【作者】 王利花；

【导师】 周云轩；

【作者基本信息】 华东师范大学 ， 自然地理学， 2014， 博士

【摘要】 长江河口海岸地区各种水动力综合作用塑造了复杂多变的河口地貌形态,促进了河口的不断演变。泥沙运动正是动力作用与地貌演变之间的纽带。如何更好地利用不同时相、不同空间分辨率、不同电磁波波段和主、被动遥感数据相结合的方式,进行长江河口及邻近海域不同尺度、不同性质水体动力参数的常规持续监测是对海洋遥感应用提出的全新挑战。据此,本文以遥感学、物理海洋学、地理信息系统等相关学科的理论为指导,基于3S技术、数值模拟技术等,选取多源遥感数据,深入研究河口及邻近海域表层水体参数(海表风场、海表流场及海表悬浮泥沙浓度)的遥感成像特征和成像机理,构建表层水体参数的遥感反演模型,实现表层水体参数的快速、大面积常规持续观测。在此基础上,辅以长江河口及邻近海域的气象数据、数值模拟数据和实测数据等,研究长江入海泥沙在各种水动力综合作用下引起的河口及邻近海域悬浮泥沙时空分布特征,探讨悬浮泥沙的扩散范围和动力机制。此项研究将有助于更好地理解河口陆海相互作用特点,为河口海岸工程、沉积地貌演变及生态环境保护等提供基础科学数据。主要研究内容包括以下4个方面：1)SAR海表风场反演选取ERS2-SAR, ENVISAT-ASAR微波雷达数据,通过改进基于2D FFT的风向反演算法,结合CMOD4风速反演模型,获取高精度高空间分辨率的海表风场。SAR风场反演结果与QuikSCAT风场产品及WRF模型风矢量结果表现了很好的一致性,风速相关系数分别为0.92和0.87,风向相关系数分别为0.95和0.85。高相关关系证明了SAR用于海表风场反演的能力,其高空间分辨率的独特优势更有利于揭示复杂多变的海岸带风场。联合开阔海域QuikSCAT风产品与海岸带地区SAR风场反演结果,可以获得全球范围内的高质量海表风场数据。定性定量评估CMOD4模型用于SAR风速反演的主要误差源,发现由于NRCS不精确导致风速相对误差最大值为45%；由于风向不精确导致的风速相对误差最大值为24%；当格网单元大小小于0.5km时,NRCS的变化很大程度上是由噪声引起的,从而影响SAR风速的精确估算。对于诸如台风这样的高风速海面风场,通过实例证实了采用CMOD5反演模型可准确的确定台风中心位置、台风空间结构及台风风速,这对于海洋灾害性天气预报预警具有非常重要的现实意义。在此基础上,SAR风场与数值模拟数据结合进行海洋动态研究是一次很好的尝试,证实了海洋遥感参数有利于数值模拟精度的提高,同时对海洋遥感数据源提出了高时相分辨率的需求。2) ASAR海表流场反演选取ENVISAT-ASAR微波雷达数据,基于多普勒质心频率异常理论反演海表多普勒流场。经方位向、距离向误差校正及去除海表风矢量对多普勒质心频率的贡献可获取海表多普勒流场。多普勒频率异常方法反演海表流速的分辨率在方位向为8km,距离向为4km。下行轨道ENVISAT-ASAR成像定位特征更适合获取长江入海及长江口邻近海域表层流场的空间变化特征。定性定量探讨了NRCS方位向剧烈梯度变化、低入射角、不精确的风矢量以及雨对多普勒流速估算的影响。当雷达入射角低于30°时,ASAR多普勒速率的误差会出现增长拐点；采用ASAR自身反演的海表风场,可降低海表风矢量对多普勒频率异常造成的误差；雨的出现导致雷达NRCS增加/降低,从而对多普勒质心频率异常产生偏差。ASAR多普勒流场与FVCOM数值模拟的海表流场吻合较好,存在较为一致的流速和流向,证实了基于多普勒质心异常理论反演ASAR海表流场的可行性和可靠性。ASAR海表流场能够反映局地海洋环境状况,对于揭示中国东海海域多尺度的海洋动态至关重要；也将有助于更好地理解ASAR影像的成像机理,提高定量化解释ASAR影像上海表流场特征的能力。3) MERIS海表悬浮泥沙浓度反演MERIS海表悬浮泥沙浓度反演结果与实测数据吻合较好,论证了基于MERIS数据的半经验半分析SERT模型用于高浊度水体泥沙反演的适用性和可靠性。洪季时,长江河口表层悬浮泥沙浓度最大可达3.0kg/m3,出现在南汇嘴及杭州湾附近；枯季时,长江河口表层悬浮泥沙浓度最大可达1.2-1.6kg/m3,出现在杭州湾及洋山港附近；汊道内表层悬沙浓度受径流和潮流影响较大,浓度出现较大波动。通常情况下,长江河口及邻近海域从徐六泾至最大浑浊带至杭州湾,表层悬浮泥沙浓度整体上呈现递增趋势,纵向上相对于上游河段、下侧海域而言,高悬浮泥沙浓度出现在最大浑浊带区域,横向上从长江口至杭州湾表层悬浮泥沙浓度不断增加。整体而言,大潮期间表层悬沙浓度大于寻常潮期间大于小潮期间；表层悬沙浓度的季节性变化显著,自徐六泾至口门表层悬沙浓度夏高冬低；南北槽汊道,表层悬沙浓度的季节性变化幅度较弱,时有转换趋势,即有时表现为夏高冬低,有时为夏低冬高；口外海滨及杭州湾区域表现为冬高夏低。4)长江河口及邻近海域表层悬浮泥沙驱动机制研究基于多源遥感数据,辅以气象数据、数值模拟数据和实测数据,探讨了长江河口及邻近海域表层悬浮泥沙驱动因子,结果表明径流对悬浮泥沙的影响主要表现在以径流作用为主的口内河段：潮流是长江口外及杭州湾的主要动力因子,制约着悬浮泥沙的分布；风向风速是控制浑水带扩散范围的一个主要因素,其变化可引起浑水带宽度大幅度的变动。更多还原

【Abstract】 The evolution characteristics of estuarine and coastal morphology are being moulded by the complicated hydrodynamic factors. The transport of sea surface sediment is the bridge between kinetic factors and geomorphology development. Therefore, how to use the combination of different temporal, spatial-resolution, electromagnetic wave and active and passive remote sensing images to routinely observe and analyze various environment kinetic parameters? This is a new challenge for the application of oceanic remote sensing. Based on these issues, multi-source remote sensing images, auxiliary meteorological data, in situ data and numerical simulation data are selected to construct the retrieval algorithms of various sea surface parameters in the estuarine and coastal area. In