Google says it can track every seagoing vessel in the world in real time:
Like its nascent project to map the ocean floor, Google's new technology to track ships on the surface takes advantage of prior investments by others. In this case, it's the Maritime Automatic Identification System, known as AIS, a system of transponders installed in all legitimate seagoing vessels that periodically transmit their position to avoid collisions even when the crews can't physically see each other due to darkness or heavy weather.But AIS can be turned off aboard ships, so this is not really the security threat it might appear to be.
AIS signals are only designed to be detectable up to 20 nautical miles away, but researchers led by Greece's University of the Aegean developed larger, land-based antenna that can pick up the signal over greater distances -- but that still only picks up vessels relatively close to shore. From overhead, however, the two satellites Google is using can detect ships anywhere on the ocean.