Using high-spectral infrared observations, we categorize the emission spectra characteristics of clear conditions as well as that of cloud layers of differing thickness and altitude. The high-spectral infrared observations are obtained from the High-spectral resolution Interferometer Sounder (HIS) described in Revercomb et al. (1989). Cloud altitude and thickness are determined using the Cloud Lidar System (CLS), as describe by Spinhirne and Hart (1990). Data were collected during two field missions: FIRE-ACE, which was undertaken May-June 1998 over the Arctic Ocean near Alaska, and the SUCCESS mission of 1996 over the plains of Kansas and Oklahoma. A cloud detection algorithm is developed based on this categorization of the unique spectral features characterizing clear and cloud conditions.