Anisotropy plot

This type of plot exploits further the redundancy found in polar plots and the solar principal plane plot. It is based on the observation that most of the interesting information is captured by measurements in the principal plane, and therefore the most significant features of the BRDF can be represented by measurements made at just three geometric configurations: nadir view, the hot-spot and the specular point. If this dramatic simplification of the BRDF can be accepted, an anisotropy index can be calculated which combines data collected at some or all of these configurations, and which can then be plotted in relation to another variable such as wavelength.

Anistropy Index = ((Hot-Spot HCRF - Specular HCRF) + Nadir HCRF) / Nadir HCRF
(Milton and Rollin, 1987)

 

Anisotropy index plot of grass lawn, concrete and evergreen dwarf shrubs. A Lambertian surface would have an Anisotropy index = 1.0. (from Milton and Rollin, 1987)

Milton and Rollin (1987) went on to devise a manually-operated goniometer optimised for the measurement of the Anisotropy Index (click here).

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