Coastal Bathymetry Research Articles

Predicting beach profiles with machine learning from offshore wave reflection spectra

Tracking and forecasting changes in coastal morphology is vital for development, risk reduction, and overall coastal management. One challenge of current coastal research and engineering is to find a method able to accurately assess the bathymetry profile along the coast and key parameters such as slope and sandbars. Traditional bathymetry measurements are obtained through echo-sounding, which is time-consuming, hazardous and costly. Using a variety of simulated cases, we test the potential of machine learning and in particular Neural Networks to reconstruct the coastal bathymetry profile from offshore sensed waves, based on shore-based wave reflection. Features such as foreshore slope, curvature, sandbars amplitude and positions can be captured.

Exploring the tidal response to bathymetry evolution and present-day sea level rise in a channel–shoal environment

Abstract. Intertidal flats and salt marshes in channel–shoal environments are at severe risk of drowning under sea level rise (SLR) ultimately ceasing their function of coastal defense. Earlier studies indicated that these environments can be resilient against moderate SLR as their mean height is believed to correlate with tidal amplitude and mean sea level. Recent morphological analyses in the German Wadden Sea on the northwestern European continental shelf contradicted this assumption as mean tidal flat accretion surpassed relative SLR, indicating that nonlinear feedback between SLR, coastal morphodynamics, and tidal dynamics played a role. We explored this relationship in the German Wadden Sea's channel–shoal environment by revisiting the sensitivity of tidal dynamics to observed SLR and coastal bathymetry evolution over one nodal cycle (1997 to 2015) with a numerical model. We found a proportional response of tidal high and low water to SLR when the bathymetry was kept constant. In contrast, coastal bathymetry evolution caused a spatially varying hydrodynamic reaction with both increases and decreases in patterns of tidal characteristics within a few kilometers. An explorative assessment of potential mechanisms suggested that energy dissipation declined near the coast, which we related to a decreasing tidal prism and declining tidal energy import. Our study stresses the fact that an accurate representation of coastal morphology in hindcasts, nowcasts, and ensembles for bathymetry evolution to assess the impact of SLR is needed when using numerical models.

Shoreline delineation and change analysis in response to sea level rise and coastal bathymetry along the coast of Visakhapatnam, India using high-resolution optical imagery

Shoreline delineation and change analysis in response to sea level rise and coastal bathymetry along the coast of Visakhapatnam, India using high-resolution optical imagery

Short-term buoyant microplastic transport patterns driven by wave evolution, breaking, and orbital motion in coast

Recently, there has been a notable rise in social and scientific interest regarding microplastic pollution in coasts where waves significantly influence flow patterns and material transport. This study explores typical short-term movement of buoyant microplastics driven by surf zone processes including wave transformation, breaking, and orbital motion. To track microplastics, Lagrangian Particle Tracking Model (PTM) coupled with Eulerian wave-current interaction model appropriate for coastal hydrodynamics was used. From the simulations, several important findings were observed. (i) In alongshore uniform beaches, lighter and larger buoyant microplastics tended to reach beach more readily. (ii) Accurate predictions of microplastic transport in the surf zone required the consideration of wave breaking. (iii) In alongshore non-uniform coastal bathymetry, rip-currents can send buoyant microplastics offshore, beyond the surf zone.

Northern cod re-establish historical migration patterns linked to capelin: insights from pop-up satellite archival tags

