A new method for the determination of ray paths as well as resulting path s
egments and partial gas columns within a layered atmosphere is presented. A
ny singularity at the tangent point is avoided. No use is made of the gross
spherical symmetry of the Earth's atmosphere. Using this approach we exami
ne the impact of the Earth's oblate shape and horizontal atmospheric inhomo
geneities on infrared limb spectra. (C) 1999 Optical Society of America.