检索结果-内蒙古大学图书馆

IEEE International Conference on Robotics and Automation (ICRA)

作者： R.M. Eustice H. Singh J.J. Leonard MIT/WHOI Joint Program in Applied Ocean Science and Engineering Woods Hole Oceanographic Institution Woods Hole MA USA Department of Applied Ocean Physics and Engineering Woods Hole Oceanographic Institution Woods Hole MA USA Department of Ocean Engineering Massachusetts Institute of Technology Cambridge MA USA

This paper presents the novel insight that the SLAM information matrix is exactly sparse in a delayed-state framework. Such a framework is used in view-based representations of the environment which rely upon scan-matching raw sensor data. Scan-matching raw data results in virtual observations of robot motion with respect to a place its previously been. The exact sparseness of the delayed-state information matrix is in contrast to other recent feature based SLAM information algorithms like Sparse Extended Information Filters or Thin Junction Tree Filters. These methods have to make approximations in order to force the feature-based SLAM information matrix to be sparse. The benefit of the exact sparseness of the delayed-state framework is that it allows one to take advantage of the information space parameterization without having to make any approximations. Therefore, it can produce equivalent results to the “full-covariance” solution.

关键词： Delay Simultaneous localization and mapping Navigation Cameras oceans Information filters Sparse matrices Information filtering Remotely operated vehicles Robot vision systems

来源：评论

学校读者我要写书评

暂无评论

Characterization of range‐dependent shallow water waveguides

引用

The Journal of the Acoustical Society of America 2005年第S1期80卷 S52-S52页

作者： George V. Frisk Ferdinand J. Diemer Peter H. Dahl Department of Ocean Engineering Woods Hole Oceanographic Institution Woods Hole MA 02543 MIT/WHOI Joint Program in Oceanography/Oceanographic Engineering Woods Hole MA 02543

A technique for characterizing range‐dependent shallow water waveguides is described. The method consists of determining the beamformed output of a horizontal array over short apertures for signals due to a cw point source. By modeling the acoustic field locally as a sum of damped normal modes and using Prony's method to perform the beamforming, the local modal structure of the waveguide can be resolved. As a result, the modal composition of the waveguide as a function of range can be determined and interpreted in terms of range‐dependent mode theories (e.g., adiabatic mode theory). In addition to identifying important propagation characteristics such as mode cutoff, the method can be used to determine range‐dependent acoustic properties of the bottom. Examples of the application of the technique to the case of propagation in a wedge‐shaped ocean are presented. [Work supported by ONR.]

关键词：

来源：评论

学校读者我要写书评

暂无评论

A modal/WKB inversion method for determining sound‐speed profiles in the ocean and ocean bottom

引用

The Journal of the Acoustical Society of America 2005年第S1期84卷 S175-S175页

作者： Kevin D. Casey George V. Frisk MIT/WHOI Joint Program in Oceanography/Oceanographic Engineering Woods Hole MA 02543 Department of Ocean Engineering Woods Hole Oceanographic Institute Woods Hole MA 02543

Two approaches to determining sound‐speed profiles in the ocean and ocean bottom using measured acoustic modal eigenvalues are examined. Both methods use measured eigenvalues and mode‐dependent assumed values of the WKB phase integral as input data and use the WKB phase integral as a starting point for relating the index of refraction to depth. Inversion method 1 is restricted to monotonic or symmetric sound‐speed profiles and requires a measurement of the sound speed at one depth to convert the index of refraction profile to a sound‐speed profile. Inversion method 2 assumes that the sound speed at the ocean surface and the minimum sound speed in the profile are known and is applicable to monotonic profiles and to general single duct sound‐speed profiles. For asymmetric profiles, inversion method 2 gives the depth difference between two points of equal sound speed in the portion of the profile having two turning points, and in the remainder of the profile it gives sound speed versus depth directly. A numerical implementation of the methods is demonstrated using idealized ocean sound‐speed profiles. The two methods are used also to determine the sediment sound‐speed profiles in two shallow water waveguide models, and inversion method 1 is used to find the sediment sound‐speed profile using data from an experiment perfomed in the Gulf of Mexico. [Work supported by ONR.]

