SI traceable data in space
The TRUTHS mission is unique in establishing high-accuracy, SI traceable data in-flight enabling a 'calibration laboratory in space'. At the heart of the TRUTHS calibration capability is the Cryogenic Solar Absolute Radiometer (CSAR) which can mimic in space, the same calibration capability and associated measurement accuracy that is delivered using this type of technology on Earth.
Alongside the SI-traceable calibration capability of the CSAR, the hyperspectral imager will also make nadir and multi-angular spectrally-resolved measurements of the ocean and land surfaces. This will support studies of the carbon cycle and underpin improvements in observations which support agriculture or pollution monitoring. It will also provide data to improve atmospheric radiative transfer codes by anchoring boundary conditions at the top of the atmosphere. In this way TRUTHS will provide the basis to improve the performance and accuracy of other EO optical missions significantly.
TRUTHS will also utilise Simultaneous Nadir Overpass (SNO) where the Earth viewing imager of TRUTHS can simultaneously, or within a few minutes, view the same part of the Earth as another in-flight satellite.
TRUTHS utilises many strategies for providing 'reference calibrations'. These include:
- Using dedicated Earth-based reference standard sites such as those of CEOS
- Near simultaneous observations of 'targets' at orbital cross-overs (the orbit of TRUTHS allows these to take place regularly over different parts of the globe)
- Calibration of the moon.
In addition to establishing benchmark measurements of the Earth itself, the TRUTHS mission plans to establish a set of internationally-accepted SI-traceable reference targets, including the sun, moon and the earth’s deserts. These could be used to provide calibrations for EO data collected by other satellites. Such reference targets are highly stable, and many have been observed by previous satellites, so could be used to back-correct archived data.
TRUTHS is a complementary mission to other satellite based earth observation missions providing a more complete picture of the Earth’s radiation imbalance which drives global warming. Alongside the FORUM and IASI-NG missions TRUTHS will enable a complete picture of the Earth’s irradiation imbalance.