基于影像间潮滩地形修正的海岸线监测研究——以黄河三角洲为例

针对潮滩环境中潮汐和坡度变化对海岸线变化监测的影响,提出一种通过两景影像计算潮滩坡降进而准确获得海岸线的方法,并利用坡降值估算潮滩体积。以岸线变化较剧烈的黄河三角洲南部的甜水沟口至小清河口的粉砂淤泥质潮滩为例进行应用研究。结合遥感影像、实测固定断面数据和水深测量数据分析表明,影像间的潮差对坡降估算值虽有较大影响,但选择合适潮位估算潮滩坡降是可行的,估算坡降的最小相对误差可达0.2%,均方根误差小于实测坡降一个数量级。1973-2009 年甜水沟口至小清河口14 个年份的岸线变化分析显示,黄河改道对本区的直接淤积影响在甜水沟向南3 km范围内,最大淤积区位于甜水沟口附近,年均淤积率31 m/a,而后在1989-2002 年海区南部出现较大幅度淤积,主要为黄河入海水沙直接或间接淤积造成的;研究时段内岸滩总体演化趋势为蚀退,最大年均蚀退速率51 m/a,黄河改道造成的海洋动力变化是影响本区海岸冲刷的主要因素。验证表明,本文方法计算的潮滩体积用于指示海滩冲淤变迁是合理可行的。

Monitoring Change and Position of Coastlines from Satellite Images Using Slope .Correction in a Tidal Flat:A Case Study in the Yellow River Delta

Tidal and landform variations have a significant impact on detection of coastline changes in a tidal flat environment.This paper presents a slope correction method of determining 1985 national height datum shoreline positions from two satellite images that take into account tidal variations.Furthermore,volumes of tidal flats are calculated by tidal flat gradient.Combination of remote sensing images,the measured cross-section data and depth measurement data analysis showed that although the inter-tidal range of the image has a greater impact on gradient estimates,estimation of tidal gradient is feasible by choosing appropriate images.The minimum error of consistency check is up to about 0.2% of estimate gradient,and root mean square error of absolute check is less than the measured gradient in an order of magnitude.Muddy-silt tidal flats were used to test this method in the south coastal area of the Yellow River Delta.Multitemporal remote sensing data of Landsat MSS and TM/ETM from 1973 to 2009,totaling 14 years,were used to examine the changing pattern of erosion and accretion of the tidal flat from Tianshuigou to Xiaoqing River estuary.Since the diversion of the Yellow River in 1976,the sediment of the river is deposited directly about 3 km from Tianshuigou southward in the study area.The maximum accretion occurs near the Tianshuigou where the coastline advanced seaward over 0.7 km with a mean net accretion rate of 31 m/a.During the period 1989-2002,rapid sedimentation happened in the southern part of the study area.Accumulation of sediment and resuspended sediment from the Yellow River is the major driving force.From 1973 to 2009,the general tendency of coastline was erosive with a mean net rate of 51 m/a.The enhanced ocean dynamics caused by the diversion of the Yellow River is the main reason.It is indicated that the volume of tidal flats is reasonable and reliable for detecting shoreline change.