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What is bathymetry and what is it used for?

Updated: Jul 12, 2023

Understand how TideWise uses autonomous vessels to offer this service

Did you know that approximately 71% of the Earth's surface is covered in water? Of that number, about 96.5% is found in the oceans and the rest is divided basically between lakes, rivers, glaciers and groundwater. Of this immensity, most of these areas and underwater ecosystems still remain unknown and unexplored.

To get to know this world better and understand more about the characteristics and topography of the bottom of rivers, seas and oceans, a technique called bathymetry is used.

In this article, we'll explain more about what bathymetry is and how autonomous vessels are transforming this market.

What is bathimetry?

Bathymetry is a technique dedicated to mapping the depths of water bodies, that is, it is the measurement and representation of the topography of the bottom of rivers, seas and oceans. In addition to measuring depth, this study also includes identifying underwater relief and creating three-dimensional maps of the sea floor.

The word “bathymetry” comes from the Greek "bathýs", meaning deep, and "metron", meaning measure. Bathymetry allows obtaining information about the physical characteristics of the sea floor, such as seamounts, mountain ranges, valleys, abyssal plains and underwater canyons.

For the port and offshore market, this service assists in monitoring the port access channel, diagnosing possible siltation, forecasting and planning dredging, maintenance of port draft, widening beaches, underwater archaeological research and much more.

How is bathymetry performed?

To carry out bathymetry, specific equipment is used, such as multibeam sonar (MultiBeam Echosounder), IMU (Inertial Measurement Unit), and high-precision positioning systems (via satellite with RTK correction). Multibeam sonar emits sound pulses towards the sea floor and measures the time it takes for the sound to return to the sensor after being reflected by submerged surfaces. Based on this sound return time and knowledge of the exact position of the vessel and its attitude (roll, pitch, yaw), it is possible to calculate the depth at a given point.

The bathymetry service is used to generate charts, blueprints and digital models (2D and 3D) of the sea floor. LiDAR sensors, on the other hand, are used to detect data through beams of light above the waterline, mapping slopes, rockfills and channel walls, for example.

The fusion of bathymetry data with Lidar data allows the three-dimensional construction of the environment in very high resolution. Allowing the client to plan or verify works and/or assets in the region of interest.

Bathymetry in Hydrographic Surveys

Although bathymetry and Hydrographic Survey are related to the study of bodies of water, there are important differences between these two concepts.

While bathymetry is restricted to the study and techniques used for measuring and mapping the depth of water bodies, the Hydrographic Survey is a more comprehensive service that encompasses both bathymetry and other relevant data, such as the collection of geospatial data related to topography land, tides, currents, water quality, underwater vegetation and other elements relevant to navigation and coastal management.

Hydrographic Survey is used to produce up-to-date nautical charts, provide information for safe navigation, support coastal engineering projects, environmental impact studies, monitor coastal areas and provide data for scientific research. By generating relevant data, a company that wants to perform this type of service needs to know and be in line with the NORMAM-25 standards.

Get to know the brazilian rule NORMAM-25:

NORMAM-25 is a standard established by the Brazilian Navy that has the guidelines for the execution of Hydrographic Surveys in the national territory. It is known as “Norms of the Maritime Authority for Hydrographic Surveys” and provides clear guidelines, establishing technical and operational requirements for companies and organizations that carry out these surveys, contributing to the production of reliable and accurate data for purposes of navigation, coastal planning, scientific research and other applications related to aquatic environments.

Some important points that are present in NORMAM-25 are:

  • Licensing: NORMAM-25 establishes the requirements to obtain the necessary authorization to carry out hydrographic surveys in Brazil. It defines the procedures for obtaining the License for Hydrographic Surveys (LLH) from the Board of Hydrography and Navigation (DHN) of the Brazilian Navy. TideWise is registered under number 424 in the Register of Entities Performing Hydrographic Surveys and under the terms of the Maritime Authority Norms for Hydrographic Surveys - NORMAM-25/DHN.

