2.4 Pressure & Acoustics

The Deep Pressure World

Pressure increases rapidly with depthβ€”approximately 1 atmosphere per 10 meters. At the deepest ocean trenches, pressure exceeds 1,000 atmospheres. Sound travels efficiently through water, making acoustics essential for ocean exploration.

Hydrostatic Pressure

$$p = p_0 + \rho g h$$

pβ‚€ = atmospheric pressure, ρ = density, g = gravity, h = depth

10 m(Recreational diving limit)
2 atm
100 m(Technical diving)
11 atm
1,000 m(Twilight zone)
101 atm
4,000 m(Abyssal plain)
401 atm
10,994 m(Challenger Deep)
1,100 atm

Sound in the Ocean

Speed of Sound in Seawater

$$c \approx 1449 + 4.6T - 0.055T^2 + 1.4(S-35) + 0.017z$$

c in m/s, T in Β°C, S in PSU, z in meters

In Air

~340 m/s

In Seawater

~1500 m/s

Ratio

~4.4Γ—

The SOFAR Channel

The Sound Fixing and Ranging (SOFAR) channel is a layer at ~1000m depth where sound speed reaches a minimum. Sound waves are refracted back into this channel, allowing them to travel thousands of kilometers with minimal loss.

Applications

  • β€’ Whale communication across ocean basins
  • β€’ Underwater navigation (acoustic tomography)
  • β€’ Submarine detection and communication
  • β€’ Monitoring seismic and volcanic activity

Sonar Technology

Active Sonar

Emits sound pulse, listens for echo. Used for depth sounding, fish finding, submarine detection.

Passive Sonar

Listens only. Detects ship/submarine noise, marine mammals, seismic events.

← Density & StratificationLight in the Ocean β†’