In the development and analysis of sophisticated detection systems, the ability to simulate background clutter provides a useful tool in assessing system performance. Infrared cloudy sky images can be generated using a technique based on the physical parameters of the background. Power spectra and radiance distribution functions for ground-based IR cloudy sky images in 3 to 5 μ and 8 to 12 μ spectral windows were determined experimentally in our previous research. The empirical power spectra and radiance distribution functions are used here as a basis to generate computer simulations of cloudy sky images. We require that the power spectrum and radiance distribution functions of the simulated image be in agreement with the functions that we obtained experimentally in our previous research. Realistic cloudy sky images were obtained. The simulated cloudy sky images retain the radiance distribution and power spectra functions of real cloudy sky IR images.