共查询到20条相似文献，搜索用时 46 毫秒
1.
The feasibility of adding an interferometric swath bathymetric system to GLORIA, a 6.6 kHz long-range sidescan sonar, is discussed. The size of GLORIA's low-frequency transducer arrays and towfish precludes significant modifications, but even without such changes bathymetric errors could be several tens of metres over a usable swath somewhat smaller than the normal GLORIA swath. A swath bathymetry based on GLORIA will have random errors depending strongly on wind speed, water depth, and swath width. Within the range of these parameters, root-mean-square bathymetry errors in the range of 1-100 m can be expected 相似文献
2.
Automatic Registration of TOBI Side-Scan Sonar and Multi-Beam Bathymetry Images for Improved Data Fusion 总被引：1，自引：0，他引：1
Deep towed side-scan sonar vehicles such as TOBI acquire high quality imagery of the seafloor with very high spatial resolution but poor locational accuracy. Fusion of the side-scan sonar data with bathymetry data from an independent source is often desirable to reduce ambiguity in geological interpretations, to aid in slant-range correction and to enhance seafloor representation. The main obstacle to fusion is accurate registration of the two datasets.The application of hierarchical chamfer matching to the registration of TOBI side-scan sonar images and multi-beam swath bathymetry is described. This matches low level features such as edges in the TOBI image, with corresponding features in a synthetic TOBI image created by simulating the flight of the TOBI vehicle through the bathymetry. The method is completely automatic, relatively fast and robust, and much easier than manual registration. It allows accurate positioning of the TOBI vehicle, enhancing its usefulness as a research tool. The method is illustrated by automatic registration of TOBI and multi-beam bathymetry data from the Mid-Atlantic Ridge. 相似文献
3.
A new bathymetry processing software package has been developed to postprocess new GLORI-B swath bathymetry data using preexisting techniques. GLORI-B bathymetry is calculated using an interferometry (phase delay) method using the modified GLORIA towfish which has parallel rows of transducers on both sides. We describe four types of artifacts observed during the first use of this new system during Legs 5 and 6 of the Gloria Expedition which surveyed the fastest spreading segment of the global seafloor spreading system and the broad chain of volcanoes near Easter Island. These artifacts include cross-track bias, along-track bias, a 'dropped edge' effect, and random noise. We describe and illustrate how we minimize these artifacts. We merge the SeaBeam 2000 bathymetry data with the GLORI-B bathymetry data to produce a final bathymetric mosaic which covers about 243,400 km2 and shows a different style of diffuse widely spread volcanism not previously observed along hotspot chains. The data are used in several studies describing seamount morphology, elastic thickness of the lithosphere, tectonic and geochemical evolution of the area, and mantle flow from a hotspot to a superfast seafloor spreading center. 相似文献
4.
While the average seafloor backscatter strength within a narrow range of grazing angles can be used as a first-order classification tool, this technique often fails to distinguish seafloors of known differing geological character. In order to resolve such ambiguities, it is necessary to examine the variation in backscatter strength as a function of grazing angle. For this purpose, a series of multiply overlapping GLORIA sidescan sonar images (6.5 kHz) have been obtained in water depths ranging from 1000 to 2500 m. To constrain the placement of acoustic backscatter measurements and to measure the true impinging angle of the incident wave, the corresponding seafloor was simultaneously surveyed using the Seabeam multibeam system. As a result of the multiple overlap, the angular response of seafloor backscatter strength may be derived for regions much smaller than the swath width. By using the derived angular response of seafloor backscatter strength in regions for which sediment samples exist, an empirical seafloor classification scheme is proposed based on the shape, variance, and magnitude of the angular response. Because of the observed variability in the shape of the angular response with differing seafloor types, routine normalization of single-pass swath data to an equivalent single grazing angle image cannot be achieved. As a result, for the case of single-pass surveys, confident seafloor classification may only be possible for regions approaching the scale of the swath width 相似文献
5.
