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Spatiotemporal shoreline dynamics of Namibian coastal lagoons derived by a dense remote sensing time series approach
International Journal of Applied Earth Observation and Geoinformation ( IF 7.5 ) Pub Date : 2018-03-20 , DOI: 10.1016/j.jag.2018.01.009
Robert Behling , Robert Milewski , Sabine Chabrillat

This paper proposes the remote sensing time series approach WLMO (Water-Land MOnitor) to monitor spatiotemporal shoreline changes. The approach uses a hierarchical classification system based on temporal MNDWI-trajectories with the goal to accommodate typical uncertainties in remote sensing shoreline extraction techniques such as existence of clouds and geometric mismatches between images. Applied to a dense Landsat time series between 1984 and 2014 for the two Namibian coastal lagoons at Walvis Bay and Sandwich Harbour the WLMO was able to identify detailed accretion and erosion progressions at the sand spits forming these lagoons. For both lagoons a northward expansion of the sand spits of up to 1000 m was identified, which corresponds well with the prevailing northwards directed ocean current and wind processes that are responsible for the material transport along the shore. At Walvis Bay we could also show that in the 30 years of analysis the sand spit’s width has decreased by more than a half from 750 m in 1984–360 m in 2014. This ongoing cross-shore erosion process is a severe risk for future sand spit breaching, which would expose parts of the lagoon and the city to the open ocean. One of the major advantages of WLMO is the opportunity to analyze detailed spatiotemporal shoreline changes. Thus, it could be shown that the observed long-term accretion and erosion processes underwent great variations over time and cannot a priori be assumed as linear processes. Such detailed spatiotemporal process patterns are a prerequisite to improve the understanding of the processes forming the Namibian shorelines. Moreover, the approach has also the potential to be used in other coastal areas, because the focus on MNDWI-trajectories allows the transfer to many multispectral satellite sensors (e.g. Sentinel-2, ASTER) available worldwide.



中文翻译:

密集遥感时间序列方法推导的纳米比亚沿海泻湖时空海岸线动态

本文提出了遥感时间序列方法WLMO(水陆监测仪)来监测时空海岸线的变化。该方法使用基于时间MNDWI轨迹的分层分类系统,目的是适应遥感海岸线提取技术中的典型不确定性,例如云的存在和图像之间的几何不匹配。将WLMO应用于1984年至2014年之间在沃尔维斯湾和桑威奇港的两个纳米比亚沿海泻湖的密集Landsat时间序列上,WLMO能够识别出形成这些泻湖的沙嘴上详细的吸积和侵蚀进展。对于两个泻湖,沙嘴向北扩展的最大距离为1000 m,这与造成沿海岸物质运输的主要北向洋流和风过程非常吻合。在沃尔维斯湾,我们还可以表明,在30年的分析中,沙嘴的宽度从1984年的750 m到2014年的360 m减少了一半以上。这种持续的跨岸侵蚀过程对未来的沙子构成了严重的风险。吐口水,这将使泻湖和城市的一部分暴露在开阔的海洋中。WLMO的主要优势之一是有机会分析详细的时空海岸线变化。因此,可以证明观察到的长期吸积和侵蚀过程随时间变化很大,因此不能先验地假定为线性过程。这种详细的时空过程模式是增进对形成纳米比亚海岸线的过程的了解的前提。此外,该方法还具有在其他沿海地区使用的潜力,因为对MNDWI轨迹的关注使之可以转移到全球范围内可用的许多多光谱卫星传感器(例如Sentinel-2,ASTER)。

更新日期:2018-03-20
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