What is Refractivity coefficient in the Viewshed Tool

[Judith89]

Hi all,

I'm looking to adjust the Refractivity Coefficient in the earth curvature correction to assess visibility for different wavelengths, however I don't understand how this input to the Viewshed tool relates to the physical parameter of refractive index.

For visible wavelengths in air, the refractive index is close to 1 (https://en.wikipedia.org/wiki/List_of_refractive_indices), whereas the default setting of Refractivity Coefficient in the Viewshed tool is 0.13. 

Does anyone know the relationship between refractive index and Refractivity Coefficient? 

[DanPatterson]

How Line Of Sight works—ArcGIS Pro | Documentation

the reference in the link may be worth consulting if your applications are different than those used by default for the tool