US naval observation (USNO)

US Naval Observation (USNO) is the American National Measurement Institute ( NMI), which manages the atomic frequency standard and the official time reference for the USA. For the exact determination of time, the institute works with more than 50 atomic frequency standards, about 40 caesium standards and more than 10 hydrogen masers.

The USNO supplies all relevant applications with time references and transmits the time signals via satellites and via terrestrialtransmitters.