The Optical Radiation Measurement (ORM) group of the National Physical Laboratory is responsible for the development of the UK's primary radiometric quantities. One of its principle aims in recent years has been to improve the accuracy of "user" measurements through improved traceability routes to the SI system of units. The Earth Observation (EO) community is arguably the most demanding, requiring specialist techniques and transfer standards.
To improve accuracy, NPL has developed a range of lamp illuminated integrating spheres, called Transfer Standard Absolute Radiance Source (TSARS). The TSARS is calibrated directly against the NPL primary blackbody source with uncertainties <±0.75% which can be maintained and confirmed following transportation, through detector stabilisation. To demonstrate the performance of NPL's new TSARS, it was taken to TNO TPD in Delft for inclusion in the radiometric characterisation of the Global Ozone Monitoring Experiment (GOME 2) - FM3.
Overall agreement to <± 1% with both TNO TPD and NASA was achieved, demonstrating consistency in international radiometric scales, since the TNO and NASA sources were calibrated traceable to NIST. It also demonstrates the practicality of achieving calibrations with uncertainties <±1%, and since the NPL TSARS is portable, allows similar levels of uncertainty in "field situations" e.g. field spectrometers, aircraft radiometers.