In May 2012–2015, 90 large (85–117 cm) Northern cod ( Gadus morhua) with pop-up satellite archival tags (PSATs) set to release 1 year later were released from offshore spawning aggregations on the northeast Newfoundland shelf. Forty-nine (54%) transmitted or were recovered; 82% migrated inshore and 15% remained offshore (balance predated). Geo-locations were based on release, capture, and surfacing positions, and at tag-recorded depths <50 m, on Kalman-predicted light-based longitudes matched with coastal bathymetry. Migrating fish moved southwestward on average 5° longitude (350 km) and 2° latitude (222 km) to the northeast coast of Newfoundland, southern Labrador, and northern Grand Bank, as historically from similar release points. Migration onset through the Labrador Current (<0 °C) and arrival inshore were correlated with capelin ( Mallotus villosus) peak spawning, inshore duration with capelin, and cod biomass. Both species were delayed a month from historical norms. The probability of a cod remaining inshore after 1 December was 50%, which could impact time-dependent surveys. Fishing exploitation was 6% and predation 5%. Northern cod have re-established historical spatial migration patterns, with capelin a key influence on timing and duration inshore.

Coastal bathymetry in central Dronning Maud Land controls ice shelf stability

Knowledge of the bathymetry of Antarctica’s margins is crucial for models and interpretations of ice-ocean interactions and their influence on ongoing and future sea level change, but remains patchy where ice shelves and multi-year sea ice block measurements. Here, we present a bathymetric model for the central Dronning Maud Land margin, based on a constrained inversion of airborne gravity data. It shows the cavities beneath the region’s two ice shelves to be much deeper than in existing bathymetric compilations, but to be shielded from Warm Deep Water ingress and basal melting by the presence of shallow bathymetric sills along the continental shelf. Over areas of multi-year sea ice, the model returns bathymetric estimates of similar accuracy to gravity interpolation-based methods over open water. Airborne gravity thus presents an opportunity to bathymetrically map hundreds of thousands of square kilometres of the most inaccessible margins of Antarctica at resolutions adequate for regional and global oceanographic and glaciological modelling and interpretation.

Satellite-derived bathymetry from correlation of Sentinel-2 spectral bands to derive wave kinematics: Qualification of Sentinel-2 S2Shores estimates with hydrographic standards

There is a pressing need for a fast and efficient satellite remote sensing tool to estimate coastal bathymetry for any coastline in the world. To date, satellite methods for deriving bathymetry have mainly focused on linking the radiometric response to a known water depth, as with SPOT, Landsat and Sentinel. Here, wave properties (static and dynamic) are approximated using the small time delay between the different color bands of Sentinel-2 to then calculate a depth using wave linear dispersion theory. In this paper, we present a spatial correlation method within the S2Shores (Satellites to Shores) Python toolbox: a processing chain/toolbox of coastal observations using methods applied to optical satellites. The resulting individual bathymetries are finally qualified according to the standards of the International Hydrographic Organization, anticipating their operational use.

Performance of Landsat ETM+, OLI and OLI-2 Imagery in ICESat-2-Aided Coastal Bathymetry: The Effect of Radiometric Resolution

Performance of Landsat ETM+, OLI and OLI-2 Imagery in ICESat-2-Aided Coastal Bathymetry: The Effect of Radiometric Resolution

A Refined Machine Learning Method for Coastal Bathymetry Retrieval Using Minimum Distance From Coastline and Geographical Features

A Refined Machine Learning Method for Coastal Bathymetry Retrieval Using Minimum Distance From Coastline and Geographical Features

Machine Learning Based Estimation of Coastal Bathymetry From ICESat-2 and Sentinel-2 Data

Machine Learning Based Estimation of Coastal Bathymetry From ICESat-2 and Sentinel-2 Data

A Geo-Itinerary to Foster Sustainable Tourism in West African Islands: Storytelling the Evolution of the Ancient Cameroon Volcanic Line Coral Reefs

This study characterizes the submerged geomorphology around Annobón, São Tomé, and Príncipe Islands, and the De Santarém–Escobar seamount in the Cameroon Volcanic Line or CVL (Gulf of Guinea, West Africa) through analyses of topographic relief and coastal bathymetry, and data from fieldwork and historical fossil collections. The clear relation between each submerged island and the seamount morphology of the CVL and the various stages of coral reef development according to Darwin’s subsidence hypothesis meets the concept of intangible geoheritage. This type of geoheritage is related to phenomena rather than to a thing, and it is usually highly evaluated by scientific communities. Academics tend to use science-based discourse to explain this theory, but it is rarely understood by non-specialist audiences. This work proposes a virtual geo-itinerary along the submerged geomorphology of the CVL islands and seamounts, which aims at telling the geohistory of the coral reefs’ origin and evolution according to Darwin’s theory, and disclosing its geoheritage contents for further sustainable uses. The resulting narrative can be used to support geotourism initiatives and to support the United Nations’ objectives for Small Island Developing States.

