;+
; NAME:
;   oclc_fwd_phiref.pro
;
; PURPOSE:
;   Calculates the refractive flux.
;
; DESCRIPTION:
;
; CALLING SEQUENCE:
;   phi = oclc_fwd_phiref(r, theta, dtheta, distobs) 
;
; INPUTS: 
;   **** All inputs in cgs units ********
;
;  r - An array of radius values from the center of the planet, in cm.
;  theta - An bending angle in radians.
;  dtheta - The derivative of the bending angle with respect
;               to readius, in radians.
;  distobs - the distance to the observer, in cm.
;
; OUTPUTS:
;  phiref - the observed flux due to refractivity only
;
; EXAMPLE 1 - scalar temperature, molecular weight
;   r = dindgen(400)*1d5 + 1200d5  ; array of r, in cm
;   km = 1e5
;   distobs = 30.*1.496e8*1.d5 ; 30 AU in cm
;   r0 = 1250d5 ; reference r in cm
;   rsurf = 1000.d5
;   nu0 = 2d-9
;   lam0 = 60.d
;   a = 0.d
;   b = 0.d
;   order = 4
;   dnu = oclc_ey92_dnu(r0,nu0,lam0,a,b, r)
;   theta = oclc_fwd_theta(r, dnu)
;   dtheta = oclc_fwd_dtheta(r, theta)
;   phiref = oclc_fwd_phiref(r, theta, dtheta, distobs)
;   phiref2 = oclc_ey92_phiref_of_r(r0, nu0, lam0, a, b, distobs, rsurf, order, r)
;
;   plot, r/1e5, (phiref-phiref2)
;   print, minmax(phiref-phiref22 )
;
; COMMENTS:
;
; REVISON HISTORY:
;   25-Aug-2006 CBO SwRI -- modified from LAY's lightcurve.pro
;- 
function oclc_fwd_phiref, r, theta, dtheta, distobs
    y = oclc_fwd_y( r, theta, distobs)    
    phiref = abs(r/y) /abs(1.d + dtheta * distobs)
    return, phiref
end