ABSTRACT
In this study, a new integrated methodology (WLRSM) for mapping tidal flats elevation is proposed, which integrates the waterline (WL) method and remotely sensed moisture (RSM) method. Level-1 DEM of tidal flats is provided by WL, and then improved furtherly by RSM. The level-1 DEM was interpolated by waterlines derived from a series of Landsat images in the year of 2019. Meanwhile, the moisture of an exposed tidal flat surface was retrieved using Landsat OLI. We subsequently investigated the relationship between level-1 DEM and moisture, and then constructed statistic models (moisture as the variable) to refine elevations.
Tidal flats, located in the boundary zone between ocean and land, are sensitive to the interaction between land and sea, and have important ecological functions, coastal protection and social and economic values. The landform of tidal flats is affected by multiple factors, such as sediment transport, hydrodynamic, biological, extreme climate and human activities (Chen, Zhang, Paterson, Thompson, Townend, and Gong, 2017).With the rise of global sea level and the intensification of human activities, tidal flats are facing serious threats. To improve our understanding of the evolution and dynamics of these continually changing ecosystems, frequent measurement of the changing topography of tidal flats is essential. However, owing to rough field conditions, it is difficult to measure the topography of tidal flats with traditional survey techniques.
The main methods to study the change of tidal flat morphology include field observation (Gong, Jin, Zhang, Zhou, Zhang, and Li, 2017) and remote sensing retrieval. Field observation (Elgar and Raubenheimer, 2011; Hughes, 2012; Vandenbruwaene, Meire, and Temmerman, 2012) has a high accuracy in obtaining data, but manual measurement, which requires a large amount of manpower and material resources, is required according with the plan, so only topographic data in a limited area and in a limited time can be obtained. Remote sensing (Bell, Bird, and Plater, 2016;Mason, Scott, and Dance, 2010; Ryu, Cho, and Won, 2001) technology can periodically and synchronously monitor a large range of areas and obtain high spatial resolution remote sensing images, which shows great advantages and potential in the study of dynamic evolution of tidal flats (Huang, Chen, Lin, Kuo, Liao, and Lin, 2017; Eom, Jinah, Choi, Jong-Kuk, Ryu, and Joo-Hyung., 2011). Therefore, many methods use remote sensing was proposed to monitor tidal flat topography and try to analyze its evolution trend, such as the waterline (WL) method (Kang, Ding, Xu, Zhang, and Ge, 2017; Mason, Davenport, and Flather, 1997; Mason, Davenport, Flather, and Gurney, 1998) and remotely sensed moisture (RSM) method (Li, Gong, Dai, Lu, Zhang, and Cybele, 2018).
