TRUTHS (Traceable Radiometry Underpinning Terrestrial- and Helio- Studies) is a proposed European Space Agency Earth Watch mission with profound implications for the calibration of data from a wide range of missions. Assimila is working with colleagues in the UK academic sector to examine requirements and advise on the implications for mission design.

TRUTHS will enable a significant upgrade of the performance of the global space-based Earth Observation system. The mission aims to improve by an order of magnitude, our ability to measure radiation coming from the Sun hitting the Earth and the component that is reflected by the Earth system back into space. The satellite will provide a so-called “climate-benchmark” dataset through direct measurement, and will also be used to cross calibrate other satellites and improve the overall data quality from the EO system. The novel aspect of the mission is that it will be the first time SI traceable measurements are made in space.

As part of its preparation for the mission, ESA needed a User Requirements Document. This was prepared by Assimila Limited as part of an international consortium led by the National Centre for Earth Observation at the University of Leicester.

Our main tasks were to define the user community, in the context of an ESA EarthWatch mission; develop a questionnaire to probe how the user community might use the data and to ascertain detailed requirements; and hand the information over in a structured way to colleagues at Imperial College who, in turn, looked at the potential impacts of user requirements on the mission design.

Given that TRUTHS will be the first metrology laboratory in space, its applications and consequences are likely to be far reaching. This user requirements project showed that the known user communities are supportive of the concept and excited about having SI traceable measurements from space.