Robust tracking of multiple objects in sector-scan sonar imagesequences using optical flow motion estimation     

Lane  D.M. Chantler  M.J. Dongyong Dai 《Oceanic Engineering, IEEE Journal of》1998,23(1):31-46

The fast update rate and good performance of new generation electronic sector scanning sonars is now allowing practicable use of temporal information for signal processing tasks such as object classification and motion estimation. Problems remain, however, as objects change appearance, merge, maneuver, move in and out of the field of view, and split due to poor segmentation. This paper presents an approach to the segmentation, two-dimensional motion estimation, and subsequent tracking of multiple objects in sequences of sector scan sonar images. Applications such as ROV obstacle avoidance, visual servoing, and underwater surveillance are relevant. Initially, static and moving objects are distinguished in the sonar image sequence using frequency-domain filtering. Optical flow calculations are then performed on moving objects with significant size to obtain magnitude and direction motion estimates. Matches of these motion estimates, and the future positions they predict, are then used as a basis for identifying corresponding objects in adjacent scans. To enhance robustness, a tracking tree is constructed storing multiple possible correspondences and cumulative confidence values obtained from successive compatibility measures. Deferred decision making is then employed to enable best estimates of object tracks to be updated as subsequent scans produce new information. The method is shown to work well, with good tracking performance when objects merge, split, and change shape. The optical flow is demonstrated to give position prediction errors of between 10 and 50 cm (1%-5% of scan range), with no violation of smoothness assumptions using sample rates between 4 and 1 frames/s  相似文献   

Spatial interaction and network structure evolvement of cities in terms of China’s rail passenger flows   总被引：4，自引：1，他引：3  

Teqi Dai  Fengjun Jin 《中国地理科学(英文版)》2008,18(3):206-213

Cities separated in space are connected together by spatial interaction （SI） between them. But the studies focusing on the SI are relatively few in China mainly because of the scarcity of data. This paper deals with the SI in terms of rail passenger flows, which is an important aspect of the network structure of urban agglomeration. By using a data set consisting of rail O-D （origin-destination） passenger flows among nearly 200 cities, inter-city rail distance O-D matrixes, and some other indices, it is found that the attenuating tendency of rail passenger is obvious. And by the analysis on dominant flows and spatial structure of flows, we find that passenger flows have a trend of polarizing to hubs while the linkages between hubs upgrade. However, the gravity model reveals an overall picture of convergence process over time which is not in our expectation of integration process in the framework of globalization and eco- nomic integration. Some driven factors for the re-organization process of the structure of urban agglomeration, such as technique advance, globalization, etc. are discussed further based on the results we obtained.  相似文献   

德州市地面沉降现状及防治对策     

孟庆峰  戴鲁旗 《山东国土资源》2008,24(11)

1 德州市地面沉降的现状及危害 地面沉降是地面在定时期内不断降低的环境地质现象，地面沉降有自然的地面沉降与人为的地面沉降。地面沉降是一种严重的地质灾害，它直接影响城市建设、工农业生产和人民生活。  相似文献   

Response of internal waves to 2005 Typhoon Damrey over the northwestern shelf of the South China Sea     

Gang Wang  Fangli Qiao  Yijun Hou  Dejun Dai  Min Lin  Qilong Zhang  Gang Wang  Baoshu Yin 《中国海洋大学学报(英文版)》2008,7(3):251-257

Continuous observation of sea water temperature and current was made at Wenchang Station (19°35′N, 112°E) in 2005. The data collected indicate vigorous internal waves of both short periods and tidal and near-inertial periods. The temperature and current time series during 18-30 September were examined to describe the upper ocean internal wave field response to Typhoon Damrey (0518). The strong wind associated with the typhoon, which passed over the sea area about 45 km south of Wenchang Sta- tion on 25 September, deepened the mixed layer depth remarkably. It decreased the mixed layer temperature while increasing the deep layer temperature, and intensified the near-inertial and high-frequency fluctuations of temperature and current. Power spectra of temperature and current time series indicate significant deviations from those obtained by using the deep ocean internal wave models characterized by a power law. The frequency spectra were dominated by three energetic bands: around the inertial frequency (7.75× 10-6 Hz), tidal frequencies (1.010-25 to 2.4×10-5 Hz), and between 1.4×10-4 and 8.3 × 10-4 Hz. Dividing the field data into three phases (before, during and after the typhoon), we found that the typhoon enhanced the kinetic energy in nearly all the frequency bands, es- pecially in the surface water. The passage of Damrey made a major contribution to the horizontal kinetic energy of the total surface current variances. The vertical energy density distribution, with its peak value at the surface, was an indication that the energy in- jected by the strong wind into the surface current could penetrate downward to the thermocline.  相似文献   

国产XBT海上比测方法研究及结果分析     

雷发美  商少平  贺志刚  汪鹏  戴昊 《海洋技术学报》2019,38(1)

随着国产投弃式温深仪(XBT)性能的提高,其使用范围和规模也逐步扩大,受某专项办的委托,厦门大学在南海东北部开展了"海洋监测设备适用性检验规范及海上试验研究(国家863计划)"项目,针对海洋技术领域研发的技术较为成熟、具备产品化条件的XBT开展检验与验证,对国产XBT的性能和实际使用情况进行分析和总结。试验中,在不同站点进行温盐深仪(CTD)现场测量,以此数据为真值对国产和进口XBT精度做评估。在较高速度走航测量时,则以进口XBT数据为参照,对国产XBT进行评估。试验结果表明,国产XBT整体上表现良好,成功率大概为80%,有些型号的国产XBT精度与进口XBT精度接近,但国产XBT无效剖面较多。同时也发现,进口XBT的精度无法满足预期比测的要求,不能准确计算出国产XBT精度,但结果仍然具有参考价值。本次试验可以为国产XBT的规模化应用和推广提供数据支持,也可为其他型号XBT/XCTD/CTD等仪器的比测提供借鉴。  相似文献   

