Subscribe to Diving Deeper

Ocean Service Feeds

What is a Podcast?

A podcast is a an audio file published on the web. The files are usually downloaded onto computers or portable listening devices such as iPods or other players.

Read more about podcasting from

Find other podcasts from the US government

Diving Deeper Shorts: Measuring Tides

Episode 18 (Apr. 19, 2012)

HOST: Today on Diving Deeper Shorts, we revisit our interview on how we measure tides and who uses tidal data from June 2010 with Tom Landon from the Center for Operational Oceanographic Products and Services.

Let's listen in.

HOST: Tom, we interviewed your colleague Steve Gill back in April 2009 about tides. Can you remind us what the difference is between tides and currents?

TOM LANDON: Well, it's actually quite simple Kate. Tides are the alternating rise and fall of the water level. It's a vertical movement in oceans, bays, rivers, estuaries, any of the water bodies along the coast. And those vertical water level movements are caused by the gravitational forces of the sun and the moon. Tidal currents on the other hand are the horizontal movement of the water. The speed and direction of the currents in those bodies of water.

HOST: So why is it important to measure tides? Who really uses this tidal data and what do they use it for?

TOM LANDON: Well Kate, there's a wide variety of uses of tidal data. NOAA uses it specifically for hydrographic and shoreline mapping support. We produce all of the nautical charts and they have to have a shoreline reference and they also have to have a reference for the depths.

Ship captains and pilots use both real-time data and averages for real-time navigation support. They want to ensure safe navigation in and out of harbors and they also want to get the most efficient commerce. So they use tide data quite a bit in their travels and one of the things they also refer to in terms of safety is a thing we call air gap, which is the distance between the bottom of a bridge and the water level.

The Army Corps of Engineers uses tide data extensively for all their dredging projects because they have to have a reference datum on how deep to dredge the channel. Coastal engineers use it for any kind of construction project along the coast - bridges, condominiums, bulkheads, anything like that. Ecosystem managers now use tide data extensively for both long-term planning and for special projects such as marsh restoration projects. A good example right now is the oil spill in the Gulf. The people who run the Hazmat group, the hazardous materials response team, they use tide data extensively to map where oil spills are going to travel and what the tide measurements might do in terms of the effect of the oil spill along the coast.

Emergency managers during hurricanes use tide data extensively to both plan for the safety of people and protection of property. Scientists and engineers both use tide data, long-term tide data, to monitor changes in sea level, sea level changes over time and they've been watching that very closely over the last ten years probably and it will become a more and more popular topic as time goes on. And then lastly even fishermen use tide data, they want to know when the best times to go fishing are.

That's all for today's Diving Deeper Shorts, where we highlight a few minutes of your favorite Diving Deeper episodes.

Want to learn more? Go to and select the June 2010 podcast archive to listen to the full interview on measuring tides.

You can catch our next episode in two weeks.