addition, the retrieved products are validated with the numerical simulated results in order to demonstrate the reliability of the algorithms. We further analyze and discuss the temporal and spatial distribution of SSC (Suspended Sediment Concentration) under comprehensive effect of various hydrodynamic interactions and its dynamic mechanism from the point of multi-source remote sensing. This study will consequentially help to better understand the features of land-ocean interactions; and provide scientific and reasonable data for estuarine and coastal engineering, sedimentary geomorphic evolution and ecological environmental protection. The major research contents are as follows.1) Sea surface wind retrieval based on SARERS2-SAR, ENVISAT-ASAR data are selected to extract high-resolution and high-precision sea surface wind through the improved2D FFT and CMOD4model. SAR-retrieved wind fields are validated with collocated measurements from QuikSCAT and products from the atmospheric Weather Research Forecasting model (WRF). In general, we found good agreement between the datasets, indicating the reliability and applicability of SAR-retrieved algorithms under different atmospheric conditions. Although QuikSCAT can only produce wind vectors with resolution up to12.5km, it is still best suited for open ocean measurements. In coastal regions, where wind fields can vary dramatically over a few km, SAR images are able to offer sub-km resolution. Therefore, we can obtain an improved global wind product by combining QuikSCAT wind products in open ocean areas with high-resolution SAR-retrieved wind fields in coastal areas. Moreover, we discussed the main inherent error sources in the process, and conducted sensitivity analyses using CMOD4to estimate the error caused by the effect of speckle, uncertainty in wind direction, and inaccuracy in normalized radar cross section (NRCS). For the high speed wind, e.g., typhoon, CMOD5model is applied and demonstrated to have the strong capability, including determination of typhoon center position, typhoon spatial structure and typhoon wind speed. These will be very helpful for the marine severe weather prediction. Finally, SAR-retrieved wind fields were applied to simulate the salinity distribution off the Changjiang estuary. The findings of this study will be valuable for wind resource assessment and development of future numerical ocean models based on SAR images.2) Sea surface velocity retrieval based on ASARBased on the Doppler centroid anomaly theory, ENVISAT-ASAR images are applied to derive the sea surface Doppler velocity. Yet, biases contaminate the Doppler centroid shift that, in turn, affect the retrieval of the range Doppler velocity. Careful corrections and bias removal is therefore highly needed to retrieve reliable signals. Azimuth bias removal from the scene NRCS gradients and range bias removal from reference data have been presented for three different ASAR scenes at Yangtze Estuary. The RMS offset of the corrected Doppler anomaly