/*
Name: Gas
Type: Air

Rayleigh scattering phase function: 

fscat(PSIsv) = a * (1 + cos(PSIsv) * cos(PSIsv)) + c

with PSIsv = phase angle (forward scattering => PSIsv = 0)

Phase function = fscat/(4*Pi)

Parameters (Lambda, Sigma, 	Albedo, a, c)
- Lambda: wavelength. It is given in micrometer
- Sigma: particle cross section. It is given in 10*-15 cm2
- a: for gases a=0.75*2*(1-t)/(2+t)
- c: for gases c=0.75*2*(1-t)/(2+t)*2*t/(1-t)
  with t = polarisation ratio (t=0.0279 at 0.65 micrometer)

Law :
Use a Rayleigh distribution for scattering :
fscat(PSIsv) = a * (1 + cos(PSIsv) * cos(PSIsv)) + c
*/
Rayleigh
/*
Lambda	Sigma		Albedo		a 			c
*/
00.300	0.5	1.00000000	0.719044332 0.041274225
10.000	0.5	1.00000000	0.719044332 0.041274225