Satellite computed bathymetry assessment – Developing satellite LiDAR methods to enhance coastal bathymetry coverage

The Satellite Computed Bathymetry Assessment (SCuBA) project implements a new photon classification approach to prepare lidar returns from the ICESat-2 satellite mission as a source of bathymetric data in suitable shallow ocean environments. SCuBA data enhances and compliments other space-borne bathymetry estimation methods for hydrographic applications and improves depth uncertainty where applicable. Incorporating SCuBA data into hydrographic projects expands and enhances data collection capabilities that can inform other empirical satellite bathymetry models and help improve navigational safety products in areas where ship-based sonar and aircraft-borne lidar surveys are not feasible.

Adjoint-based high-order spectral method of wave simulation for coastal bathymetry reconstruction

Bathymetry is an important factor affecting wave propagation in coastal environments but is often challenging to measure in practice. We propose a method for inferring coastal bathymetry from spatial variations in surface waves by combining a high-order spectral method for wave simulation and an adjoint-based variational data assimilation method. Recursion-formed adjoint equations are derived to obtain the sensitivity of the wave surface elevation to the underlying bottom topography to any desired order of nonlinear perturbation. We also develop a multiscale optimisation method to eliminate spurious high-wavenumber fluctuations in the reconstructed bathymetry data caused by sensitivity variations over the different length scales of surface waves. The proposed bottom detection method is validated with a realistic coastal wave environment involving complex two-dimensional bathymetry features, non-periodic incident waves and nonlinear broadband multidirectional waves. In numerical experiments at both laboratory and field scales, the bathymetry reconstructed from our method agrees well with the ground truth. We also show that our method is robust against imperfect surface wave data in the presence of limited sampling frequency and noise.

Assessing coastal bathymetry and climate change impacts on coastal ecosystems using Landsat 8 and Sentinel-2 satellite imagery

Coastal ecosystems are facing heightened risks due to human-induced climate change, including rising water levels and intensified storm events. Accurate bathymetry data is crucial for assessing the impacts of these threats. Traditional data collection methods can be cost-prohibitive. This study investigates the feasibility of using freely accessible Landsat and Sentinel satellite imagery to estimate bathymetry and its correlation with hydrographic chart soundings in Port Klang, Malaysia. Through analysis of the blue and green spectral bands from the Landsat 8 and Sentinel 2 datasets, a bathymetry map of Port Klang's seabed is generated. The precision of this derived bathymetry is evaluated using statistical metrics like Root Mean Square Error (RMSE) and the coefficient of determination. The results reveal a strong statistical connection (R2 = 0.9411) and correlation (R2 = 0.7958) between bathymetry data derived from hydrographic chart soundings and satellite imagery. This research not only advances our understanding of employing Landsat imagery for bathymetry assessment but also underscores the significance of such assessments in the context of climate change's impact on coastal ecosystems. The primary goal of this research is to contribute to the comprehension of Landsat imagery's utility in bathymetry evaluation, with the potential to enhance safety protocols in seaport terminals and provide valuable insights for decision-making concerning the management of coastal ecosystems amidst climate-related challenges. The findings of this research have practical implications for a wide range of stakeholders involved in coastal management, environmental protection, climate adaptation and disaster preparedness.

