水下机器人视频图像高效压缩方法研究     

李庆忠  王冰 《热带海洋学报》2009,28(4):1-5

水下视频图像压缩一直是有限带宽水声信道实时传输海量视频数据的关键技术之一。本文首先介绍了目前水下机器人和水下视频图像压缩研究存在的主要问题，并综合分析了目前几种高效视频压缩方法的特点并探讨了进一步研究的方向。此外，根据水下视频的成像特点，提出了高效的全局与局部运动混合补偿方案和基于小波变换的预处理方法。初步实验结果表明：本文提出的预处理方法可以有效去除视频图像中存在的大量视觉冗余和空间冗余，提出的混合运动补偿方案可以获得很高的压缩编码效率；但必须进一步研究快速、有效的全局运动估计方法。  相似文献   

时变多径水声信道的仿真研究   总被引：1，自引：0，他引：1  

牛富强  杨燕明  郭长勇  刘贞文 《台湾海峡》2009,28(4):586-591

本文针对浅海水声信道的时变特性，基于射线理论引入海洋参数——强度起伏参数Φ、不均匀度参数A，建立有效的时变多径信道模型，并采用Matlab工具进行仿真．仿真结果表明，该模型相比于确定性模型更容易理解、更真实．文中给出的模型和结论能够为实际通信系统中发射接收机深度等的选择和设计提供一定的参考和依据，有助于对水声信道的了解．  相似文献   

Experiments on vision guided docking of an autonomous underwater vehicle using one camera   总被引：1，自引：0，他引：1  

Jin-Yeong Park  Bong-huan Jun  Junho Oh 《Ocean Engineering》2009,36(1):48-61

This paper introduces an underwater docking procedure for the test-bed autonomous underwater vehicle (AUV) platform called ISiMI using one charge-coupled device (CCD) camera. The AUV is optically guided by lights mounted around the entrance of a docking station and a vision system consisting of a CCD camera and a frame grabber in the AUV. This paper presents an image processing procedure to identify the dock by discriminating between light images, and proposes a final approach algorithm based on the vision guidance. A signal processing technique to remove noise on the defused grabbed light images is introduced, and a two-stage final approach for stable docking at the terminal instant is suggested. A vision-guidance controller was designed with conventional PID controllers for the vertical plane and the horizontal plane. Experiments were conducted to demonstrate the effectiveness of the vision-guided docking system of the AUV.  相似文献   

Nekton distribution and midwater hypoxia: A seasonal,diel prey refuge?     

Sandra L. Parker-Stetter  John K. Horne 《Estuarine, Coastal and Shelf Science》2009

Hypoxia affects the distribution of pelagic nekton (i.e., fish and large invertebrates) in both marine and freshwater systems. Bottom hypoxia is common, but midwater oxygen minimum layers (OMLs) also develop in marine offshore regions, fjords, and freshwater lakes. Studies of nekton responses to OML in marine ecosystems have primarily occurred in deep, offshore regions with thick, persistent OMLs. Our study examined the response of pelagic nekton to an OML in a shallow temperate fjord, Hood Canal, WA, U.S.A. Using acoustics, we quantified vertical distribution of nekton at two sites (Hoodsport and Duckabush) before (July) and after (September) OML development. Both Hoodsport and Duckabush had strong OML between 10 and 35 m in September, with lower (minimum 0.63 mg L⁻¹) oxygen levels at Hoodsport compared to Duckabush (1.58 mg L⁻¹). The OML did not affect daytime distribution of fish or invertebrates, with both occupying depths >60 m. At night in July, with no OML, invertebrates migrated into waters <20 m and fish dispersed to within 15 m of the surface at both sites. In the presence of the September OML, invertebrates migrated into waters <20 m, but the upper limit of fish vertical distribution stopped at the base of the OML (35 m) at Hoodsport. Fish vertical distribution at Duckabush was less pronounced within and above the OML (10–35 m) than it had been in July. Our results suggest that the OML did not affect invertebrate vertical distribution, but did affect fish vertical migration, and may provide a seasonal, diel prey refuge.  相似文献   

