Question for ATC Met Observers

[MightyGem]

In this modern age, are temperature observations still taken from mercury thermometers in a Stevenson screen, or have electronic sensors taken over?

[Grandad Biggles]

I guess it varies from palce to place At EGTC we still have the Stevenson Screen

[niknak]

Every airport still has a Stevensons Screen - there's no other way that I know of getting accurate temperature readings.
The vast majority now get the temperature readings displayed on automated readouts via the electronic wizardry from the screen to the tower, giving temperature/dewpoint and relative humidity - amongst other things.

[MightyGem]

Thanks, just checking my facts for a briefing.

[EastCoaster]

We use both - the electronic wotsits for all the regular obs, but the oldy-worldy mercury thermometers in the Stevenson screen are maintained as a backup in case of failures, and also for comparison to make sure the new-fangled ones are workin right!

[Dont tell um pike]

Heres the unpleasant technical answer.....Enjoy !

Taken from CAP 746 which is utterly thrilling (onist)

5 Requirements for Temperature and Dew Point Measurement

5.1 Introduction
This section details the performance criteria and siting of temperature and dew point measuring equipment installed at UK aerodromes.

5.2 Siting
The sensors should be mounted at a height of 1.25 to 2 metres, above an earth or grass surface. The sensors shall be exposed in an instrument housing, which provides protection from atmospheric radiation and water drops either as precipitation or fog.

5.3 Performance

5.3.1 The equipment shall be capable of measurement to an accuracy better than plus or minus 1.0 degrees Celsius for air temperature and dew point, over the following range:

Table 7 Tolerance values of sensors and equipment

Variable - In Tolerance-Operating Range-Recoverable Range
Temperature - minus 25° C to plus 50° C minus 30° C to plus 70° C
Humidity - 5 to 100% RH condensing 0 to 100% RH condensing



NOTE: Dew point shall be displayed for temperatures below zero; frost point should not be displayed.
5.3.2 Temperature and dew point measurements shall be measured to a resolution of 0.1 degrees Celsius.
5.3.3 Electronic sensor(s) shall be sampled at minimum of once per minute.
5.4 Backup
Alternative sensors may be used and mounted in an appropriate location on the aerodrome for use e.g. in a screen attached to the North facing wall of the observer’s building. The accuracy of the sensor shall be capable of measurement to an accuracy better than plus or minus 1.0 degrees Celsius for air temperature and dew point.

DTUP :8

So in short screen YES mercury NO

[TheOddOne]

As Far As I Know, there is now NO Stevenson screen at LGW. We have 2 automated weather stations supplied by Vaisala and owned/operated by National Air Traffic Services (NATS). This data is fed to a PC in the Tower and also to the Met Office at Exeter. This forms the Semi Automated Met Observation System (SAMOS). An Assistant in the Tower looks at the data displayed on the screen to make sure that it makes sense compared with the view out of the window. This data is then allowed to update the Aerodrome Terminal Information System (ATIS). At this stage, any further remarks can also be added to the ATIS messge. The data transmitted to the Met Office becomes the MET Actual Report (METAR).

The lovely patch of grass that the Stevenson Screen stood on in front of the Met Observer's building is now a sea of mud and is occupied with garbage skips. The Met Observer is likewise long gone. Sic Transit Gloria Mundi.

Cheers,
TheOddOne