Scheirer Daniel S. Fornari Daniel J. Humphris Susan E. Lerner Steven 《Marine Geophysical Researches》2000,21(1-2):121-142
High-resolution, side-looking sonar data collected near the seafloor (100 m altitude) provide important structural and topographic information for defining the geological history and current tectonic framework of seafloor terrains. DSL-120 kHz sonar data collected in the rift valley of the Lucky Strike segment of the Mid-Atlantic Ridge near 37° N provide the ability to quantitatively assess the effective resolution limits of both the sidescan imagery and the computed phase-bathymetry of this sonar system. While the theoretical, vertical and horizontal pixel resolutions of the DSL-120 system are <1 m, statistical analysis of DSL-120 sonar data collected from the Lucky Strike segment indicates that the effective spatial resolution of features is 1–2 m for sidescan imagery and 4 m for phase-bathymetry in the seafloor terrain of the Mid-Atlantic Ridge rift valley. Comparison of multibeam bathymetry data collected at the sea-surface with deep-tow DSL-120 bathymetry indicates that depth differences are on the order of the resolution of the multibeam system (10–30 m). Much of this residual can be accounted for by navigational mismatches and the higher resolving ability of the DSL-120 data, which has a bathymetric footprint on the seafloor that is 20 times smaller than that of hull-mounted multibeam at these seafloor depths (2000 m). Comparison of DSL-120 bathymetry with itself on crossing lines indicates that residual depth values are ±20 m, with much of that variation being accounted for by navigational errors. A DSL-120 survey conducted in 1998 on the Juan de Fuca Ridge with better navigation and less complex seafloor terrain had residual depth values half those of the Lucky Strike survey. The quality of the bathymetry data varies as a function of position within the swath, with poorer data directly beneath the tow vehicle and also towards the swath edges.Variations in sidescan amplitude observed across the rift valley and on Lucky Strike Seamount correlate well with changes in seafloor roughness caused by transitions from sedimented seafloor to bare rock outcrops. Distinct changes in sonar backscatter amplitude were also observed between areas covered with hydrothermal pavement that grade into lava flows and the collapsed surface of the lava lake in the summit depression of Lucky Strike Seamount. Small features on the seafloor, including volcanic constructional features (e.g., small cones, haystacks, fissures and collapse features) and hydrothermal vent chimneys or mounds taller than 2 m and greater than 9 m2 in surface area, can easily be resolved and mapped using this system. These features at Lucky Strike have been confirmed visually using the submersible Alvin, the remotely operated vehicle Jason, and the towed optical/acoustic mapping system Argo II. 相似文献
6.
Pierre Cervenka Christian De Moustier Peter F. Lonsdale 《Marine Geophysical Researches》1994,16(5):365-383
Acoustic backscatter images of the seafloor obtained with sidescan sonar systems are displayed most often using a flat bottom assumption. Whenever this assumption is not valid, pixels are mapped incorrectly in the image frame, yielding distorted representations of the seafloor. Here, such distortions are corrected by using an appropriate representation of the relief, as measured by the sonar that collected the acoustic backscatter information. In addition, all spatial filtering operations required in the pixel relocation process take the sonar geometry into account. Examples of the process are provided by data collected in the Northeastern Pacific over Fieberling Guyot with the SeaMARC II bathymetric sidescan sonar system and the Sea Beam multibeam echo-sounder. The nearly complete (90%) Sea Beam bathymetry coverage of the Guyot serves as a reference to quantify the distortions found in the backscatter images and to evaluate the accuracy of the corrections performed with SeaMARC II bathymetry. As a byproduct, the processed SeaMARC II bathymetry and the Sea Beam bathymetry adapted to the SeaMARC II sonar geometry exhibit a 35m mean-square difference over the entire area surveyed.On leave at the Naval Research Laboratory, Code 7420, Washington D.C. 20375-5350. 相似文献
7.
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
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9.
This paper reports a comparative study of digital enhancement techniques using spatial filtering to improve the geologic interpretation of side-scan sonar GLORIA images. Seven algorithms for speckle reduction with window sizes of 3×3-7×7 pixel and various numbers of iterations were tested for cosmetic purposes, and also to improve subsequent image processing. The filtered images were evaluated using both quantitative and qualitative techniques. It was determined that a normalized inverse gradient weighted smoothing scheme, with a 3×3 pixel filter and five iterations, allows a significant speckle reduction without blurring the edges in the GLORIA image which correspond to geological structures. Three local contrast enhancement techniques were also tested and evaluated to increase the perception of these geologic structures. Subtracting the gradient magnitude twice, calculated with spatial filters of a 5×5 pixel on smoothed images, was found to enhance most GLORIA images. Texture analysis methods developed for GLORIA images of mid-oceanic ridges and based on edge detection and orientation determination by spatial filtering are also presented. It enables the GLORIA mosaic of the Rodriguez triple junction (Indian Ocean) to be partitioned into regions of preferred orientation corresponding to the different seafloor fabrics generated at each arm of the triple junction 相似文献
10.
