A snow depth sensor is an electrically-powered active device with on-board data-processing that measures the distance between the sensor and the ground surface beneath it.

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.