Information about a fire's perimeter is a prerequisite for the control of large fires, whether caused by nuclear war, lightning, or man's carelessness. Visual aerial reconnaissance is usually limited by smoke. Location of a fire's perimeter with respect to surrounding terrain is difficult to determine at night by visual means. The alternative is use of slow-moving ground scouts who must often times traverse rugged terrain either in vehicles or on foot. A promising development, which combines the advantage of aerial observation with the ability to penetrate darkness and smoke, is the airborne infrared scanner. Particles associated with forest fire smoke cause serious scattering of light rays in the visible spectrum. At infrared wavelengths, this scattering is minimal, and useful information about a fire.