National Physical Laboratory

'NPL in Space' - new calibration satellite required to make accurate climate change prediction

Earth
(Image courtesy of iStockphoto)

Dr Nigel Fox, Head of Earth Observation and Climate at NPL, is the lead author of a new paper published in Philosophical Transactions of the Royal Society A, that puts forward a solution to the current uncertain climate models which impair long-term climate strategies.

The solution put forward by the paper is the TRUTHS (Traceable Radiometry Underpinning Terrestrial- and Helio- Studies) mission, a concept conceived and designed at NPL. This would see a satellite launched into orbit with the ability to make climate measurements ten times more accurate and give us models on which we could make important decisions about the future. In essence, it becomes 'NPL in Space'.

The Earth's climate is undoubtedly changing, but how fast and what the implications will be are unclear. Our most reliable models rely on data acquired through a range of complex measurements. Most of the important measurements - such as ice cover, cloud cover, sea levels and temperature, chlorophyll (oceans and land) and the radiation balance (incoming to outgoing energy) - must be taken from space, and for constraining and testing the forecast models, made over long timescales. This presents two major problems.

Firstly, we have to detect small changes in the levels of radiation or reflection from a background fluctuating as a result of natural variability. This means measurements are made on decadal timescales - beyond the life of any one mission, and thus demands not only high accuracy but also high confidence that measurements will be made in a consistent manner.

Secondly, satellites, particularly optical usually lose their calibration during the launch, and this drifts further over time.

The result is varying model forecasts. Estimates of global temperature increases by 2100, range from ~2-10 ºC. Which of these is correct is important for making major decisions about mitigating and adapting to climate change: for instance, how quickly are we likely to see serious and life threatening droughts in which part of the world; or, if and when do we need to spend enormous amounts of money on a new Thames barrier? The forecasted change by all the models is very similar for many decades, only deviating significantly towards the latter half of this century.

The TRUTHS satellite makes spectrally resolved measurements of incoming solar radiation and that reflected from the ground, with a footprint similar in size to half a rugby field. The unprecedented accuracy allows benchmark measurements to be made of key climate indicators such as: the amount of cloud, or albedo (Earth's reflectance) or solar radiation, at a level which will allow differences in climate models to be detected in a decade (a third that of existing instruments). Its data will also enable improvements in our knowledge of climate and environmental processes such as aerosols, land cover change, pollution and the sequestration of carbon in forests.

TRUTHS will be the first satellite to have high accuracy traceability to SI units established in orbit. The novelty of TRUTHS lies in its on-board calibration system. The instruments on the TRUTHS satellite will be calibrated directly against an on-board primary standard - an instrument called a CSAR (Cryogenic Solar Absolute Radiometer).

The project, which would be led by NPL, is being considered by different organisations. The European Space Agency has recommended looking into ways to take it forward, possibly as a collaboration with other space agencies. NASA is also keen to collaborate formally.

Nigel Fox said:

"Taking this forward would be an excellent investment for the UK, or any other country which supports it. This is not only an effective way to address the problem of understanding climate change, but also an excellent opportunity for business."

The full reference for the paper is: Phil. Trans. R. Soc. A (2011) 369, 4028-4063 doi:10.1098/rsta.2011.0246

Nigel Fox delivered a lecture on this subject as part of NPL's Celebrating Science lecture series, which can be viewed here

Click here for more details on TRUTHS

For more information, please contact Nigel Fox

Last Updated: 3 May 2012
Created: 21 Sep 2011

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