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IMAGE VELOCITY SENSOR SUBSYSTEM 

AD HOC REVIEW GROUP 

FINAL REPORT 

SEPTEMBER 1968 

BRIAN O'BRIEN, CHAIRMAN 

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IECREPRIAN 

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I. INTRODUCTION 

The Image Velocity Sensor problem has been a critical item 

since the beginning of the MOL Program because it is essential to the 

performance of the unmanned system and highly desirable for the manned 

version of MOL. At the time MOL was originally conceived, the image 

tracking function was to be a manual task and the automatic tracking, by 

means of a closed loop device such as an Image Velocity Sensor, was not 

yet considered technically practical. In the early phase of the MOL 

Program several schemes were proposed and, eventually, because of 

the criticality of this problem, three approaches, presented by Itek, 

Goodyear, and Hycon, were started. 

In the spring of 1968 significant problems were uncovered when 

General Electric conducted some of the early simulations and tests on 

the breadboard models supplied by each of the three subcontractors. 

The problem of whether appropriate closed loop image tracking techniques 

could be perfected in time for the required integration into the system 

became a critical program concern. The program development schedule 

called for elimination of one of the three competing contractors and 

General Electric recommended the termination of the Itek contract. MOL 

program management, however, elected to continue with the three because the other subcontractors were also having difficulties and there 

were some questions concerning General Electric's test and evaluation 

techniques. 

In view of the foregoing, it was decided to convene an IVS Ad Hoc 

Committee to review the MOL image tracking problem, to compare the 

proposed approaches and, if appropriate, to recommend alternate methods 

for accomplishing the image tracking task. Ideas such as laser ranging 

and open loop operations with the aid of precise celestial target referencing 

were proposed as alternate schemes. 

While the Committee was being formed, General Electric and 

the subcontractors continued with their work and made significant progress toward eliminating some of the deficiencies discovered in earlier 

tests. The Committee convened on 20 September and after a review of 

the subcontractors' work and the General Electric evaluation process, 

it was the consensus of the Committee that the MOL Program can proceed 

with the selection of one of the proposed schemes and that it is probable 

that target tracking will be adequate to meet system requirements, and 

the introduction of alternative schemes would serve no useful purpose. 

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Some questions remain on the validity of the specifications, 

the fundamental understanding of the various schemes, the ultimate 

choice of subcontractor, the validity of the simulation, and the operation of the system in the presence of clouds. These subjects and 

the Committee's recommendations are discussed below. 

II. SPECIFICATIONS 

1. Status 

a. General 

The critical performance requirements which are 

being applied to the IVS vendors by GE are, in some cases, more severe 

than is required by the DORIAN system. In some cases, the performance requirements, as established by the Air Force, are well understood. 

In other cases, the specification is a considered choice based on a desirable characteristic which appears obtainable at little penalty. It is 

recognized that these matters deserve continued intensive attention, but 

there appears to be no instance where a significant problem is being 

created. Detailed discussions with Aerospace personnel involved in 

formulating the specifications indicated that each issue of concern to the 

Committee was recognized by Aerospace and was under consideration. 

b. Light Level Performance 

No formal specification has yet been made. The revised Wiener spectrum indicated as forming the current requirement 

was a matter of disagreement between Aerospace and GE. It appears 

that, assuming the more favorable IVS illumination as a result of using 

all the diverted light below 15° sun angle, the anticipated specification 

is reasonable with a questionable area remaining in the region of high 

illumination and low modulation. There is a question about the specification of Wiener spectrum at 100 feet per cycle. For purposes of vendor 

selection and proof of feasibility of devices, it appears desirable to agree 

to a Wiener spectrum box outline (see Figure 1) quickly and refine it as 

necessary later. 

c. Dynamic Range 

The IVS is required by GE to operate over 0-600 P rad/ 

sec. The 600 A rad/sec is considered by GE to represent both open loop 

performance and residual rate at end of slew plus 3 seconds. It appears 

that in either case the number could be lower, but the large capture rate 

requirement is stated to be achievable by all vendors. The Air Force, 

however, should consider carefully the specification of open loop performance with the goal of best optical. performance without IVS lock-on. 

