ICOA, WMO, and FAA(NOAA) standards apply, as well as regional interpretations.
There is usually more than one sensor (anemometer) position, but all measure the wind velocity at the standard height of 10 meters above the surface.
METAR Wind Velocity
Wind velocity in a METAR is stated as the measured or estimated mean of each component over the 10 minutes prior to the time of issue of the METAR, unless there are significant variations during this 10 minute period. For direction, this means 60 degrees or more of arc but less than 180 degrees provided that the mean speed during the previous 10 minutes has been more than 3 knots.
In the case of speed, variations from the mean wind speed (both above and below it) are reported when the variation from the mean speed has exceeded 10 kts. Such variations are expressed as the maximum and minimum speeds attained and must also be included if the maximum wind speed in a 10 minute period has exceeded the 2 minute average wind speed at the same location in that period. Any gust value which has occurred in the most recent two minute period will of course also be part of the calculation of average wind speed
ATIS Wind Velocity
ATIS wind velocity is latest two minute average. The wind direction broadcast is given in degrees true. The mean wind speed is supplemented by the value of the highest and lowest gusts within the 10 minutes prior to issue time if either exceeds the METAR-specified minimum difference increment away from the mean.
ATIS broadcasts are usually only updated between the regular change times if the wind direction changes by more than 30 degrees or the 2 minute average wind speed changes by more than 5 kts over a five minute interval.
ATC Wind Velocity Reports
Display of wind velocity information to ATC at major airports usually allows at least the reporting by RTF of both the ‘average wind’ - that over a two minute period updated every minute - and ‘instant wind’ - the value at that exact time. The latter is usually used only where high wind speeds and their associated greater fluctuations in speed and direction prevail.