High-Resolution Intertidal Topography from Sentinel-2 Multi-Spectral Imagery: Synergy between Remote Sensing and Numerical Modeling

Fabrice Papa,Stéphane Calmant,Marufa Ishaque,A.K.M. Saiful Islam,MD Nazmuddoha Ansary,Fabien Durand,Yann Krien,Laurent Testut,Md Jamal Uddin Khan

doi:10.3390/rs11242888

Abstract

The intertidal zones are well recognized for their dynamic nature and role in near-shore hydrodynamics. The intertidal topography is poorly mapped worldwide due to the high cost of associated field campaigns. Here we present a combination of remote-sensing and hydrodynamic modeling to overcome the lack of in situ measurements. We derive a digital elevation model (DEM) by linking the corresponding water level to a sample of shorelines at various stages of the tide. Our shoreline detection method is fully automatic and capable of processing high-resolution imagery from state-of-the-art satellite missions, e.g., Sentinel-2. We demonstrate the use of a tidal model to infer the corresponding water level in each shoreline pixel at the sampled timestamp. As a test case, this methodology is applied to the vast coastal region of the Bengal delta and an intertidal DEM at 10 m resolution covering an area of 1134 km 2 is developed from Sentinel-2 imagery. We assessed the quality of the DEM with two independent in situ datasets and conclude that the accuracy of our DEM amounts to about 1.5 m, which is commensurate with the typical error bar of the validation datasets. This DEM can be useful for high-resolution hydrodynamic and wave modeling of the near-shore area. Additionally, being automatic and numerically effective, our methodology is compliant with near-real-time monitoring constraints.

Highlights

Many coastal regions around the world are facing an increased exposure to flood hazard and related losses because of the growing population and economy
We present here an application of our method to infer a digital elevation model (DEM) of the near-shore intertidal zone over the whole Bengal delta
We demonstrated the utility of a good hydrodynamic modeling framework, instead of depending on ancillary in situ data

Summary

Introduction

Many coastal regions around the world are facing an increased exposure to flood hazard and related losses because of the growing population and economy. The waterline method is one of the most widely used [6,7,8,9] In this approach, the horizontal position of the land-water boundary (i.e., shoreline of a coast) is determined from remotely sensed images using image processing techniques. When the horizontal position of this shoreline is combined with the independent knowledge of the water level at this location, at the time of image acquisition, the relative height of the shoreline can be inferred Replicating this process over a range of tidal water levels gives an estimation of the topography between highest-water (generally observed at high tide of spring tide) and the lowest-water (generally observed at low tide of spring tide) shorelines. Bishop-Taylor et al developed an intertidal digital elevation model (DEM) for Australia coast at 25 m resolution using a relative intertidal extent model developed from 30 years of Landsat archive and global tidal modeling [13,14]

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