DORIAN 

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d. Linearity 

The null region requirement of + 10% monotonic 

appears reasonable. The large signal region requriement of + 25% 

monotonic with no saturation until 6001 rad/sec is overly severe, but 

does not seem to limit the IVS vendors. 

e. Accuracy 

NA rad/sec. This value seems achievable and 

reasonable, although a slightly larger value could be accepted in view 

of the remainder of the budget contributions to the over-all specification 

of 4214rad/sec. 

2. Recommendations 

a. Determine the Wiener spectrum illumination region 

to be specified as soon as possible, but continue to study the implications 

of the specification intensively. 

b. Obtain a tightened specification for open loop performance based on acceptable optical performance without IVS lock-on. 

c. Monitor the IVS specifications levied by GE and insure 

that the Performance of the IVS under conditions of good DORIAN performance is not jeopardized by attempting to meet the extremes 

of the specification and, similarly, to insure that unessential complication 

of the IVS is not introduced. 

III. IVS SELECTION 

1. General Observations 

In the Committee's judgment, none of the subcontractors exhibited a complete understanding of the possible behavior of his own 

system. This may be an unfair judgment. The Committee believes, however, that in the best interests of the MOL Program, a basic understanding 

of the Goodyear and Hycon systems should be developed before a final 

selection between them is made. Considering not only the immediate problem of the current MOL Program, but also the future, e.g. , the search 

for higher resolution, one should also include the Itek system in this 

analysis. Since the three systems operated on different principles, the 

Air Force should thoroughly understand these differences and examine 

the limitations of each in environments other than those now specified 

for MOL. It is likely that each scheme will have special advantages in 

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particular environments. It may also result that even in the specified 

MOL environment of rates, contrasts, light levels, etc., peculiar advantages or difficulties will be found. 

A basic understanding of the several systems would permit 

an analysis which could answer, for example, such questions as: 

As presently mechanized, the Itek system works on 

information in the high frequency part of the Wiener spectrum of the 

scene. Goodyear and Hycon work on much lower spatial frequencies. 

What are the limitations or possibilities in applying the Itek principle 

to other parts of the spectrum? What part of the spectrum should be used 

by the sensors? For example, is there a band of spatial frequencies over 

which all scenes have similar Wiener spectral intensities? If so, which 

of the three systems can best be optimized to work in this band, and what 

advantages, other than scene-insensitivity, are gained? Goodyear works 

with quantities which are quadratic in illumination level, while Itek and 

Hycon are intrinsically linear in illumination level. Hence, one would 

expect the Itek and Hycon principles to degrade more gracefully as one 

designs for lower and lower light levels. Are there interesting light 

levels at which this phenomenon has a useful effect? 

The Committee would feel more confident in a final selection 

if there was available an evaluation of all of the systems within a framework as basic as that suggested by the preceding questions. 

Z. Subcontractor System Evaluation 

a. Itek 

The Itek system works by integrating the effect of 

image smear over a period of about 44 ms. The resulting smoothing 

effect reduces the high frequency content of the Wiener spectrum of the 

image, and the servo generates a compensating motion which maximizes 

that spectral content of the image. The spectral band in question, said 

to be around fifteen feet per cycle, is such that the Itek system will be 

inherently more sensitive to image focus than the others. 

Since the Itek device works on scene content in the 

region of fifteen feet per cycle, the present specificatitm, which is keyed 

to wave lengths of 100 feet per cycle, is not directly applicable to its 

design considerations. 

Itek has chosen to work with a standard vidicon and 

standard TV scan rates. This gives Itek a sampling system with a 

particular fixed upper limit on its bandwidth, and fixes the integration 

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time in a not very controllable way. It is likely that an optimum 

system using these principles would require both an integration time 

different from the present 44 ms, and an internal sampling rate different from 30 scans per second. The TV method can be made to work, 

but the approach has not progressed far enough to be considered a 

candidate for DORIAN. 

Itek representatives stated that the addition of an 

image intensifier ahead of the vidicon would increase the light sensitivity 

and have certain other advantages. 