Cross-Comparison of the “BathySent” Coastal Bathymetry to Sonar Measurements and Ratio Model Technique: Pilot Sites in the Aegean Sea (Greece)

The proposed novel “BathySent” approach for coastal bathymetric mapping, using the Copernicus Sentinel-2 mission, as well as the assessment and specification of the uncertainties of the derived depth results, are the objectives of this research effort. For this reason, Sentinel-2 bathymetry retrieval results for three different pilot sites in Greece (islands of Kos, Kasos, and Crete) were compared with ground-truth data. These data comprised high-resolution swath bathymetry measurements, single-beam echosounder measurements at very shallow waters (1–10 m), and the EMODnet DTM 2018 release. The synthetic tests showed that the “BathySent” approach could restitute bathymetry in the range of 5–14 m depth, showing a standard deviation of 2 m with respect to the sonar-based bathymetry. In addition, a comparison with the “ratio model” multispectral technique was performed. The absolute differences between conventional Earth Observation-based bathymetry retrieval approaches (i.e., linear ratio model) and the suggested innovative solution, using the Sentinel-2 data, were mainly lower than 2 m. According to the outcome evaluation, both models were considered to provide results that are more reliable within the depth zone of 5–25 m. The “ratio model” technique exhibits a saturation at ~25 m depth and demands ground calibration. Though, the “BathySent” method provides bathymetric data at a lower spatial resolution compared to the “ratio model” technique; however, it does not require in situ calibration and can also perform reliably deeper than 25 m.

S2SHORES: A PYTHON LIBRARY FOR ESTIMATING COASTAL BATHYMETRY

Understanding coastal zone dynamics covering large spatial and dense temporal scales is paramount to understand and mitigate emerging coastal issues relating to climatological changes. However, the uncertainties on the coastal zone risks are still too large to predict effectively impacts on an overall increasing coastal population. Prediction, by deploying numerical models for waves, tide, and currents in the coastal zone, requires accurate and up-to-date bottom boundary conditions (bathymetry) to simulate coastal hydrodynamics accurately, let alone predict morphological change. There are three main approaches for estimating coastal bathymetry using satellite sensors: 1) linking water depth to a spectral response (colour), 2) underwater photogrammetry and 3) linking wave kinematics to a water depth. Here, we present S2Shores (Satellite to Shores), a python library that detects and extracts local wave parameters (geometry and kinematics) to derive coastal bathymetry.

EXTREME WAVES IN SHALLOW WATER AND DREDGED CHANNELS FOR DIRECTIONAL SEAS

Extreme wave conditions at coastal structures located offshore of natural coastlines and the zone of wave breaking are influenced by the deepwater wave conditions, the coastal bathymetry between deepwater and the structure, and the ongoing growth, generation and decay of waves across the coastal shelf. At locations where the coastal shelf is relatively flat, the gradually reducing water depths can limit the significant and maximum wave heights and crest elevations that may be encountered. If a coastal structure is located in deeper water than the bathymetry of approaching waves, for example port or navigation structures located in dredged channels or basins, coastal engineers need to consider wave conditions in the shallower approach waters and the transformation and propagation of waves across the dredged area. The directional characteristics of wave spectra in this situation can have a significant impact on extreme wave conditions that occur within the dredged basin. This paper presents insights into extreme wave conditions for gently sloping natural seabed profiles and also within a dredged basin, for directional seas which occur within the direct path of severe storms; for example, tropical cyclones.

