HF Radar detected water wave velocity over the Northern Jiangsu Shoal

应用雷达波dOPPlEr正频移与负频移信号联解波速和径向流速方法,在2011年7月苏北浅滩高频地波雷达观测试验中实现潮间浅滩海面波浪传播速度的观测.基于频移与波速两级数据质量控制后统计的苏北浅滩平均波速平面分布图,可分辨出与潮间浅滩、水下岸坡和潮汐水道等浅滩地貌单元相关的波速分区格局.同步检验表明:雷达观测波速与现场观测水深的关系统计意义上遵循微幅波理论,径向流速较大条件下的波速观测质量较好,复杂地形所致双向波速不等现象导致波速观测质量降低,高频地波雷达是潮间浅滩动态遥感监测的潜在工具.High-frequency(HF) radar systems can provide wave velocity and radial current by identifying and tracking frequency shifts in the peaks of the Doppler spectra of the ocean backscatter corresponding to the advection of the Bragg wave.Data used in this study was collected by HF radar experiment for the Northern Jiangsu Shoal in July 2011.A distribution of monthly average wave velocity was generated with data that is quality controlled particularly.The intertidal flat, offshore shoal and tidal channel, associated with low speed area, high speed area and high speed belt respectively, could be distinguished by the HF radar mapped wave velocity distribution.After compared with datasets of field measurement and calculate results, it is revealed that(1) the relationship between water depth and monthly average wave velocity fits the theory of Airy Wave,(2) large radial currents may rise measurement accuracy of wave velocity, and 3) mismatch of approaching and leaving wave velocity related to complex topography may reduce measurement accuracy.海洋公益性行业科研专项经费(201005012;201005006); 国家自然科学基金(40876031); 国家高技术研究发展计划(2012AA091701); 江苏省科技计划项目基础研究计划(SBK201150144)资

Spatial and temporal variations in salt-marsh vegetation in Wanggang area,Jiangsu coast,based upon TM imagery analysis

通过对2002~2003年度3个时相的Landsat TM图像进行监督分类处理,研究了盐沼植被的分布和变化。结果表明,目前盐蒿和大米草(Spartina anglica)占据的面积很小,年际变化不大,由于滩涂围垦的影响其面积还在进一步缩小。互花米草(Spartina alterniflora)成为优势种,占据了大部分的盐沼面积,向海蔓延显著,扩张的趋势还在持续,其覆盖面积的年增长速率可达18%。Wanggang area is a typical region of tidal flats.In the 1960s and 1980s,Spartina anglica and Spartina alterniflora were artificially introduced, respectively,to this area.Appearance of Spartina marshes changed the sedimentary environment of the tidal flats.Using Landsat-TM data,the vegetation change and consequent modifications to the geomorphology of the tidal flat system were analyzed.Firstly,field observation and sampling were undertaken to investigate the biological feature of the three main salt-marsh species: Suaeda salsa,Spartina anglica and Spartina alterniflora.Observations in the four different seasons show that summer represents a period of rapid growth.In autumn the plants have the highest biomass.Thus,3 Landsat-TM images from 29 July 2002,24 July 2003 and 28 October 2003 were used to map the vegetation distribution and annual change.Using the in situ data,spectral features obtained show that Bands 3,4 and 5,in combination with field observations,contain sufficient information to distinguish the 3 different kinds of plants.Supervised classification using Bands 3,4 and 5 with in situ calibration was performed to derive the distribution pattern of the vegetation in Wanggang areas.The result shows that:(1) Spartina alterniflora is expanding towards the sea,with a rate of several hundred meters per year;(2) in the upper part of the inter-tidal zone,Suaeda salsa and Spartina anglica are distributed near the sea dyke,but reclamation has reduced the area of these two kinds of marshes;and(3) from 2002 to 2003,the area covered with Spartina alterniflora increased by 18%.国家自然科学基金重点项目(40231010);; 教育部博士点基金项目(20020284007

Characteristics of the large-scale sandwaves,tidal flow structure and bedload transport over the Taiwan Bank in southern China

对2006年8月所获台湾浅滩的底质、水深、多层位流速、流向以及CTD观测数据进行了分析,探讨了台湾浅滩大型沙波区水流的时空分布特征、沉积物输运过程及影响因素,结果表明,台湾浅滩动力作用较强,底质为粗砂,其上发育的沙波波长为325~822 m,波高为14.4~20.3 m,较接近由前人总结的沙波波高、波长的关系式计算出的波高和波长。沙波波峰、波谷、迎水面和背水面流速以12.5 h为周期沿顺时针方向旋转;底部最大流速出现在半日潮周期的同一时段,对应的方向均为偏南方向,且沙波迎水面的流速大于背水面的。在两个半日潮过程中研究区域的沉积物输入量大于输出量,处于淤积状态。在潮流作用下沉积物输运量较少,沙波脊线移动较小,而台湾浅滩有较大规模的沙波运动,故认为改造沙波的主要作用力应该是风暴流。在观测的断面中涨潮推移质输运量大于落潮的,且第一个半日潮涨落潮的输运能力均较第二个半日潮的大,这可能与潮流的流速-时间不对称特征及潮能变化形式有关。On the basis of the measurement of current velocity within the water column,water depth and physical properties of seawater over the Taiwan Bank in August 2006,the spatial and temporal characteristics of current velocities over large-scale sandwaves,together with the process of sediment transport,are analyzed.The results show that the sandwaves,14.4~20.3 m in height and 325.4~821.8 m in length,are formed under the conditions of strong current that is acting upon the bed consisting of coarse-grained sediments,with a height-length relationship similar to those identified elsewhere in previous studies.Currents at the sandwave crest,trough,stoss-side and lee-side turn in a clockwise manner with a period of 12.5 h.In the bottom layer of the water column,the largest velocity occurred at the same phase of each semidiurnal cycle,which was directed to the south;furthermore,the velocities on the stoss-side are larger than on the lee-side.During the two semidiurnal tidal cycles,the amount of sediment imported into the study area was larger than output,indicating that accretion was taking place.The sediment transported by tidal current was relatively weak,which could cause only slow migration of sandwaves.However,according to satellite observations,the sandwave migration can be high over the Taiwan Bank.This phenomenon may be caused by the strong currents associated with storm events.At the cross-section studied,sediment transport was more intensive during the flood than during the ebb,and the net fluxes varied for different semidiurnal tidal cycles,indicating the effects of the time-velocity asymmetry and the tide phase.国家自然科学基金资助项目(40476023