On an engineering basis this requires handling high 

voltages in the image intensifier which are undesirable if other means 

are available. 

b. Goodyear 

The correlation device is in an advanced stage of 

development, and probably will be suitable for the DORIAN system. It 

operates on quantities which are quadratic in both illumination and modulation (unless slicing takes place). The full implications of these facts 

are not understood by the Committee. However, such a system is 

normally plagued by the basic limitation of correlation techniques when 

used for servo purposes. If the true correlation of the compared scenes 

is low, the uncertainty of the calculated or derived correlation is very 

large. This results in noisy or spurious signals and attendant servo 

stability troubles. While the method of using and inserting the IVS 

signals into the scan mirror servo may protect it from spurious commands, 

this limits the usefulness of the correlation method. Roughly, the true 

correlation of the compared scenes must be high (above 70%) to have a 

certainty of the derived correlation value better than 50%, which probably 

means the correlation device will require frequent recycling under actual 

scene conditions. However, the long focal length and consequent narrow 

acquisition angles of the DORIAN system seems to promise sufficiently 

high actual correlation between the stored and compared scenes that the 

method is expected to work. The practical response when recycle time 

is considered may be somewhat slower than described. This correlation 

device having no moving parts is passive in a mechanical vibration producing sense. 

The Goodyear device works on what could be called 

a "matched filter" technique. Considerable analysis is available on 

this technique, most of which would have to be modified somewhat to 

include the effects of the large and variable "dc" component of the optical 

signals. It is not yet fully clear what spatial frequencies in the scene 

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are important to the operation of the present Goodyear device, although it is probably the lower frequencies. (This is evidenced by the 

fact that the system is insensitive to defocus.) An analysis in terms 

of matched filters might suggest ways of optimizing this frequency 

selection against focus changes and changes in scene. 

The contractor's belief that his "dynamic null" 

problem is an artifact of the simulator seems to the Committee to be 

correct. However, the question should be examined with greater analytical power than the Committee has seen applied to it. The Committee 

has already suggested certain additional tests and a good analysis may 

suggest more definitive ones, or even show that present data are already 

adequate. 

The subcontractor showed that his correlation can 

be used for contrast enhancement, but his discussion was inadequate to 

demonstrate exactly how this capability could be effectively exploited. 

Neither did he show whether, were it exploited, it would lead to useful 

advantages in performance. The Committee believes that more understanding is required before the usefulness of this feature can be evaluated. 

The subcontractor mentioned several modifications 

to his system which would add new features not covered by the present 

MOL requirement or specifications. The Committee suggests that the 

Air Force may be interested in having these matters explored further. 

However, the Committee does not believe that they are relevant to the 

choice that must soon be made. 

c. Hycon 

The Hycon system makes a comparatively direct 

measurement of velocity. Its operation can be, if the designer chooses, 

linear in applied illumination and contrast. Its operation depends for 

the most part upon principles well known and understood in electrical 

engineering. The vendor has ready control over the spatial frequencies 

to which his system is sensitive, and has exercised this control for optimization. 

Even within the framework of his present mechanization, he has a wide latitude of design choice in selecting the important 

parameter of operation. The principles he exploits can be adapted to 

designs for an even wider range of operating conditions. 

It appears to the Committee that Hycon's remaining 

problem, in the present instance, "Scalloping," can be solved adequately 

IECRETYRIAN 

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by shaping the illumination across the field. Analytically, the problem 

is like that of illuminating an antenna for minimum side lobes or designing a filter for minimum echoes. Analysis provides both a solution 

and an estimate of its limitations. 

Hycon asserts that the weight and bulk of their 

system can be reduced. This appears likely. The signal drop-out 

problem experienced in test appears adequately handled by the feedback 

memory technique. This device has a mechanically active element; 

namely, the rotary chopper disc which rotates at 30 Hz. With careful 

attention to bearings and balance, the residual vibratory disturbance 

should not cause difficulty. This device appears at this writing to be 

the most applicable to the DORLAN system IVS requirement. 

IV. CONCLUSIONS 

1. With respect to the selection of a contractor and system 

for the MOL mission, the Committee agreed that: 

a. On the basis of information now available, either 

Goodyear or Hycon could be selected with relatively high confidence 

of success. 

b. There is no reasonable possibility that, by the time 

a decision must be made, the level of confidence in Itek will be comparable to that in either of the others. 

c. A selection between Goodyear and Hycon will depend 

upon engineering, and possible programmatic, factors which the Committee 

is not prepared to judge in this report. 

