In the development and analysis of sophisticated IR detection and recognition systems it is necessary to have a priori knowledge of the background clutter. The spatial power spectrum and the spatial autocorrelation functions are used to analyze the spatial structure of ground-based infrared cloudy sky images. The experimental results obtained for ground-based IR cloudy sky images do not fit the analytical model of the Wiener spectrum that is frequently used to describe natural clutter sources in the infrared. The spatial structure of ground-based cloudy sky IR images was found to be dependent on the percentage cloud cover in the image. A corrected model is developed that relates the spatial structure of cloudy sky images to the percentage cloud cover in the image.