Fig. 3:

Normalized BRDFs for the 99% and 10% nominal reflectance plaques at 550 nm for the two viewing geometries considered in this study (section 3.3). For reference, the BRDF of a perfectly reflective lambertian surface is 0.318 sr⁻¹. $\rho \left({\theta }_{\text{v}},\lambda \right)$ is the integral of $f_{\text{r}}\left({\theta }_{\text{i}},{\varphi }_{\text{i}},{\theta }_{\text{v}},{\varphi }_{\text{v}},\lambda \right)$ over all incident solid angles. Inner to outer concentric circles represent zeniths of 15°, 40° and 90°. Data presented in orthographic projection (r = cos θ).