14-26] NEW DEVELOPMENTS 801 



bandwidth. The same effect is obtained by using multiple-element detectors 

 even though the time constant of each element may be low. In all cases for 

 any use whatever, the best system will be that which, for any fixed param- 

 eters, exhibits the break in the curve at the proper point and has the 

 highest ordinate value over the required temperature range. 



Such curves should be extremely useful from the design point of view. 

 For example, \i v jh requirements are not compatible with the location of the 

 break in the curve, the obvious factor available for trading purposes is the 

 A<^. An increase in A0 will cause AT to increase, but either the bandwidth 

 may be decreased or the scan rate increased. Choosing the latter, the value 

 of vjh is accordingly increased. In leaving the bandwidth alone, the 

 decrease in (AT X ^4>)~^ may be found, and a new plot will show a decreased 

 ordinate value, but the break in the curve has been pushed to higher 

 effective scan-rate values. Thus the optimum point of operation may be 

 determined, with comparisons for a change in any one parameter or 

 combination of parameters. A plot of the type discussed appears in Fig. 

 14-29. The values chosen and curves drawn are not at all representative of 

 actual values but are used merely to indicate the kind of information that 

 may be obtained. 



14-26 NEW DEVELOPMENTS 



Research and development in the infrared field promise many improve- 

 ments and new features that will extend the tactical and strategic usefulness 

 of IR ground mapping techniques. Major advances in detector sensitivities, 

 both spectral and absolute, will be realized. Evolutionary improvements in 

 optical systems, cooling systems, and materials will contribute to the 

 increasing efficiency of present high-speed scanning systems. 



The advanced development of matched line arrays and two-dimensional 

 mosaics of detector elements offers aid in the quest for higher scan rates for 

 the immediate future. These arrays are simply sets of single elements 

 placed very close together, each with its own electrical connections. 

 Adjacent elements thus look at adjacent regions in object space. The effect 

 is to increase the instantaneous field of view at the cost of system resolution. 

 The advantage thus purchased may be applied as greater total field 

 coverage, slower scanning speed, less bandwidth, greater data rate, etc., 

 or perhaps more profitably, as optimum compromises among these param- 

 eter variations. The major development problems are matching between 

 elements, and adequate (i.e. sufficiently noise-free) switching among 

 elements. 



Revolutionary changes in IR ground mapping may be anticipated with 

 the introduction of highly sensitive image tubes. Research is being done on 

 both photoconductive and thermally sensitive electron-scanned image 



