珠江河口潮周期泥沙动态输移特征遥感反演分析

Remote Sensing Analysis of Sediment Transport Dynamics under Tidal Action in the Pearl River Estuary

珠江河口属粤港澳大湾区核心水域,战略位置重要,区内河网密布交错,河道、河口区径流与潮流相互作用,泥沙运动较为复杂。泥沙输移是河床演变的物质来源,直接关系到粤港澳大湾区防洪、供水、航运安全。文章利用高分四号卫星高频次影像数据开展珠江河口区潮周期内水表层泥沙定量反演,结合野外观测数据,以枯季2019-12-28及洪季2020-06-20两期多时相数据为例,探究潮周期内珠江河口泥沙含量时空分布。结果表明,高分四号卫星影像数据大气校正平均绝对百分比误差为18.85%;基于高分四号卫星影像数据近红外、红波段与蓝波段比值构建了泥沙反演模型,实现对珠江河口区间隔2 h日变化尺度泥沙输移连续动态监测,其中洪、枯季最优模型MAPE误差分别为30.00%、23.54%。反演结果能较为形象地展示河口区整体泥沙动态输移特征,与实测站点泥沙质量浓度相比,反演结果在潮周期泥沙质量浓度变化趋势上相一致,实现了珠江河口区径潮作用下面上泥沙动态输移的特征分析。该方法为复杂河口泥沙输移大范围业务化监测提供了新的思路,同时为珠江河口泥沙输移数值模拟与遥感监测提供了交叉验证的新思路。

The Pearl River Estuary is the core water area of the Greater Bay area of Guangdong,Hong Kong,and Macao.The river net of the Pearl River Delta is dense and staggered,and its sediment transport process is complex due to the influence of runoff and tides.While sediment transport is a key process in river evolution,it is directly related to the flood control water supply and shipping safety of the Greater Bay area.To investigate the extent of the effect of sediment transport on the Greater Bay area,we analyzed the inversion of water surface sediment under tidal action using in-situ data,high-frequency GF-4 satellite image data(including multi temporal images),water quality,and reflection spectrum data from December 28,2019 and June 20,2020.The Mean Absolute Percentage Error(MAPE)value for atmospheric correction was 18.85%.We built several sediment inversion models based on the near-infrared,red,and blue band ratio of the GF-4 satellite image data.The best suited models for the flood and dry seasons had MAPE errors of 30%and 23.54%,respectively.We further obtained the continuous dynamic monitoring results and the daily change of sediment transport in the Pearl River Estuary at an interval of 2 h.The high frequency remote sensing inversion results gave a clear picture of the overall sediment transport dynamics of the estuary.Compared with the in-situ sediment concentration,the inversion results were consistent with the variation of sediment concentration in the tidal cycle.Moreover,we analyzed the dynamic characteristics of sediment transport under the influence of runoff tide.We found that with the rising tide,the overall suspended sediment concentration in Lingding Bay decreased considerably,Lingding Bay is a trumpet shaped estuary located outside the Pearl River Estuary.The north area of Neilingding Island is affected by human activities,thus the riverbed is degraded owing to reduced sediment input and reduced sediment resuspension to the surface.This creates a large water area of low suspended sediment content under the rising tide.Under the ebb tide,water with high suspended sediment content diffuses into the Macao Coastal Waters along the west bank of Lingding Bay.However,the southeast sediment diffusion is restricted by the backwaters from the Humen ebb current.Our method provides a new approach for large-scale operational monitoring of sediment transport in complex estuaries;furthermore,it provides a new strategy of cross-validation between the numerical simulation and remote sensing monitoring of sediment transport.