Calibration procedures and measurement results of a fast semi-hemispherical spectro-radiometer in VIS and NIR

A small, fast and rugged spectro-radiometer without moving parts for angular resolution for the fast acquisition of large amounts of BRDF data over wavelength to be compiled into libraries is being developed. The system consists of an elliptical mirror which maps a semi-hemisphere onto a CMOS-detector with a dynamic range of MOO. Radiometric measurements over a wide spectral range from VIS to NIR over 7 deacades (10(-5) W/m(2) to 100 W/m(2)) require a pixelwise calibration taking into account the spectral characteristics of the light sources, potentially used filters and the CMOS-detector itself. Also the elliptical mirror has a reflectivity which is a function of the incident angle, the wavelength and polarization of the collected light. All these influences have to be taken into account, if a proper radiometric measurement shall be conducted. The paper deals with the instrument design and mainly with its calibration, and gives some measurement results.