Human civilization is driven by its unappeasable drive for exploration. We explored and mapped every inch of our planet, at least the rocky part. We also explored and mapped our closest neighbors in the universe, the Moon, Mars, and Venus. But we still didn’t map the ocean.

What Drives Humanity to Map the Ocean Depths

alt Global Seafloor Topology Image Source: NOAA

The depths of the ocean are the most mysterious place in the world. Even the surfaces of the Moon and Mars are explored in more detail compared to the ocean floor. At the moment, we have a complete map of the seafloor. The thing is, its accuracy is about 5 kilometers. For comparison, our map of the Moon has 7-meter accuracy while the Mars Map is accurate to 100 meters, with 60 percent of its surface having 20 meters accuracy. The latest version of GEBCO (General Bathymetric Chart of the Oceans) grid, a high accuracy map of the ocean floor, covers just 15 percent of the surface.

While that looks comically low, there’s a reason for it. Mapping the seafloor is incredibly complex and expensive. GEBCO, an NGO that plans to map the whole seafloor, is at the moment the only organization with that goal. It’s cooperating with other entities such as the Nippon Foundation, IHO (International Hydrographic Organization) and others, but the project is still far from being completed.

Mapping the seabed is expensive and far from being as easy as mapping the surface of our planet. First of all, you need expensive equipment and lots of ships at your disposal. Second, oceans make more than two-thirds of the Earth’s surface (71 percent), double the amount of continents. And the entire global sea traffic is covering only a tiny fraction of the surface. Immense parts of the ocean are never visited by ships and other seafaring vessels. But there are official plans to map the entire seafloor. The reasons are as diverse as they get.

The seafloor is still a mystery compared to the Earth’s surface

The first and the most general reason is simple – the ocean floor is still a huge mystery compared to the Earth’s surface. Our atlases are accurate as they get and satellite-based imagery allowed humanity to map every inch of our planet’s surface. But depths below are shrouded in darkness.
The scientific community wants to create a detailed map of the seafloor because this would be a huge scientific achievement that will benefit the whole world in many different ways. The ultimate goal for bathymetry (the study of underwater depth and topography of lake and ocean floor) is to create an accurate topographic map of the seafloor.

Finally, humans are curious creatures with an immense drive for exploration. And while that drive is at the moment focused on outer space, some people and organizations focus on what's below. As we already mentioned GEBCO plans to map the entire seafloor in detail. The project, called Seabed 2030 is well underway.

Scientist need accurate ocean floor maps in order to construct global ocean circulation models

Scientific reasons for mapping the seabed aren’t just general and without practical goals. Oceanographers and climate scientists need accurate seabed maps in order to construct global ocean circulation modes. These models can be used for the research of phenomena that have a global reach, such as the Gulf Stream and other ocean currents.

The climate change we’re facing today affects these currents, but also creates other types of phenomena, such as El Nino. El Nino affects the climate and accurate maps of the ocean floor can help climatologists in creating precise models of the phenomena. In other words, accurate seafloor maps can help us better understand climate change and find ways to fight it.

Various seafloor installations demand accurate bathymetric data

The most important economic reason for creating accurate maps of the ocean floor is that seafloor installations can benefit from it. Laying huge underwater cables to carry internet signal between continents; laying pipelines for transporting oil, natural gas, and other resources; erecting offshore drilling rigs. They all demand accurate seafloor data. While private-owned companies’ reasons for mapping the seafloor differ greatly from NGO’s and scientists’, sharing the collected data can help in mapping the ocean floor.

Marine biologists can greatly gain from accurate seafloor maps

High-res bathymetric data can help marine biologists. The process of mapping the bottom of the ocean can discover new species and increase the knowledge of underwater biomes. The topography of the seafloor is also important. It can help scientists to locate where different species reside, allowing them to have a better understanding of the seabed biology.

Rescue attempts and hazard monitoring

The infamous case of Malaysia Airlines flight MH370 showed how flawed our seafloor topography data is. The search teams had to wait for a detailed map of the area to be made because the one used was deeply flawed. This prevented teams to deploy underwater vessels to investigate the seafloor. Bathymetric data collected by ships showed that the old map was highly inaccurate and that it varied greatly compared to new data.

alt Difference between altimetry and multibeam barometry data of the portion of seafloor where search for MH370 took place Image Source: Australian Government

This is why global high-def bathymetric data is needed. If something similar happens in the future, search and rescue teams will have accurate data from the start, allowing them to deploy inspection instruments from the moment they arrive at the site, instead of having to wait a long time for accurate seafloor data to be collected.

There’s also underwater hazard monitoring that can profit from high-def floor data. Monitoring hazards such as underwater volcanoes can be beneficial in protecting residents of coastal regions around the world. Further, detailed bathymetric data of the seafloor can provide resources for a better understanding of tsunamis and ways they are created and how they advance across the ocean. There’s, of course, the part that includes changes on the seafloor and also protecting underwater installations such as rigs, piping, and cables.

Seafloor mining

Finally, there’s the seafloor mining. This mining technique requires accurate seafloor data. Sadly, mining the seafloor could have devastating consequences on marine life and underwater ecosystems. It can also negatively impact research for new medicines. Luckily, the recent collapse of the largest deep-sea mining venture gives hope that the UN will impose a moratorium on the practice.

