几种新型量测仪器在河工模型试验中的应用

对长江防洪模型中地形测量系统、流速测量系统和泥沙测量系统中利用的URI-Ⅲ三维地形测量系统、UPIV测流系统、光学后向散射仪、激光粒度分析仪等几种新型仪器的原理、组成及其应用情况进行了介绍.新型量测仪器缩短了试验数据提取和分析的时间,但三维地形测量系统难以测量曲率和宽深比变化较大的河工模型,UPIV测流系统不宜应用在过高含沙量和过深的水流中,0BS受模型沙颜色的影响较大、其反演的含沙量不一定能代表河流中测点的含沙量.     

堤防溃口冲刷试验中三维激光扫描技术的应用

采用非接触式数据获取方法,利用三维激光扫描仪对堤防溃口土体进行扫描,然后结合ArcGIS进行逆向建模,得出堤防溃口冲刷模型剖面图及时段冲刷量,并与实测冲刷量进行了对比.结果表明:①采用三维激光扫描技术能够方便快捷地获取堤防冲刷模型表面的点云数据,并可准确地在计算机中建立起以点云为基础的数字化冲刷过程模型；②三维激光扫描...     

长江口南 北槽悬沙遥感反演模型研究

为了给长江口航道治理及区域水土资源开发提供技术支持,利用2006~2008年卫星遥感影像数据和长江口多点实测含沙量数据,建立悬沙遥感反演模型,对长江口南、北槽泥沙含量进行了深入研究。结果表明：在含沙量小于0.2 g/L的低含沙量区,遥感反射率与水体含沙量之间呈线性关系;而在含沙量大于0.2 g/L的中高含沙量区,遥感反射率与含沙量之间呈对数关系。长江口大潮与小潮期的含沙量差异明显,按大、小潮分别建立遥感反演模型的精度较高。利用该模型可较好地反演出长江口南、北槽的含沙量场,并据此推断悬沙可能是造成北槽航道淤积的主要泥沙来源。     

联合机载激光测深波形和点云的水陆识别方法研究

水陆识别在河口海岸带水陆资源管理和科学研究中具有重要作用.利用机载激光测深(Airborne Li-DAR bathymetry,ALB)回波波形和点云信息可实现水陆交界区域高精度和高分辨率水陆识别.但在复杂海陆环境区域,采用ALB波形特征或三维点云高程特征的传统识别方法具有各自不足.针对复杂海陆环境区域高精度水陆识别...     

基于国产卫星多光谱影像的河流水体浊度遥感联合反演研究

基于集合建模思想,在水体光谱特征分析与敏感波段选择基础上,集成多种遥感反演模型优势,构建了河流水体浊度多光谱遥感联合反演模型(Combined Model-BP,CM-BP)。选择汉江中下游典型河段为研究区,利用2012—2013年原位观测数据,以具有较高时间分辨率和空间分辨率的国产卫星数据作为多光谱遥感数据源,测试评估了CM-BP浊度遥感反演模型适用性,并与传统波段组合模型进行精度比较,基于反演结果分析了研究区浊度时空分布特征。结果表明:基于集合建模思想构建的CM-BP模型的反演精度、适应性及稳定性均高于波段组合模型;从光谱分辨率、时空分辨率等角度考虑,环境与灾害监测预报小卫星星座系统、高分一号卫星、资源三号等国产卫星多光谱遥感数据是河流水体水质反演优选数据源;国产卫星遥感数据可以满足河流水体水质高精度、实时性与大尺度等遥感反演需要,为河流水环境监测研究提供数据基础。     

基于地面三维激光扫描及VR技术的BIM工程应用研究

基于激光扫描技术,对某能源站内部设备进行激光扫描,探讨了扫描点云流程,研究了激光点云联机渲染方式,针对BIM工程图纸不全的情况,提出以激光点云配合二维图纸建模的手段,为今后类似BIM工程三维空间信息的建立提供了一种新的解决思路,同时基于Unity3D三维游戏引擎,研究了VR设备及原理,探索了虚拟现实技术在BIM模型中的应用。     

