New Satellite Will Make Climate Studies More Accurate

Calibration of the hyperspectral sensors mounted on satellites is the cause of some of the uncertainty, according to Nigel Fox of the UK’s National Physical Laboratory near London. Hyperspectral sensors monitor radiation from the Earth and the Sun over a broad range of frequencies. They can measure many parameters, such as the amount of aerosols in the troposphere, the health and life cycle of crops, and the average temperature of the Earth. When these satellites are launched, the violence of the launch can ruin the sensors’ calibration. The only way to recalibrate them is to compare them with the devices on other satellites, which have also experienced a violent launch, and may also have become less sensitive or have lost their calibration over time.

Because of uncertainties in calibration, there is a significant uncertainty in observations of Earth from space. For example, there is a 0.3 percent margin of error in measurements of the total solar radiation reaching the Earth. A change of 0.3 percent is enough to induce a global temperature change of 2°C, which would be enough to trigger a mini ice age such as the one Europe experienced in the 17th century.

Fox says that the only way to solve the satellite calibration problem is to perform calibrations in orbit. He and his colleagues have designed a satellite, Traceable Radiometry Underpinning Terrestrial and Helio Studies (TRUTHS), which could reduce uncertainties by a factor of ten. TRUTHS would be the first unmanned probe to calibrate its instruments in space. For example, it would filter specific wavelengths of light directly from the Sun and use these to fine-tune its sensors. Other Earth observation satellites could then use TRUTHS for their own calibration.