基于Landsat影像的杭州湾最大浑浊带年际变化研究

Inter-Annual Variability of the Turbidity Maximum Zone in Hangzhou Bay Based on Landsat Imagery

  • 摘要: 杭州湾最大浑浊带(turbidity maximum zone,TMZ)受自然和人类活动的双重影响,年际变化显著。为探究杭州湾水域TMZ和表层悬浮泥沙浓度的年际变化特征,优选1984-2015年间30幅Landsat卫星影像,建立杭州湾水域表层悬沙浓度反演模型,模型经实测数据验证,平均相对误差为23.3%。对每张卫星影像进行悬沙浓度反演,进而提取TMZ面积数据。结果表明,杭州湾悬沙浓度面积分布类型均为正偏分布,且偏态系数由0.63增长至2.03,高悬沙浓度区域占比不断缩小。杭州湾各区域悬沙浓度均呈下降趋势,北岸芦潮港站下降趋势最为显著,减幅达73%。杭州湾TMZ面积年化下降率为4.57%,大于长江和钱塘江年输沙量的年化下降率3.74%。河流来沙减少和潮滩围垦导致的当地泥沙来源减少及水流携沙能力降低是影响TMZ面积降低的重要因素。

     

    Abstract: The areas of the turbidity maximum zone (TMZ) in Hangzhou Bay changed with the anthropogenic activities in the past several decades. Thirty Landsat images of the bay, covering the period from 1984 to 2015, were collected to examine the variation of the TMZ and surface suspended sediment concentration (SSC) in the bay. The surface SSC was retrieved from the Landsat images. The error between the retrieved SSC and the observed data was 23.3%. Then the TMZ areas were calculated using the remote sensing data. Results show that the SSC values had a more asymmetric distribution pattern from 1984 to 2015, with low turbid area increased, as shown by the coefficient of skewness. From 1984 to 2015, the SSC values decreased in almost the entire bay. The Luchaogang station in north shore witnessed the largest decrease of about 73%. The annual trend ratio of the TMZ areas was -4.57%, while the annual trend ratio of sediment load was -3.74%. Hence, the inter-annual variability of the TMZ areas is supposed to be affected by the combined effects of the reduction of the riverine sediment discharge, as well as the tidal flat reclamation around Hangzhou Bay.

     

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