基于声回波特性的引水隧洞表面声点云去噪

针对基于声波反射原理的隧洞内表面损伤探测过程易受水体环境噪声、多径噪声及检测设备自身噪声干扰问题，提出一种基于声回波特性的引水隧洞内表面声点云去噪方法。该方法利用声回波固有宽度特性形成的多回波数据点及声波叠加特性形成的数据点高强度值，并结合点云空间位置信息实现团状立体隧洞内表面声点云的噪声滤波；构建系列试验以验证不同敏感参数对所提方法去噪效果的影响，并与其他经典点云滤波算法结果进行对比分析。结果表明，所提方法在隧洞内表面声点云模型的平滑、去噪及重建精度上均优于传统激光点云滤波算法。该方法可为引水隧洞内表面损伤的检测及重大水资源配置工程灾变预防提供支撑。     

三星堆月亮湾城墙遗址覆土方量计算

利用三维激光扫描技术获取三星堆月亮湾城墙遗址区高精度三维激光点云,实现了任意边界挖填方量的精确计算。采用IDL编制了海量激光点云存储与管理软件LIDARVIEW,应用海量激光点云网格分块技术和动态四叉树空间索引方法实现了海量激光点云数据的存储与管理。提出基于网格分块的地表植被和建筑物的自动过滤技术,建立三星堆月亮湾城墙遗址现状地表的DEM模型。结合三星堆月亮湾城墙遗址的覆土设计方案,得到月亮湾城墙遗址覆土后地表DEM数据和覆土四周边界数据。最后利用覆土前后地表的DEM数据,对三星堆月亮湾城墙遗址覆土方量进行计算。工程实例表明,该方法可以快速、高效地解决复杂工程的挖填方的方量计算。     

基于航空高光谱的囫囵淖尔水体浊度反演建模

针对机载 Headwall 高光谱成像仪对水质监测能力的验证, 利用 2018 年 9 月 17 日航空高光谱数据和 17 个准同步实测水体浊度数据分别构建囫囵淖尔水体浊度波段比值反演模型、一阶微分反演模型和偏最小二乘反演模型, 估算同日的囫囵淖尔水体浊度的空间分布。研究结果表明: 利用机载 Headwall 高光谱数据构建的 3 个浊度反演模型, 验证均方根误差 RMSE 均小于验证样本浊度的极值差 5. 3 NTU, MRE 均小于 10% , 机载 Headwall 高光谱成像 仪能够较好地观测水体浊度差异; 在囫囵淖尔, 基于 Headwall 高光谱数据的偏最小二乘模型建模精度高于波段比 值模型和一阶微分模型, 决定系数 R2 达到 0.95, 综合误差 CE 为 1. 74% , 最适用于囫囵淖尔水体浊度的反演; 2018 年 9 月 17 日囫囵淖尔东部水域浊度范围为 21. 2~ 54.4 NTU, 呈现出北低南高的趋势, 湖中心区域水体浊度较低, 南部水域受水中藻类的影响, 水体浊度较高。利用航空高光谱遥感影像实现了浊度的定量反演, 为航空高光谱遥感数据用于水质参数反演提供借鉴。     

基于高光谱数据的汉江中下游典型河段水体悬浮物遥感反演

选择汉江中下游典型河段作为研究区域,利用2012—2013年实测水质数据及高光谱数据,基于有效信息变量筛选和神经网络算法构建研究区水体悬浮物浓度高光谱反演模型,分析评价了模型性能与估测效果,讨论了研究区水体悬浮物浓度分布特征。研究结果表明:基于变量投影重要性指数和神经网络优势构建的高光谱反演模型在反演精度、稳定性和适应性方面表现出优异的性能;而对于基于简单相关性分析构建的单波段模型和比值模型而言,建模样本选择对模型精度有较大影响,导致模型反演精度、稳定性和适用性较差;汉江中下游典型河段水体总悬浮物浓度整体上在18.8~187.0 mg/L之间变化,季节性差异明显,即春、夏两季悬浮物浓度低于秋季。     

EVALUATING SHALLOW‐WATER BATHYMETRY FROM THROUGH‐WATER TERRESTRIAL LASER SCANNING UNDER A RANGE OF HYDRAULIC AND PHYSICAL WATER QUALITY CONDITIONS

