MODTRAN2 (1992) is the most recent version of MODTRAN, the Moderate Resolution Atmospheric Radiance and Transmittance Model, first released by the Geophysics Directorate, Phillips Laboratory, in 1990. It encompasses all the capabilities of LOWTRAN 7, the historic 20 cm-1 resolution radiance code, but incorporates a much more sensitive molecular band model with 2 cm-1 resolution. For inversion algorithm applications, MODTRAN2 must prove to be sufficiently accurate when calculating layer- specific perturbations. First steps in establishing this capability have recently been accomplished. DREV (Defence Research Establishment Valcartier, Canada), in conjunction with the Geophysics Directorate, has taken measurements with a surface-based Bomem interferometer (approximately 1 cm-1 resolution), with full supporting sonde profiles (z, T, p, and relative humidity). This suggests that the derivative matrices, typically required for inversion algorithms, may be readily (and rapidly) calculated using MODTRAN whenever its spectral resolution is adequate.