it is believed to be adequate for the investigation of most signal processing aspects of the sonar system. The theory of the simulation is developed and several examples are presented and discussed. In addition, some preliminary results are presented from a sea test that used the air-sea interface as a surrogate seafloor 相似文献
4.
A procedure is suggested in which a relative calibration for the intensity output of a multibeam echo sounder (MBES) can be performed. This procedure identifies a common survey line (i.e., a standard line), over which acoustic backscatter from the seafloor is collected with multiple MBES systems or by the same system multiple times. A location on the standard line which exhibits temporal stability in its seafloor backscatter response is used to bring the intensity output of the multiple MBES systems to a common reference. This relative calibration procedure has utility for MBES users wishing to generate an aggregate seafloor backscatter mosaic using multiple systems, revisiting an area to detect changes in substrate type, and comparing substrate types in the same general area but with different systems or different system settings. The calibration procedure is demonstrated using three different MBES systems over 3 different years in New Castle, NH, USA. 相似文献
5.
声学方法进行海底沉积物遥测分类:综述 总被引：5，自引：0，他引：5
本文讨论利用声学遥测方法进行海底沉积物分类的目的、用途及该项技术的发展背景和现状。重点介绍目前主要的用于浅、表层沉积物分类的声学遥测方法，包括选通等幅脉冲、宽频带脉冲、连续线性扫频脉冲等正入射方法和侧扫声呐、多波束测深等斜入射方法。回顾它们的发展历史，评述它们的技术现状，并讨论它们的进一步发展 相似文献
6.
Remote estimation of surficial seafloor properties through the application Angular Range Analysis to multibeam sonar data 总被引：2，自引：2，他引：2
The variation of the backscatter strength with the angle of incidence is an intrinsic property of the seafloor, which can
be used in methods for acoustic seafloor characterization. Although multibeam sonars acquire backscatter over a wide range
of incidence angles, the angular information is normally neglected during standard backscatter processing and mosaicking.
An approach called Angular Range Analysis has been developed to preserve the backscatter angular information, and use it for
remote estimation of seafloor properties. Angular Range Analysis starts with the beam-by-beam time-series of acoustic backscatter
provided by the multibeam sonar and then corrects the backscatter for seafloor slope, beam pattern, time varying and angle
varying gains, and area of insonification. Subsequently a series of parameters are calculated from the stacking of consecutive
time series over a spatial scale that approximates half of the swath width. Based on these calculated parameters and the inversion
of an acoustic backscatter model, we estimate the acoustic impedance and the roughness of the insonified area on the seafloor.
In the process of this inversion, the behavior of the model parameters is constrained by established inter-property relationships.
The approach has been tested using a 300 kHz Simrad EM3000 multibeam sonar in Little Bay, NH. Impedance estimates are compared
to in situ measurements of sound speed. The comparison shows a very good correlation, indicating the potential of this approach for
robust seafloor characterization. 相似文献
7.
An experiment aboard the Scripps Institution of Oceanography's RV Thomas Washington has demonstrated the seafloor mapping advantages to be derived from combining the high-resolution bathymetry of a multibeam echo-sounder with the sidescan acoustic imaging plus wide-swath bathymetry of a shallow-towed bathymetric sidescan sonar. To a void acoustic interference between the ship's 12-kHz Sea Beam multibeam echo-sounder and the 11-12-kHz SeaMARC II bathymetric sidescan sonar system during simultaneous operations, Sea Beam transmit cycles were scheduled around SeaMARC II timing events with a sound source synchronization unit originally developed for concurrent single-channel seismic, Sea Beam, and 3.5-kHz profile operations. The scheduling algorithm implemented for Sea Beam plus SeaMARC II operations is discussed, and the initial results showing their combined seafloor mapping capabilities are presented 相似文献
8.
多波束测深系统声速校正 总被引：13，自引：0，他引：13
海水声速是多波束测深系统进行水深测量的基本参数之一,声速剖面正确与否直接影响测量结果的精度和可靠性。声速校正为多波束测深系统提供了正确的声速剖面,根据声速剖面垂向上的变化规律,对原始声速数据进行科学采点,运用软件方法或实验方法对声速剖面进行编辑获得声速数据,最终取得合理可靠的水深值。这里对南海SA12试验区采集的声速资料进行了分析,以SeaBeam2100多波速测深系统为例,对声速校正的技术方法进行了探讨。 相似文献
9.
10.
