The European Space Agency (ESA)'s Traceable Radiometry Underpinning Terrestrial- and Helio-Studies (TRUTHS) mission will provide traceable International System of Units (SI) measurements of incoming solar radiation and of radiation reflected from Earth back out into space, with which to calibrate data from other satellites and to provide high-accuracy Earth’s radiation data to climate modelling scientists.

It will host two main instruments: the Cryogenic Solar Absolute Radiometer and the Hyperspectral Imaging Spectrometer as well as the novel onboard calibration system.

Together, these instruments will make continuous measurements of both incoming and Earth reflected solar radiation. These two observations will be used to evaluate the Earth’s energy-in to energy-out ratio.

Essentially, the amount of incoming solar energy compared to the amount that bounces back to space controls our climate. An accurate knowledge of these energy exchanges is fundamental to understanding and monitoring change.