Illumination and Visibility of Radar and Sonar Displays Proceedings of a Symposium (1958) / Chapter Skim
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Session III - Display Requirements Imposed by Visual Factors
Session III - Display Requirements Imposed by Visual Factors
Pages 77-140
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From page 77... ...
Erdmann and Robert D Myers, Rome Air Development Center TARGET DETECTION AS A FUNCTION OF SIGNAL-TO-NOISE RATIO, PULSE REPETITION FREQUENCY, AND SCAN RATE J
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From page 78... ...
Two experiments were designed to measure separation thresholds as a function of target size, luminance, and amount and direction of contrast between target and background, for sharply defined rectangular targets, In three other experiments, the curvature and luminance gradient of the target's edges were varied as well. Discrimination improved with luminance, contrast, and definition of target's edge.
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From page 79... ...
slides; Fl, F2, filters; PL, projection lens; Ml, M2, M3, mirrors; Rl, R2, semireflectors; MSl, MS2, micrometer screws; D, dial; VS, viewing screen; K, long; P projector; CP, crossed Polaroids.
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From page 80... ...
Experiments 1 and 2 were concerned with the determination of separation thresholds for rectangular targets with sharp edges, ire a variety of sizes and height/width ratios and under a number of luminance and contrast conditions.
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From page 81... ...
Separation thresholds based on "together" and "apart" scores combined, Three independent checks supported the conclusion that the dark-target thresholds were higher. A further check on the effect of background size indicated that it had no significant effect within the limits of the present experiment.
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From page 82... ...
3. Separation thresholds based on "together" and "apart" scores combined, in terms of visual angle as a function of luminance at two contrasts for l/2-in.
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From page 83... ...
4. Separation thresholds based on "together" and "apart" scores combined, in terms of visual angle as a function of luminance at two contrasts for '/2-in.
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From page 84... ...
Summary Separation thresholds were measured for two simulated radar targets. The targets were varied in size, curvatureof-edge, blurring-of-edge, luminance, hue, and saturation.
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From page 85... ...
1. Apparatus: Ll, _ cells; F - filters; W - wedges; R - reflectors; T - targets; PL - projection lens; VS viewing scren; K - loot; S - subject; MS - micrometer screw.
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From page 86... ...
In Figs. 2 and 3, separation thresholds in minutes are plotted as a function of luminance as with the achromatic data in the preceding report, but, in the present instances the luminance range from 0-1 to 20 ft-1 is spread over the entire scale.
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From page 87... ...
2. Separation thresholds in terms of visual angle as a function of luminance, based on "together" and "apart" judgments combined, for colored targets on a green bacl~ground, at three different luminance contrasts.
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From page 88... ...
3. Separation thresholds in terms of visual angle as a function of luminance, based on "together" and "apart" judgments combined, for three kinds of edge characteristics.
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From page 89... ...
On blurred edges, the tendency to interact with wavelength is most marked for small targets and low luminances, but occurs in some degree with larger sizes and higher luminances. So far as these data have implications for operational radar, the main one would appear to be: beware of blue targets.
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From page 90... ...
There doesn't seem to be much information on curved edges. It seemed worthwhile to include them as a kind of check, especially since the question of form is important in many of these operational situations.
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From page 91... ...
This experiment was riot designed to investigate these cues but to answer a very practical question, viz., what is the dynamic range of an inter~sity-modulated, PI CRT? Stated differently, over what range of background input levels will detection of noise- or reverberation-masked signals be optimal?
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From page 92... ...
Does the dynamic range of the CRT change with grid bias setting? Is there an optimum bias setting for all input levels, or does the optimum shift as background input changes?
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From page 93... ...
settings. Figure 2 shows how detection varied as a function of input level with grid bias voltage as the parameter.
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From page 94... ...
In terms of operator performance, then, 38-v bias gave the greatest dynamic range even though it did not provide the lowest threshold at all input levels. It should be emphasized that the particular values of bias voltage and input level in this experiment probably apply only to this particular CRT and circuit.
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From page 95... ...
The Canadian people, also, are doing the same thing: the noise levels are very low, probably because they're working in radar and we're interested in sonar. Knoll: If I recall correctly, Mr.
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From page 96... ...
Certain things would be a little clearer to me, for example, the relation of these findings to the data on intensity discrimination, if we did have luminance measurements. As you know, luminance measurements of the cathode-ray oscilloscopes are not easy to come by, but certainly there are methods for obtaining them, and I think that if they could be expanded and more generally used' then the correlation of data on CRT viewing and such topics in the study of vision as intensity discrimination could be more readily achieved.
