Bathymetry
The Catalan Coast is a territory of great natural and economic value, with great biodiversity and strategic relevance for various human activities. To guarantee effective management of this area, it is essential to have accurate bathymetric data on the seabed, which allows a better understanding of its morphology and the identification of marine habitats.
The ICGC, commissioned by the Directorate General of Environmental Policies and the Natural Environment, has produced a series of bathymetric products for the Catalan coast. This project has been co-financed by the FEuropean Maritime and Fisheries Fund 2014-2020 (EMFF), and is based on the integration of different sources of information. The data includes bathymetric measurements of the seabed obtained using sonar, as well as LIDAR data and other topographic measurements carried out during the years 2022, 2023 and 2024.
The Topobathymetric Elevation Model shows us the relief of both the emerged part of the coast up to about 50 m away from the coastline, and the submerged part up to a depth of 50 m with a resolution of 1 m.
The topobathymetric model is distributed as a single raster file in Cloud Optimized GeoTIFF format of 32 bits with a mesh size of 1 m, internal georeferencing, pyramids and lossless LZW compression.
All products derived from the bathymetry of the Catalan coast are distributed in the form of mosaics without subdivision by sheets. The coordinate system adopted is the official one in Catalonia: ETRS89 reference system and orthometric heights using the EGM08D595 geoid model.
Imatge
| Geoinformation from the Cartographic and Geological Institute of Catalonia subject to a Creative Commons International Recognition 4.0 license More information |
Description
The Topobathymetric Model is a regular grid of points that describe the morphology of both emerged and submerged terrain. In addition to the terrain, the model includes rigid structures such as buildings, breakwaters, retaining walls, etc. Vegetation, vehicles, bridges, and other elements with a lesser impact on water dynamics are not considered. Each point contains the orthometric elevation in meters of a 1x1 m terrain cell. This means that points above the geoid surface have a positive elevation, and points below it have a negative elevation. This distinction roughly coincides with emerged and submerged points, respectively.
Just as contour lines on a topographic map connect points of the same altitude, isobath lines connect points of the same depth beneath the water surface. This is a graphical representation that allows for visual identification of areas of the seafloor with greater or lesser slopes and the presence of mountains, depressions, troughs, and submarine spurs.
Most of the bathymetry, totaling between 0 and -15 m, was captured in the summer of 2022 using airborne LiDAR with bathymetric capabilities. Unlike terrestrial LiDAR, bathymetric LiDAR has a wavelength that allows it to penetrate shallow waters and obtain seafloor data. This technique yields excellent results at a very low cost and has been used wherever possible. The two main exceptions are the area of influence of Barcelona air traffic control due to low-altitude flight restrictions and the Fangar Pass in the Ebro Delta, due to the abundance of suspended sediments that interfere with the bathymetric LiDAR signal.
Geographic distribution of data capture.
Data capture.
Submerged terrain areas that could not be captured using bathymetric LiDAR were captured using echosounders. Echosounders are instruments similar to ship-based sonars that allow the distance from the ship to the seafloor to be determined from the propagation time of an acoustic wave through the water. The shallowest areas, between 0 and -3 m, were captured mainly using single-beam echosounders from unmanned surface vessels (USVs). The deeper areas, between -3 and -50 m, were captured using multifaceted echosounders from manned vessels. To complement echosounding along the intertidal zone, between +1 m and -1 m, topographic profiles were created to ensure a smooth connection between emerged and submerged terrain. Finally, to obtain information on the emerged areas of the topobathymetric model along the central coast, data from a land-based LiDAR flight were used. The capture characteristics are equivalent to those of territorial LiDAR.
The result of primary data capture is an irregular point cloud of highly variable density. To generate a continuous topobathymetric model, the point cloud must be refined. First, noise is removed and the points are classified to distinguish those that will be included in the model (seafloor, terrain, buildings, breakwaters, outfalls, etc.) from those that will not (vegetation, vehicles, suspended sediments, water surface, ships, etc.). Furthermore, given the diversity of capture technologies used, it is necessary to standardize the data sources to avoid discontinuities and gaps that do not address any terrain characteristics. Once the point cloud has been refined, a continuous surface is triangulated, the holes where it was impossible to obtain seafloor information are interpolated, and the final model is generated in raster format.
Main technical features
All products derived from the bathymetry of the Catalan coast are distributed as mosaics without sheet subdivision. The coordinate system used is the official one in Catalonia: the ETRS89 reference system, and orthometric elevations are based on the EGM08D595 geoid model.
Distribution features:
- The topobathymetric model is distributed as a single raster file in 32-bit Cloud Optimized GeoTIFF format with a 1 m grid pitch, internal georeferencing, pyramids, and lossless LZW compression.
- The isobath maps are distributed as a single vector dataset in different formats (ESRI Shapefile and OGC GeoPackage). The isobath offset is 1 m. Each isobath element contains an "ELEMENT" attribute with the elevation associated with the isobath in meters. Rendering styles are included, highlighting master curves with a 10 m interval.
Capture data and capture technologies:
- Bathymetric LiDAR capture was carried out during the summer of 2022 and covers most of the Catalan coast, specifically between the Ebro Delta and Calafell Beach in the south and between Mataró and Portbou in the north.
- Terrestrial LiDAR capture was carried out between December 2022 and January 2023 and includes the emerged part of the central coast between Calafell Beach and Mataró.
- Multiface echosounder capture from a manned boat was carried out between late 2021 and early 2023 and covers the entire stretch between -10 and -50 m, some areas of the central coast between -3 and -10 m, and most of Els Alfacs Bay.
- Single-bundle echosounder capture from an unmanned vessel (USV) was carried out between 2022 and 2023. It includes shallow areas (0 to -3 m) of the central coast and the Ebro Delta.
- The topographic profiles of the intertidal zone of the central coast were carried out between 2022 and 2023.
Development of the final topobathymetric model
To develop the final topobathymetric model, the noise associated with the initial data capture is first reduced to improve its accuracy. The differences between capture technologies are then minimized to achieve a uniform texture and a more homogeneous model. Artifacts are also removed, identifying elements specific to the territory and eliminating others, such as suspended sediments, posidonia, or boats, that can distort the result. Finally, the remaining holes in the data-deficient areas are interpolated, applying specific techniques according to the size of the hole to complete the model.
Featured use cases
Topobathymetric
Topobathymetric models are the basis for geoinformation that allows for the generation of derivative products such as isobath maps with various equidistances. They can also be used as a final product for simulations such as flood risk analysis, storm effects, sediment transport, volumetric differences in beach sand between different dates, etc.
Isobates
Isobates are the basic information for maritime charts. The published isobath map lacks the necessary elements for maritime navigation. It is derived from the topobathymetric model and represents the same information but expressed using isobaths, or lines that join points of equal depth, so that this information can be analyzed in vector format.