2. With respect to a consideration of whether to terminate one 

or more contractors now or when to terminate all but one, the Committee 

observes: 

a. There seems to be no immediate benefit to the MOL 

Program in continuing Itek. 

b. The advantage in continuing both of the other contracts 

for the present are: first, the value of competitive pressure and, second, 

the possibility that further exploration of some of the engineering factors 

(e.g., weight, power, vibration, reliability) will show a clear advantage 

to the MOL Program in one of the approaches. 

c. The principal disadvantages to continuing more than 

one contractor probably li e in the costs of testing and in the demands on 

GE and Aerospace talents. 

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V. RECOMMENDATIONS 

a. It is recommended that the present phases be completed 

on all devices, except that further tests be conducted by General Electric 

only on the Goodyear and Hycon devices, and that the Itek device be 

sent to the Avionics Laboratory for further study. It is recommended 

that the Goodyear device be carefully reviewed for possible correlation 

with real scenes that may limit its effective response. 

b. It is recommended that the Hycon device be reviewed for 

correction of the signal drop-out that may be experienced under real 

scene conditions. Attention should be given to bearing noise vs. life 

in the Hycon device rotor to insure that the residual 30 Hz mechanical 

disturbance does not cause any difficulty in the adjacent optical or camera 

units. 

c. It is recommended that both the Goodyear and the Hycon 

devices be continued even though they both probably will not meet the 

low modulation-high illuminance corner (Wiener spectrum diagram -

Figure 1) of the present tentative specification. 

d. It is recommended that upon successful completion of the 

test program, an early final choice be made between the Goodyear and 

the Hycon devices. 

VI. SUPPLEMENTARY SUBJECTS 

1. Simulator 

The IVS simulator appears to be a good design, but there 

are certain defects which seem to penalize the Goodyear more than the 

Hycon device. The first, which is fundamental, is that reasonable space 

limitations require short working distances from device to target platen, 

so that the field angles are much higher than those to be encountered 

in MOL. It is recommended that General Electric and Goodyear explore 

this to their mutual satisfaction so that allowance can be made in the 

interpretation of test results. 

A second defect is the specular reflection from the semigloss photographic paper used in the target. It should be possible to 

reduce this either by good matte paper or by combining high gloss (or 

ferrotyped) paper with properly placed flood lights. It is recommended 

that this be done. 

There are uncertainties about the behavior of IVS on three 

dimensional targets with shadows. Since a three dimensional model is 

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already completed, it is recommended that the engineering models 

of Goodyear and Hycon b e tested on the simulator using this model 

as well as the flat print for target. The high gloss paints on this 

model may have to be dulled. More important, it should be recognized 

that even with a model in correct scale, the perspective will be distorted 

by the short working distance which may complicate IVS performance, 

so that test results should be interpreted with caution. 

2. Clouds 

At the request of the Air Force, all contractors spoke to 

the question of IVS operation in the presence of clouds. Ingenious ideas 

came forth, but all discussion was speculative. 

The Committee believes that the Air Force must clarify 

its own understanding of the requirement to operate in the presence of 

clouds, before this issue can be used as a criterion for choice between 

IVS systems. Indeed, the Committee believes that this clarification 

should take place before money is spent with contractors in attempting 

to meet a cloud requirement. 

The basic question is: How important is it for the system 

to operate in the presence of clouds? In the MOL environment, this 

spawns more complicated questions: 

How often, when the primary target is obscured, can one 

successfully photograph an alternate? How good is the resulting photograph, and how much does this quality improve with good IVS sensing? 

What then are the requirements to be met by a useful IVS? 

The Committee saw no evidence that the Air Force had 

addressed these questions, and recommends that none of the contractors 

be required to demonstrate their device's capability in the presence of 

clouds until it is better understood by the Air Force. 

It is suggested that the open loop tracking capability to 

permit good photography if the IVS loses track in the presence of clouds 

be improved as much as reasonably possible. 

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GE Proposed Curve 

4;s, 

„0,4c7"/' 

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150 800 3200 3P". 

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20,000 

10,000 

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Preliminary Systems Office Curve to Define 

Environment Extremes 

Average Brightness (Foot-Lamberts) 

Note: All data referenced to tracking mirror input at 

80 nm altitude. 

Figure 1. IVS Power Spectral Density and Brightness 

Operating Regime. 

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