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INTRODUCTION TO THE DORIAN IVS SYSTEM 

10 September 1968 

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INTRODUCTION TO THE DORIAN IVS SYSTEM 

Intrinsic to the concept of the Dorian system is the need for precision 

image velocity compensation in order to maximize the resolution performance 

of the optical system. 

Fundamentally, the problem is depicted in Figure 1, which shows a plot of 

ground resolution versus focal length. As the focal length is increased, the 

effect of the film graininess is diminished because of the relative size difference 

between the lens point spread function and the film grains. However, the light 

density in the image plane decreases inversely as the (f no. )

2

, and thus exposure 

time must be increased proportionally. If an image velocity rate exists, the 

smear then is the product of the rate times the exposure time. Therefore, in 

order to maximize the resolution, the longest focal length was picked within the 

practical constraints of the manageable image velocity. 

Initially, the allowable rates selected for image velocity were determined as 

those feasible with manned tracking and were set accordingly at a value of 

In addition to this tracking error, there are additional contributors 

in the form of vibration and servo drive system noise errors. These terms, as 

indicated in Figure 2, added to a total budget of .(rss). 

During the manned development (because of concern with the political sensitivity of manned overflight and cost effective reasons), it-was decided that the 

Dorian capability should also be available in an unmanned configuration. At this 

point, studies of potential devices to perform the manned tracking function were 

undertaken, and the image velocity sensors now under development were identified. 

--, 

TheThree different concepts are being pursued by Itek, Goodyear, and Hycon. 

Itek device is basically a vidicon scanning device with mechanically introduced 
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modulation of the image to provide a drive error signal for nulling. The 

Goodyear device involves the use of a correlation tube which electronically 

performs a mathematical correlation of the present scene with a formerly 

stored scene, and again through suitable modulation, provides an error signal 

for the servo drive. The third device is the Hycon image velocity sensor which 

utilizes a reticle wheel to modulate both a reference light and the scene, and 

by sensing phase changes provides an error signal proportional to the scene 

motion. A somewhat more complete description of the operation of these devices 

is presented in Appendix A. 

In developing these devices, the requirements were specified in order to 

assure proper operation. The rate accuracy requirement was chosen at 

in that it was shown to be feasible by early simulation and was sufficiently 

close to the manned tracking value to be compatible with the Dorian optical system 

optimization. The response times, in terms of slew and settle, were principally 

set by the frequency response of the basic instruments. 

The initial capture rate of_'sec was established as a feasible rate 

using projected navigational accuracies, target location, and elevation errors. 

These data are given in Figure 3. 

In addition to the rate and slew time requirements, an important specification 

parameter is the scene characteristics for which the sensor must work. A complete "scientific" description of typical scene characterigtics is not currently 

available for sensor design. However, the description of the brightness variations 

in typical scenes as a function of spatial frequency has been addressed. This 

descripticm. provides an estimate of the scene brightness ,modulation present over 

which a given sensor must be capable of operation. These data, combined with 

the sensor sensitivity, provide a measure of the amount of signal available over 

a given noise threshold level (i.e., signal-to-noise ratio predictions for signal 
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While the contrast of the scene is used generally to describe, at least in a 

qualitative sense, the image quality expected of a photographic system, it is 

unsuitable for specifying sensor performance because it does not describe the 

instantaneous changes in brightness as the sensor scans across the scene. 

Therefore, in order to describe a meaningful set of parameters, the Wiener 

spectrum approach was used. That is to say, the statistical properties achieved 

in scanning the scene are used to describe the scene brightness characteristics. 

The Gambit and Gambit3systems use a focus sensor which is dependent on scene 

• 

modulation. Assuming the Dorian target areas are of the same general type, data 

from this sensor should be indicative of the requirements for operation of the IVS 

on the Dorian system. In developing the scene characteristic specifications for 

Dorian, large amounts of G3 focus data were used to calculate the Wiener spectrum brightness properties of the scenes, and the specifications were set for the 

Dorian system which would essentially capture 95 percent or better of the conditions that occurred on theSe flights. 

