Pro ray_scat, wave, ht, ray_coef, kray, nden ;
; Returns the:
;	Rayleigh Scattering Coefficient = ray_coef [km-1]
;	Rayleigh Scattering Cross section = kray [cm^2 / molec]
;	Number Density of Molecules at altitude Ht [km] = nden [molec/cm^3]
;
; Given inputs of the:
; Altitude = ht [km]
; Wavelength = wave [nm]
;
; Note - The altitude approximation was developed ; For a cold Polar Summer Mesopause [T=138K] ; And for tangent heights between 45 & 90 km. ;	Over those altitudes it has an RMS error of about 1.2 %
; Uncertainties in the true atmospheric density profile ;	far exceed this error.
;	Using this procedure outside that height range [45 to 90 km],
;	 probably will be hazardous to your program! ;
a0=36.5646
a1=0.4099
a2=-1.4575e-2
a3=1.7965e-4
a4=-8.2898e-7
lnden = a0 + a1*ht + a2*ht^2 + a3*ht^3 + a4*ht^4 
nden = exp( lnden )
; nden = Number Density Molecules at Altitude = ht [molec/cm^3] ;
a = 3.97423e-16
b = 1.13667e+4
c = 4.58890e+7
kray = a / ( wave^4 - b*wave^2 - c )
; kray = Rayleigh Cross Section [ cm^2 / molec ] ;
ray_coef = nden*kray*1e5
; ray_coef = Rayleigh Scattering Coefficient [km-1] ;	at a height = ht.
;	The factor of 1e5 converts from [cm-1] to [km-1].
;
END
;
;Date: Tue, 17 Jun 1997 12:53:37 -0400
;From: shettle@poamb.nrl.navy.mil (Eric Shettle) To: debrest@cpi.com, oliveroj@db.erau.edu, thomas@poamb.nrl.navy.mil, 
;wevans@trentu.ca
;Subject: IDL Procedure for Rayleigh Scattering Coefficient 
;Dear All,
;Here is my IDL Procedure to calculate the Rayleigh Scattering coefficients as a function of Wavelength and Altitude for a cold Summer Mesopause [T=138K]. It is valid over an altitude range of 45 to 90 kilometers. It also calculates the molecular number density, over the same altitude range, with an RMS error of 1.2 % This altitude range should handle most the altitudes for looking at our PMC results.
;Eric