monitoring:weather=yes は man_made=monitoring_station との組み合わせで、測候所（気象観測施設）を示します。気象観測ネットワークはふつう政府機関によって運営されていますが、私的機関によって運営されるものも増えており、趣味の気象観測者もいます。私的な測候所は地面に固定されていない場合あり、 OSM の検証可能性の原則に合わないことがあるので、公的な測候所について行います。以下では、公的な測候所に基づいて説明します。
WMO recently launched OSCAR/Surface (Observing Systems Capability Analysis and Review Tool) that aims to replace the old WMO Volume A station inventory. You can search for stations and get their metadata. Please note that the identifier displayed there under "WMO index No" represents the ref:wigos=* identifier but not the old WMO station identifier ref:wmo=*. The WMO station identifier is often part of the WIGOS identifier as last 5 digits.
If known, these tags should definitely being added as they add valuable information.
- name=* - stations normally have the name of the city/town or facility (airport) where they are located, this name should be always in the country's language and alphabet (e.g. Палић for Serbian station 13067)
- int_name=* - provide a transliteration/romanization for name=* if necessary (e.g. Palić for Палић), in addition add a proper name:lang_translit tag to specify the transliteration scheme used (see also Multilingual_names)
- ref:wmo=* - WMO associates a unique id to each registered station (e.g. 11035). To each country a range of ids is allocated. This id makes it possible to map transmitted weather data to a particular station.
- ref:wigos=* - The above mentioned WMO station identifier is currently phased out and being replaced by the WIGOS (WMO Integrated Global Observing System) identifier.
- ref=* - if no ref:wmo is available, other identifiers used to associate data with the station.
- ref:icao=* - ICAO associates a unique identifier to each airport (e.g. LOWW). The first two characters identify the region and often also the country. If the station is located at an airport this identifier should be added since METARs contain this identifier and this allows to map them to a particular station.
- ele=* - elevation information helps in performing reducing pressure values to mean sea level for comparability (see Mean sea level pressure for details).
Note on callsigns: Some agencies use callsigns for their non-airport stations that mimic the ICAO codes. These should NOT be tagged with ref:icao=*. Instead another key ref:*=* should be used, if these callsigns need to be added. Often this is not necessary as they have only local importance.
Note on elevation information: Often station listings mention two different types of elevation information (WMO calls it Hp - elevation of the station - and Hha - ground elevation or altitude of aerodrome). Often the barometer is located within the Stevenson screen so the two values deviate only by few meters (as temperature is measured 2m above ground). Sometimes the barometer is somewhere else e.g. on the roof of a building, so there could be more deviation. For ele=* always the ground elevation (or Hha) should be used as this corresponds to the normal usage on OSM.
- operator=* - mentioning the operating agency helps in classifying stations, abbreviations should be used
- fixme=* - indicating necessary improvements, if data is missing or if position is not precise etc. (e.g. fixme=position if position is not exact).
Weather monitoring stations normally monitor more than one parameter at once. There are radar stations, dedicated stations for monitoring precipitation (often operated by hydrological agencies and often measuring also temperature for diffentiating between rain and snow), radiosonde locations and normal weather stations (which often measure temperature, humidity, pressure, precipitation, wind and sun duration). Standard monitored parameters may differ between countries. An overview over instruments of a common U.S. airport station can be found at wikipedia.
- weather:barometer=yes/no - barometers are used to monitor atmospheric pressure, located within the Stevenson screen or elsewhere (e.g. in Austria located within station switchboard).
- weather:ceilometer=yes/no - a ceilometer is used to monitor the height of a cloud base (it is also possible to monitor aerosol concentration). This instrument is often used at airports.
- weather:humidity_sensor=yes/no - to measure relative humidity, often capacitive or resistive sensors that are cheaper than psychrometers (see below) are used in private weather stations. Psychrometers are often used in official monitoring stations.