The fine‐scale structure of the water–sediment boundary in fluvial environments is dynamic and complex, influencing near‐bed flows, sediment transport and instream ecology. However, accurate high‐resolution surveying of marginally or partially inundated areas of river channels is problematic. Previous work has shown that terrestrial laser scanning (TLS) through relatively shallow‐water columns using standard green‐wavelength equipment introduces errors of <5 mm in a static, clear water column. This paper presents seven laboratory and field tests of through‐water TLS under variable flow velocities, depths, suspended sediment concentrations, water colour levels and scan ranges. Flow velocity decreased point accuracy only for supercritical flows, whereas point density decreased as a function of both water depth and suspended sediment concentration. A similar point return threshold was observed for water colour variations with no grains in suspension. Conversely, point precision and accuracy were a function of suspended sediment concentration alone (a threshold of 0.11 g L^?1 was observed). Field tests showed larger errors (<10 mm) and lower point precisions. A clear‐water depth‐penetration limit of 0.68 m was identified. Fluvial bathymetry acquired from through‐water TLS is presented for a gravel/boulder bed reach. Despite observed limits, these experiments demonstrate that our approach provides centimetre‐resolution bathymetry and sub‐aerial survey in an integrated dataset without the need for the following: (i) additional financial resources; (ii) concurrent depth measurements; or (iii) extra field effort for bathymetry acquisition, thereby enabling regular surveys to characterize the fine‐scale structure of channel beds and to constrain the geomorphic effect of individual flood events. Copyright © 2013 John Wiley & Sons, Ltd.     

Effect of the Three Gorges Reservoir on vertical distribution of suspended sediment concentration and estimation accuracy of depth-average concentration in downstream reaches

The sediment regime in the middle Yangtze River has been significantly changed from quasi-equilibrium to nonequilibrium since the impoundment of the Three Georges Reservoir (TGR). To understand the effects of the TGR on vertical distribution of suspended sediment concentration (SSC) and estimation accuracy of mean concentration, vertical sediment concentration and flow velocity data at the Shashi and Jianli hydrological stations in the reach before and after the impoundment were collected. Comparisons and analysis of vertical profiles of SSC before and after the TGR impoundment show that after the impoundment of the TGR, due to the coarsening of sediment particle size, the reduction in sediment load, and the significant decrease in sediment saturation, the vertical distribution of SSC in the downstream reaches became more uneven under medium and low water flows, which was reflected in the vertical gradient and the fluctuation degree of SSC significantly increased. In addition, the depth-average sediment concentrations were calculated by the selected-point method and the mean values calculated by the “multi-point method” were regarded as the “true mean” to evaluate the accuracy of the mean value calculated by the “few-point method.” It was found that the relative errors for the selected-point method were mainly positive before impoundment but mainly negative after impoundment. Additionally, the correction factors of one-point, two-point, and three-point methods and the position of the near-bed substituted point for the five-point method were given to reduce the error when the point measurements were used to calculate the depth-average sediment concentration in the downstream reaches.     

Stochastic Simulation of Daily Suspended Sediment Concentration Using Multivariate Copulas

An estimation of daily suspended sediment concentration (SSC) is required for water resource and environmental management. The traditional methods for simulating daily SSC focus on modeling the SSCs themselves, whereas the cross-correlation structure between SSC and streamflow has received only minor attention. To address this issue, we propose a stochastic method to generate long-term daily SSC using multivariate copula functions that account for temporal and cross dependences in daily SSCs. We use the conditional copula method to construct daily multivariate distributions to alleviate the complications and workload of parameter estimations using high-dimensional copulas. The observed daily streamflow and SSC data are normalized using the normal quantile transform method to relax the computationally intensive model of building daily marginal distributions. Daily SSCs can thus be simulated through the multivariate conditional distribution using previous daily SSC and concurrent daily streamflow values. The proposed method is rigorously examined by application to a case study at the Pingshan station in the Jinsha River Basin, China, and compared with the bivariate copula method. The results show that the proposed method has a high degree of accuracy, in preserving the statistics and temporal correlation of daily SSC observations, and better preserves the lag-0 cross correlation compared with the bivariate copula method. The multivariate copula framework proposed here can accurately and efficiently generate long-term daily SSC data for water resource and environmental management, which play a critical role in accurately estimating the frequency and magnitude of extreme SSC events.

     

徐六泾站悬移质含沙量比测与精度分析

通过长江口徐六泾断面大规模的跨越不同水情的现场测流试验,发现利用声学多普勒流速剖面仪(AD-CP)信号推算垂线平均含沙量,与传统值相比,平均相对误差绝对值小于5%,且误差呈正态分布。因此,升级现有的徐六泾浮标测流系统(以ADCP取代现有的ADP),可以实现徐六泾断面的在线实时输沙率监测,填补长江口泥沙站网的空白,为长江口相关规划、设计、科研等提供基础资料。     

Estimate of Suspended Sediment Concentration from Monitored Data of Turbidity and Water Level Using Artificial Neural Networks