关键词：

来源：评论

学校读者我要写书评

暂无评论

Low‐frequency diffraction from a free surface coupled to a semi‐infinite elastic surface as modeled by sea ice properties

引用

The Journal of the Acoustical Society of America 2005年第S1期85卷 S50-S50页

作者： Peter H. Dahl George V. Frisk MIT/WHOI Joint Program in Oceanography/Oceanographic Engineering Department of Ocean Engineering Massachusetts Institute of Technology Cambridge MA 02139 Department of Ocean Engineering Woods Hole Oceanographic Institution Woods Hole MA 02543

This paper discusses the solution of a low‐frequency plane wave incident upon a semi‐infinite elastic plate, such as an Arctic ice lend or free edge, using the Wiener‐Hopf method. By low‐frequency it is meant that the elastic properties of the plate are adequately described by the thin plate equation. For example, in a floating ice sheet, this translates into frequency‐ice thickness products that are ≲ 150. A key issue here is the fluid loading pertaining to sea ice and low‐frequency acoustics, which cannot be characterized by simplifying heavy or light fluid loading limits. An approximation to the exact kernel of the Wiener‐Hopf functional equation is used here, which is valid in this midrange fluid loading regime. The farfield diffracted pressure is found, which includes a fluid‐loaded, sub‐sonic (relative to the water) flexural wave in the ice plate. Comparisons are also made with the locally reacting approximation to the input impedance of an ice plate. The combined effects of the ice lead diffraction process represent loss mechanisms that contribute to the transmission loss in long‐range Arctic acoustic propagation.

关键词：

来源：评论

学校读者我要写书评

暂无评论

A self‐consistent theory of wave propagation and scattering through weakly inhomogeneous media

引用

The Journal of the Acoustical Society of America 2005年第S1期85卷 S70-S70页

作者： Dajun Tang George V. Frisk MIT/WHOI Joint Program in Oceanography/Oceanographic Engineering Department of Ocean Engineering Massachusetts Institute of Technology Cambridge MA 02139 Department of Ocean Engineering Woods Hole Oceanographic Institution Woods Hole MA 02543

A unified perturbation approach to wave propagation and scattering in weakly inhomogeneous media is presented. By separating the total wave field into an averaged coherent propagation part and a random scattering part, a set of coupled wave equations is found. The problem of a wave propagating in a random medium is changed to a problem of a pair of coupled waves propagating in a deterministic medium with randomly distributed sources. This method not only improves upon the conventional Born approximation for the scattered field, but also gives the attenuation behavior of the coherent propagating field related to the statistics of the random media. Examples of underwater acoustic waves in an inhomogeneous water column and an inhomogeneous bottom are given.

关键词：

来源：评论

学校读者我要写书评

暂无评论

An integral equation approach to range‐dependent boundary value problems in ocean acoustics

引用

The Journal of the Acoustical Society of America 2005年第S1期83卷 S117-S117页

作者： Peter H. Dahl George V. Frisk MIT/WHOI Joint Program in Oceanography/Oceanographic Engineering Woods Hole Oceanographic Institution Woods Hole MA 02543 Department of Ocean Engineering Woods Hole Oceanographic Institution Woods Hole MA 02543

In ocean acoustics, the introduction of range discontinuities, for example, the water‐to‐ice canopy surface, creates a mixed boundary value problem. In this paper, an exact solution of certain mixed boundary value problems is discussed using the Wiener‐Hopf method. A key attribute of this approach is that it is not fundamentally numerical in nature and allows additional insight into the mathematical and physical structure of the acoustic field due to range discontinuities. The problem discussed here is a canonical one: A plane wave is incident upon a planar surface where the boundary condition changes from Dirichlet (free surface) to Neumann (hard). The boundary conditions addressed in this problem are highly idealized renditions of what happens, when, say, a plane wave is incident upon a water‐to‐ice canopy surface; nevertheless, important features of the diffraction process are produced here, and the solution gives considerable insight into the process. The solution of the diffracted potential is partitioned into two components: a field consisting of cylindrical waves weighted by a polar gain function, resulting from the artificial source created by the discontinuity in the boundary; and a field containing a residue contribution which restores field continuity along the line corresponding to specular reflection. Contour plots of equal pressure amplitude show how the component fields superimpose such that the boundary conditions are maintained, and how energy is redistributed across the angular spectrum in the diffraction process. The latter is related to mode coupling due to boundary changes in waveguide problems. [Work supported by ONR.]

关键词：

来源：评论

学校读者我要写书评

暂无评论

Visually augmented navigation in an unstructured environment using a delayed state history

Visually augmented navigation in an unstructured environment...

引用

IEEE International Conference on Robotics and Automation (ICRA)

作者： R. Eustice O. Pizarro H. Singh MIT/WHOI Joint Program in Applied Ocean Science and Engineering Massachusetts Institute of Technology Cambridge MA USA Department of Applied Ocean Physics and Engineering Woods Hole Oceanographic Institution Woods Hole MA USA

This work describes a framework for sensor fusion of navigation data with camera-based 5 DOF relative pose measurements for 6 DOF vehicle motion in an unstructured 3D underwater environment. The fundamental goal of this work is to concurrently estimate online current vehicle position and its past trajectory. This goal is framed within the context of improving mobile robot navigation to support sub-sea science and exploration. Vehicle trajectory is represented by a history of poses in an augmented state Kalman filter. Camera spatial constraints from overlapping imagery provide partial observation of these poses and are used to enforce consistency and provide a mechanism for loop-closure. The multi-sensor camera + navigation framework is shown to have compelling advantages over a camera-only based approach by: 1) improving the robustness of pairwise image registration, 2) setting the free gauge scale, and 3) allowing for a unconnected camera graph topology. Results are shown for a real world data set collected by an autonomous underwater vehicle in an unstructured undersea environment.