Use of a high-resolution profiling sonar and a towed video camera to map a Zostera marina bed,Solent, UK     

A. Lefebvre  C.E.L. ThompsonK.J. Collins  C.L. Amos 《Estuarine, Coastal and Shelf Science》2009

Seagrasses are flowering plants that develop into extensive underwater meadows and play a key role in the coastal ecosystem. In the last few years, several techniques have been developed to map and monitor seagrass beds in order to protect them. Here, we present the results of a survey using a profiling sonar, the Sediment Imager Sonar (SIS) and a towed video sledge to study a Zostera marina bed in the Solent, southern UK. The survey aimed to test the instruments for seagrass detection and to describe the area for the first time.  相似文献   

Precise Positioning of Underwater Static Objects without Sound Speed Profile     

Fanlin Yang  Xiushan Lu  Jiabiao Li  Litao Han  Zuoya Zheng 《Marine Geodesy》2013,36(2):138-151

A new method of positioning underwater static objects is presented based on Global Positioning System (GPS) acoustics. It adopts a model in which the ranging errors follow a quadratic relation with the travel time of acoustic signals. A least squares technique is used to estimate the effective sound speed. The precise location of an object can then be made. The simulation shows that the method is capable of determining the three-dimensional position with an accuracy of 5 cm in a water depth of 500 m. The operating time is respectively 5–10 minutes in 50–100 m depth and 20–30 minutes in 500 m depth.  相似文献   

A long‐range and high‐resolution underwater acoustic positioning system     

Tomoyoshi Takeuchi 《Marine Geodesy》2013,36(3-4):225-231

Abstract

It is desired to track the location of an underwater data collecting platform using acoustic range data. A long‐range and high‐resolution acoustic system for underwater locating has been investigated. The system provides continuous and highly accurate tracking of a platform referenced to bottom‐mounted buoys. Each reference buoy contains an acoustic transponder, which is used to obtain ranging data from the transponder to the platform. The transponder has a signal source that is phase‐modulated by a maximal‐length binary sequence and a correlation processing unit to be capable of detecting received acoustic signals with high SNR in a noisy environment or in attenuation due to long‐range propagation, and to identify multipath acoustic signals. The acoustic system has been designed and sea tests tried. The results of that experiment have yielded capability of a submeter underwater acoustic positioning system.  相似文献   

典型东海黑潮锋环境下的声场分布异常分析     

张旭  刘艳  孙杰 《台湾海峡》2013,32(3)

东海黑潮锋作为中国近海的一类特殊海洋学现象,对水声传播产生的复杂影响已受到关注,但对其影响机制的认识还较为欠缺.应用BELLHOP水声学数值模型分析了典型东海黑潮锋环境下的声场特性,结果表明:穿过锋面时声线干涉伴随的声能强弱空间分布出现明显偏移,同时波导中泄漏的声能对锋面非均匀环境引起的传播损失进行了补偿,使波导区域之外的声能变化小于5dB(声波频率为1 kHz).相比之下,从外海暖水混合层向近海传播时表面声道的瓦解可使传播损失突然增大10 ～ 15 dB(声波频率为1 kHz).东海黑潮锋环境下的声场能量异常分布体现了海底地形和水文环境的共同影响,地形条件对声场样式起支配性作用,而锋面引起的非均匀水文环境则是使声能空间分布出现异常变化的关键调制性因素.  相似文献   

Use of a two-frequency algorithm to determine size and abundance of plankton in three widely spaced locations   总被引：2，自引：1，他引：1  

Mitson  R. B.; Simard  Y.; Goss  C. 《ICES Journal of Marine Science》1996,53(2):209-215

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Geostatistics for fish stock assessments: a review and an acoustic application   总被引：4，自引：5，他引：4  

Petitgas  Pierre 《ICES Journal of Marine Science》1993,50(3):285-298

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