The only realistic way of collecting world-wide data on the state of our planet is via satellite sensors which measure the solar energy reflected from the Earth's atmosphere and surface. The accuracy and reliability of this data over a lengthy period is hugely important.

Image Supplied Copyright NPL

 The challenge is, however, that the launch of these satellites can often affect the calibration of the sensors, making confidence in results dubious. Once in orbit, the satellites need 'post-launch' calibration. An easy way to achieve this is via field instruments strategically placed around the world in so-called 'calibration sites'. These must be visible to the satellite station so are typically positioned in deserts or grassland. Here the instruments provide the in-situ data from Earth to validate the satellite measurements.

The National Physical Laboratory of the UK contacted Lovibond Tintometer to assist in the design of its GRASS (Gonio RAdiometric Spectrometer System) field instrument. In order to avoid discrepancies caused by the Earth's albedo  (which satellites cannot directly measure), it was necessary to develop an understanding of the angular reflectance of terrestrial surfaces. The Lovibond^® expertise in light diffraction and optics was instrumental in developing a system capable of measuring reflected sunlight over half a hemisphere at 30-degree intervals ie 0°, 30°, 60°, 90°, 120°, 150° and 180°.   

GRASS comprises of 36 cameras each consisting of an entrance optic and an optical fibre. The fibres feed to a set of multiplexers, which give one optical output that can be coupled to a spectrometer and thus give traceability to SI units.

GRASS is now being used by UK researchers to provide data for comparison with satellite information and develop a better understanding of Climate Change.