ESA’s FORUM mission is an upcoming Earth Explorer mission which will provide new insight into the Earth's radiation budget and how it is controlled. FORUM will be able to measure radiation with wave lengths longer than 15 microns in the infrared spectrum, which has never been done before from space, allowing the detection of water vapour and ice clouds absorption features in the atmosphere.

Water vapour is the largest single greenhouse gas and also a carrying mechanism transporting energy around the globe, making it a major driver of weather patterns.

Only space-based monitoring can measure water vapour concentrations on a global basis, either measuring vertical columns of water vapour or assessing atmospheric humidity through a cross section of the atmosphere. Detailed mapping of water vapour promises to help increase the accuracy of weather predictions, especially for rainfall. Water vapour is also important as a chemical compound, both in the troposphere as a source of the hydroxyl radical, the most important oxidant in the troposphere, and in the stratosphere where it has an influence on ozone depletion, especially in the Polar Regions.

Water vapour can be measured with a multitude of different techniques including passive microwave sensors, Infrared sensors, Ultraviolet/visible/near-infrared imagers, and Limb sounding, as well as in-situ techniques such as balloons and sensors aboard commercial aircraft.

Featured Educators

• Dr Hilke Oetjen, Forum Mission Scientist, ESA

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