Abstract
The Earth’s climate is undoubtedly changing; however, the time scale, consequences, and causal attribution remain the subject of significant debate and uncertainty. Detection of subtle indicators from a background of natural variability requires measurements over a time-base of decades. This places severe demands on the instrumentation used, requiring measurements of sufficient accuracy and sensitivity that can allow reliable judgements to be made decades apart. The International System of Units (SI) was developed to address such requirements, providing a reference framework tied to invariant constants of nature. However, ensuring and maintaining SI traceability of sufficient accuracy in instruments orbiting the Earth presents a significant new challenge to the Earth Observation and metrology communities. This paper describes a new satellite mission, called Traceable Radiometry Underpinning Terrestrial- and Helio- Studies (TRUTHS), which enables, for the first time, high-accuracy SI traceability to be established in orbit. The direct use of a ‘primary standard’ and replication of the terrestrial traceability chain extends the SI into space, in effect realizing a ‘metrology laboratory in space’ providing and enabling SI-traceable measurements of unequivocal accuracy in the solar reflective domain—an enabling element of an international space-based climate observing system. TRUTHS will not only provide a benchmark of the radiation state of the planet (incoming and outgoing) from which to compare change in the shortest time possible, but also facilitate an upgrade in performance of the Earth Observing system as a whole, through ‘in-orbit’ reference calibration.
Highlights
The 21st Conference of the Parties (COP 21) exemplified the intense political, scientific, and public debate about climate change
Traceable Radiometry Underpinning Terrestrial- and Helio- Studies (TRUTHS) incorporates this requirement in Table 2, it should be noted that with threshold values this may only be achieved through reference calibration of other sensors, with goal values for Signal to noise ratio (SNR) this may be globally achievable by TRUTHS, but the temporal coverage may not be adequate for some applications
This resultant high accuracy is only achievable in an indirect manner through a process known as ‘system vicarious calibration’ using ocean buoys fitted with well-calibrated radiometers at very specific locations namely, MOBY and Boussole
Summary
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