The additional requirements of the sensor, such as its specific time constants 

and frequency responses, are related to the properties of the tracking mirror 

drive loop and are not fundamental requirements in the sense of mission-oriented 

operations. More specific explanation of the specification development is given 

in Appendix B. 

In order to evaluate the performance of the sensors, a test program has been 

developed which ultimately will allow the selection of one of these sensors for 

incorporation in the Dorian system. The initial phase of this test program was 

a series of bench tests and tests run on a simulator which presented the scene to 

the IVS in such a way that the velocity at the center of the scene was zero, and 
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major additional effort in order to resolve them. They include the dynamic null 

problem which is characterized by fluctuating erreneous IVS outputs as the 

instrument traverses stereo angles from fore to aft through nadir. Generally, 

the instrument performed satisfactorily around nadir to angles of 10-15° off 

nadir, but developed major out-of-spec vacillations outside of this area. This 

problem is associated with the fact that the spatial frequency content in the scene is 

not uniformly distributed; as the stereo and obliquity angles change, the scene 

content changes, and the average velocity at the optical axis changes also. Another 

way of stating the problem is that the centroid of zero velocity drifts out of tolerance 

about the optical axis. 

The second major problem is that the instruments generally were too insensitive 

and could not operate down to low enough levels of scene modulation. An additional 

problem peculiar to the Goodyear instrument was a drift in transient rate errors 

which may be contributable at least in part to the test conditions. The Itek instrument, while exhibiting little dynamic null type problems, had the additional problems of scene and error dependent nonlinear gains, scene dependent bias, and 

large transport lag associated with the vicidon frame rate time. The test program 

is described in Appendix C. 

The need for more instrument sensitivity primarily is related to the Goodyear 

and Itek instruments and has been partially solved by increasing the amount of 

light available to the IVS from the main optical system. In addition, improvements 

in the tubes appear to make operation within specification feasible. 

There are several schemes applicable for alleviating or solving the dynamic 

null problem such as aperture shading, aperture control,f and electronic limiting, 

all of 'which show a reasonable degree of promise. If the solutions to the dynamic 

null-problem fail to solve it completely, the other alternative would be at extreme 
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stereo and obliquity angles to relax the specification tracking requirements on 

tracking rate. Obviously, this is undesirable in that it lessens the resolution 

of the resulting product, although the extent may be quite modest. 

The results of the tests show a capability, at this time demonstrated by 

the Hycon instrument only, to work over most of the modulation light level specification, with the exception of cases of very low modulation at high average light 

level, In general, this case can exist if the scene consists of a snowfield with a 

small portion of it containing a target area of buildings or other high modulation 

content items. Therefore, the question arises as to what the system operation 

should be under these conditions. One approach is to use the rate data obtained 

from previous targets, and from it compute the proper rate for the upcoming target, and if the IVS fails to provide rate data as good as the computed data, the 

computed data alone would be used. While the present navigation and control system 

has not been required to perform better than the /sec capture rate of the 

IVS or flight crew, by using various software techniques for computing the bias, 

the rate achievable can be the order of . For comparison, the■ 

rate will result in Dorian system performance comparable to that of 

the G3 system. Thus, for the vast majority of targets, the IVS would provide 

Dorian quality imagery and for those few where insufficient modulation exists 

with high average light level, G3 level pictures could be obtained for the unmanned 

system, and in the manned case, Dorian quality can still be achieved through manual 

• 

operation. 

An associated problem with the IVS sensor is the case where within the 3,000 

feet or so field of view at the ground level of the sensor,tpart of the scene is 

obscured by a cloud edge. Here, the extent of the problem depends on the 
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magnitude of the cloud modulation and the altitude difference of cloud to target, 

which will contribute to the total sensor error. Therefore, the question arises 

as to the desired discrimination ability of the IVS against cloud data. 

