A brief history of underwater acoustics: Part I

It’s amazing to think that while we can image individual stars and planets within galaxies millions of light years away (one light year equals ~10^13 kilometers!), we have only recently began imaging the topography of the seafloor that makes up 70% of the Earth’s surface, the very planet we live on!

hello_seafloor

Fundamentally, this is because neither light nor electromagnetic waves can penetrate very far into water, which makes the whole business of mapping the seafloor significantly more difficult than looking at the stars. So while explorers like Copernicus and many others before him have been peering into the depths of the universe for the past several centuries, it was not until very recently, the last half of the 20th century, that underwater imaging technologies have been developed and used to gaze into the abyss that is the ocean floor.

The initial motivation for such endeavors was militaristic; having the capacity to detect the location of naval vessels, especially submarines, was a critical component of the Allied Forces toolkit developed during World War I and used to defeat the Germans in World War II. The basic concept behind such technology is that acoustic waves, or sounds, travel very far in water before dissipating. Therefore, if you are able to listen to the sounds of the ocean and hear something uncharacteristic, say a ship plowing through the water, you could then try to determine the direction that sound is emanating from. And since acoustic waves are carried for large distances, it is conceivable that a ship, or better yet a submarine, is detectable long before it reaches your position. Today this technology is known as sonar, which is an acronym for sound navigation and ranging.

After such military efforts came to fruition, industry and science communities were able to further develop and apply such methods for their own interests. In particular, underwater acoustics is used to detect and monitor fish populations as well as to map the topography of the seafloor and its subsurface, the latter of which is the basic tenet behind our goals for the MIST expedition.

Look out for Part II in the coming days! And for your viewing pleasure, what exploring the depths of the ocean looks like today.

 -Samer