共查询到20条相似文献，搜索用时 31 毫秒
1.
《Oceanic Engineering, IEEE Journal of》2009,34(3):269-284
2.
Mean–Standard Deviation Representation of Sonar Images for Echo Detection: Application to SAS Images
This paper addresses the detection of underwater mines echoes with application to synthetic aperture sonar (SAS) imaging. A detection method based on local first- and second-order statistical properties of the sonar images is proposed. It consists of mapping the data onto the mean-standard deviation plane highlighting these properties. With this representation, an adaptive thresholding of the data enables the separation of the echoes from the reverberation background. The procedure is automated using an entropy criterion (setting of a threshold). Applied on various SAS data sets containing both proud and buried mines, the proposed method positively compares to the conventional amplitude threshold detection method. The performances are evaluated by means of receiver operating characteristic (ROC) curves. 相似文献
3.
The Cramer-Rao lower bounds on the cross-track translation and rotation of a displaced phase-center antenna (DPCA) in the slant range plane between two successive pings (known as DPCA sway and yaw in what follows) are computed, assuming statistically homogeneous backscatter. These bounds are validated using experimental data from a 118-182-kHz sonar, showing an accuracy of the order of 20 microns on the ping-to-ping cross-track displacements. Next, the accuracy required on the DPCA sway and yaw in order to achieve a given synthetic aperture sonar (SAS) beampattern specification, specified by the expected SAS array gain, is computed as a function of the number P of pings in the SAS. Higher accuracy is required when P increases to counter the accumulation of errors during the integration of the elementary ping-to-ping estimates: the standard deviation must decrease as P/sup -1/2/ for the DPCA sway and P/sup -3/2/ for the yaw. Finally, by combining the above results, the lower bounds on DPCA micronavigation accuracy are established. These bounds set an upper limit to the SAS length achievable in practice. The maximum gain Q in cross-range resolution achievable by a DPCA micronavigated SAS is computed as a function of the key SAS parameters. These theoretical predictions are compared with simulations and experimental results. 相似文献
4.
It is shown that azimuthal ambiguities are not eliminated by the nulls of a sonar (or radar) beam pattern and have a definite influence on image quality. In synthetic aperture systems that are strongly limited in spatial sampling, particularly in ocean borne synthetic aperture sonar (SAS) and spaceborne synthetic aperture radar (SAR), azimuthal ambiguities will corrupt the images unless special measures are taken. These azimuthal aliases may be reduced by emphasizing the centermost portion of the available synthetic aperture length, and deemphasizing the endmost portions. This minimizes the effects from synthetic array elements that most strongly contribute to aliases 相似文献
5.
Suboptimal processing schemes, the application of which is not widespread in synthetic aperture sonar processing, are described with reference to seafloor imaging. It is shown that their application can result in a significant increase of the azimuth resolution of the sonar system with respect to the resolution due to its physical beamwidth, without imposing unreasonable constraints on the sonar platform trajectory. 相似文献
6.
A new highly precise source of data has recently become available using multibeam sonar systems in hydrography. Multibeam sonar systems can provide hydrographic quality depth data as well as high-resolution seafloor sonar images. We utilize the seafloor backscatter strength data of each beam from multibeam sonar and the automatic classification technology so that we can get the seafloor type identification maps. In this article, analyzing all kinds of error effects in backscatter strength, data are based on the relationship between backscatter strength and seafloor types. We emphasize particularly analyzing the influences of local bottom slope and near nadir reflection in backscatter strength data. We also give the correction algorithms and results of these two influent factors. After processing the raw backscatter strength data and correcting error effects, we can get processed backscatter strength data which reflect the features of seafloor types only. Applying the processed backscatter strength data and mosaicked seafloor sonar images, we engage in seafloor classification and geomorphy interpretation in future research. 相似文献
7.
Processing Multibeam Backscatter Data 总被引：1，自引：0，他引：1
A new highly precise source of data has recently become available using multibeam sonar systems in hydrography. Multibeam sonar systems can provide hydrographic quality depth data as well as high-resolution seafloor sonar images. We utilize the seafloor backscatter strength data of each beam from multibeam sonar and the automatic classification technology so that we can get the seafloor type identification maps. In this article, analyzing all kinds of error effects in backscatter strength, data are based on the relationship between backscatter strength and seafloor types. We emphasize particularly analyzing the influences of local bottom slope and near nadir reflection in backscatter strength data. We also give the correction algorithms and results of these two influent factors. After processing the raw backscatter strength data and correcting error effects, we can get processed backscatter strength data which reflect the features of seafloor types only. Applying the processed backscatter strength data and mosaicked seafloor sonar images, we engage in seafloor classification and geomorphy interpretation in future research. 相似文献
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9.
