Mapping the Unknown: How Multibeam Sonar Works

Exploring the ocean is a tall order. Aside from its enormity, its extreme depths, unforgiving pressures, shrouded visibility, and freezing temperatures hinder deeper and farther explorations. Even if the search is narrowed to a particular location, sending divers and robots can also be expensive and pose safety risks.

Hence, creating a targeted approach to ocean exploration is needed for more efficient and effective efforts. This is where seafloor mapping comes in. Marine scientists regard seafloor mapping as the first step in investigating oceans, preventing oceanographers from “flying in blind” when it comes to vast waters.

Seafloor or seabed mapping is done to study and record the ocean floor’s shape, features, and habitats, employing sonar, multibeam echosounders, and underwater vehicles in doing so. It creates a map of the seafloor’s topography, measuring its depth and identifying objects found in the exploration.

One of the leading technologies for seafloor mapping is multibeam sonar. Sonar, which stands for Sound Navigation and Ranging, was discovered in the 1920s and has two main types: active and passive. The multibeam sonar, on the other hand, was developed in the 1960s to cover a wider area, with the sound distributed in a fan-shaped manner.

When mapping, the active multibeam sonar is used to emit a pulse of sound into the ocean, creating an echo. The depth is determined by the time it takes to send the sound and receive the echo.

It also collects backscatter, or data on the geological makeup of the seafloor and its objects. Backscatter is based on the intensity of the reflected echo, with hard, rocky seafloors reflecting more sound and softer portions with less.

Multibeam sonar can make 3D bathymetric maps, featuring a detailed account of the underwater terrain and its volcanoes, canyons, trenches, and more. It makes use of multiple physical sensors called the transducer array, placed directly on a ship’s hull, covering the areas under the ship and each of its sides.

Mapping the ocean from the surface is indeed substantial, but it also produces lower-resolution maps, perfect mostly for broad imaging. So, to supplement this, sonar can also be used underwater, attached to remotely operated vehicles (ROVs) or autonomous underwater vehicles (AUVs) for higher-resolution maps.

Once all the data has been collected, hydrographers with computers on the ship will process it and create the seafloor maps. Warmer colours (red and orange) in the image represent shallower areas, while cooler colours (yellow, green, blue, and violet) correspond to deeper areas. Processed backscatter data will also reveal 3D structures like shipwrecks, dense layers of organisms, bubble plumes, and more. 

Maps from these multibeam sonar surveys are helpful in targeting specific areas in the vast ocean. In that way, marine scientists can explore more efficiently and effectively, allowing them to decide with confidence on future activities and policies.

Mapping the seafloor proves beneficial to the following areas:

• Discovering marine life: Data from sonar imaging can reveal seamounts, hydrothermal vents, or ridges that are known as biodiversity hotspots. These areas are rich with information on underwater habitats, the organisms present, and their ecological patterns.
• Better marine navigation: Seafloor maps can aid in setting safer routes for ships, significantly reducing risks, delays, and accidents.
• Identifying resources: Valuable resources like oil, gas, minerals, and even fisheries can be perceived through seabed mapping. For example, bubble plumes can indicate gas deposits, leading to their discovery and management.
• Disaster readiness: Detailed mapping can help in understanding natural hazards like tsunamis and coastal flooding.
• Further scientific research: Data from such maps present a timeline of discoveries that can guide the scientific sector on where to next innovate, improve, and explore. The government and other private organisations involved can also use these maps in supporting research in the field.
• Heightened protection: Seafloor mapping aids in the monitoring of vulnerable marine sites and ecosystems. This subsequently furthers conservation efforts through record-keeping and utilisation of data to back environmental policies.

The future of seafloor mapping and sonar technology looks bright with major strides being made by stakeholders in the sector.

First, when it comes to seafloor mapping, collating data, and storing it, an initiative called Seabed 2030 was launched in 2017 under the partnership of the Nippon Foundation and the General Bathymetric Chart of the Oceans (GEBCO). Its vision is to map the entire ocean by 2030, enjoining the help of global industries, governments, researchers, scientists, explorers, and academia.

At present, Seabed 2030 has mapped around 24.9% of the ocean, leaving about 75% yet to be surveyed. This is already a huge jump from 2019 numbers, only amounting to 15%.

Second, in terms of sonar and ocean mapping technology, more and more advancements are sprouting to address challenges. Significant trends in these tech innovations include:

• the use of AI and ML in creating supercomputers to process data more efficiently;
• mounting MiDAR instruments to submersibles to map the ocean floor using light to transmit data;
• streamlining data collection and storage by making it available to the public through easy-to-use software interfaces;
• improving underwater map resolution from surface vessels;
• and automating reviews of data gathered from ocean exploration to ease the time and effort needed in compiling them.

Even one team from MIT in 2024 started developing a surface-based sonar system that could accelerate small- and large-scale operations using aircraft vehicles. This is poised to map the seafloor 50 times more than the rate of underwater vehicles and 100 times the resolutions of surface vessels.

The question of understanding and protecting unknown waters can only be addressed by simply making it known. But with the present challenges in ocean exploration, the answer to such a question makes it less simple.

Innovations like the multibeam sonar are a definite aid in unlocking the ocean’s mystery. It provides significant data all while lessening costs, risks, and unfocused efforts.

The benefits of seafloor mapping fully materialize with the use of multibeam sonar, enabling better protection and management of our waters, their ecosystems, and marine resources.

But it certainly has a long way to go. More innovations should sprout to advance ocean mapping, alongside united efforts from stakeholders and organisations.

For it is through collective development that we can understand and map the earth’s great and watery unknown.

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