Measured-predicted molecular spectra at band-line resolution

- ERIM-1975 radiance transmittance spectra for H2O-CO2 in short-midwave infrared.
- Comprehensive line strengths-frequencies from NASA-H2O and CDSD-CO2.
- Merged line-band model based on broadened line-sum spectral cross section.
- Empirical line-width function yields near-exact spectral match for all test conditions.

Early ERIM measurements of hot-through-cold gas (CO2, H2O, N2) emission-absorption spectra are replicated by modern line-band computations that incorporate independent fundamental line strength-frequency information. Close agreement is achieved for all cases by empirical adjustment of the line broadening function.Line spectra for CO2 and H2O computed at 0.001 cm−1 resolution were integrated to 3.2 and 14 cm−1 using a triangular slit function consistent with ERIM measurements for the 4.3 and 2.7 μm spectral regions. Band spectra computed at 0.1 cm−1 resolution give close agreement with spectra generated at higher resolution.The findings demonstrate a merged line-band model for nonuniform path radiance and transmittance based on the line-sum spectral cross section for each piecewise-uniform path segment. The band-and-line transmittance become equivalent at high spectral resolution.