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c======================================================================= subroutine o2cont(v,sigma,alpha,beta) 1,1
c
c     this routine is driven by frequency, returning only the
c     o2 coefficients, independent of temperature.
c
c  *******************************************************************
c  *  these comments apply to the colume arrays for:                 *
c  *       pbar*ubar(o2)                                             *
c  *       pbar*ubar(o2)*dt                                          *
c  *   and pbar*ubar(o2)*dt*dt    where:  dt=tbar-220.               *
c  *  that have been compiled in other parts of the lowtran code     *
c  *                                                                 *
c  *  lowtran7 compatible:                                           *
c  *  o2 continuum subroutine for 1395-1760cm-1                      *
c  *  modified by g.p. anderson, april '88                           *
c  *                                                                 *
c  *  the exponential temperature employed in the fascod2 algorithm  *
c  *  (see below) is not readily suitable for lowtran.  therefore    *
c  *  the exponentials have been linearly expanded, keeping only the *
c  *  linear and quadratic terms:                                    *
c  *                                                                 *
c  *  exp(a*dt)=1.+ a*dt + (a*dt)**2/2. + ....                       *
c  *                                                                 *
c  *     exp(b*dt*dt)=1.+ b*dt*dt + (b*dt*dt)**2/2. + ....           *
c  *                                                                 *
c  *  the product of the two terms is:                               *
c  *                                                                 *
c  *     (1. + a*dt + (a*a/2. + b)*dt*dt )                           *
c  *                                                                 *
c  *  this expansion only works well for small values of x in exp(x) *
c  *                                                                 *
c  *  since dt = t-220., the approximation is very good until        *
c  *  t.gt.260. or dt.gt.40.   at t=280, the maximum errors are still*
c  *  less than 10% but at t=300, those errors are as large as 20%   *
c  *******************************************************************
c
c     the following comments are excerpted directly from fascod2
c
c      this subroutine contains the rogers and walshaw
c      equivalent coefficients derived from the theoretical
c      values supplied by roland drayson. these values use
c      the same data as timofeyev and agree with timofeyev's results.
c      the data are in the form of strengths(o2so) and two
c      coefficients (o2a & o2b),  which are used to correct for
c      temperature. the dependency on pressure squared
c      is contained in the p*wo2 part of the constant.
c      note that since the coefficients are for air, the
c      the strengths are divided by the o2 mixing ratio for
c      dry air of 0.20946 (this is assumed constant).
c      original formulation of the coefficients was by larry gordley.
c      this version written by earl thompson, july 1984.
c
c
common/o2c/ o2dray(74),o2c001(74),o2s0(74),o2a(74),o2b(74),
x v1o2,v2o2,dvo2,npto2
sigma =0
alpha =0
beta  =0
if(v .lt. 1395) go to 30
if(v .gt. 1760) go to 30
c
c
call o2int (v,v1o2,dvo2,npto2,c,o2s0,a,o2a,b,o2b)
c
c
c
c     old 'fascod2' temperature dependence using block data arrays
c
c     c(j)=o2s0(i)* exp(o2a(i)*td+o2b(i)*td*td) /(0.20946*vj)
c
c     new coefficient definitions for lowtran formulation
c
alpha= a
beta=a**2/2.+b
sigma=c/0.20946
c
c     new 'lowtran7' temperature dependence
c
c     this would be the coding for the lowtran7 formulation, but
c       because the t-dependence is included in the amounts, only
c       the coefficients (sigma, alpha & beta) are being returned
c
c     c(j)=sigma*(1.+alpha*td+beta*td*td)
c
30    return
end
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