1. Mapping
Technology

2. Lead Line Method
Oldest method in which a weighted line is lowered into the ocean until it touches the ocean floor.

3. Echo-sounder
Older method in which a beam of sound waves is bounced off the ocean floor to measure water depth.
Accuracy affected by pitch & roll of boat, temp. differences, gaps in points.

4. Multi-beam Sonar Uses a row of many beams to collect
data on a wide swath of the seafloor,
rather than a single line. Swath is 3x’s as
wide as the depth of the water.
Computer controlled, so
movement of the ship doesn’t affect the data.

5. Thimble Shoal Channel between Islands 1 2 of the Chesapeake Bay Bridge-Tunnel

7. Seismic Profiling
Uses powerful shock waves to map rock structures under the sediment.
Different frequencies
will penetrate to
different depths.
Note: Before doing this
scientists have to listen
for any marine mammals
in the area.

8. Side Scan Sonar
Provides useful pictorial info, but no numerical data. A “fish” is towed behind a vessel sending out sonar waves.
It reports the strength of the return, providing some approximation of the bottom material conditions.

9. Sidescan sonar taken near Island 4 of the Chesapeake Bay Bridge-Tunnel

11. A plane wreck found at the bottom of a lake during a routine, practice
sweep of a lake bottom using side-scan sonar.

12. Click here and let’s see them at work…

13. Sea-Surface Altimetry
Satellite uses radar to measure the height of the sea surface, which reflects the shape of the sea floor.
Higher elevations, like
mountains, have more
mass so their gravity
attracts a water bulge
up to 30 m high.