Automatic Weather Observing System(AWOS)

Sources • AC 150/5220-16E - Automated Weather Observing Systems (AWOS) for Non-Federal Applications - with Change 1 – Document Information" • Wikipedia • DBT Transportation Services • U.S. DEPARTMENT OF TRANSPORTATION, FEDERAL AVIATION ADMINISTRATION Air Traffic Organization Policy ORDERJO6560.20C SUBJ: Siting Criteria for Automated Weather Observing Systems Introduction

 Definition  Why  Background  Types and Data Provided  Components  Data Dissemination  Site Requirement  Representative Prices  Next Steps Definition

Automated Weather Observing System (AWOS) is a fully configurable airport weather system that provides continuous, real time information and reports on airport weather conditions. Why Acquire AWOS?

• Safety

• Services

• Revenue Generation Background

• Most AWOS systems are operated, maintained and controlled by state or local governments and other non-Federal entities. • A standard AWOS costs $120,000 to $170,000, plus $5,000 to $7,000 per quarter to maintain. • A standard AWOS is typically classified as AWOS III P/T Types and Data Provided

• AWOS A: barometric pressure and altimeter setting (in inches of Mercury)

• AWOS I: wind speed and wind gusts (in knots), wind direction, variable wind direction, temperature and dew point (in degrees Celsius), altimeter setting and density altitude

• AWOS II: all AWOS I parameters, plus visibility and variable visibility (in miles)

• AWOS III: all AWOS II parameters, plus sky condition (in oktas), cloud ceiling height (in feet), and liquid precipitation accumulation (in inches)

• AWOS III P: all AWOS III parameters, plus precipitation type (rain, snow and sometimes drizzle) identification

• AWOS III T: all AWOS III parameters, plus thunderstorm detection (via a cloud-to- ground lightning detector)

• AWOS III P/T: all AWOS III parameters, plus precipitation type identification and thunderstorm detection. AWOS III P/T Components

Visibility sensor Older - a beam of visible light is Present weather sensor transmitted from its transmitter to receiver head. The extinction (falling precipitation) coefficient is derived from the Ice-free wind sensor amount of light lost in the air. Uses a Light Emitting Diode Weather Identifier (LEDWI) to Older - wind vane and cup Newer - uses a beam of infrared determine if and what type of light which is sent from one end precipitation is falling. The LEDWI Newer - sound waves to of the sensor toward the sensor measures the scintillation measure wind speed and receiver. The amount of light (sparkling) pattern of the direction. The measurement is scattered by particles in the air. precipitation falling through the based on the time it takes for This is then converted to visibility sensor's infrared beam an ultrasonic pulse to travel from one transducer to another AWOS III P/T Components (cont.)

Dew point sensor

Ceilometer Thermometer Utilizes a chilled mirror that is cooled to the point where a fine film of condensation forms on the mirror's Uses an upward-pointing laser Operates under the principle that surface. The temperature of the mirror at this condition beam ceilometer to detect the electrical resistance varies with is equal to the dew point temperature amount and height of clouds. temperature. A platinum wire The laser is pointed upward, resistive temperature device and the time required for measures the ambient air reflected light to return to the temperature. station allows for the calculation of the height of the cloud base. AWOS III P/T Components (cont.)

Thunderstorm sensor Many automated airport weather stations within the United States use the National Lightning Detection Network (NLDN) to detect lightning via the Automatic Lightning Detection and Reporting System (ALDARS). The NLDN uses 106 sensors nationwide to triangulate lightning strikes. Data from the detection Precipitation grid is fed into ALDARS, which in turn sends messages to each Accumulation Freezing rain sensor automated airport station Gauge informing it of the proximity of any Reports freezing rain via the lightning strikes. resonant frequency of a vibrating Essentially a weighing rod. The resonant frequency However, some stations now have their own lightning sensor to gauge. Precipitation decreases with increasing actually measure lightning strikes at the site rather than requiring an continuously accretion (additional mass) of ice, external service. This thunderstorm sensor works by detecting both accumulates within hoarfrost, freezing fog, freezing the flash of light and momentary change in the electric field the collector, and as drizzle, rime, or wet snow. the weight increases, produced by lightning. When both of these are detected within a precipitation is few milliseconds of each other, the station registers a possible recorded. lightning strike. Data Dissemination

• Data dissemination is usually via a VHF frequency (108-137 MHz) at each airport broadcasting the automated weather observation.

• Most automated weather stations also have discrete phone numbers to retrieve real- time observations telephonically.

• In the United States, the AWOS/ASOS Data Acquisition System (ADAS), a computer system run by the FAA, polls the systems remotely, accessing the observations and disseminating them worldwide electronically in METAR format. Site Requirement – 500 Radius Clear Zone

The [wind] sensor must be mounted at 30 to 33 feet (9 to 10 meters) above the average ground height within a radius of 500 feet (150 meters). All obstructions (e.g., vegetation, buildings, etc.) must500’ Clear Zone be at least 15 feet lower than the height of the sensor within the 500 foot radius and be at least 10 feet lower than the height of the sensor from 500 to 1000 feet ( see figure 2-2).

… if difficult to achieve, a less desirable location may have to be selected; however, after installation, the sensor(s) must demonstrate that accurate and reliable information is being provided. If the wind information is not accurate and reliable, resolution is required. Resolution may require that the sensors be relocated or turned off. Wind sensor mounting on the roof of buildings, including an air traffic control tower (ATCT) should be avoided. Turbulent wind flow is present in the vicinity of rooftops. Engineering a structure on an existing building that would be tall enough to account for such turbulent wind flows would be complicated and costly. One Vender’s Prices Next Steps

• Seek Funding

• Canvass Market

• Site Selection / Survey