Processing and analysis of Simrad multibeam sonar data 总被引：1，自引：0，他引：1
Neil C. Mitchell 《Marine Geophysical Researches》1996,18(6):729-739
The common approach to analysing data collected with multibeam and sidescan sonars is to visually interpret charts of contoured bathymetry and mosaics of seabed images. However, some of the information content is lost by processing the data into charts because this involves some averaging; the analysis might uncover more information if done on the data at an earlier stage in the processing. Motivated by this potential, I have created a software system which can be used to analyse data collected with Simrad EM1000 (shallow water) and EM12 (deep water) multibeam sonars, as well as to generate bathymetry contour charts and backscatter mosaics. The system includes data preprocessing, such as navigation filtering, depth filtering (removal of outlying values), and amplitude mapping using the multibeam bathymetry to correctly position image pixels across the swath. The data attributes that can be analysed include the orientation and slope of the seafloor, and the mean signal strength for each sounding. To determine bathymetry attributes such as slope, the soundings across a number of beams and across a series of pings are grouped and a least-squares plane fitted to them. Bathymetric curvature is obtained by detrending the grouped data using the least-squares plane and fitting a paraboloid to the residuals. The magnitudes and signs of the paraboloid's coefficients reveal depressions and hills and their orientations. Furthermore, the seafloor geology can be classified using a simple combination of these attributes. For example, flat-lying sediments can be classified where the backscatter, slope and curvature fall below specified values. 相似文献
11.
Image processing techniques are discussed that correct distortions in GLORIA II side scan sonar imagery including water column
offset, slant-range distortion, multiple returns, aspect ratio, speckle noise, striping, and cross-track power drop-off. The
software operates within NASA's ELAS image processing system and is applied to the original 12-bit GLORIA II data. Procedures
are discussed for generating large scale mosaics and three-dimensional overlays with sea floor bathymetry. The results are
shown in four sonographs acquired off the southern coast of California. 相似文献
12.
Robert T. Bird Roger C. Searle Valerie Paskevich David C. Twichell 《Marine Geophysical Researches》1996,18(6):651-661
We have replaced the usual band of poor-quality data in the near-nadir region of our GLORIA long-range sidescan-sonar imagery with a shaded-relief image constructed from swath bathymetry data (collected simultaneously with GLORIA) which completely cover the nadir area. We have developed a technique to enhance these pseudo-sidescan images in order to mimic the neighbouring GLORIA backscatter intensities. As a result, the enhanced images greatly facilitate the geologic interpretation of the adjacent GLORIA data, and geologic features evident in the GLORIA data may be correlated with greater confidence across track. Features interpreted from the pseudo-sidescan may be extrapolated from the near-nadir region out into the GLORIA range where they may nt have been recognized otherwise, and therefore the pseudo-sidescan can be used to ground-truth GLORIA interpretations. Creation of digital sidescan mosaics utilized an approach not previously used for GLORIA data. Pixels were correctly placed in cartographic space and the time required to complete a final mosaic was significantly reduced. Computer software for digital mapping and mosaic creation is incorporated into the newly-developed Woods Hole Image Processing System (WHIPS) which can process both low- and high-frequency sidescan, and can interchange data with the Mini Image Processing System (MIPS) most commonly used for GLORIA processing. These techniques are tested by creating digital mosaics of merged GLORIA sidescan and Hydrosweep pseudo-sidescan data from the vicinity of the Juan Fernandez microplate along the East Pacific Rise (EPR). 相似文献
13.
A procedure for postprocessing bathymetry data provided by a phase-measuring sidescan sonar system is presented. The data were collected with the SeaMARC II system, and are generally characterized by a high level of noise and uneven spatial sampling. Before any spatial filtering is applied, data are selected to remove most of the obvious artifacts and to retain instantaneous depth profiles whose slant ranges increase monotonically from a central location to the edges of the swath. An extrapolation scheme, patterned after a potential field, is proposed to fill gaps in the coverage or to extend the bathymetric swath to that of the corresponding sidescan image when regridding the data to a rectangular frame. To fill the near nadir gap typically found in these data, a specific interpolation methodology is developed that takes into account the slant range of the first bottom return as received by the sidescan sonar itself or by a shipboard echo-sounder. Spatial low-pass filtering is applied through convolutions with parabolic windows whose width is proportional to the footprint of the acoustic beam along track and roughly 1/8 of the swath width across track. Mismatches of contour lines between adjacent tracks are reduced through a statistical method design to correct systematic profile errors 相似文献
14.
