Communication with Submarines and Underwater Vehicles

- Overview

Communicating with submerged submarines and underwater vehicles (UUVs/AUVs) uses specialized methods because water blocks standard radio waves; methods include Extremely Low Frequency (ELF) radio for deep, slow commands; acoustic modems (SONAR) for shorter-range underwater voice/data (like "Gertrude"); deploying antenna buoys for surface-level radio/satellite comms; and emerging tech like laser/optical or advanced acoustic-RF gateways (TARF) for air-to-water links, balancing stealth with bandwidth needs, with data often stored and forwarded when possible. 

1. Methods for Deep Submerged Submarines (Military): 

• ELF (Extremely Low Frequency) Radio: Uses massive land-based antennas to send signals (like "the message") that penetrate deep into the ocean, allowing subs to receive commands without surfacing, though data rates are extremely slow (minutes for a few characters).
• Satellite/Radio Buoys: Submarines can release buoyant buoys with antennas to send/receive encrypted data via satellite or radio when near the surface, offering much faster speeds but compromising stealth.

2. Methods for Underwater Vehicles & Short Range:

• Acoustic Modems: The primary method for UUVs and AUVs; converts digital data to sound waves (acoustic signals/SONAR) for transmission through water, using modems and transducers.
• Underwater Telephones ("Gertrude"): Uses underwater acoustic waves (voice frequency) for short-range communication between vessels, like a sub and a nearby ship.
• Tethered Links: For ROVs (Remotely Operated Vehicles), a physical fiber optic cable provides high-bandwidth, real-time data and power.

3. Bridging Air & Water (Emerging):

• TARF (Translational Acoustic-RF): Uses surface vibrations caused by underwater sound to allow radar in the air to "hear" underwater acoustic signals, enabling air-to-water communication.
• CUUUWi (Communication Using Underwater Ultrasonic Wireless): Ultrasonic signals can bridge the gap between surface mobile devices/SATCOM and underwater assets.

4. Challenges & Solutions: 

• Water Absorption: Saltwater absorbs radio waves quickly, making deep comms hard.
• Stealth vs. Bandwidth: Deeper comms are stealthier but slower (ELF); surfacing or using buoys offers high bandwidth but increases risk.
• Autonomous Data Handling: AUVs often store data and transmit it when they surface or connect to a gateway, similar to how phones queue messages.

[More to come ...]