Time series video analysis of bubble release processes at natural hydrocarbon seeps in the Northern Gulf of Mexico

This research quantifies the rate and volume of oil and gas released from two natural seep sites in the Gulf of Mexico: lease blocks GC600 (1200 m depth) and MC118 (850 m depth). Our objectives were to determine variability in release rates and bubble size at five individual vents and to investigate the effects of tidal fluctuations on bubble release. Observations with autonomous video cameras captured the formation of individual bubbles as they were released through partially exposed deposits of gas hydrate. Image processing techniques determined bubble type (oily, gaseous, and mixed: oily and gaseous), size distribution, release rate, and temporal variations (observation intervals ranged from 3 h to 26 d). A semi-automatic bubble counting algorithm was developed to analyze bubble count and release rates from video data. This method is suitable for discrete vents with small bubble streams commonly seen at seeps and is adaptable to multiple in situ set-ups. Two vents at GC600 (Birthday Candles 1 and Birthday Candles 2) were analyzed. They released oily bubbles with an average diameter of 5.0 mm at a rate of 4.7 bubbles s⁻¹, and 1.3 bubbles s⁻¹, respectively. Approximately 1 km away, within the GC600 seep site, two more vents (Mega Plume 1 and Mega Plume 2) were analyzed. These vents released a mixture of oily and gaseous bubbles with an average diameter of 3.9 mm at a rate of 49 bubbles s⁻¹, and 81 bubbles s⁻¹, respectively. The fifth vent at MC118 (Rudyville) released gaseous bubbles with an average diameter of 3.0 mm at a rate of 127 bubbles s⁻¹. Pressure records at Mega Plume and Rudyville showed a diurnal tidal cycle (24.5 h). Rudyville was the only vent that demonstrated any positive correlation (ρ = 0.60) to the 24.5 h diurnal tidal cycle. However, these observations were not conclusive regarding tidal effects on bubble release.     

Daily to seasonal cross‐shore behaviour of quasi‐persistent intertidal beach morphology

In this study, an intertidal bar and trough system on the beach of Noordwijk, The Netherlands was monitored over a 15‐month period in order to examine the daily to seasonal sequential cross‐shore behaviour and to establish which conditions force or interrupt this cyclic bar behaviour. The beach morphology (bars and troughs) was classified from low‐tide Argus video images based on surface composition. From the classified images, time series of the landward boundary of the bar and of the trough were extracted. The time series of the alongshore‐averaged boundary positions described sawtooth motion with a period between 1 and 4 months, comprising gradual landward migration followed by abrupt seaward shifts. The abrupt seaward shift appeared to be a morphological reset induced by storm events, which lasted at least 30 h with a large average root‐mean‐square wave height (≥2 m) and offshore surge level (≥0·5 m), and a small trough (<20 m wide) in the pre‐storm beach morphology. The time series of the boundary positions exhibited very little longer (seasonal) scale variability, but somewhat larger smaller (daily) scale variability. The bar boundary was found to be more dynamic than the trough boundary. Copyright © 2007 John Wiley & Sons, Ltd.     

基于高速公路视频图像的能见度计算

能见度作为重要的气象观测因素之一,影响高速公路行车安全.基于视频资料的能见度计算方法类似于人眼的感知方式,具备对恶劣天气条件和复杂场地的适应性.基于安徽省2016年10月17日、12月1日和7日的3次大雾天气过程,选取跨省分布的3个高速公路站点,使用对应时次下视频图像灰度值均方差与能见度观测值建立计算模型.结果表明：1）随着大雾天气过程变化,模型计算结果较好体现了能见度的变化规律,对高速公路行车具有指导意义;2）基于视频图像的能见度计算方法类似于人眼观测,能见度越高,人眼分辨地物清晰度越高,图像均方差越大;3）由于监测原理和环境差异,能见度测量值与模型计算结果之间存在误差,理论上大雾空间分布越均匀,能见度仪和监控摄像头距离越近,计算误差越低.     

