The NPL Gonio RAdiometric Spectrometer System (GRASS)

Increasingly satellites have the capability and requirement to measure surfaces at multiple angles, and additionally, due to the variations in slope angle and aspect, few remotely sensed data sets are immune to multi-angular effects. Since such measurements need to be calibrated or at least validated against real ground data we need to improve the accuracy of multi-angular field measurements. A new instrument has been designed, in conjunction with the Natural Environmental Research Council (UK) Field Spectroscopy Facility (FSF) and the University of Southampton for this purpose. The GonioRAdiometric Spectrometer System (GRASS) has been developed at the National Physical Laboratory, which provides quasi-simultaneous, multi-angle, multi-spectral measurements of Earth surface reflected sunlight to support vicarious calibration of satellite sensors operating in the optical region. The instrument will ultimately be available for use by UK researchers through the FSF to provide data to develop a better understanding of the anisotropy of natural targets, which can be used to reduce errors in climate modelling. It will also be utilised for the characterisation of “reference standard” test sites