The History of Underwater Mapping

In the past, the seafloor was considered as a flat surface without any topographic variety. We thought that the seafloor is flat and boring but with the rise of seafaring, we discovered that seafloor around the world’s coasts is greatly varied and includes lots of dynamics. Ridges, slopes, sudden changes in the topography of the floor led seafarers to map the seafloor for safe routes near coastlines.

alt Lead line survey from a catamaran hull in Alaska, 1942. Image Source: NOAA

These early attempts at mapping the coastal regions started in ancient Egypt and they didn’t advance much for millennia. They included using sounding poles (long poles with marks indicating various depths) to mark shallow waters near the coastline. Surveyors would then mark the depth of the floor and write it down on a map. Later on, the pole was replaced with lead lines that worked similarly but were able to reach greater depths.

Sounding poles and lead lines were used since ancient times until the early 20th century. These primitive sounding techniques allowed sailors to map the ocean floor for safety reasons. Also, they were combined with other techniques to determine the position of a vessel. Finally, by coating the lead with animal fat, it was possible to gather samples of the seabed.

alt The first realistic bathymetric map, showing the Gulf of Mexico Image Source: arcgis.com

These primitive technologies were replaced with a more precise, but still mechanical way of mapping the seafloor. The wire drag is a tool that allowed for greater precision compared to regular sounding lines. Wire drag surveys required two ships. A wire, equipped with weights and buoys, would be attached to the two ships and it then would be dragged between two points on the ocean floor. When the wire would stumble across a change in the topography (slopes and ridges), it would become stretched, allowing surveyors to mark changes.

The 20th century marked the arrival of modern-sounding techniques. The earliest, first used on ships during the 1920s, was single beam echo sounding. In other words, a sonar. By implementing a sonar, bathymetry entered the modern era that finally allowed mapping the seafloor in great detail.

Techniques Used Today

The single-beam echo sounding is still occasionally used, but it is mostly replaced by other, more advanced bathymetry techniques.

alt Image Source: NOAA

Single beam echo sounding

The basic sonar technique. It uses one emitter that emits and receives acoustics signals. These signals travel to the ocean floor and back. When they arrive at the surface and are detected by the sonar emitter, the travel time is calculated and thus the depth of the ocean floor.

The single-beam echo sounding replaced techniques that were used for thousands of years and marked a major increase in speed and accuracy of ocean floor mapping. But compared to other modern techniques, this one is slow, inefficient, and lacks accuracy.

Multibeam echo sounding

The next step in multibeam sonar-based sounding technology. Instead of using one emitter, multi-beam sounding used up to 120 transducers installed to the ship hull. They emit a series of sound beams. So instead of mapping the seafloor one point at a time, multi-beam echo sounding allows for the floor to be mapped much faster, in a line covering an area across each side of the ship.

This technique is accurate up to 10 meters and allows ships to create strips of bathymetry data instead of narrow lines, which are created with single beam sounding. Multibeam echo sounding is the dominant seafloor mapping technique today.

The technique can result in even greater accuracy if used by autonomous underwater vehicles. They travel near the ocean floor and can map the floor from altitude of just 20 meters. This way the accuracy can reach less than 1 meter.

Satellite-derived bathymetry

This technique is used in shallow waters where water clarity is high enough to allow satellites to map the bottom of the sea. The surveys are done by multispectral imagery, from visible to infrared electromagnetic spectrum. Satellite-derived bathymetry cannot be used for deep see mapping.

alt Image Source: Earthmagazine.org

Satellite altimetry

The second satellite-based technique can be used for mapping deep seafloor. In fact, satellite altimetry was used in creating the aforementioned map of the ocean floor. Mapping is done using altimeters, which measure the height of the ocean surface. The height is affected by changes in the seafloor – the gravitational effects are small but measurable by altimeters in satellites.

This technique is great for mapping immense areas of Earth’s oceans. The downside is the low resolution, which can reach 5 kilometers at best.

LIDAR (Light detection and ranging)

Finally, we have the LIDAR technique. This one is also used for shallow waters since it’s based on light. It works by emitting laser pulses from an aircraft flying above the sea and measuring their return. The depth is then calculated from the time difference between the arrival of the laser beam from the water surface and the seafloor. It isn’t really popular since it cannot be used in deep waters and because satellite-derived bathymetry can cover larger areas in less time.

What Awaits Us in the Future

At the moment, the majority of efforts in mapping the ocean floor is done by manned vessels. While there are research vessels doing the mapping, the data is also gathered by military vessels, trading ships, and privately owned ships. But in order to gather data of the entire seafloor, we need the help of unmanned vessels. It’s because trading routes and routes of military ships cover just a small fraction of the world’s oceans. The similar can be said about private ships (such as yachts) travels. And research ships cannot cover the massive swaths of the world’s oceans. It would take immense amounts of time and money.

alt Unmanned surface vessel SEA-KIT Maxlimer Image source: xyht.com

This is why using autonomous vehicles is the key to mapping the entire seafloor. They don’t have to be operated by humans. They can cover huge areas in a shorter time than manned ships. They can carry and launch autonomous underwater vehicles (AUVs), which can map the seafloor in detail. Only if we start utilizing unmanned vessels can we reach the goal of mapping the seafloor by 2030, which is the main objective of the Seabed 2030 initiative.