Sounding party off USCS Brig FAUNTLEROY. 1857-Earliest picture of Coast Survey sounding operations. Watercolor by James Madison Alden, nephew of Lieutenant Commanding James Alden.
“At about 9 p.m., I felt the vessel graze the bottom... I grabbed my cap, and rushed up the steps leading to the spar deck... and immediately afterward heard the most dreadful and agonizing sounds as the ship hurled herself on the reef... the call of the boatswain: ‘All hands prepare to abandon ship,’ I heard above all of this din. I could hardly walk the decks; the pounding and jumping of the ship swaying me from side to side."
- Capt. R. O. Crisp on the loss of the revenue cutter Tahoma after hitting an uncharted reef on the south side of the Aleutian Islands, Alaska on September 20, 1914
If Alaska had been a U.S. state in 1914, the reef that wrecked the Tahoma might have been on Captain Crisp’s navigation charts. This is because more than a hundred years earlier, in 1807, President Thomas Jefferson established the Survey of the Coast to chart the U.S. coastline to make the coasts of our nation safe for navigation. A top priority of the Coast Survey was (and is) to create charts that show the shape of the coasts, currents, and the depth of coastal waters. Gathering information needed for these charts is called “hydrography,” and people who do this work are known as “hydrographers” (“hydro” means water, and “grapher” is one who writes).
Today, hydrographers working for NOAA’s Office of Coast Survey continue the work begun by the Survey of the Coast. These scientific nomads travel around the coasts collecting information needed for up-to-date charts that guide ships in and out of U.S. ports. The most basic job of hydrographers is taking measurements of water depth (called “soundings”).
Modern hydrographers use sidescan and multibeam sonar and satellite-based global positioning systems (GPS) to produce very detailed pictures of the sea floor. For many years though, hydrographers used lead lines to make depth measurements. A lead line is a rope or line with a 10-pound lead weight attached to the end. The hydrographer lowers the line into the water until the weight reaches the bottom. Markings on the line show how much line has been let out, which is equal to the depth of the water. Depth soundings made with lead lines are accurate, but they take a lot of time and only give information about single points of the sea bottom—so many lead line measurements are needed to accurately survey a given area.
Here’s a way to get a feel for hydrographic surveying with a lead line—and you don’t even have to get your feet wet!
This activity is most challenging if you have one or more friends who also make a sounding box and set up a model seafloor inside the box. Then you can trade sounding boxes and compete to see who can discover everything on an unknown seafloor.
For each sounding box you will need:
The Coast Mappers by Taylor Morrison
Mapping the Seas by Walter Oleksy
Maps and Globes by Harriet Barton
The Story of Maps and Navigation (Signs of the Times) by Anita Ganeri
Small Worlds: Maps and Map Making by Karen Romano Young
NOAA’s Office of Coast Survey homepage: nauticalcharts.noaa.gov
NOS’s hydrographic survey page: oceanservice.noaa.gov/facts/hydrography.html
Take a look at historical maps and charts: historicalcharts.noaa.gov/about.php