Features of the Seafloor

How do we know what’s down there?

Studying the ocean and the seafloor is incredibly difficult.  It's not like we can strap on a backpack and go for a walk!  Humans are not adapted to exist in an aqueous environment.  We need special equipment to study the oceans.

That hasn't stopped people from trying. 

Sounding weights have been used for thousands of years by sailors to measure the depth of the ocean.  The weight can be a stone or other heavy object that is tied to a rope that is knotted off at regular intervals, then is lowered into the ocean to check how deep the water is.  Or isn't, as most were used to make sure the water was deep enough for the boat to sail in.

Leadline surveys work like sounding weights, but with small bits of lead instead of stones. 

Echo sounding is a method of measuring seafloor depth using powerful sound pulses. There are many conditions that can cause echo sounders to produce inaccurate data.  Another problem is that it only measures the depth in one location.  Imagine you're in a dark, windowless room, and all you have to help you get to the door is one flashlight.  You'll be able to find your way, but the flashlight only illuminates a small area at a time.

Now, imagine you have several flashlights.  The light illuminates a larger area, allowing you to see more and in greater detail.  That is one of the differences between sounding weights/leadline surveys/echo soundings and multibeam systems.   Multibeam systems can provide more accurate measurements than echo sounders do, and can collect data from as many as 121 beams to measure the contours of the ocean floor.  Not only do you see a larger area, but in 3D.

Satellite Altimetry measures the sea surface height from orbit. Satellites can bounce 1,000 pulses of radar energy off the ocean surface every second.  In addition, they can be used to measure various conditions on the ocean surface, including current speed, water temperature, and wave height. Radar altimetry can be used to estimate water depth and therefore features on the seafloor

There is a vast array of other tools as well, tailored to the specific need of the area of study.  NOAA's "Ocean Explorer: Observing Systems and Sensors" page provides a good list of some of the equipment they use to study the oceans.

Why Study the Oceans?

Our planet is over 2/3rds water - and only 5% or so of the seafloor has been explored.  The ocean does a lot for Earth:  it's an integral part of the hydrologic cycle, moderates the planet's climate, is a carbon sink, and the phytoplankton that call it home produce most of the oxygen we breathe.

In March 2014, Malaysian Airlines flight MH370 disappeared on its way to Beijing from Kuala Lumpur.  An exhaustive search failed to find the plane, but it yielded a wealth of information about the seafloor that we didn't know before.

The image below shows the level of detail for both satellite-derived bathymetry (fuzzy areas at the top left and bottom right) and multibeam bathymetry.  Search teams used the more detailed multibeam imagery in areas where they thought the plane might be.  In doing so, they were able to map in detail features like debris flows and landslide scarps.

Below are two videos, both on ocean exploration in general, and the NOAA Ship Okeanos Explorer.   The first video is from just before the Okeanos Explorer was launched, and Dr. Ballard discusses what he hopes we will learn from its voyages.  The second celebrates the Okeanos Explorer's ten-year anniversary.   As you watch both, note the following:

• Has the Okeanos Explorer lived up to it's potential?
• In what way(s) has the Okeanos Explorer changed ocean exploration?