The optical technologies group has provided calibration services for a variety of Earth observation instrumentation, some of which include:

• Mirror Reflectance
• MODIS witness mirrors
• GERB witness mirrors
• Solar diffuser calibrations
• ATSR+
• Detectors
• Meteosat
• GERB. One of the biggest challenges in the calibration of GERB was the calibration of spectral response of each of 256 pixels of the blackened thermopile array. This calibration required measurements over the spectral range 300 μm to 30 μm in fine spectral detail. Uncertainties of < 1% were required.
• Calibration of Sources
• SUSIM
• SOLSPEC
• Reflectance Panels - The Bidirectional Reflectance Distribution Function (BRDF) of reference white reflection plaques is of critical importance to the EO community. They are regularly used to convert Solar Irradiance into radiances for calibration of instrumentation pre- and in-flight. They also commonly provide the reference target for calibration of field instruments. At NPL we have two facilities for BRDF calibrations, one laser based and a second using conventional sources. Measurements are routinely made over the spectral range 300 to 2500 nm, with an uncertainty of <0.2 % in the visible. We are also carrying out work to develop improved (stable) reference white diffusers and have recently demonstrated the potential of a new standard material in an experiment for CEOS.