History of Bathymetry: Early Methods

With Google Maps readily available at our fingertips, it’s pretty safe to say that the world has been mapped out. Has it though? Our oceans make up 71 percent of the Earth, but their depths are not accurately mapped out entirely. This series will explain the techniques used in the past and present to record this information, and new methods we hope to put into practice in the future.

Bathymetry is the study of the depths of water in oceans, lakes, and seas from the surface to the bottom. The depths of the ocean vary greatly, so seafarers and scientists have had to rely on methods to calculate this information.

Bathymetry has been around longer than you might think. The first technique of bathymetry started in ancient times and was used up until the 1870s. This method was to lower a weighted, heavy rope into the water from the side of a ship. The depth of the sea was determined by measuring the length of rope needed to reach the sea floor. This rudimentary method was useful in knowing how deep the water was at one specific point so that the ships wouldn’t run aground on an unsuspecting sandbar. There were many downsides to this method because it didn’t take into account currents in the water that could drag the rope or the movement of the ship. Even in the best conditions, the rope could only determine the depth of one specific point on the sea floor.Measuringoceandepthswithrope

The 19th century was when people started investigating and recording the depths of the ocean for scientific discovery and commercial interests. In 1840, British scientist,  Sir James Clark Ross, used the method of lowering a weighted hemp rope and created the first bathymetric map of the Gulf of Mexico. While not very accurate, this map showed features of the Gulf of Mexico that were unknown prior to this time.

In the 1870s, Sir William Thomson attempted to counter the problems posed with the heavy rope method by inventing the Kelvin Sounding Machine. The Kelvin Sounding Machine was much more sophisticated and used piano wire weighted with a lead sinker, instead of rope and could quickly be dropped to the bottom of the ocean floor, saving a lot of time and effort. As long as a determination of the ship’s forward motion was made, this movement would not skew the results as they did before. One of the downsides to this machine was that it still only measured one singular point in the ocean floor, which was still not an accurate representation of the varying depths of the seabed.

These early methods helped grow the study of bathymetry and inspired future scientists to improve the methods. Check out my blog next month as we explore how technological advances changed bathymetry during the 20th century.