14-22] INTRODUCTION TO INFRARED RECONNAISSANCE 787 



estimate of the rated resolving power of present photographic films for 

 large-signal response is about 100 lines per millimeter. 



4. Enlargement Resolution — It can be assumed that the enlarger 

 resolution is equal to that of the camera lens. 



For these typical values the overall resolution of the photographic system 

 is found to be about 40 lines per millimeter. Since the resolving limit of the 

 CRT is of the order of 10 lines per millimeter, the photographic system 

 should not represent a limiting factor in determining the number of 

 resolvable lines. The above considerations have been in terms of the 

 number of resolvable lines to be obtained in the photographic process. 

 The final resolution will be affected also by the dynamic range of the film. 

 If the final map is to be a positive print, the total range of signal amplitudes 

 must be compressed within the rather narrow range of present photographic 

 papers, with a resultant loss of contrast. If the negative is to be viewed 

 with a projector, a much wider range of contrast will be available. 



As the reader has probably already concluded, the ultimate resolution of 

 a mapping system involves such a large number of different parameters that 

 the actual resolution that will be obtained must be determined by actual 

 operation of the system. However, knowledge of the effect of the various 

 parameters enables the system designer to make a reasonable estimate. 



14-21 FUTURE POSSIBILITIES IN AIRBORNE ACTIVE 

 GROUND MAPPING SYSTEMS 



Two areas that appear to be among those most likely to provide signifi- 

 cant improvements in future mapping systems are antennas, and display 

 and data processing systems. The maximum dimensions of physical arrays 

 are obviously limited, but synthetic arrays show promise of making it 

 possible to achieve large antenna dimensions effectively without large 

 physical dimensions (see Paragraph 6-7). New advances in display and 

 data processing systems include techniques for image enhancement through 

 video data processing and optical filtering. 



14-22 INTRODUCTION TO INFRARED RECONNAISSANCE 



Reconnaissance by the reception of naturally radiated infrared energy 

 provides intelligence that is difficult to obtain by other means. Photog- 

 raphy in the visible spectral region and radar at microwave frequencies 

 "see" the purely physical aspects of targets and terrain. Infrared mapping 

 "sees" a scene because of its heat content and contrast. While infrared 

 reconnaissance will generally provide poorer resolution than photographic 

 reconnaissance, it can produce several unique types of tactically useful 

 information. Experienced interpretation of infrared pictures yields 



