Goniometric realization of reflectance scales at NPL

United Kingdom scales for diffuse reflectance in the ultra-violet to near-infrared region are realized at National Physical Laboratory using goniometric techniques, while the mid-infrared scale is based on measurements with a hemisphere reflectometer. Both of these scales have changed recently. In the ultra-violet to near-infrared region this took place on adoption of the goniometrically realized scale which replaced the previous scale traceable to NRC and PTB, while in the mid-infrared the scale change was based on the development of a new direct absolute technique which allowed a re-determination of the diffuse reflectance of BaSO4. Dissemination of the UV/vis/NIR scale will still in the main rely on integrating sphere techniques, and this requires the use of reference standards calibrated using the goniometric technique. The new scale is found to be 0.4 - 0.5 % higher than the previous scale in the visible region, while harmonization with the mid-infrared at 2.5 μm has made good progress, thereby ensuring an independent and continuous scale from the ultra-violet to the far-infrared.