The most usual measurement is that of relative humidity. The measurement is typically done in a shielded but at the same time ventilated surrounding, created by a so-called "radiation screen" see Fischer Barometer and R.M. Young. The humidity measurement is typically combined with a temperature measurement.

Special housings with louvered screens are manufactured by Metspec.

Well known combined humidity/temperature measurements are manufactured by Vaisala and Rotronic.

In general there are 3 different sensor principles. The above methods use absorption of humidity: so called sorption methods.

These methods will work quite well under most circumstances, however when there is a cold climate, where humidity level is low (mountain, polar, or upper air measurements) a condensation method can be recommended. Hygrometers based on this principle are generally called chilled mirror hygrometers. Manufacturers: Meteolabor, Paroscientific and Buck Research. Chilled mirror hygrometers are also used for laboratory and field reference measurements.

The third measurement principle is absorption of electromagnetic radiation by water vapor (ultraviolet and infra red absorption hygrometers). These are used for tracking fast humidity fluctuations.

Calibration equipment is made by Thunder Scientific.

In some occasions a high frequency humidity sensor will be used. Different types are manufactured. Wittich & Visser manufactures a Lyman Alpha hygrometer, Campbell Scientific employs a Krypton Hygrometer and Li-Cor an infra-red hygrometer.

For humidity- or water varour profiles across the boundary layer also microwave profilers and tethered balloons can be used.