Pan-European Satellite-Derived Coastal Bathymetry—Review, User Needs and Future Services

Abstract

Low-lying coastal zones are home to around 10% of the world’s population and to many megacities. Coastal zones are largely vulnerable to the dynamics of natural and human-induced changes. Accurate large-scale measurements of key parameters, such as bathymetry, are needed to understand and predict coastal changes. However, nearly 50% of the world’s coastal waters remain unsurveyed and for a large number of coastal areas of interest, bathymetric information is unavailable or is often decades old. This lack of information is due to the high costs in time, money and safety involved in collecting these data using conventional echo sounder on ships or LiDAR on aircrafts. Europe is no exception, as European seas are not adequately surveyed according to the International Hydrographic Organisation. Bathymetry influences ocean waves and currents, thereby shaping sediment transport which may alter coastal morphology over time. This paper discusses state-of-the-art coastal bathymetry retrieval methods and data, user requirements and key drivers for many maritime sectors in Europe, including advances in Satellite-Derived Bathymetry (SDB). By leveraging satellite constellations, cloud services and by combining complementary methods, SDB appears as an effective emerging tool with the best compromise in time, coverage and investment to map coastal bathymetry and its temporal evolution.

Coastal Zone Changes in West Africa: Challenges and Opportunities for Satellite Earth Observations

“…Coastal areas are notoriously expensive and difficult to measure and monitor using in situ techniques (Benveniste et al 2019;Melet et al 2020;Cesbron et al 2021). Due to the lack of consistent mapping regimes, the evolution of West African coasts is partially known and the processes driving these dynamics are poorly described (i.e., global climate change is still perceived as the dominant driver of coastal evolution, while local human pressure is often dominant and rather poorly documented; Dada et al 2021).…”

“…To derive nearshore bathymetry, ocean color can be derived from optical missions such as Sentinel-2 and Landsat, from which water depth, seafloor features, and turbidity can be derived simultaneously or independently (Caballero et al 2019;Salameh et al 2019;Monteys et al 2015;Li et al 2021;Cesbron et al 2021). The calculated bathymetry is not the depth of the consolidated sediment bedrock, but the depth of the suspended sediment layers in the mud.…”

Coastal Bathymetry Estimation from Sentinel-2 Satellite Imagery: Comparing Deep Learning and Physics-Based Approaches

“…Coastal areas are under a constant multitude of pressures resulting from different natural forces. The ability to reliably track and measure the nearshore bathymetry over time is critical for a wide array of applications including coastal development and management, coastal risk monitoring and mitigation, coastal science studies, among others [1,2]. Traditional in situ bathymetric measurements using echo-sounding or Light Detection and Ranging (LiDAR) are time-consuming and expensive [3] and are preconditioned on a number of environmental factors such as the navigability of the site to be surveyed [4], in addition to a multitude of logistical constraints [5,6].…”

“…Methods based on the radiative transfer of light in water as a function of depth and wavelength (i.e., color-based methods) can be used to estimate depth in optically shallow waters [17][18][19][20][21][22]. Such methods are sensitive to the optical properties of seawater and are generally limited to clear and non-turbid waters [1,23]. Other methods based on wave kinematics extract wave features from satellite imagery such as the wave phase shift and wave number to estimate depth using the linear dispersion relation [24] (described in more detail in Section 2).…”

Performance and Uncertainty of Satellite-Derived Bathymetry Empirical Approaches in an Energetic Coastal Environment

“…A major obstacle to the availability of accurate large-scale bathymetric data is the high cost (in terms of acquisition and/or post-treatment) associated with conventional observation systems, i.e., echo sounders on ships and LiDAR on aircraft. As a result, and due to constantly enhanced instrument features, radar [8] and optical [9] satellite imagery is expected to be a key complementary tool for generating bathymetry maps in the coming years. Two distinct approaches are used to retrieve Satellite-Derived Bathymetry (SDB).…”