An Efficient Computational Approximation to the Lorentz Line Molecular Absorption Coefficient.
TEXAS UNIV AT EL PASO DEPT OF ELECTRICAL ENGINEERING
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A rapid and accurate approximation to the Lorentz line molecular absorption coefficient has been developed which significantly reduces the time of line-by-line transmittance calculations. By separating computations required for each spectral line, atmospheric level, and absorbing gas under consideration, arithmetical operations are minimized. Time tests were conducted while computing the monochromatic absorption coefficient for five frequency channels in the 4.3 micrometers band. The approximation was compared to the evaluation of the Lorentz line shape Standard manner for a 33 level atmosphere and an average of 1000 absorption lines per region. Absorption coefficient values computed by this approximation agreed to those computed in the standard fashion to at least three decimal places regardless of molecule type, channel, or atmospheric level. Average percent-relative errors were typically .0001 for H2O .0001 for CO2 .001 for N2O .00000001 for CO. For transmittance calculations over a band, time savings can be predicted by analyzing the required number of arithmetical operations. For 1,000 spectral lines over a bandwidth of 25cm and a step increment of 0.02cm, a reduction in computation time of 450 is anticipated.
- Atmospheric Physics
- Atomic and Molecular Physics and Spectroscopy