viewing elevation angle derivations

1. viewing elevation angle from viewing zenith angle

   symbol	description	unit	variable name
   \(\alpha_{V}\)	viewing elevation angle	\(deg\)	viewing_elevation_angle {:}
   \(\theta_{V}\)	viewing zenith angle	\(deg\)	viewing_zenith_angle {:}

   The pattern : for the dimensions can represent {time}, or no dimensions at all.

   \[\alpha_{V} = 90 - \theta_{V}\]