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From page 97... ...
As noise increases, threshold signal voltage also increases, and the influence of grid bias upon detectability decreases. The number of signal pulses has not specifically been the subject of previous research.
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From page 98... ...
The CRT was operated with second-anode voltage at 6000 v. Other simulated electronic parameters of the CRT included a range of about 50 mix an antenna rotation rate of 10 rpm' and a pulse repetition frequency of 400 per sec.
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From page 99... ...
was determined.0 Then a predetermined grid bias voltage and noise level were simulated on the indicator. The particular grid bias values ranged from 1 to 6 above VRI in 1-v steps, and the specific noise voltages, taken as an rms measures were 0.07 (noise-free)
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From page 100... ...
2. Threshold signal voltage as a function of grid bias, with video noise voltage as the parameter.
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From page 101... ...
Grid bias and noise level have the effect upon signal detection reported in an earlier paper.0 A change in grid bias voltage has its maximum effect upon visibility at low noise levels. A peak occurs at about +4 v from VRI.
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From page 102... ...
4. Threshold signal voltage as a function of number of signal pulses, at various levels of video noise.
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From page 103... ...
5 was derived: log V 0.7 + 0.3N 0.5 log R (2) where V represents signal voltage, N stands for noise voltage, and R is the number of signal pulses.
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From page 104... ...
In fact' for 8 or 12 pulses, signal-to-noise ratio seems to have already passed through a minimum at about 2.2v. It is also probable ~ · ~ ~ · · ~ .` ~ ~ 1 · 1 that, If determination of threshold signal voltage could have been obtained for one and two signal pulses at the two highest noise levels (2.2 and 3.2 v)
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From page 105... ...
7. Signal-to-noise ratio in decibels shown as a function of number of signal pulses for an optimum grid bias, with video noise voltage as the parameter.
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From page 106... ...
Thus, holding pulse repetition frequency and antenna rotation rate constant, as in this experiments maintains a constant background brightness, and the main effect of increasing the number of signal pulses is to enlarge the pip area. These two effects upon the physical stimuli (changing background luminance and changing area)
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From page 107... ...
You made the statement that' because we have a logarithmic relation between two of the variables investigated' the "comparability" between this rule and Piper's law should not be overlooked? - 7 Erdmann: I just added that as an interesting afterthought, since number of pulses actually determined the area of the signal and signal voltage controlled brightness.
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From page 108... ...
But I do know that from the engineering point-of-view it is advantageous, when you have greater-thanunity signal-to-noise ratio, to use a higher brightness level and also to increase the speed of the repetition of the hits. Below the noise level, there's a different situation because both voltages are operating in the same region.
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From page 109... ...
The B-scan simulator supplied the indicator with the azimuth and range sweeps and the video information consisting of both target signal and noise. The simulator was devised in such a manner that scan rate, pulse repetition frequency (prf)
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From page 110... ...
The spot size of the indicator was ~ mm in diameter. The distribution of the target returns on the Indicator ot the system was determined for the various prfs and scan rates used.
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From page 111... ...
The pulse train was then fed into the I-F mixer. The I-F mixer also received the output of the noise generator, which was set up so that three different noise levels could be selected with signal-to-noise ratios of +6, +2, and-2 db.
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From page 112... ...
A five-way analysis of variance was performed with the number of correct identifications of target position as the dependent variable and with signal-tonoise ratio, pulse repetition frequency, antenna scan rate, observers, and replications as the main sources of variance. The results of this analysis showed that all main effects are statistically significant at the 0.001 level and that all first-order interactions with signal-to-noise ratio are significant at the same level.
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From page 113... ...
3. The mean PD for the various scan rates is shown as a broken line.
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From page 114... ...
The curves for higher scan rates? 100 and 120 degrees per see, seem to saturate at a level of PD below that of the lower scan rate of 50 degrees per sec.
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From page 115... ...
hits per scan (scan rate parameter)
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From page 116... ...
I should like to ask a question concerning the rate of the pulse repetition. As I remember, you were dealing with pulse repetition rates of many hundreds per see, so this is an entirely different order of magnitude from the pulse repetition rate discussed by Captain Erdmann.
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From page 117... ...
