杭州湾混浊水体表面光谱测量及光谱特征分析

Surface Spectral Measurement and Characteristics Analysis of Turbid Water in Hangzhou Bay

悬浮泥沙是近海水体的主要光学活性物质之一，了解其光谱特征是建立准确遥感反演算法的基础。在我国典型高含沙海域——杭州湾的南北岸分别布设连续监测站位，采用水面之上光谱观测方法，利用美国ASD便携式地物光谱仪测量混浊水体的反射光谱，并且同步采集表层水样获取含沙量数据。研究结果表明：杭州湾水体表层含沙量较高，且随潮汐发生显著变化；水体反射率光谱曲线随含沙量浓度增大也相应升高，不同波长处升高幅度不同；通过光谱微分的方法分析水体反射率光谱特征，发现第一个反射峰出现“红移现象”；表层含沙量和对应MODIS各光谱通道的遥感反射率有不同的相关性，大于650nm的长波通道的相关系数较大，400-550nm短波通道的则较低；选取MODIS第2通道对应的遥感反射率利用最小二乘法进行回归分析取得了较好的拟合效果，可以作为杭州湾水体含沙量遥感反演的主要波段。

Suspended sediment is one of the major optically active substances in coastal waters. The knowledge of its spectral characteristics is the basis for developing precise remote sensing inversion algorithms. Two separate continuous monitoring stations were set near the northern and southern coast of Hangzhou Bay separately, which is typically turbid area in China coastal waters. The above-water measurement method and the American ASD portable spectroscope were adopted to measure the water surface reflectance spectrum. The sediment concentrations of surface water were synchronously acquired when measuring waterleaving radiance. Results show that the sediments concentration is comparatively high and changes dramatically according to tide cycle. The reflectance spectrum at different wavelengths rises corresponding to the increase in sediments concentrations with dif- ferent extent. When using first derivative method to analysis the spectral characteristic, it can be found that the first reflectance peaks of reflectance spectra appear to shift to long wavelength. There are different correlations between sediment concentrations and each MODIS channel reflectance, which are above 0. 5 in 650 nm or longer wavelengths channels and below 0.5 in 400-550 nm channels. The fitting result of regression analysis is preferable with MODIS channel 2 （841--876 nm） and in situ sediment concentrations using least square method, with R^2 of exponential above 0. 8, which indicated that the MODIS channel 2 can be used for surface water suspended sediments remote sensing inversion, particularly in turbid waters such as bays and estuaries.