How do the pros measure humidity? I have used a wet/dry bulb setup to estimate humidity, and it appears that the Argentinian meteorological service uses one in Antarctica as well.

Wikipedia sez:


  Humidity measurement is among the more difficult problems in basic metrology. According to the WMO Guide, "The achievable accuracies [for humidity determination] listed in the table refer to good quality instruments that are well operated and maintained. In practice, these are not easy to achieve." ...Hygrometers must be calibrated in air, which is a much less effective heat transfer medium than is water, and many types are subject to drift so need regular recalibration. A further difficulty is that most hygrometers sense relative humidity rather than the absolute amount of water present... 


Question: In practice, how do weather reporting stations measure humidity? Is there a difference between remote locations and those where people visit regularly? Does there tend to be a difference between instruments used in arctic and tropical conditions?
The WMO report Instruments and Methods of Observation has a chapter on Measurement of humidity and a separate chapter on Measurement of upper-air pressure, temperature, humidity. The first deals with instruments used for surface measurements. The second deals with instruments used for measuring vertical profiles, which have to deal with a larger range of temperatures and pressures.

For the surface instruments they list:


Gravimetric: take an air sample, extract all the water and weigh it (typically  used for calibration);
Chilled mirror: dewpoint or frostpoint: used for observations and for calibration;
Salt-solution: matching vapour pressure of a salt solution to atmospheric vapour pressure: used in automated weather stations;
Psychrometric: comparing wet or ice bulb temperature with actual temperature - used in observations and calibration;
Sorption methods: using hair or an alternative which stretches when wet, or using a material with a electrical resistance or capacitance that changes when wet.


In other words, the professionals use a lot of different methods.