A radiative transport band model method for prediction and analysis of high spectral resolution radiometric measurements. Atomic and molecular line center absorption is determined from finite spectral bin equivalent widths. A mathematically exact expansion for finite bin equivalent widths provides high accuracy at any desired spectral resolution. The temperature and pressure dependent Voigt line tail spectral absorption contributing to each spectral bin is pre-computed and fit to Pade approximants for rapid and accurate accounting of neighboring-to-distant lines. A specific embodiment has been incorporated into the MODTRAN.TM. radiation transport model.