关键词： Navigation Delay History Cameras Underwater vehicles Robot vision systems Sensor fusion Motion measurement Mobile robots Robustness

来源：评论

学校读者我要写书评

暂无评论

Micro-bathymetric mapping using acoustic range images

Micro-bathymetric mapping using acoustic range images

引用

oceanS

作者： C. Roman H. Singh MIT/WHOI Joint Program in Applied Ocean Science and Engineering Massachusetts Institute of Technology Cambridge MA USA Department of Applied Ocean Physics and Engineering Woods Hole Oceanographic Institution Woods Hole MA USA

This work focuses on the creation of high resolution micro-bathymetric maps using a high frequency pencil beam sonar. These maps typically cover areas of 10's to 100's of square meters. Data is collected using a sonar mounted to an underwater vehicle that can be positioned at discrete locations on the sea floor or flown in a survey pattern above the bottom. Specifically, we are focused on improving the accuracy of these terrain maps by merging sonar pings taken from multiple vantage points over the same location. This requires the adaption of data registration techniques to handle errors related to the sonar sensor. The registration can also be modified to incorporate the navigation data available from an instrumented underwater vehicle. A two axis scanning sonar was used to gather data in the form of densely sampled range images. The data registration works on the 3D projection of these range images in a scan-matching manner. Through this process regions occluded in a single scan are filled with data available from other scans and individual pings which show a poor return are removed. Refined estimates of the scan vantage points are also generated during the registration. The initial estimates of these locations are provided by navigation data. The practical application of this work complements photographic mapping when visibility is limited. It also provides additional measurements which can be used to improve vehicle navigation.

关键词： Sonar navigation Sonar measurements Remotely operated vehicles Underwater vehicles Sea floor Underwater acoustics Layout oceans Acoustical engineering Acoustic beams

来源：评论

学校读者我要写书评

暂无评论

Coherent source direction estimation for three-row bathymetric sidescan sonars

Coherent source direction estimation for three-row bathymetr...

引用

Proceedings of the oceanS '99 MTS/IEEE - Riding the Crest into the 21st Century

作者： Xu, Wen Stewart, W.Kenneth MIT/WHOI Joint Program in Applied Ocean Physics and Engineering Cambridge United States

In the context of three-row bathymetric sidescan sonars, a coherent source direction estimator (CSDE) is proposed to resolve two sources from different direction. This method is compared with the ESPRIT-based approach using different sonar models. The simulations show that CSDE works very well for highly coherent sources and at the signal-to-noise ratio above 10dB while the ESPRIT-based method is quite robust for the incoherent source signal model. In addition, CSDE gives the source time series estimation on the basis of the direction estimation as well.

关键词： Sonar

来源：评论

学校读者我要写书评

暂无评论

Coherent source direction estimation for three-row bathymetric sidescan sonars

Coherent source direction estimation for three-row bathymetr...

引用

oceanS

作者： Wen Xu W.K. Stewart MIT/WHOI Joint Program in Applied Ocean Physics and Engineering Cambridge MA USA Virtual Marine Associates Inc. Fort Pierce FL USA

In practical applications with bathymetric sidescan sonar, the multipath reflection and other directional interferences are the key limiting factors for a better performance. To deal with this problem, a multiple-row system can be used to resolve the multipath reflections from the direct signal instead of smoothing the measurements over some time and/or angle intervals as previously widely investigated. However, most current algorithms for signal direction-of-arrival estimation fail when the sources from different directions are coherent, which often occurs in a shallow water multipath environment. In the context of three-row bathymetric sidescan sonars, this paper proposes a coherent source direction estimator (CSDE) to resolve two sources from different directions. This method is compared with the ESPRIT-based approach using different sonar data models. The simulations show that CSDE works very well for highly coherent sources at the angular separation of 10/spl deg/ between two sources and at the signal-to-noise ratio above 10 dB while the ESPRIT-based method is quite robust for the incoherent source signal model. In addition, CSDE gives the source time series estimation on the basis of the direction estimation as well. Analyses to the interference field associated with the sidescan sonar show that a model with two or three simultaneously received signals describes even some shallow water fields very well. These preliminary results suggest that the combination of above two approaches could replace the currently used differential phase technique to get a better performance in shallow water without significant increase of the system cost.

关键词： Sonar measurements Reflection Interference Signal resolution Sonar applications Smoothing methods Time measurement Direction of arrival estimation Water resources Data models

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：