GERB (Geostationary Earth Radiation Budget)

NPL provided the expertise and support equipment to determine the spectral response of the GERB (Geostationary Earth Radiation Budget) instrument, currently flying on Meteosat Second Generation, at Imperial College London. This amongst other measurements involved the transportation to Imperial of a large frame Kr+ laser and support equipment from NPL. This laser illuminated an integrating sphere to provide a few high accuracy monochromatic spectral radiance measurements of the GERB instrument and demonstrated the relative flexibility of the NLRF as a calibration tool.

The GERB series of instruments were calibrated in terms of absolute spectral radiance using sources specifically designed and calibrated at NPL. The instrument measures spatially resolved Earth radiance in two channels, Solar reflected and thermal emitted with target uncertainties of 1% and 0.5 % respectively. NPL provided black bodies and a lamp illuminated spectral radiance standard (TSARS). In the latter case the uncertainty required was significantly lower than was being provided to any other customer.

Compact High Resolution
Imaging Spectrometer.

CHRIS (Compact High Resolution Imaging Spectrometer)

During the calibration of CHRIS (Compact High Resolution Imaging Spectrometer), built by Sira Electro-optics Ltd (now part of Surrey Satellite Technology Ltd)- currently in flight on the ESA Proba platform, several primary facilities were used. The ultra high temperature black body (UHTBB) was used directly to provide a known radiance and also used to simulate solar irradiance for calibration of an on-board calibration monitor. In addition, out-of-field stray light was characterised using a highly collimated beam of laser radiation from the NPL NLRF. During the calibration CHRIS was maintained in a class 100 environment within an NPL laboratory.

TSARS Calibrating GOME2-FM3.

GOME 2 -FM3

To demonstrate the flexibility and performance of TSARS, a collaborative project was established with TNO TPD in Delft. As part of this project, one of the TSARS was taken to TNO TPD in Delft to be included in the radiometric calibration of the Global Ozone Monitoring Experiment (GOME 2) – FM3. Overall agreement to <± 1% with both TNO TPD and NASA was achieved. (Pegrum, et al., 2004)

Reference

• Pegrum, H., E. Woolliams, N. Fox, L. V. Riel, G. Otter and M. Kowalewski. (2004). Calibration of the NPL Transfer Standard Absolute Radiance Source (TSARS) and its use with GOME 2 – FM3 Spectral Radiance measurements. In 11th International Symposium on Remote Sensing, Sensors, Systems, and Next-Generation Satellites VIII (eds S. P. N. Roland Meynart, Haruhisa Shimoda;), Proc. SPIE. pp 503-514. Maspalomas, Spain