Abstract: Remote sensing is the science of deriving information about objects from images acquired by remote instruments. Nonlinear model of radiative transfer, which describes physical phenomenon of energy transfer in the form of electromagnetic radiation, is used for constructing forward models for obtaining radiances by instruments onboard spacecraft. We describe the forward model for the Earth Observing System (EOS) Microwave Limb Sounder (MLS) onboard Aura satellite. We then describe the analytic computation of Jacobians and the inverse method for estimating the atmospheric composition from radiances. The approach is based on Bayesian formulation, and an associated energy function is minimized using nonlinear estimation methods.