From: Accurate analytic approximation for the Chapman grazing incidence function
Index | Reference | Approximation of the Chapman function |
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(a) | \({\text {Ch}}(X,\zeta ) \approx \exp \left[ \frac{\frac{1}{2}\zeta ^2}{1-0.115\zeta ^2-\alpha (X)\zeta ^4}\right] ,\) | |
\(\alpha (X)=\frac{16}{\pi ^4}\left\{ 1-(\pi /2)^2[0.115+ 1/\ln (X\pi /2)]\right\}\) | ||
(b) | Fitzmaurice (1964) | \({\text {Ch}}(X,\zeta )\approx \sqrt{\frac{\pi X}{2}}{\text {erfc}}\left( \sqrt{\frac{X}{2}}\cos \zeta \right) \exp \left( \frac{X}{2}\cos ^2\zeta \right)\) |
(c) | Swider (1964) | \({\text {Ch}}(X,\zeta )\approx -X\cos \zeta +\sqrt{1+X(1+\sin \zeta )}\Biggl \{\sqrt{X(1-\sin \zeta )}\) |
\(+\frac{\sqrt{\pi }}{2}{\text {erfc}}\left[ \sqrt{X(1-\sin \zeta )}\right] \exp [X(1-\sin \zeta )]\Biggr \}\) | ||
(d) | \({\text {Ch}}(X,\zeta ) \approx \sec (\zeta -d),\quad d = 3.88 X^{-1.143}\left[ \sec \left( A\zeta \right) -0.834\right]\), | |
\(A = 1.0123 -1.454 X^{-1/2}\) | ||
(e) | \({\text {Ch}}(X,\zeta ) \approx \frac{1}{2}\Biggl [\cos \zeta +\sqrt{\frac{\pi X}{2}}{\text {erfc}}\left( \sqrt{\frac{X}{2}}\cos \zeta \right) \exp \left( \frac{X}{2}\cos ^2\zeta \right) \Biggr .\) | |
\(\Biggl .\times \left( \frac{1}{X}+1+\sin ^2\zeta \right) \Biggr ]\) | ||
(f) | Huestis (2001) | \({\text {Ch}}(X,\zeta ) \approx \sqrt{\frac{\pi X}{(1+\sin \zeta )}}{\text {erfc}}\left[ \sqrt{X(1-\sin \zeta )}\right] \exp \left[ X(1-\sin \zeta )\right]\) |