automated surface observation system
automated surface observation system (ASOS)
A surface weather observing system implemented by the U.S. National Weather Service, the Federal Aviation Administration, and the U.S. Department of Defense in the United States. The system is designed to support aviation operation and weather-forecasting activities. The ASOS provides continuous minute-by-minute observation and performs the basic observing functions necessary to generate an aviation routine weather report (METAR) and other aviation weather information. ASOS information may be transmitted over a discrete VHF (very high frequency) or the voice portion of a local navigational aid.