Abstract
Satellite-Derived Bathymetry (SDB) has significant potential to enhance our knowledge of Earth’s coastal regions. However, SDB still has limitations when applied to the turbid, but optically shallow, nearshore regions that encompass large areas of the world’s coastal zone. Turbid water produces false shoaling in the imagery, constraining SDB for its routine application. This paper provides a framework that enables us to derive valid SDB over moderately turbid environments by using the high revisit time (5-day) of the Sentinel-2A/B twin mission from the Copernicus programme. The proposed methodology incorporates a robust atmospheric correction, a multi-scene compositing method to reduce the impact of turbidity, and a switching model to improve mapping in shallow water. Two study sites in United States are explored due to their varying water transparency conditions. Our results show that the approach yields accurate SDB, with median errors of under 0.5 m for depths 0–13 m when validated with lidar surveys, errors that favorably compare to uses of SDB in clear water. The approach allows for the semi-automated creation of bathymetric maps at 10 m spatial resolution, with manual intervention potentially limited only to the calibration to the absolute SDB. It also returns turbidity data to indicate areas that may still have residual shoaling bias. Because minimal in-situ information is required, this computationally-efficient technique has the potential for automated implementation, allowing rapid and repeated application in more environments than most existing methods, thereby helping with a range of issues in coastal research, management, and navigation.
Highlights
Seafloor mapping plays a pivotal role in using and managing the world’s oceans in a way that is in accordance with the United Nations Sustainable Development Goal 14 (“Life below water - conserve and sustainably use the oceans, seas and marine resources”) that aims to achieve a better and more sustainable future by 2030 [1]
Prior to implementing the multi-temporal approach with Sentinel-2A/B images in Cape Lookout (Figure 1b), we estimated bathymetry for several single scenes in order to evaluate the impact of varying turbidity
The heterogeneous impact of water quality on satellite bathymetry is evident in the comparison between Airborne Lidar Bathymetry and satellite data (Figure 3a,b) and the residual errors (Figure 3c,d)
Summary
Seafloor mapping plays a pivotal role in using and managing the world’s oceans in a way that is in accordance with the United Nations Sustainable Development Goal 14 (“Life below water - conserve and sustainably use the oceans, seas and marine resources”) that aims to achieve a better and more sustainable future by 2030 [1]. We develop a framework for using satellite data to retrieve valid bathymetry in shallow water with moderate and varying turbidity This approach uses the capabilities of the Sentinel-2 Multi Spectral Imagers (MSI) of the Copernicus programme, which include 10 m spatial resolution in the visible bands, five-day routine revisit, and freely available data. In this context, researchers have hypothesized that a higher temporal resolution would allow the development of guidelines for repeatable shallow water mapping approaches at regional to global scales [9,10,22].
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