788 



AIRBORNE NAVIGATION AND GROUND SURVEILLANCE 



information concerning physical features, heat distribution, targets, 

 present and recent activity of targets, rate of activity, and the presence 

 of camouflaged targets such as underground factories. The ability of IR 

 systems to provide information which can complement radar and photo- 

 graphic intelligence has resulted in considerable development effort in 

 this field. 



All objects above absolute zero radiate electromagnetic energy. An 

 appreciable portion of this energy lies in the infrared spectrum. Within 

 the broad assumption that an object is a perfect absorber and perfect 

 emitter (a black body) it radiates infrared energy in accordance with the 

 Planck radiation law. It is this infrared energy which, obeying the laws 

 for visible radiation, is received and focused, thus creating a thermal image. 



14-23 



BASIC PRINCIPLES CONCERNING IR GROUND 

 MAPPING 



Infrared mapping requires a scanning procedure in which the sensing 

 element or elements are exposed to radiation from a small area (or areas) 

 of the ground at any one instant. The angle thus subtended by this ground 

 area at the optics is the instantaneous field of view. Fig. 14-23 shows this 



Detector 



Imaging Optics 



Instantaneous Angular 

 Field of View 



Instantaneous 

 Field of View 



Direction of 

 Aircraft Motion 



Direction of Scan 



Object Space 

 Fig. 14-23 Instantaneous Field of View. Fig. 14-24 Linear Scan Pattern. 



