Fig. 1. Principle of BRDF measurement and the BiRT-2.0 BRDF measurement system

Fig. 2. Coordinates of field distributions in the spatial and Fourier domains. (a) Space coordinates; (b) Fourier domain coordinates

Fig. 3. Radiance coordinate diagram under Fourier optical transform

Fig. 4. Variation trend of incident angle with cos⁴θ

Fig. 5. Sub-aperture stitching principle

Fig. 6. Samples to be tested and the scratch measured under microscope

Fig. 7. Experimental scheme

Fig. 8. Angular scattering spectrum of the standard diffuse plane

Fig. 9. Angular scattering spectrum of the mirror

Fig. 10. Angular scattering spectrum of the scratched mirror

Fig. 11. BRDF comparison of the standard diffuse plane

Fig. 12. BRDF comparison of the mirror

Fig. 13. BRDF comparison of the scratched mirror