Understanding bathymetry and its importance
Bathymetry is the science of measuring ocean depths and relief to determine the topography of the seabed. It is an essential pillar for understanding deep-sea marine habitats, making extractive industries safer and more efficient, and studying the evolution of the seabed over the long term.
- Detailed knowledge of bathymetry is essential for engineering projects requiring submerged foundations, such as the construction of pipelines or offshore wind turbines.
- It is also indispensable for underwater geology research, precise seabed mapping and tsunami forecasting.
- Finally, bathymetry plays an important role in achieving the Sustainable Development Goals (SDGs), in particular the SDG aimed at conserving and sustainably exploiting the oceans, seas and marine resources.
How do I take a bathymetric survey?
To carry out a bathymetric survey, several steps must be followed. First of all, mission preparation is essential. This includes defining the line spacing you wish to measure.
Next, you’ll need to choose the right measuring instrument for the job. Bathymetric sounders are generally used for this task. They can be single-beam or multi-beam, depending on the specific needs of your project.
When carrying out the survey, you’ll need to navigate the water in a predefined pattern, often in parallel lines. The data will then be collected using your measuring instrument.
Finally, this data needs to be processed and analyzed, often using specialized software. This creates a bathymetric map illustrating the underwater relief.
Bathymetry equipment
Bathymetry, which involves measuring water depths to map the seabed, relies on a range of specialized equipment. Let’s take a closer look at the essential equipment used by our center of expertise in this technical discipline.
The bathymetric drone
An autonomous marine drone is a key tool in the field of bathymetry. Its compact design makes it easy to transport for hydrographic and bathymetric surveys. It offers a 100% autonomous solution for precise mapping of the seabed, whether for inland waters, ports, rivers or underwater exploration.
They are generally equipped with state-of-the-art sensors that guarantee centimetric precision in all environmental conditions. This precision is made possible by the integration of a multi-band GNSS RTK for data reception. The drone can be used by a single operator, adding to its practicality and ease of use.
The bathymetric measurement system
A bathymetric measurement system is equipped with a single-beam bathymetric echosounder which, combined with an RTK GNSS receiver, enables the processing and storage of water depth measurements synchronized with a precise geo-referenced position.
Two types of sounder can be supplied: single-frequency (SF) or dual-frequency (DF), depending on specific mission requirements. Some models are particularly appreciated for their integrated web server, which makes hydrographic operations very intuitive. It generally requires no special training to operate, making it accessible to a wide range of users.
How to read and interpret bathymetric charts?
The process of reading and interpreting bathymetric maps is an important step in bathymetry. These maps provide a visual representation of the seabed, helping to understand depth variations and underwater relief. Bathymetric or isobath lines, which represent areas of similar depth, are an essential component of these maps.
To read a bathymetric chart, we generally refer to the legend, which indicates the depth scale and sometimes the nature of the seabed (sandy, rocky, etc.). Deeper areas are often represented by darker colors or lines closer together, signifying a steeper slope.
Interpreting these maps, on the other hand, requires a certain amount of expertise. For example, fishermen use these maps to locate favorable fishing areas, while researchers can use them to study marine habitats.
Tools such as bathymetric sounders and dedicated software can also be used to obtain more precise and detailed bathymetric maps. These tools are essential for reading and interpreting bathymetric data.
How do you measure the depth of a lake? Method and technique
To measure the depth of a lake, we generally use a method called sounding. The process involves the use of an echo sounder, an instrument that sends sound waves down to the lake bed. These waves bounce back to the echo sounder. By measuring the time it takes for these waves to return, we can determine the distance between the echo sounder and the bottom of the lake, i.e. its depth.
The accuracy of this method depends on several factors, not least the speed of sound in water, which can vary with temperature, salinity and pressure. It is therefore essential to calibrate the echo sounder correctly to obtain accurate measurements.
In addition to the echo sounder, other tools can be used to measure the depth of a lake, including :
- Leaded rope: a rope weighted at one end and lowered into the water until it touches the bottom. We then note the length of rope needed to reach the bottom, which gives a measure of depth. This method is less accurate than sounding, but can be useful in shallow areas or when an echo sounder is not available.
- Remote sensing bathymetry: this technique uses satellite or aerial images to estimate the depth of lakes. It is particularly useful for large lakes or hard-to-reach areas. However, it also requires precise calibration and knowledge of image processing to obtain reliable results.
Once depth data has been collected, it can be used to create a bathymetric map of the lake, which shows variations in depth and can help to understand its morphology and ecosystem.
Bathymetry and topography: a relevant comparison
Bathymetry and topography are two closely related disciplines, but they focus on different environments. While topography studies the relief of the earth’s surface, bathymetry is concerned with underwater relief.
Bathymetry maps the seabed using bathymetric surveys. These are carried out using instruments such as multibeam echo sounders or single-beam bathymeters.
Topography, on the other hand, is generally carried out using terrestrial measuring instruments. However, the aim of these two disciplines is similar: to create an accurate representation of the terrain for a better understanding of the environment.
In the case of bathymetry, the data collected is often presented in the form of a digital terrain model or DTM, which offers a 3D visualization of the seabed.
Despite their differences, bathymetry and topography have similar applications:
- They are used in hydroelectric projects to determine the best location for installations.
- They are necessary for the engineering design of underwater or land-based structures.
- They play a crucial role in boating safety by providing essential information for navigation.
Bathymetry and topography are two complementary disciplines, whether for studying the seabed or the land surface.
The potential of bathymetry in Quebec
Bathymetry, as a seabed mapping technique, has considerable potential in Quebec, an area rich in aquatic resources. Whether for water management, aquatic ecosystem studies or infrastructure planning, the applications are numerous.
The use of bathymetric data, for example, can contribute to better management of Quebec’s lakes and rivers. Bathymetric inventories provide invaluable information on these aquatic environments, helping to preserve and enhance them.
Bathymetry can also play a key role in the study of climate change. By analyzing variations in underwater topography, it is possible to understand the dynamics of aquatic environments and their responses to climatic variations.
Finally, bathymetric data can be used to support land-use planning projects. They provide precise information on underwater relief, essential for planning infrastructure such as dams and bridges.