Ever since humans began crossing bodies of water, there have been tools to help us do so safely. Although earlier depth-measuring techniques are rudimentary in comparison to the advanced techniques NOAA uses today, they still managed to do their primary job: figure out how deep a certain area of water might be. Here are a few examples of approaches that have been applied over the years…
Sounding Pole: This might be a practical method for determining the depth of a smaller body of water such as a river, as the ancient Egyptians did with the Nile, but by no means would poking a stick deep into water help us determine the depth of something like the ocean. Even today people may use a sounding pole in order to determine the depth of a shallow body of water.
Lead Line: Likely used by the ancient Greeks and Egyptians (and used up through 1930), this method involved attaching a weight to a line of rope or wire and then measuring how far it went before hitting the bottom. Accounts of this method have appeared in early Greek texts as well as the Bible.
Echo Sounder: It wasn’t until 1913 that humans figured out how to use sonar technologies, but we didn’t use this acoustic sounding technique to measure ocean depth until 1924 when NOAA’s precursor, the U.S. Coast and Geodetic Survey, installed a single beam echo sounder on one of its ships. Even after that, many surveys were still conducted with lead lines until early 1940.
Today, NOAA still uses echo sounder technology to chart the ocean, but now they use advanced multi-beam echo sounders as opposed to the single beam sounders used throughout the 20th century. Even with the most accurate technology available, areas must be resurveyed frequently due to gradual shifts in the ocean that occur over time. Thankfully, the OceanGrafix print-on-demand charts are based on the very latest information available.