- weather:psychrometer=yes/no - a psychrometer is used to monitor dew point temperature and compute relative humidity, mostly located within the Stevenson screen; most sophisticated automated solutions use chilled mirror dewpoint psychrometers, cheaper humidity sensors include capacitive or resistive sensors (see above).
- weather:lightning_detector=yes/no - a lightning detector monitors lightning activity by observing the arrival of electro-magnetic waves produced by lightning at the detectors and calculating runtime differences to compute locations. Lightning detectors are often separate from normal weather stations and are also often operated by different agencies (e.g. ALDIS in Austria is a joint venture of the Austrian power transmission grid provider and the Austrian electrotechnical association).
- weather:ombrometer=yes/no - an ombrometer monitors liquid precipitation and has the form of a bucket. There exist also dedicated ombrometers often operated by hydrological agencies that measure temperature in addition to distinguish between snow and rain.
- weather:precipitation_indicator=yes/no - stations often use infrared beams to determine if there is currently falling precipitation. Some instruments may also be able to distinguish between types of preciptiation. Precipitation indicators can be necessary in cases where precipitation amount is too low to be recognized by ombrometers.
- weather:radar=yes/no - weather radar is used to monitor the horizontal and vertical distribution as well as the type (rain, drizzle, snow, hail) of precipitation.
- weather:snow_height_sensor=yes/no - automated snow height sensors operate with ultrasound.
Solar/Direct/Atmospheric radation (Sun Duration)
- weather:pyranometer=yes/no - a pyranometer is used to monitor solar irradiance. This instrument is often mounted on a pole or tower. Sunhine duration can be computed from irradiance values (exceeding 120 W/m2).
- weather:pyrgeometer=yes/no - a pyrgeometer is used to monitor atmospheric infra-red radiation. It measures downward long wave radiation and so a radiation balance between surface and atmosphere can be computed.
- weather:pyrheliometer=yes/no - a pyrheliometer is used to monitor direct beam solar irradiance. This instrument is often mounted on a pole or tower. Using this instrument for monitoring sunshine duration is more exact than computing it from pyranometer values (see above).
- weather:grass_minimum_thermometer=yes/no - to monitor ground temperature and detect ground frost, the thermometer is placed 5 cm above a grassy surface.
- weather:soil_thermometer=yes/no - to monitor soil temperature often in different depths.
- weather:thermometer=yes/no - a thermometer is used to monitor air temperature 2 m above ground and is located within the Stevenson screen.
Vertical Layering of Atmosphere
- weather:radiosonde=yes/no - radiosondes are basically weather balloons to monitor the vertical layering of the atmosphere. Radiosonde locations are often at airports as the vertical structure there is important for landing or starting aircraft. Radiosondes monitor different variables at once (such as temperature, pressure, wind speed/direction). Often they are tracked through GPS or radar. Radar for tracking radiosondes may look like precipitation radar on aerial imagery (like the radiosonde radar at Wien-Hohe Warte).
- weather:forward_scatter_sensor=yes/no - a forward scatter sensor is mostly used to monitor runway visual range at airports, but can be used to monitor visibility in general. Another instrument used for this purpose are transmissometers (see below).
- weather:transmissometer=yes/no - a transmissometer is mostly used to monitor runway visual range at airports, but can be used to monitor visibility in general. Another instrument used for this purpose are forward scatter sensors (see above).
- weather:anemometer=yes/no - to monitor wind speed and wind direction (not necessary to differentiate between wind speed and wind direction as the professional standard are now ultrasonic anemometers which monitor both variables by design). Often located on a pole or tower as wind is monitored 10 m above ground.
Note on instrument names: There are two ways of indicating the equipment of a weather station: naming the instruments or naming the variables that are monitored. Both ways have drawbacks as there are different ways of measuring a variable and this may lead to more choices and possible inconsistency. However, naming instruments has some advantages. First, with naming variables (e.g. precipitation) there is no way to distinguish between precipitation indicators, ombrometers and also precipitation radars. Second, naming instruments captures also quality differences as e.g. psychrometers are more exact than capacitive or resistive humidity sensors.