is approximately to6.0Hz, corresponding to a horizontal Doppler velocity of29cm/s at35°incidence angle. In this study, the Doppler method yields estimates with a resolution (azimuth, range) of about8km×4km and substantial overlaps. The orientation of the ENVISAT-ASAR tracks with respect to the Changjiang River outflow implies that the descending tracks are most attractive for the range Doppler shift observation. Uncertainty analysis of ASAR Doppler velocity are also discussed with regard to the strong azimuthal NRCS gradients, low radar incidence angle, inaccuracy in wind field and the presence of rain cells. The ASAR surface current velocities are particularly sensitive to inaccuracies in the wind correction. Using wind fields accurately retrieved from the ASAR images yield the most accurate retrieval of the ASAR surface current. The inter-comparison and validation of the ASAR-derived Doppler velocities against the surface velocity field derived from numerical ocean model simulations shows promising results. The Doppler measurements therefore have the capability to derive innovative estimates of surface velocities at Yangtze Estuary. These Doppler based velocity retrievals from ASAR images of the Yangtze Estuary area are valuable as they reveal the multi-scale dynamics around the East China Sea. Furthermore, the ASAR Doppler velocities have the capability to provide sufficiently accurate spatial information for validation of high resolution coastal models.3) Suspended Sediment Concentration retrieval based on MERISThe SERT model coupled with a multi-conditional algorithm scheme is introduced and validated with in situ measurements using MERIS-in situ data matchups. The results are considerably accurate and reliable. Spatially, the SSC from Xuliujing downward to the turbidity maximum to Hangzhou Bay increases constantly under normal conditions; SSC during spring tide is larger than that in ordinary tide than that in neap tide. SSC in Yangtze estuary presents significant seasonal changes, in the inner estuary it showing higher concentration during summer than during w. inter; while in the outer estuary it presenting higher concentration during winter than during summer. In the North Passage and South Passage regions, SSC reveals unobvious seasonal changes and exists a transformation trade; sometimes it shows higher concentration during winter than during summer, sometimes it is the other way around. Temporally, the SSC show a neap-spring tidal cycle and seasonal fluctuations.4) Driving factors research on Yangtze suspended sediment distributionBased on multi-source remote sensing data, meteorological data and in situ data, we discuss the main driving factors of Yangtze suspended sediment distribution. It is concluded that Yangtze runoff control sediment distribution in the inner estuary; tidal currents are the predominant factors related to sediment distribution in the outer estuary and Hangzhou Bay areas; wind direction and wind speed control the diffusion area of SSC.更多还原