The Microwave Humidity Sounder (MHS) detects microwave radiation emitted from the surface of the Earth. As the radiation passes through the atmosphere, it is partially absorbed by the moisture in the atmosphere (such as cloud cover, precipitation and ice crystals); hence the signal received at the MHS instrument is attenuated. By sampling at different frequencies, the apparent attenuation at different layers in the atmosphere can be determined, from which an atmospheric humidity profile can be derived.