Mention that exact hemispherical Fresnel albedo formula is available.

Author: portsmouth

index.html

@@ -1643,6 +1643,7 @@
 \begin{equation}
   E_F(\eta) \approx \ln \biggl( \frac{10893\eta - 1438.2}{-774.4\eta^2 + 10212\eta + 1} \biggr) \ .
 \end{equation}
+(The more complicated exact formula is also provided in [#d'Eon2021], which we do not reproduce here).
 Values of $E_F(\eta)$ for $\eta < 1$ are related to the values for $\eta > 1$ via:
 \begin{equation}
     E_F(\eta) = 1 - \eta^2 \bigl(1 - E_F(1/\eta)\bigr) \ .