Hydrography: The Survey Work Behind Every Safe Voyage

Every ship that reaches port safely depends on work done long before it sailed. Hydrography — the science of measuring and describing the physical features of navigable waters and the coasts beside them — tells mariners how deep the water is, what the seafloor looks like, and where the dangers hide.

By mapping water depth, the shape of the seafloor and coastline, possible obstructions and the physical features of water bodies, hydrography keeps the maritime transportation system moving safely and efficiently. Credit: NOAA.

What hydrographers do

Hydrographic surveyors study bodies of water to see what the "floor" looks like. They measure water depth and search for shoals, rocks and wrecks that could endanger navigation. They also collect information on:

• water levels and tides
• currents
• temperature
• salinity

How the survey is done

The main tool is the multibeam echo sounder. As the ship passes over the survey area, its beams sweep the seafloor, bounce off the bottom and return to the ship, where the depth is recorded.

A hydrographer studies multibeam sonar data to build a 3-D image of the floor of Kachemak Bay. Credit: NOAA.

What the data becomes

NOAA's Office of Coast Survey conducts hydrographic surveys of U.S. waters and uses the data for two main products:

• Nautical charts — the essential maps for safe marine navigation.
• Hydrographic models — baseline data for research and for marine geospatial products and services.

The surveys also feed NOAA's Integrated Ocean and Coast Mapping program, which supports building structures on the seafloor, laying pipelines and cables, dredging, anchoring and understanding fish habitats.

By the numbers

Sources

Based on "What is hydrography?" from NOAA's National Ocean Service, a work of the United States government in the public domain.