A bathymetry is a topographic survey of the relief of surfaces whose terrain is covered by water, that is:
- The seabed or the bottom of riverbeds
- Swamps
- Wetlands
- Lakes
- Reservoirs
- Etc. Any cartography of the bottoms of different bodies of water.
It could be said that bathymetry is the underwater equivalent of altimetry. The result of this bathymetric survey is usually a bathymetric map. A bathymetric map (or bathymetric chart) typically represents the seabed relief using isograms. Military forces, scientists and the general public use bathymetric maps to study the ocean floor and obtain specific information. They can also be used to determine the distance travelled by a ship or vessel over land or water.
How is a bathymetric survey carried out?
The earliest bathymetric surveys were performed using heavy rope or cable segments lowered from the side of a vessel, but this is an extremely inefficient technique. Today, wide-swath sonars and single-beam and multi-beam echo sounders are used. The latter system emits sound waves that measure the distance between the surface and the seabed, as well as objects suspended in the water or resting on the bottom.
The difference between single-beam and multi-beam sounders is that a single-beam sounder measures depth at a single point, so by moving the vessel using a single-beam system, a bathymetric line is obtained. On the other hand, a multi-beam system measures the depth of an entire line, so as the vessel moves, a bathymetric area is produced (fan-shaped data coverage).
In addition to sonar, some devices include a GNSS system to accurately determine the position of the vessel or device performing the bathymetric survey.
When are bathymetric surveys used?
The applications of bathymetric surveys are very broad:
- To determine the depth of an area, which is essential to assess whether a vessel can safely enter and leave a port without difficulty or damage.
- To estimate stored water volumes in bodies of water and understand riverbed dynamics by identifying scour zones and sediment deposition areas, which can sometimes lead to the formation of islands within a river.
- To obtain navigation information in large rivers. Bathymetric surveys are a key input for any hydraulic modelling software, enabling the evaluation of flood wave propagation for hydrological forecasting purposes.
- For beach stabilisation and restoration, navigation charting and surveying. In addition to being essential for the success of coastal projects, some surveys are required by governmental institutions as part of permitting procedures and are mandatory at the preliminary project stage.
Unlike terrestrial surveys, bathymetric surveys are much more complex and require specific vessels and equipment to make measurements possible.
Because this is a highly specialised field, it is advisable to seek guidance from professionals with experience in carrying out this type of project. At Global Geosystems, we are distributors of the VE115 unmanned vessel, currently one of the best solutions available for bathymetric surveys.
Contact us if you would like more information about our solutions. Our specialists have more than 20 years of experience in the field of topography.