We apply an onion-peeling inversion to simulated imaging Fabry-Perot interferometer (FPI) observations for retrieving altitude profiles of neutral temperatures and winds in the thermosphere in order to investigate the effects of realistic gradients in thermospheric parameters on the retrieved parameters. A forward model is developed that simulates the interference spectrum observed by an FPI using the redline (630.0 nm) and greenline (557.7 nm) emissions simulated based on climatological models. This forward model is applicable to both ground- and satellite-based simulations and generates a two-dimensional interference ring pattern. We simulate both a single-band ground-based FPI and a dual-band satellite-based FPI in order to study the effects of realistic vertical and horizontal gradients on the retrieved parameters.