A humidity sensor is an instrument used to measure relative humidity and dew point. Air temperature measured by thermometers can be used to make the humidity calculations, as well as dry and wet bulb thermometers, at observation stations worldwide before data is used by the Met Office and later accumulated in the MIDAS dataset.

Linked documentation:
The Met Office Fact-sheet #17 – Weather Observations on Land (see linked documentation) describes the instrumentation further and includes diagrams of the apparatus set-up. For more information on which instruments are used to collect measurements within specific station networks, the Met Office Surface Data Users Guide, describes the meteorological surface data and how it is obtained in the Met Office Database - MIDAS.