SME
Oceanography
Ocean basins
Use this for “A ship’s echo sounder hears the ping return 6.4 s after sending it. How deep is the floor, and which part of the basin is that?”
Diagram
The seafloor is 4,800 m under the ship.
This is an example. Type your own values to start a new problem.
d (m)
=
v (m/s)
×
t (s)
÷
2
Formulas
d
=
v
×
t
2
4,800
=
1,500
×
6.4
2
Assumptions
•
The ping goes down and back, so half the two-way time is the trip one way.
•
Sound speed changes with temperature, salinity and pressure by a few percent; 1,500 m/s is the usual mean.
•
Rough depths: the shelf under 200 m, the slope to about 3,000 m, abyssal plains 4,000 to 6,000 m, trenches deeper.
Step-by-step
WE KNOW
t = 6.4 s, v = 1,500 m/s
FIND
depth (d)
Step 1 · Find depth (d)
Use d = v × t ÷ 2
Speed times time is the path down and back; the depth is half of it.
d
=
1,500
×
6.4
2
d
=
9,600
2
d
=
4,800
m
Check
Put the numbers back in. Both sides should match.
4,800
=
1,500
×
6.4
2
✓
Topic check
See what you know: 5 questions on this topic
New questions each time. Pass to mark it complete.