R. C. Searle T. P. Le Bas N. C. Mitchell M. L. Somers L. M. Parson PH. Patriat 《Marine Geophysical Researches》1990,12(1-2):21-39
This chapter presents a summary of the image-processing techniques being used at present in the Institute of Oceanographic Sciences Deacon Laboratory's GLORIA long-range sidescan sonar system. It begins with a brief review of the development of GLORIA, and then describes in outline the present shipboard data acquisition, recording and replay system, including simple image-processing techniques that can be used on-board ship. Next, a detailed form of the sonar equation is developed, and this is evaluated factor-by-factor, to demonstrate the effects of beam directivity, refraction and water depth on the form of intensity variation to be expected in the final image. Finally, we discuss recent developments in shore-based image-processing. These include the development of improved radiometric corrections to normalize range-dependent intensity variations, recovery of true backscattering levels and estimation of backscattering coefficients, and combination of GLORIA with other data sets into single, colour digital images. As an example of the last process we show a digital mosaic of sonar data from the Southwest Indian Ridge, coloured as a function of depth derived from Sea Beam data in the same area. 相似文献
15.
海底三维可视化技术及应用 总被引：2，自引：1，他引：1
海底地形地貌能表现海洋世界重要的空间信息,也是常规光学和电磁手段难以探测的水下区域。应用侧扫声纳技术可以反演海底地貌,同时多波束测深技术得到的水深数据重建数字水深模型,二者结合创建三维海底空间景观。利用海洋探测技术和三维可视化技术进行海底地形地貌三维仿真和分析,并对其应用进行探讨。 相似文献
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17.
There is a pressing need for standardization of data derived from bathy‐metric swath‐mapping systems. Currently several dozen multibeam and sidescan sonar data formats exist within the oceanographic community, and more can be expected as new systems are developed. Without some standardization of swath‐mapping data formats, the capability for use and integration of data from different systems will be severely compromised. This paper presents a strategy for organizing swath bathymetry data in a logical modular fashion that will allow data from all current swath bathymetric sonar systems to be stored and accessed in a common fashion. We have chosen the approach of defining compact efficient modules for each logically independent portion of a data record and storing it in a manner that is portable between diverse computer architectures and operating systems. This approach is extensible to accommodate new types of data. Although specifically developed for swath bathymetry, this format is also capable of supporting digital sidescan data and other types of swath data. 相似文献
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It is shown that useful relative backscatter strengths can be calculated from GLORIA long-range side-scan sonar data using a simple acoustic model. The calculation was performed on GLORIA side-scan sonar data collected during 1987 in the southern Indian Ocean. GEOSECS hydrographic information was used to access the effects of refraction (ray bending and aspherical spreading signal losses). Sea Beam bathymetry was used to correct the effective insonified area and compute the grazing angle. A major difficulty in performing this calculation over the terrain chosen (mid-ocean ridge topography) was one of adjusting navigation so that small features in Sea Beam and GLORIA data matched. Preliminary results show a 10-dB falloff in backscatter strength with decreasing grazing angle (10°-40°) at 6.5 kHz over what must presumably be a rough surface (extruded basalts and breccias) 相似文献
20.
The authors present a method for obtaining parameters for Sea Beam swath bathymetry which describe the characteristics of abyssal-hill topography. The basic quantity used in the analysis is the distribution of topographic slopes in a region. A convenient means for parameterizing these slopes is through unit vectors that are normal to small patches of the seafloor; the normal vectors are decomposed into azimuthal and dip components. It is found that the azimuthal distribution of the vectors provides a first-order indication of the dominant elongation directions in the topography, including multiple lineations when they are present. It is shown that the slope statistics are relatively independent of long-wavelength depth variations and are robust even if large anomalous features such as seamounts and fracture zones are included in the section of bathymetry analyzed 相似文献