Automated airport weather station

In the United States, there are several varieties of automated weather stations that have somewhat subtle but important differences.

[3] The AWOS-C is the most up-to-date FAA owned AWOS facility and can generate METAR/SPECI formatted aviation weather reports.

The measurement is based on the time it takes for an ultrasonic pulse to travel from one transducer to another, which varies depending on - among other factors - the wind speed.

NWS and FAA ASOS stations and most of new AWOS installations are currently equipped with ultrasonic wind sensors.

Automated airport weather stations are not yet able to report hail, ice pellets, and various other intermediate forms of precipitation.

Automated airport weather stations do not have a separate sensor for detecting specific obscurations to vision.

Instead, when visibility is reduced below 7 statute miles, the system uses the reported temperature and dew point to determine an obscuration to vision.

If relative humidity is low (i.e., there is a large difference between the temperature and dew point), haze is reported.

If relative humidity is high (i.e., there is a small difference between the temperature and the dew point), mist or fog is reported, depending on the exact visibility.

[13] Automated airport weather stations use an upward-pointing laser beam ceilometer to detect the amount and height of clouds.

The laser is pointed upward, and the time required for reflected light to return to the station allows for the calculation of the height of the cloud base.

Automated airport weather stations use a temperature/dew point sensor (hygrothermometer) designed for continuous operation which normally remains on at all times, except during maintenance.

The hygrometer measures the dew point by directing a light beam from a small infrared diode to the surface of the mirror at an angle of 45 degrees.

The electronics continuously tries to stabilize the signal levels to the power amplifier to maintain the mirror temperature at the dew point.

To ensure safe separation from terrain and other obstructions, high degree of accuracy and reliability is required from a pressure sensor.

The original precipitation accumulation measuring device used for automated airport weather stations was the heated tipping bucket rain gauge.

The collector, which is heated to melt any frozen precipitation such as snow or hail, funnels water into a two-chamber, pivoting container called a bucket.

That amount of weight causes the bucket to tip on its pivots, dumping the collected water and moving the other chamber under the funnel.

[17] Automated airport weather stations report freezing rain via the resonant frequency of a vibrating rod.

Data from the detection grid is fed into ALDARS, which in turn sends messages to each automated airport station informing it of the proximity of any lightning strikes.

This thunderstorm sensor works by detecting both the flash of light and momentary change in the electric field produced by lightning.

This can be either due to physical damage (either natural or human caused), mechanical wear, or severe icing during winter weather.

Research is also ongoing to produce more robust systems which are less vulnerable to natural damage, mechanical wear and icing.