  • Technical specifications: The standard establishes the technical specifications for the equipment used in hydrographic surveys, including bathymetric systems, multibeam sonar and other relevant instruments. It defines accuracy and performance criteria to ensure the quality of collected data.

  • Operational procedures: NORMAM-25 establishes the operational procedures that must be followed during hydrographic surveys. This includes information on mission planning, data collection methods, data processing and analysis, and the generation of cartographic products.

  • International norms: The norm also makes reference to international norms and standards established by the International Hydrographic Organization (IHO), ensuring that hydrographic surveys carried out in Brazil comply with the best practices and international standards. Tidewise's technology is capable of producing Special Order IHO quality bathymetry (survey) information.

For more information about NORMAM-25, visit the Brazilian Navy website.

Use and advantages of autonomous vessels in bathymetric surveys

Autonomous vessels have proven to be increasingly useful and advantageous for offering bathymetric survey services. In addition to greater safety and lower operating costs, the use of a USV (Uncrewed Surface Vessel) also has a smaller carbon footprint when compared to conventional vessels.

Other favorable points of the use of uncrewed vessels are:

  • Efficient data collection: Autonomous vessels can operate continuously, which allows for more efficient data collection. They can cover predefined routes in a systematic way, covering large areas precisely and for long periods, without the need to change crew.

  • Flexibility and Adaptability: The USV Tupan, TideWise's autonomous vessel, is a versatile USV that can be designed and adapted to suit different types of marine environments. They can operate in shallow areas, in coastal waters and in remote areas where access is challenging for manned vessels. In addition, they can be configured to adapt to different depths and tidal conditions.

  • Greater accuracy and resolution: The USV Tupan can be equipped with high-precision data collection systems, such as multibeam sonar, which allow for more detailed and accurate bathymetry data collection. This results in maps and models of the seafloor with higher resolution and quality.

These are just some of the advantages of using uncrewed vessels to carry out bathymetric surveys. Here at TideWise, the USV Tupan is capable of performing this type of service extremely efficiently and reliably.

How can TideWise help you with Hydrographic Survey work?

TideWise is the first and most experienced operator of unmanned boats in Brazil to register with the CHM (Centro de Hidrografia da Marinha), and the first to obtain permission to perform Category A special order hydrographic surveys. using technical specifications that allow the data obtained to be used in the updating of nautical documents.

Here at TideWise, we have already integrated the USV Tupan with sensors from several manufacturers, such as R2sonic, Norbit and Kongsberg capable of performing bathymetry in waters up to 600m deep. This attests to the ability of our autonomous vessel to perform this type of service with extreme flexibility.

As case studies, we can present a bathymetry operation that we performed in Belgium in 2022 and another operation that we performed in Rio de Janeiro/RJ in 2023. Both operations are representative for their originality, breaking paradigms in the shipbuilding industry.

In the first operation, we carried out an offshore asset inspection service in an offshore wind complex in the North Sea in Belgian territorial waters. This operation included activities above and below the waterline (find out more details by watching the video below), however, let's stick to the scope of the operation's bathymetry. We carried out the inspection of just over 15 km of subsea cabling at depths ranging from 25 to 35m and distance from the coast of approximately 30 to 40 km, using the Norbit iWBMS multibeam echo sounder installed on the USV Tupan. This sensor has the capacity to perform water bathymetry of up to 600m in depth and the collected data were processed by the NaviSuite Kuda processing package, from the Danish company EIVA. This stage of the operation took approximately 1h45, with a total propagated uncertainty (TPU) of less than 0.25m.

For more details on the operation, check out the article in the German magazine German Wind Power, which features reports from the Innovation and Offshore Asset Managers of the company Elia Group, a customer of the service. Watch the video of the operation carried out in Belgium:

In partnership with Kongsberg, we also carried out an autonomous Category A bathymetry with our USV Tupan, a demonstration of an unprecedented system in the country. For the demonstration, we used the Kongsberg EM 2040P Multibeam EchoSounder sensor, the industry's first wideband 3-sector multibeam echo sounder, now available as a 200 - 700 kHz system.

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