TRUTHS (Traceable Radiometry Underpinning Terrestrial- and Helio- Studies): A Mission to Achieve "Climate Quality" Data
Fox, Nigel1; Green, Paul1; Woolliams, Emma1; Winkler, Rainer1; Brindley, Helen2; Russell, Jacqui2; Smith, Dave3; Cutter, Mike4; Barnes, Andrew4; Lobb, Dan4
1National Physical Laboratory, UNITED KINGDOM; 2Imperial College London, UNITED KINGDOM; 3RAL Space, UNITED KINGDOM; 4Surrey Satellite Technology Limited, UNITED KINGDOM
Our climate is changing. Predictions of the long term trend of this change, identifying the key processes and drivers, and the manifestation of these changes on society rely upon the predictive capabilities of sophisticated, but highly complex simulation models. The output of these models is the cornerstone of international and national efforts to assess the magnitude of the foreseen changes and guides the policy decisions that select effective mitigation and adaptation strategies.
These model predictions clearly need to be validated against an observational dataset. However, since the key indicators of climate change may only vary by a few percent per decade, the absolute accuracy of such an observational dataset also needs to be very small to allow detection and provide some means of validating/discriminating and improving the climate models. The quality of currently available datasets is not adequate to meet the requirements for climate benchmarking. The current strategy of overlapping missions of similar instruments and normalisation via the coinciding data, together with insufficient knowledge of instrument performance degradation over their lifetime means this approach cannot produce the long term record at the required accuracy.
The only means of achieving robust data sets of sufficient quality and accuracy is through traceability to SI units, regularly re-established and guaranteed throughout the lifetime of a mission. TRUTHS (Traceable Radiometry Underpinning Terrestrial- and Helio- Studies) is a mission proposal that does just that. TRUTHS will measure the key optical radiometric quantities: the incident solar irradiance (total and spectrally resolved) and reflected solar spectral radiance from the Earth in-orbit, but is also in effect a "standards laboratory in orbit" taking the primary standard from the lab onto the satellite mimicking the on-ground calibration traceability chain, attaining the small uncertainties necessary to adequately test the climate model predictions.