Cross‐Shelf Penetrating Fronts of Buoyant Coastal Currents Around the Headland

AbstractBuoyant coastal current induced by riverine outflow often propagates along the coast in the direction of coastal trapped wave. However, it is uncertain how the buoyant coastal current interacts with irregular coastal bathymetry. Measured surface salinity distributions indicate that the buoyant coastal current, which is induced by the Changjiang River plume, frequently penetrates offshore around the curved headlands in the Zhoushan Islands. This signal can also be seen in satellite chlorophyll data, reflecting its importance in cross‐shelf exchange both physically and ecologically. To understand the variation and underlying dynamic mechanisms of these penetrating fronts, realistic and idealized numerical experiments were conducted. The results indicated that the penetrated water salinity was about 30–32 psu, with a horizontal penetration scale of tens of kilometers. Curvature and self‐organizing map analyses suggested that it was a frequent event with an approximately 2‐week spring‐neap cycle from generation to decay. It more likely occurred in transition seasons such as spring and autumn, owing to the runoff accumulation and gentle wind conditions. Smoothing the topography would substantially eliminate the penetrating fronts. Idealized model experiments suggested that headland‐induced river plume penetration was a type of curved topography‐induced current separation. The criterion for this to occur is u/fRc > 1, in which u is the current velocity, f is the Coriolis parameter, and Rc is the curvature radius. In this case, the headland is too sharp that the Coriolis force could not balance the centrifugal force. Once penetrated, the buoyant water was further transported by the ambient Taiwan Warm Current.

Confronting turbidity, the major challenge for satellite-derived coastal bathymetry

Monitoring the complex seafloor morphology that drives the functioning of shallow coastal ecosystems is vital for assessing marine activities. Satellite-derived bathymetry (SDB) can provide a crucial dataset for creating the bathymetry maps needed to understand hazards and impacts produced by climate change in vulnerable coastal zones. SDB is effective in clear water, but still has limitations in application to areas with some turbidity. Here, using the twin satellites Sentinel-2A/B, we integrate water quality information from the satellite with a multi-temporal compositing method to demonstrate a potential for comprehensively operational bathymetric mapping over a range of environments. The automated compositing method diminishes the turbidity impact in addition to inferring the maximum detectable depth and removing optically deep-water areas. Examining a wide range of conditions along the Caribbean and eastern coast of the U.S. shows detailed bathymetry as deep as 30 m at 10 m spatial resolution with median errors <1 m when compared to high-resolution lidar surveys. These results demonstrate that the model adopted can provide useful bathymetry in areas that do not have consistently clear water and can be extended across multiple geographic regions and optical conditions at local, regional, and national scales.

Using fishers’ knowledge to determine the spatial extent of deep-water spawning of capelin (Mallotus villosus) in Newfoundland, Canada

IntroductionOn the Newfoundland-Labrador Shelf, Canada, capelin (Mallotus villosus) is a key forage fish that migrates annually from offshore to spawn within coastal embayments. Although capelin are thought to primarily spawn on beaches in this region, they also spawn subtidally in deeper water (5–40 m), where their eggs remain throughout incubation. The spatial extent of subtidal (i.e. “deep-water”) spawning habitat in coastal Newfoundland is unknown and is a research priority for fishers and management.MethodsWe collaborated with capelin fishers to identify putative deep-water spawning sites as a first step in determining the contribution of deep-water spawning to capelin recruitment. Given limited fine-scale coastal bathymetry and seabed habitat type data, which impeded spatial modeling to determine suitable capelin spawning habitat, this science-industry research collaboration was key to addressing this knowledge gap.ResultsThrough two years of multi-bay fisher interviews, 84% of interviewed fishers (56 interviewees) reported having observed deep-water spawning and identified a broad distribution of putative spawning sites throughout coastal Newfoundland. The majority of fishers indicated inter-annual variation in beach and deep-water spawning habitat use, and most interviewees linked this variation to temperature and capelin abundance. Further collaborations with fishers during boat-based surveys, we sampled 136 unique sites within 12 search areas in eastern Placentia Bay and 26 unique sites within six search areas in Bonavista Bay. Underwater video surveys combined with sediment sampling revealed seven previously undocumented deep-water spawning sites.ConclusionThe deep-water spawning areas derived from these fisher interviews can now be used to build a time series for monitoring capelin spawning habitat use alongside citizen-based beach monitoring data, as a general capelin stock health indicator in a weight of evidence approach for the science advisory process.