Measurement of the spatial distribution of the spectral response variation in the field of view of the ASD spectrometer input optics / Martin P. Lévesque, Stéphane Giroux, Jean-Pierre Ardouin.: D68-2/122-2014E-PDF

A new goniometer is under development. It will be used for the measurement of the spectro-polarimetric BRDF (Bidirectional Reflectance Distribution function). For practical reasons, the selected spectrometer is an ASD field spectro-radiometer. Its optical head is built with an optical fibre cable bundle that makes it easy to use. Only the optical head has to be mounted on the goniometer, the main body of the spectrometer remains aside. The ASD spectrometer has several input optics (bare fibres, lenses and telescopes) and several tests were conducted to determine which one is the best for the goniometer. The conclusion: none of them. By construction, the ASD spectrometer does not have a homogeneous field of view (FOV). The optical fibre bundle does not uniformly sample the FOV. This can be partly solved by defocusing the optics. But, all the tested optics suffers from severe spectral dispersion or other artefacts. However, a simple optical design based on the use of an off-axis mirror can do the job. This will be used for the optical reading head of the goniometer.

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