Processing of high-frequency multibeam echo sounder data for seafloor characterization 总被引：9，自引：0，他引：9
Processing simultaneous bathymetry and backscatter data, multibeam echosounders (MBESs) show promising abilities for remote seafloor characterization. High-frequency MBESs provide a good horizontal resolution, making it possible to distinguish fine details at the water-seafloor interface. However, in order to accurately measure the seafloor influence on the backscattered energy, the recorded sonar data must first be processed and cleared of various artifacts generated by the sonar system itself. Such a preprocessing correction procedure along with the assessment of its validity limits is presented and applied to a 95-kHz MBES (Simrad EM 1000) data set. Beam pattern effects, uneven array sensitivities, and inaccurate normalization of the ensonified area are removed to make possible further quantitative analysis of the corrected backscatter images. Unlike low-frequency data where the average backscattered energy proves to be the only relevant feature for discriminating the nature of the seafloor, high-frequency MBES backscatter images exhibit visible texture patterns. This additional information involves different statistical distributions of the backscattered amplitudes obtained from various seafloor types. Non-Rayleigh statistics such as K-distributions are shown to fit correctly the skewed distributions of experimental high-frequency data. Apart from the effect of the seafloor micro-roughness, a statistical model makes clear a correlation between the amplitude statistical distributions and the signal incidence angle made available by MBES bathymetric abilities. Moreover, the model enhances the effect of the first derivative of the seafloor backscattering strength upon statistical distributions near the nadir and at high incidence angles. The whole correction and analysis process is finally applied to a Simrad EM 1000 data set. 相似文献
11.
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13.
David C. Mosher 《Marine Geophysical Researches》2011,32(1-2):25-35
Most modern submarine geohazard investigations rely heavily on multibeam sonar data, yet there are limitations to these data that must be respected. Disregard of fundamental aspects of spatial sampling, averaging and interpolation, and statistical parameters that accompany all forms of measurement, can lead to over-interpretation of data. Beam spreading and sounding density govern spatial resolution and therefore limit seafloor features that are resolved and interpreted as indicative of geohazards. These resolution limitations are shown with a synthetic model of the seafloor convolved with a spherically spreading wavefront approximated with a spherical smoothing algorithm. This simulation shows the inability to resolve metrics of objects, as well as determine critical parameters such as slope angles with increasing water depth. As well, real case examples are presented showing these effects on identification of targets, slope angles and pockmarks. Misinterpretation of seafloor features is common in multibeam data, particularly without the benefit of coincident subbottom data. Thus it is critical to image the third dimension below the seafloor. Finally, seafloor mapping for geohazards is just one step in a geohazard assessment: it is critical to know frequency of recurrence of geohazard events and their modern geologic context in order to appropriately assess risk. 相似文献
14.
一种分层海底反向散射模型 总被引：1，自引：1，他引：0
In order to predict the bottom backscattering strength more accurately, the stratified structure of the seafloor is considered. The seafloor is viewed as an elastic half-space basement covered by a fluid sediment layer with finite thickness. On the basis of calculating acoustic field in the water, the sediment layer, and the basement, four kinds of scattering mechanisms are taken into account, including roughness scattering from the water-sediment interface, volume scattering from the sediment layer, roughness scattering from the sediment-basement interface,and volume scattering from the basement. Then a backscattering model for a stratified seafloor applying to low frequency(0.1–10 kHz) is established. The simulation results show that the roughness scattering from the sediment-basement interface and the volume scattering from the basement are more prominent at relative low frequency(below 1.0 kHz). While with the increase of the frequency, the contribution of them to total bottom scattering gradually becomes weak. And the results ultimately approach to the predictions of the high-frequency(10–100 kHz) bottom scattering model. When the sound speed and attenuation of the shear wave in the basement gradually decrease, the prediction of the model tends to that of the full fluid model, which validates the backscattering model for the stratified seafloor in another aspect. 相似文献
15.
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
16.
A two-scale roughness model for bottom backscattering (Novarini and Caruthers) was applied to multibeam sounder data (95 kHz) from Browns Bank (south of Yarmouth, Nova Scotia, Canada). In order to better understand frequency and incident angle dependence of backscattering, acoustic-calibration data (1-6 kHz) were collected from the same area and treated with the same model. The frequency and incident angle dependence of bottom backscattering in the multibeam and acoustic-calibration data were compared. Backscattering due to large-scale roughness was most relevant at near-normal incidence (<7°) and it was more dominant in the low-frequency range, and was strongly dependent on incident angle. Volume scattering was least dependent upon incident angle. It was the dominant factor at the large incident angle. Bragg scattering was the most significant over a very wide frequency range and was more important for high frequency (>5 kHz) and small incidence, but not near-normal incidence 相似文献
17.