Personnel contemplating the use of these scopes suggested the possibility that the viewing of flickering lights over a prolonged period of time might cause deleterious effects on the scope observer. Lights flickering at the rate of 4, 8, or 12 c were presented on a simulated radar scope for periods up to 2 hr to determine whether or not prolonged viewing did affect observer performance.
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From page 118... ...
Thus, the total time required by the subject to respond correctly to changes in the number of non-flickering lights could be obtained by subtracting the response clock reading from that of the first timer. Readings were taken by the experimenter every 5 min and provided a basis for measuring the cumulative latency of correct responses by successive 5-min intervals throughout a session.
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From page 119... ...
The cumulative latency was calculated for correct responses to changes in the number of non-flickering lights made by each subject during an entire session. These cumulative latencies were expressed as percentages of the session length.
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From page 120... ...
1' 2, and 3 that the functions for the various flicker rates tend to be displaced systematically on the ordinate, with the higher rates apparently increasing the latency of correct responses. In order to verify this phenomenon, three subjects were tested for 30 min on each of the three flicker-rate conditions, as well as on the control condition.
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From page 121... ...
3. Effect of varying flicker rate on response time for 1 20-min session.
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From page 122... ...
However7 a finding of particular interest is the difference in performance obtained as a function of the flicker rate of the field lights. The smallest latency was obtained for non-flickering lights presented alone.
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From page 123... ...
There were four steady lights presented against a background of twelve flickering lights. Periodically, the experimenter changed randomly the location and number of the steady lights.
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From page 124... ...
The experiment duplicated exactly the size of scope and flicker rate. The lights on our display were closer to the orange end of the spectrum, while the scope display appeared to offer signals closer to the blue end.
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From page 125... ...
The six restricted areas ranged from 0.1875 to 6.0 in. Four noise levelss light, medium, heavy, and no noise, were utilized.
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From page 126... ...
The total viewing area subtended a visual angle of 36.8°. The center of the ring was located 3 ill.
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From page 127... ...
The four noise levels were: O (no noise at all) , 1 (light noise)
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From page 128... ...
The latencies for the total viewing area for the light, medium, and heavy noise conditions are 5.6, 6.2, and 6.3 see, respectively. In general, the results indicate that within the limits of this experiment, any restriction of the search area is an improvement over utilizing a non-restricted area, and that target detection is best for search diameters of 1.5 in.
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From page 129... |
From page 130... ...
Comments following Weasner's paper: Graham: Thank you, Mr. Weasner, for a very interesting and very clear result.
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From page 131... ...
1' the two frontal widths Se and Sg are shown as having angular frontal sizes be arid be while in the lower part of Fig. 1, the two depth intervals Xef and X 7h are shown as producing the binocular disparities orb- OLf and OLn OCh.
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From page 132... ...
1 that the frontal size Se' together with the depth interval Xef, defines an object having a frontal and a depth component and thus a particular three-dimensional shape. The perceived shape of this (the nearer)
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From page 133... ...
(2~) The term Ee/6'e in equation 2 is the perceived size per unit of angular frontal size at the distance De and is therefore (within limits)
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From page 134... ...
This is the case of perfect frontal size constancy mentioned above. When n 1, equation 4 becomes: (4)
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From page 135... ...
1, the problem is to determine the size of X97t which will be perceptually equal to (or in the more general case be some perceived multiple of) the perceived size of Xef.
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From page 136... ...
However, observers will differ in the amount of frontal constancy they evidence in a articular binocular situation and the above equations indicate the direction of the consequences of these differences.
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From page 137... ...
From equation 32, the change in the depth X required to maintain a constant perceived shape of a three-dimensional object of constant frontal size S increases linearly with distance, independent of the amount of frontal constancy present. But, from equation 29, the amount of binocular disparity or linear depth required to produce a particular value of m for a particular value of S is not independent of n.
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From page 138... ...
All this assumes, of course, that the only cue to the perceived distance between the pair of objects is the binocular disparity cue from these objects. When the binocular disparity cues between one of the pairs of objects and additional objects is considered, or when other cue systems are introduced to influence the perception of the depth interval, the situation may become more comple.~° Certainly, additional experimental data are needed, not only to test further the validity of the point of view presented in the above equations, but to extend our information concerning the psychophysical scaling of three-dimensional space to increasingly complex situations.
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From page 139... ...
This account, I think, will have-again I say if it is validated a good influence on the psychology of depth perception. It is sometimes said that if you are paying most of your atteention to retinal disparity, geometrical optics, and topics of that sort, you are not really a psychologist; you are something else.
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