How do submarines know where they are?
Submarines cannot use GPS underwater because radio waves are absorbed by seawater. Instead, they navigate using sonar mapping, fiber optic gyroscopes to determine orientation, and accelerometers to measure movement and distance traveled.
Summary
The transcript addresses how submarines determine their location and orientation underwater, a challenge created by GPS's reliance on radio waves that cannot penetrate seawater effectively. While submarines near the surface can deploy antennas for GPS, this method becomes impossible even a few centimeters below the surface. The transcript outlines three primary navigation methods submarines employ. First, sonar can be used to map the seafloor and compare it against existing maps, though this approach is impractical for submarines attempting to remain undetected due to the loud acoustic signals produced. Second, submarines use fiber optic gyroscopes to determine their heading and rotation. These devices work by sending two beams of light in opposite directions through a fiber optic coil; when the submarine rotates, the different distances traveled by each beam cause them to return out of phase, allowing the computer to calculate the rotation rate. Third, submarines employ accelerometers to measure acceleration and determine distance traveled. These devices use a small weight attached to a vibrating crystalline quartz beam; when the submarine accelerates, the weight's inertia alters the beam's tension or compression, which changes the frequency of vibration similar to how tightening a guitar string raises its pitch. By measuring these frequency shifts, the submarine's computer can calculate acceleration and derive the vessel's position and distance traveled.
Key Insights
- GPS stops working even a couple of centimeters below the water surface because radio waves are easily absorbed by seawater
- Submarines can map the seafloor using sonar and compare it to previously made maps, but this method is impractical for stealth operations due to loud acoustic signals
- Fiber optic gyroscopes determine submarine direction by measuring the phase difference of two light beams traveling in opposite directions through a coil when the submarine rotates
- Accelerometers in submarines use a vibrating crystalline quartz beam where the weight's inertia changes the beam's vibration frequency during acceleration, analogous to how tightening a guitar string raises its pitch
- By measuring tiny frequency shifts in the quartz beam, the submarine's computer can calculate acceleration and determine the vessel's position and distance traveled
Topics
Transcript
[0:00] Here's a question. How do submarines know where they are? I mean, near the surface, they can just stick out an antenna above the water to use GPS. But if the antenna is even a couple of centimeters below the surface, the GPS will stop working because it uses radio waves that are easily absorbed by seawater. So, as an alternative, a submarine can actually use its sonar to map out the seafloor, and then it can compare those maps to maps that [music] were made in the past. But if you're trying to stay hidden in your submarine, blasting loud sonar waves probably isn't [0:30] a good idea. So most submarines rely on something quieter. To work out…
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