What’s the difference between hydrography and oceanography?

The fields of oceanography and hydrography have areas that overlap in their study of the ocean. However, hydrography’s goal is navigation safety, while oceanography branches off into many different disciplines, with many different underlying goals.

Some historians consider oceanography an offshoot of hydrography. Oceanography is a relatively new scientific field, only established over two hundred years ago, while navigators have been making charts of the ocean and its adjacent lands for hundreds of years longer.

A scuba diver swims above a coral reef, with a group of small fish visible in the clear blue ocean water.

A diver collects data on the condition of coral reefs in the Mariana Islands as part of the National Coral Reef Monitoring Program. Since the goal behind this effort was conservation rather than navigation, this effort would fall under the field of oceanography.

Oceanography is truly interdisciplinary because it’s the study of many topics and systems. Biological oceanographers and marine biologists study ocean plants, animals, and ecosystems. Chemical oceanographers explore seawater’s composition and the processes that affect it. Geological oceanographers investigate the seabed and the processes that form underwater mountains, canyons, and valleys. Physical oceanographers study the ocean’s waves, currents, eddies, and tides, as well as coastal erosion, the transport of sand on and off beaches, and interactions between the atmosphere and the ocean.

Certain aspects of oceanography are essential to hydrography; for instance, physical oceanographers may study water density to understand how it affects ocean currents. Hydrographers also need to determine the ocean’s water density, so they can obtain accurate measurements of the seabed when they create nautical charts.

A NOAA research vessel at sea with a small yellow buoy floating in the foreground under a cloudy sky.

In July 2018, the NOAA Ship Fairweather made the first successful launch of an uncrewed surface vehicle, or USV, for an operational hydrographic survey from a NOAA vessel in an area of the Arctic that had never been surveyed. NOAA partnered with the University of New Hampshire’s Joint Hydrographic Center to explore the use of USV for hydrographic data collection.

Both oceanographers and hydrographers are concerned with predicting how the physical conditions of the ocean and adjacent lands may change over time. While a biological oceanographer may be concerned with how these changes may impact ecosystems, like coral reefs, hydrographers are concerned with how these changes will affect safe navigation.