Fig. 2
From: Accurate analytic approximation for the Chapman grazing incidence function
Accuracy of analytical approximations of the Chapman function as a function of solar zenith angle \(\zeta\) for scale parameter \(X=500\). The dashed lines show the formulas found in the literature and solid lines correspond to approximations introduced in the present article: a Green & Barnum approximation (Green and Barnum 1963), b Fitzmaurice approximation (Fitzmaurice 1964), c Swider approximation (Swider 1964), d Titheridge empirical formula (Titheridge 1988), e Kocifaj formula (Kocifaj 1996), f Huestis asymptotics, 1 term (Huestis 2001), g present work, Eq. (35), h present work, Eq. (36)