Automated Surface Observing System

Automated Surface Observing System
Famartin · CC BY-SA 4.0 · source
Name	Automated Surface Observing System
Caption	A typical ASOS installation at a general aviation airport.
Manufacturer	Multiple contractors for the National Weather Service
Developed	Late 1980s–1990s
Type	Automated weather station
Used by	National Weather Service, Federal Aviation Administration, Department of Defense

Automated Surface Observing System. It is a joint weather observing network in the United States managed by the National Weather Service, the Federal Aviation Administration, and the Department of Defense. The system provides continuous, real-time meteorological data critical for aviation safety, public forecasting, and climatological research. Replacing many manual observations, it forms the primary surface weather observing network across the nation.

Overview

The network serves as the foundational source for surface-based weather observations across the continental United States, Alaska, Hawaii, and several U.S. territories. Primary data users include air traffic controllers at facilities like Denver International Airport and forecasters at offices such as the Storm Prediction Center. Observations are transmitted via the Automated Weather Observing System data link and integrated into numerical models run by the National Centers for Environmental Prediction. The system's design emphasizes reliability and consistency to support operations at locations ranging from major hubs like Hartsfield–Jackson Atlanta International Airport to remote sites in Death Valley National Park.

Components and sensors

A standard installation integrates multiple environmental sensors on a Instrument Landing System or similar platform. Core measurements come from a ceilometer for cloud height, a present weather sensor for precipitation type, and a transmissometer for visibility in fog. Temperature and dew point are measured with a hygrothermometer, while wind speed and direction are detected by an anemometer and wind vane. A tipping bucket rain gauge measures liquid precipitation, and a freezing rain sensor activates during winter storms. Pressure data is derived from a barometer, and a lightning detection network like Earth Networks provides supplementary information. All sensors connect to a central data collection platform for processing.

Deployment and network

Over 900 systems are installed nationwide, with dense coverage at facilities overseen by the Federal Aviation Administration such as Chicago O'Hare International Airport and Los Angeles International Airport. The Department of Defense maintains systems at bases like Naval Air Station Pensacola and Edwards Air Force Base. The National Weather Service coordinates sites in support of the Advanced Weather Interactive Processing System at forecast offices from the Weather Forecast Office, Miami to the Weather Forecast Office, Seattle. Installations follow strict siting criteria to avoid obstructions from structures like the Willis Tower or terrain features in the Rocky Mountains.

Data products and applications

Generated reports, known as METAR and SPECI, are disseminated globally via the Aeronautical Fixed Telecommunications Network. This data is vital for issuing Terminal Aerodrome Forecasts and supporting the Next Generation Air Transportation System. Meteorologists at the Aviation Weather Center and the National Hurricane Center utilize the information for warnings and forecasts. The long-term record supports climate change studies conducted by the National Climatic Data Center and informs projects like the U.S. Climate Reference Network. Data also feeds public-facing platforms such as NOAA Weather Radio and the Integrated Public Alert and Warning System.

History and development

Planning began in the late 1980s following initiatives by the National Research Council to modernize the National Weather Service. The initial contract was awarded in the early 1990s, with systems becoming operational by the mid-1990s, coinciding with the deployment of the NEXRAD radar network. Key development involved collaboration between the National Oceanic and Atmospheric Administration and contractors like AlliedSignal. The system officially replaced the older Automated Weather Observing System and many manual observations performed by personnel at locations like the National Meteorological Center. Upgrades have continued, integrating new sensor technologies from companies like Vaisala.

Operational considerations

While highly automated, the system requires regular maintenance by technicians from organizations like the NOAA Commissioned Officer Corps. Observations can be augmented by certified human observers from the Air Force Weather Agency or Naval Meteorology and Oceanography Command during significant events like Hurricane Katrina. Limitations include sensor icing during nor'easters affecting Boston Logan International Airport or dust contamination in regions like the Mojave Desert. Data quality is monitored by the Meteorological Assimilation Data Digest System, and backup power is essential for resilience during events like the 2003 Northeast blackout.

Category:Meteorological instrumentation and equipment Category:Aviation meteorology Category:National Weather Service