Reliability of recharge rates estimated from groundwater age with a simplified analytical approach     

Yanhui Dong  Yueqing Xie  Jun Zhang  Andrew J. Love  Xin Dai 《水文研究》2021,35(5):e14160

Groundwater age is often used to estimate groundwater recharge through a simplified analytical approach. This estimated recharge is thought to be representative of the mean recharge between the point of entry and the sampling point. However, given the complexity in actual recharge, whether the mean recharge is reasonable is still unclear. This study examined the validity of the method to estimate long-term average groundwater recharge and the possibility of obtaining reasonable spatial recharge pattern. We first validated our model in producing reasonable age distributions using a constant flux boundary condition. We then generated different flow fields and age patterns by using various spatially varying flux boundary conditions with different magnitudes and wavelengths. Groundwater recharge was estimated and analysed afterwards using the method at the spatial scale. We illustrated the main findings with a field example in the end. Our results suggest that we can estimate long-term average groundwater recharge with 10% error in many parts of an aquifer. The size of these areas decreases with the increase in both the amplitude and the wavelength. The chance of obtaining a reasonable groundwater recharge is higher if an age sample is collected from the middle of an aquifer and at downstream areas. Our study also indicates that the method can also be used to estimate local groundwater recharge if age samples are collected close to the water table. However, care must be taken to determine groundwater age regardless of conditions.  相似文献   

济宁南部优质大米产地土壤地球化学特征   总被引：2，自引：0，他引：2  

谭肖波  薄本玉  周付彬  戴振芬  陈洪年 《山东国土资源》2009,25(7):42-45

对济宁南部优质大米产地的不同层位土壤样品的分析结果进行统计，分析了土壤元素的分布特征，证实除P的含量稍低于山东省平均值外，其他元素含量均高于山东省平均值，土壤质量良好，营养水平较高。但Cu，F，As，cd，Pb，Hg，cr在土壤中原始含量偏高，是潜在污染源和引发地方病的隐患。通过土壤环境质量评价和土壤肥力评价，结果表明该区土壤环境质量较好，大部分地区肥力优良或尚可，但个别地段因重金属污染超标成为质量较差区，应引起人们的重视，以确保粮食生产安全。  相似文献   

Sublimation over seasonal snowpack at the southeastern edge of a desert in central Eurasia     

Hong‐Fei Zhou  Xin‐Jun Zheng  Baojia Zhou  Qiong Dai  Yan Li 《水文研究》2012,26(25):3911-3920

The Gurbantonggut Desert, China, is an ideal site for study of sublimation from the snowpack because there are sparse vegetation and simple topography, and the wind speed is not large enough to blow snow into the atmosphere from the snowpack. Daily sublimation was measured by manual snow lysimeters at 8:00, and an automatic weather station was deployed at the top of a stout longitudinal dune chain at the southeastern edge of the desert. It is shown that on a daily scale, there was an extremely significant no‐intercept linear relationship between the measured sublimation and that calculated by the bulk aerodynamic method, although the former was only 83.8% of the latter. It is also demonstrated that ?10°C and 2 m/s were the thresholds where the sublimation varied with the air temperature and the wind speed. When these two thresholds were exceeded, the sublimation accelerated. However, the air temperature and the wind speed at 2 m above the ground averaged ?17.2°C and 1.3 m/s, respectively, and the percentages of the time when the air temperature was below ?10 °C and the wind speed was below 2 m/s were 76.9% and 85.1%, respectively. As a result, the rate of sublimation was quite low most of the time, and the thin snowpack remained in a quasi‐static state until the melt stage started. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Meta‐analysis of flow modeling performances—to build a matching system between catchment complexity and model types          下载免费PDF全文

Lu Zhuo  Qiang Dai  Dawei Han 《水文研究》2015,29(11):2463-2477

Hydrological models play a significant role in modelling river flow for decision making support in water resource management. In the past decades, many researchers have made a great deal of efforts in calibrating and validating various models, with each study being focused on one or two models. As a result, there is a lack of comparative analysis on the performance of those models to guide hydrologists to choose appropriate models for the individual climate and physical conditions. This paper describes a two‐level meta‐analysis to develop a matching system between catchment complexity (based on catchment significant features (CSFs)) and model types. The intention is to use the available CSF information for choosing the most suitable model type for a given catchment. In this study, the CSFs include the elements of climate, soil type, land cover and catchment scale. Specific choices of model types in small and medium catchments are further explored with all CSF information obtained. In particular, it is interesting to find that semi‐distributed models are the most suitable model type for catchments with the area over 3000 km², regardless of other CSFs. The potential methodology for expanding the matching system between catchment complexity and model complexity is discussed. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

对华跨境技术转移影响因素研究   总被引：5，自引：2，他引：3  

司月芳  王岱  王丰龙 《地理科学》2019,39(2):259-266

基于分国别的技术引进合同数据,探讨对华跨境技术转移的空间分布及其影响因素。研究发现,美国、日本、德国、芬兰、英国和法国等技术先进国家始终是中国技术引进的主要来源国。亚洲的印度、马来西亚、泰国等在对华技术转移中的重要性也逐渐增强。对华跨境技术转移主要受技术势差、地理距离与技术通道等因素的影响。技术来源国与中国的技术势差越大、距离越近,技术溢出的强度越大;海外华人网络和跨国公司在华投资作为技术通道促进了海外技术向中国的转移。  相似文献