Shallow-water imaging multibeam sonars: A new tool for investigating seafloor processes in the coastal zone and on the continental shelf 总被引：8，自引：1，他引：8
John E. Hughes Clarke Larry A. Mayer David E. Wells 《Marine Geophysical Researches》1996,18(6):607-629
Hydrographic quality bathymetry and quantitative acoustic backscatter data are now being acquired in shallow water on a routine basis using high frequency multibeam sonars. The data provided by these systems produce hitherto unobtainable information about geomorphology and seafloor geologic processes in the coastal zone and on the continental shelf.Before one can use the multibeam data for hydrography or quantitative acoustic backscatter studies, however, it is essential to be able to correct for systematic errors in the data. For bathymetric data, artifacts common to deep-water systems (roll, refraction, positioning) need to be corrected. In addition, the potentially far greater effects of tides, heave, vessel lift/squat, antenna motion and internal time delays become of increasing importance in shallower water. Such artifacts now cause greater errors in hydrographic data quality than bottom detection. Many of these artifacts are a result of imperfect motion sensing, however, new methods such as differential GPS hold great potential for resolving such limitations. For backscatter data, while the system response is well characterised, significant post processing is required to remove residual effects of imaging geometry, gain adjustments and water column effects. With the removal of these system artifacts and the establishment of a calibrated test site in intertidal regions (where the seabed may be intimately examined by eye) one can build up a sediment classification scheme for routine regional seafloor identification.When properly processed, high frequency multibeam sonar data can provide a view of seafloor geology and geomorphology at resolutions of as little as a few decimetres. Specific applications include quantitative estimation of sediment transport rates in large-scale sediment waves, volume effects of iceberg scouring, extent and style of seafloor mass-wasting and delineation of structural trends in bedrock. In addition, the imagery potentially provides a means of quantitative classification of seafloor lithology, allowing sedimentologists the ability to examine spatial distributions of seabed sediment type without resorting to subjective estimation or prohibitively expensive bottom-sampling programs. Using Simrad EM100 and EM1000 sonars as an example, this paper illustrates the nature and scale of possible artifacts, the necessary post-processing steps and shows specific applications of these sonars. 相似文献
18.
A computer code that simulates multibeam echo‐sounding over realistic (three‐dimensional) bathymetry was used to compare available sounding systems. Two‐dimensional modeling dealt with the resolution of seafloor bathymetry and with the effect of postprocessing algorithms for some typical multibeam systems. The 2‐D bathymetric inputs were idealized bottom features. Three‐dimensional modeling dealt with the gross character of the seafloor, as detected by echo‐sounding systems. The 3‐D bathymetric inputs were realizations of terrain generated by a stochastic model of seafloor roughness. Three‐dimensional modeling indicated that the sounding system may slightly shift the location of peaks within the beam footprint. In addition, the simulated measurements were more sensitive to low‐wavenumber features (i.e., large‐scale roughness) than to high‐wavenumber features (i.e., small‐scale roughness). Resolution gradually decreased with increasing distance from centerline, due to the increasing footprint size of beams at increasing angular distance from the vertical. Lineated terrain was also smoothed by simulated echo‐sounding; lineations may indeed remain undetected if sounding system parameters are not properly selected. Inversion of the simulated measurements indicated that echo‐sounding measurements are dependent not only on the characteristics of the sounding system itself, but on other factors such as the character of the roughness and the orientation of the survey relative to the strike of lineations. The modeling technique provides a way to quantify the system response of a multibeam echo‐sounding system. This work resulted in recommendations as to the most appropriate system for an application in an area of rough bathymetry, and it led to the establishment of criteria for comparing multibeam systems in future applications. 相似文献
19.
Recent developments in seafloor imaging and mapping techniques greatly improved our capability of identifying marine geohazards affecting continental margins. Geomorphic features can be detected in great detail by high-resolution multibeam imaging and regarded as geohazard indicators; the most common include slide scars and deposits, canyon headscarps and steep erosional flanks, fault-related seafloor unevenness, mud volcanoes, pockmarks, gravity flow deposits, erosional scours and bedforms indicating sediment mobility at diverse temporal/spatial scale. These processes are widespread on Italian continental margins and are potential indicators of geohazard for human settlements and infrastructures in the offshore and coastal zones. The national Project MaGIC (Marine Geohazards along the Italian Coasts) aims at documenting potential geohazards based on the acquisition of high-resolution multibeam bathymetry and on the production of maps of the geohazard-related geomorphic features for most of the Italian continental margins. With reference to this issue, we discuss some of the most frequent problems dealing with reconnaissance, interpretation and cartographic representation of geohazard-related geomorphic features at a regional scale. 相似文献
20.
Tests of models for high-frequency seafloor backscatter 总被引：3，自引：0，他引：3
Jackson D.R. Briggs K.B. Williams K.L. Richardson M.D. 《Oceanic Engineering, IEEE Journal of》1996,21(4):458-470
The interaction of high-frequency sound with the seafloor is inherently a stochastic process. Inversion techniques must, therefore employ good stochastic models for bottom acoustic scattering. An assortment of physical models for bottom backscattering strength is tested by comparison with scattering strength data obtained at 40 kHz at three shallow water sites spanning a range of sediment types from fine silt to coarse sand. These acoustic data are accompanied by sediment physical property data obtained by core sample analysis and in situ probes. In addition, stereo photography was used to measure the power spectrum of bottom relief on centimeter scales. These physical data provided the inputs needed to test the backscatter models, which treat scattering from both the rough sediment-water interface and the sediment volume. For the three sites considered here, the perturbation model for scattering from a slightly rough fluid seafloor performs well. Volume scattering is predicted to be weak except at a site having a layer of methane bubbles 相似文献