Propeller underwater radiated noise: A comparison between model scale measurements in two different facilities and full scale measurements

The prediction of propeller induced pressure fluctuations and underwater radiated noise is a subject of great and increasing interest in marine engineering. Nevertheless, the full-scale prediction of these negative effects, even though based on dedicated model scale tests represents still a challenging task. This is due to different phenomena, among which scale effects on cavitation and ship wake, confined environment and near field effects in model tests play an important role; the analysis of these problems is made difficult by the rather limited amount of available data from sea trials and to the complexities of the phenomena, most of which related to cavitation on the propeller blades, that are present in the measurements carried out in cavitation tunnels, depressurized towing tanks or circulating channels.In the present work, the subject has been studied with reference to a four blades conventional CP propeller of a coastal tanker.Cavitation tunnel tests have been carried out in two rather different facilities, at UNIGE cavitation tunnel and at SSPA large cavitation tunnel.Results from model scale tests processed with different treatments are then compared with full scale measurements performed by SSPA on the same propeller in terms of cavitation extension and radiated noise.The analysis is aimed at assessing the effectiveness of different experimental setups, testing procedures and scaling laws.     

深水AUV系统湿模态分析

以国家科技重大专项研制的深水AUV系统为研究对象,借助商业软件ANSYS,从一个新的角度——AUV湿模态分析,研究了各种外界激励的频率特性。为避免AUV发生共振,应保证AUV所受到的各种外界激励的频率远低于AUV的第7阶固有频率,基于此,我们对AUV航行时的干扰源、AUV搭载的机械结构以及AUV附属结构的对于AUV本体的产生的激励频率进行了计算。计算结果显示,低于AUV本体的固有频率,不会对AUV的稳定性产生影响,实现了AUV本体振动不会影响各传感器的正常工作的设计。     

海岸带实时实地视频观测ARGUS技术

区别于传统的定时定点野外测量方法,近年来各种遥感监测技术被应用于海岸带的实地观测领域。其中基于岸线的近岸实时实地视频观测技术(ARGUS系统)可获取大范围、长时间内的海岸带动力环境要素实测资料(诸如波浪、水流、岸线、地貌特征等),在海岸工程研究领域被广泛应用。通过对ARGUS系统的回顾,叙述了该技术的发展概况、视频数据类型和特点、图像分析方法和实际应用举例,同时简介了我国第一套ARGUS系统的构建。此外,也简要介绍了X波段雷达影像系统和红外线摄像系统在海岸工程研究中的应用。期望进一步推动上述近岸视频观测技术在我国海岸工程研究中的应用,为海岸带的综合管理利用和合理开发规划提供相应的科学支撑,同时促进各相关学科间(如海岸工程、测绘、图像分析等)的交叉合作。     

面向高耸古塔的无人机视频环拍实景三维建模方法

针对高耸古塔的实景三维建模效率低、成本较高的问题,本文提出一种无人机三相位环拍视频匀分帧建模方法。选用配备单镜头相机的小型多旋翼无人机,布设高、中、低3个相位分别对高耸古塔进行环拍视频采集并进行匀分帧处理。选取宁夏银川市兴庆区承天寺塔为试验对象进行实例建模,并与广泛使用的无人机拍照摄影式倾斜摄影建模方法对比,从建模效率、建模空三质量及整体模型质量3方面对比两种采集方式的建模效果。结果表明,本文方法的建模效果优于无人机倾斜摄影的三维建模效果,在优化采集过程和简化设备条件的基础上,保证了模型的完整度,提升了建模效率和建模质量。     

突发灾害监控与决策系统的设计与实现

现代社会,面对高危或人类无法到达的区域,如森林火场现场视查、地震灾情查看、城市等狭窄地段的高楼消防救灾、核辐射现场勘察检测等,基于无人机的无线通信系统,由于体积小和机动灵活,通过信息传感采集、视频现场捕捉,能安全、有效地获取现场灾情情况信息。然后数据通过中继传到后台,存入后台数据库。利用采集到的现场信息与ArcGIS Server发布的GIS相关服务,通过ArcGIS API for Flex对数据进行快速分析处理,使采集信息可视化,同时进行突发灾害模拟预测,准确定位事发地点,评价灾害影响范围,查找救援最短路径等。本文设计并实现了基于无人机突发灾害监控与决策系统,同时重点介绍系统的设计、组网的关键技术、视频压缩、基于GIS的数据处理与分析以及系统实现的功能。     

Precise Positioning of Underwater Static Objects without Sound Speed Profile

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.     

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

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.