In-situ spectral reflectance measurement of off-axis paraboloidal reflector with a large aperture for radiometric calibration

Off-axis paraboloidal reflector with a large aperture is often used as a collimator in radiometric calibration system in the space environment or a simulator for space carrier. Spectral reflectance measurement of the reflector is an important issue that determines the accuracy of radiometric calibration, especially, for imaging spectrometer. Currently, the reflectance of the reflector is generally measured by the sample contrast method. So, only a small sample of the reflector rather than the whole can be measured. In order to overcome this limitation, a method for in-situ measuring spectral reflectance of off-axis paraboloidal reflector, especially, with a large aperture, is proposed in this paper. First of all, the proposed in-situ measurement approach is designed according to in-situ contrast measurement. Then, the proposed measurement is realized and evaluated in experiment for measuring spectral reflectance of an off-axis paraboloidal reflector with an aperture of 110 mm. Finally, the influence of prodigious temperature fluctuation on the measurement is experimentally investigated and the impact of optical devices and environment on the uncertainty is analyzed. The total experimental uncertainty is obtained as 4.2%. The experimental results proved that the spectral reflectance of the reflector will decrease when the experimental temperature falls from 20 °C to −100 °C and the decrease degree is different for different wavelength bands.