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
10.
《Oceanic Engineering, IEEE Journal of》2009,34(4):476-484
11.
《Oceanic Engineering, IEEE Journal of》2009,34(3):262-268
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13.
Rongxing Li 《Marine Geodesy》2013,36(2-3):115-127
Shape from shading is one of the methods that derive geometric information of objects from analysis of monocular images. Application of this technique to underwater sonar images enables the conversion of imposed reflectance characteristics in sonar images to shape information, namely, slopes, about the seafloor surface. A combination of this shape information and available sparse distributed depth points results in improved dense bathymetric data. The reconstruction of shape models of seafloor surfaces from sonar images is treated as an inverse problem and is solved by the regularization theory. Sparse gridded points are used for boundary constraints. The regularization is implemented as a relaxation procedure with a hierarchical structure of multiresolution grids. 相似文献
14.
de Heering P. Simmer K.U. Ochieng-Ogolla E. Wasiljeff A. 《Oceanic Engineering, IEEE Journal of》1994,19(1):73-83
Conventional processing of synthetic aperture sonar (SAS) data is equivalent to a two-dimensional matched filter operation. In principle, two-dimensional deconvolution improves the resolution of the processed image. However, its direct implementation is generally impractical, due to numerical problems. The paper discusses the development of iterative algorithms that efficiently perform the deconvolution of broadband synthetic aperture data and gives examples of their application. It is concluded that, in many cases, the proposed approach is preferable to more classical solutions 相似文献
15.
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
16.
《Oceanic Engineering, IEEE Journal of》2009,34(3):294-306
17.
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
18.
Larry A. Mayer 《Marine Geophysical Researches》2006,27(1):7-17
Over the past few years there have been remarkable and concomitant advances in sonar technology, positioning capabilities,
and computer processing power that have revolutionized the mapping, imaging and exploration of the seafloor. Future developments
must involve all aspects of the “seafloor mapping system,” including, sonars, ancillary sensors (motion sensors, positioning
systems, and sound speed sensors), platforms upon which they are mounted, and the products that are produced. Current trends
in sonar development involve the use of innovative new transducer materials and the application of sophisticated processing
techniques including focusing algorithms that dynamically compensate for the curvature of the wavefront in the nearfield and
thus allow narrower beam widths (higher lateral resolution) at close ranges . Future developments will involve “hybrid”, phase-comparison/beam-forming
sonars, the development of broad-band “chirp” multibeam sonars, and perhaps synthetic aperture multibeam sonars. The inability
to monitor the fine-scale spatial and temporal variability of the sound speed structure of the water column is often a limiting
factor in the production of accurate maps of the seafloor; improvements in this area will involve continuous monitoring devices
as well as improved ocean models and perhaps tomography. Remotely Operated Vehicles (ROV’s) and particularly Autonomous Underwater
Vehicles (AUV’s) will become more important as platforms for seafloor mapping systems. There will also be great changes in
the products produced from seafloor mapping and the processing necessary to create them. New processing algorithms are being
developed that take advantage of the density of multibeam sonar data and use statistically robust techniques to “clean” massive
data sets very rapidly. A range of approaches are being explored to use multibeam sonar bathymetry and imagery to extract
quantitative information about seafloor properties, including those relevant to fisheries habitat. The density of these data
also enable the use of interactive 3-D visualization and exploration tools specifically designed to facilitate the interpretation
and analysis of very large, complex, multi-component spatial data sets. If properly georeferenced and treated, these complex
data sets can be presented in a natural and intuitive manner that allows the simple integration and fusion of multiple components
without compromise to the quantitative aspects of the data and opens up new worlds of interactive exploration to a multitude
of users. 相似文献
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20.
Distinct side-scan sonar, RADARSAT SAR, and acoustic profiler signatures of gas and oil seeps on the Gulf of Mexico slope 总被引：4，自引：0，他引：4
S. M. De Beukelaer I. R. MacDonald N. L. Guinnasso Jr. J. A. Murray 《Geo-Marine Letters》2003,23(3-4):177-186
We examined bubble streams from four natural seep sites on the upper continental slope of the Gulf of Mexico. Synthetic aperture radar images verified surface oil slicks over sites with oily bubbles but not over those with non-oily bubbles. Non-oily bubbles produced high backscatter on side-scan sonar records, but were difficult to detect with acoustic profilers. Oily bubbles produced clear signatures extending from the seafloor to the near-surface on acoustic profiles and produced acoustic shadows on side-scan sonar records. We hypothesize that the bubbles oily coating causes the different signatures, since all bubbles were resonant at the tested frequencies. 相似文献