Electronic or chilled mirror dew point hygrometers offer the highest precision for measuring atmospheric moisture. Through an electronic mechanism, this device uses a chilled mirror to detect condensation on its surface. Created in the 1960s, these hygrometers need regular mirror cleanings and calibrations, as well as a skilled operator to keep high accuracy.
Hair and other materials, such as animal membranes, wood and paper, change dimensions when they absorb moisture from the air. Invented in 1783, the mechanical or hair hygrometer is a popular topic in school science fairs, as it is easily made. The production of hair hygrometers started to decrease in the 1960s, but they are still used when high precision is unnecessary.
Also called a psychrometer, the wet-and-dry-bulb hygrometer consists of two mercury-in-glass thermometers. The bulb of one thermometer is covered with a cloth that is always kept moist via capillary action; the other is kept completely dry. Continuous evaporation of the water from the surface of the wet bulb keeps its temperature lower than that of the dry bulb. The relation between the temperatures marked on the dry and the wet thermometers indicate the air's relative humidity.
Satellites are used to measure humidity on a global scale, which is important in weather forecasting and in the monitoring of climate conditions. The Microwave Humidity Sounder, or MHS, is a satellite designed to scan through the atmosphere, detecting microwave radiation emitted from the surface of the earth. Microwave detection is affected by the quantity of humidity present in the atmosphere. MHS satellites can detect alterations in humidity across the diverse layers of the atmosphere, generating accurate profiles on atmospheric humidity, a factor that also influence temperatures at the surface.