Artificial neural networks (ANNs) are promising alternatives for the estimation of suspended sediment concentration (SSC), but they are dependent on the availability data. This study investigates the use of an ANN model for forecasting SSC using turbidity and water level. It is used an original method, idealized to investigate the minimum complexity of the ANN that does not present, in relation to more complex networks, loss of efficiency when applied to other samples, and to perform its training avoiding the overfitting even when data availability is insufficient to use the cross-validation technique. The use of a validation procedure by resampling, the control of overfitting through a previously researched condition of training completion, as well as training repetitions to provide robustness are important aspects of the method. Turbidity and water level data, related to 59 SSC values, collected between June 2013 and October 2015, were used. The development of the proposed ANN was preceded by the training of an ANN, without the use of the new resources, which clearly showed the overfitting occurrence when resources were not used to avoid it, with Nash-Sutcliffe efficiency (NS) equals to 0.995 in the training and NS = 0.788 in the verification. The proposed method generated efficient models (NS = 0.953 for verification), with well distributed errors and with great capacity of generalization for future applications. The final obtained model enabled the SSC calculation, from water level and turbidity data, even when few samples were available for the training and verification procedures.     

顾及水面比降的河道水面三维可视化方法

水面三维可视化是实现数字流域逼真展示的重要技术手段,现有水面三维可视化技术普遍未考虑天然河道水面比降的特性,难以适用于大尺度、流域级的河道水位过程三维可视化。提出了一种顾及水面比降的河道水面三维可视化方法,首先对河道水面边界多边形进行边界点增密与多边形三角化,然后基于河道水位过程数据对多边形边界点的高程进行插值与调整,最后基于调整后的三角网进行水面绘制。试验以三峡库区水位过程数据为基础进行了河道水面三维可视化,结果表明该方法能够有效表达天然河道的水位渐变过程。     

长江口浑浊带近底泥沙浓度变化

基于近底边界层四角架系统观测的水沙过程完整资料,对近底悬浮泥沙浓度的变化及其动力响应关系进行了分析.结果表明:1)近底悬浮泥沙浓度变化过程的特征是多峰性.在一个潮周期内,一般会出现四次明显的悬浮泥沙浓度峰值;2)水体中始终存在一个背景含沙浓度;3)流速的大小并不是决定近底悬浮泥沙浓度大小的唯一决定性因素.潮流加速度、憩流阶段形成的背景泥沙浓度以及床面可供起动的泥沙量同样起重要的作用;4)泥沙浓度变化和动力的响应关系可以归为四类:第一类正响应过程(悬浮泥沙浓度随流速的增大而增大)、第一类负响应过程(悬浮泥沙浓度随流速的增大而减小)、第二类负响应过程(悬浮泥沙浓度随流速的减小而增大)和第二类正响应过程(悬浮泥沙浓度随流速的减小而减小).综合分析紊动扩散作用、泥沙的起动和沉降作用及床面泥沙的供应率,对近底层悬浮泥沙浓度和动力响应变化的四个过程进行了详细的解释.     

基于Budyko理论的北京地区实际蒸散发估算及特征研究

为了探究近些年北京地区实际蒸散发的时空变化特征,采用基于Budyko理论的傅抱璞经验模型,对北京地区1980-2016年实际蒸散发进行了估算;并根据Mann-Kendall趋势分析、相关分析等方法,对研究区实际蒸散发的时间变化特征、空间格局以及影响因素进行了探讨;为提高傅抱璞经验模型在研究区的适用性,依据北京地区历史时期水文气象数据,结合水量平衡法对该模型参数进行了校准和验证。结果表明:优化参数后的经验模型在研究区具有较高的模拟精度,且适用性较强;北京地区多年实际蒸散发均值为447 mm;时间尺度上,呈不显著的下降趋势;空间上,表现出明显的空间异质性,其中,蓟运河山区的蒸散发最大,其次为潮白河流域东部;实际蒸散发的这种时空变化特征与区域降水量密切相关。     

一种单样含沙量计算方法探讨

对水面较宽、河床不稳定、主流和含沙量横向分布有变化的测站，其单断沙关系通常不好，虽然可用多条垂线沙样混全作为单沙，但仍难满足整编要求，从输沙率测验原理出发，分析了影响单断沙关系的主要因素，提出了流量加权计算单沙的方法。并详细介绍了制作单断沙关系的步骤。该方法运用于宜昌水文站后得到了单一稳定的单断沙关系，可满足整编要求，且提高了精度，该方法还具有操作简便，不增加外业测验工作量等特点。