Deep-sea robotics: the numbers
Why deep-sea vehicles are hard to build, in figures, with sources.
Pressure
NOAA: For every 33 feet (10.06 meters) you go down, the pressure increases by one atmosphere.
(NOAA Ocean Service)
| Depth | Pressure (bar) | Force on window (tonnes) |
|---|---|---|
| 10 m | 1 | 0.1 |
| 100 m | 10 | 1.0 |
| 1,000 m | 101 | 10.2 |
| 2,000 m | 201 | 20.5 |
| 4,000 m | 402 | 41.0 |
| 6,000 m | 603 | 61.5 |
| 11,000 m | 1106 | 112.8 |
Computed with seawater density 1025 kg/m³ and g = 9.80665 m/s². Real seawater gets slightly denser with depth, so true pressures are a little higher (about 1–2% at 4,000 m).
Navigation without GPS
GPS does not work underwater
, so a submerged vehicle's position estimate drifts until it can surface for a new fix (NOAA Ocean Exploration). Deep vehicles therefore combine dead reckoning (inertial sensors, compass, depth and speed) with acoustic positioning, where sound pulses between the vehicle and beacons or a surface vessel give its range and bearing.
FAQ
- What is the difference between an ROV and an AUV?
- An ROV (remotely operated vehicle) is an uncrewed underwater robot connected to a ship by cables, through which an operator controls it. An AUV (autonomous underwater vehicle) has no tether and follows a pre-programmed mission.
- How does an underwater robot navigate without GPS?
- GPS does not work underwater, because the ocean absorbs the radio signals. Vehicles combine dead reckoning (inertial sensors, compass, depth and speed) with acoustic positioning against beacons or a surface vessel, and correct their position with GPS when they surface.
- How much pressure is there at 4,000 metres?
- About 402 bar above surface pressure, roughly 400 times the air pressure at sea level. On a 10 x 10 cm window that is a force of about 41 tonnes.
ROV and AUV definitions: NOAA Ocean Service.