Earth is the only planet known to have water on its surface. But what lies beneath the deep water bodies is unknown. Only a mere 5 per cent of the oceans have been explored and even what we know is all through satellite imagery.
Thanks to all the ocean documentaries, we assume the ocean floor to be an even bed of sand with colourful reef in-between and shoals of fish swimming around them swiftly! In reality, ocean floor (and the surface of all other huge water bodies like seas, rivers, and lakes) is anything but even. It is full of mountains, valleys, ridges, crests and troughs. Here is where the need arises in understanding the ocean floor and mapping it.
Bathymetry – measurement of depth and ocean floor mapping
The measurement of the depth of water in oceans, seas or lakes is known as ‘Bathymetry’. It is the underwater equivalent of topography. Bathymetric maps look like topographic maps, which use lines to show the shape and elevation of land features. In topographic maps, the lines connect points of equal elevation, whereas bathymetric maps connect points of equal depth. A circular shape marked with similar colours indicates shallow waters or an ocean trench or a seamount.
In ancient times, sailors and navigators would conduct bathymetric measurements by throwing a heavy rope over the side of a ship and recording the length of rope it took to reach the seafloor. These measurements, however, were inaccurate and incomplete. With increased research and technological advancement, today it is much easier to chart bathymetric maps. By means of sonar technology, high resolution maps with better precision can be produced by a single ship within considerably lesser time and with minimal human efforts.
Bathymetric measurements are made by means of Multibeam Echo Sounders that feature hundreds of very narrow beams that send out sound pulses. These array of pulses provides very high angular resolution. Angular resolution is the ability to measure different angles, or points of view, of a single object. Having high angular resolution means a single feature of the seabed — like the top of an undersea mountain — would be measured from a variety of angles, from the sides as well as the top.
Multibeam echo sounders continuously map the portion of the ocean floor perpendicular to the path of their movement. They compensate the movements of the boat at sea, further increasing the measurement’s accuracy. They can also provide information about the physical characteristics of a seafloor feature. For instance, they can indicate whether the feature is made of hard or soft sediments.
When the search area is too deep to explore with ship-based mapping and are prone to climatic variations and strong ocean currents, Autonomous Underwater Vehicles (AUVs) are used. These are submarines equipped with underwater robotic technology. They are faster, provide higher-resolution seafloor surveys including hazard assessment, with much fewer capital costs and increased access to the ocean. Unlike Multibeam bathymetry system which costs higher, require technical expertise and float on the ocean’s surface, AUVs are much less expensive and can go deep into the oceans for a better picture. They are best suited for open stretches of water.
Advantages of Bathymetry
The oceans feature a world of vivid marine life full of beauty and mystery. It is from where life evolved and still houses life from since the era of evolution of life. At deep levels of the oceans, where it is constantly dark, there live unique, strange and diverse sets of life beyond the definition of evolution and adaptation. Mapping the ocean floor can give a sneak peek into this interesting ecosystem.
Knowledge of undersea features can assist in the understanding of oceanic currents and also help predict possible disasters. For instance, underwater features like seamounts and trenches can influence the direction of currents; alter the strength and path of cyclones, hurricanes and tsunamis and volcanoes within the oceans can alter the temperatures or even create an island overnight.
Along with mapping of the seafloors, it can also help find mineral ores, oil deposits, rare and precious metals and treasures of the reefs. It also helps in understanding the exact habitats of marine life and hence benefit commercial fisheries. However, we have to use this technology conscientiously and remember our greater responsibility of not causing any harm to our marine biosystem.