RESEARCH ON VISIBILITY: DEFLECTION-MODULATED SCOPES 



109 



bear on special problems. In passing, it 

 may be noted that the development of re- 

 liable scales of subjective brightness (18) 

 may aid materially in the rationalization of 

 these visual functions. 



Basic Parameters of Electrical System 



In the whole train of electrical events from 

 the initial broadcast of the pulse of energy, 

 through its echoing and reception and ampli- 

 fication, there are numerous stages at which 

 influence on the final pip can be exerted. 

 Most of these affect its intensity; some may 

 affect its shape. Many of them — particu- 

 larly those which affect signal strength — will 

 ultimately determine visibility in about the 

 same fashion, no matter what the form of the 

 indicator tube's display. Some of the rela- 

 tionships are critically dependent on display 

 forms. Even leaving out minor factors such 

 as construction imperfections, tube fife, and 

 such, there is a long list of system parameters 

 that presumably could affect signal detec- 

 tion. The major ones are: 



Most of these have been studied on some 

 kind of scope but only a few have been 

 studied on more than one. There have been 

 four major investigations made: one on an 

 A-scope by Haeff (16), one on a PPI by 

 Payne-Scott (44) and one using both an A- 

 scope and a PPI by the M. I. T. group (1). 

 The fourth is a continuing series of investiga- 

 tions on PPI's by several experimenters at 

 the Systems Research Laboratory of the 

 Johns Hopkins University. Both Haeff and 

 Payne-Scott have attempted to summarize 



the effects of the significant parameters in 

 equation form, Haeff using three parameters 

 for the A-scope and Payne-Scott using four 

 for the PPI. Payne-Scott's equation in- 

 cludes two additional constants based on 

 "average" visual abilities of the observer; 

 viz., one for brightness discrimination and 

 one for area discrimination. Except for the 

 M. I. T. group^ which has pubHshed no 

 theory to date but which is supposed to have 

 developed one, other investigatiors have re- 

 stricted themselves to empirical studies of 

 inter-variable relationships. The possible 

 combinations of 14 electrical parameters 

 alone constitute a formidable array of possi- 

 ble experiments! It is doubtful whether it 

 is worthwhile to attempt now an over-all 

 mathematical expression for detectability for 

 even one class of scopes, for the simple reason 

 that a great many visual and psychological 

 factors enter into detectability which are 

 largely uIlkno^vn. These will be discussed 

 in the next section. If understood in the 

 context of their limitations, equations can, 

 of course, be useful in stimulating thought 

 and new research. 



Research on Visibility: Deflection- 

 Modulated Scopes 



Only two representative studies will be 

 fisted here; others exist, but are not as com- 

 prehensive. These two are engineering 

 studies concerned mainly with electrical pa- 

 rameters. 



Haeff of the Naval Research Laboratory 

 (16) investigated pulse repetition frequency 

 from 30 to 1670 pulses per second, pulse 

 length from 2.5 to 20 microseconds, i-f band- 

 width from .005 to 1.0 megacycles, and video 

 bandwidth from .015 to 2.0 megacycles. He 

 found that detectability varied directly with 

 pulse length and with repetition frequency. 

 There was an optimal band pass which was 

 the reciprocal of the pulse length, although 

 later Ashby et al. (1) showed that it may be 



^ A final report of the M.I.T. studies is pre- 

 sumably forthcoming as Volume 24 in the Radia- 

 tion Laboratory series (45). 



