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CEOS EO HANDBOOK – MEASUREMENTS
Measurements > Atmosphere >
Atmospheric Humidity Fields

The observations for water vapour (atmospheric humidity) are a core requirement for weather forecasting and are largely dealt with in the framework of the Coordinating Group for Meteorological Satellites (CGMS). The 3-dimensional field of humidity is a key variable for global and regional weather prediction (NWP) models that are used to produce short- and medium-range forecasts of the state of the troposphere and lower stratosphere.
Detailed MeasurementDescription*InstrumentsTimeline
Atmospheric specific humidity (at surface)
Link: 		In a system of moist air, the ratio of the mass of water vapor to the total mass of the system. Conventionally measured at 2 m height [Unit of measurement- g/kg]0 instruments
Atmospheric specific humidity (column/profile)
Link: 		Vertical profile of the specific humidity in the atmosphere - Requested from surface to TOA (layers: LT, HT, LS, HS&M) + Total column - Physical units: [ g/kg ] for profile, [ kg/m2 ] for total column - Accuracy unit: [ % ] for profile, [ kg/m2 ] for total column.66 instruments
Water vapour imagery
Link: 		Level-1 product (not a geophysical parameter). Multi-channel imagery covering wavelengths in the range 0.4-14 µm including water vapour bands for atmospheric tracing in clear-air at more levels (e.g., for winds) - Accuracy expressed as Modulation Transfer Function (MTF) at the Nyquist spatial wavelength (twice the resolution). Actually [ MTF-1 ] is used, so that smaller figures correspond to better performance, as usual.2 instruments
* Description adapted from WMO.
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