In the early unmanned system discussions, it was proposed to operate 

the system on the IVS value if it was within the updated computed value and if 

not, to use the computed value, thus insuring picture quality of useful intelligence value. However, if cloud discrimination could be implemented, some 

additional number of pictures could be obtained approaching Dorian quality in 

the unmanned case. An additional factor in this concept is the fact that while 

the cloud edge is discriminated against, the centroid of tlie remaining scene 

velocity is no longer centered on the optical axis. This will result in errors, 

because the camera across-the-format device is built to take out differential 

format velocity errors assuming the center of the field is corrected. When the 

centroid of the tracked velocity point is not in the center of the field, significant 

errors will be introduced. 

The present plan is to specify the IVS performance excluding clouds from 

the field of view and implement further studies in terms of implementation 

approaches and error contributions. Upon conclusion of these studies, the 

capability will either be included in the Dorian system or recommended for 

future advanced technology effort. 

In conclusion then, the specifications for the IVS have been established 

based on manned system optimization data, operating experience on the G system, 

and the intrinsic properties of the servo drive system in which the sensor has to 

operate. Performance to date indicates that while problems have been identified, 

reasonable solutions are in work that will allow operatibn within specification 

over most of the desired operating regime. By utilization of the calculated rate 

command for the very infrequent cases of scene conditions where the sensor mal- 


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APPENDIX A 

IVS DESCRIPTIONS 

Goodyear 

1. The Goodyear IVS is functionally a spatial (two-dimensional) 

correlation detector. The system seeks to null the rate error by searching 

for a maximum of the spatial correlation function and tracking with whatever 

rate correction is necessary to maintain maximum correlation. The sensor 

consists of the "Correlatron" tube and an appropriate null-seeking feedback 

control loop. To perform the spatial correlation operation requires a series 

of time-related steps beginning with the "write" mode, in which the scene is 

initially stored on the intermediate storage grid or screen of the Correlatron 

tube. This stored scene will serve as a reference throughout the remainder 

of the cycle. During the "read" mode, the actual input scene is imaged on 

another screen placed in front of the storage plane, producing an equivalent 

electron beam replica of the scene. (See Fig. A-1.) The electron replica 

continues on to intersect the storage plane, and an output signal results 

which is a measure of the correlation, or agreement, between the stored 

and projected images. This signal is maximum when the two images are 

identical in every detail. The electron replica, while in transit to the 

storage plane, may be deflected in two (independent) orthogonal axes by 

magnetic field-producing coils. 

At any time after initial storage, with non-zero input image motion, 

the actual scene will be displaced from the stored scene in the direction and 

distance described by the velocity vector times the elapsed time, resulting 

in a less than maximum correlation result. The field coils are energized to ' 

bring the actual scene to coincide, as much as possible, with the stored 

scene, and the degree of drive necessaryto do this is a measure of the distance transversed, or equivalently of the scene- rate. The feedback loop acts 

to maintain the displaced electron replica in coincidence with the stored image, 

giving analog data on the rate in each orthogonal axis, until the stereo angle 

change becomes too great. A block diagram of the sensor processing configuration is presented in Fig. A-2. At this time an "erase" mode is initiated 

and the entire cycle is repeated, with a new stored image and tracking acqui- 
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Itek 

2. The Itek IVS depends for its operation upon the integration 

effect on a scene moved across a vidicon face and the fact that the high 

frequency content of a random signal is diminished in relation to the amount 

of "smear" of the signal. Figures A- 3, A.4 and A-5 present a block diagram, 

pictorial schematic and summary of the operating principles of the Itek 

sensor, Consider the sensor with zero input rate. The input scene is 

imaged on the (fixed) vidicon tube face and by means of a nutator is swept 

sinusoidally across the tube face at a frequency equal to one-half the frame 

rate and in a direction parallel to the scan lines. (The sensor is capable 

of operation in both axes due to an arrangement of mirrors which transmit 

a portion of the input scene rotated through 90 degrees to the vidicon face. 

The complication is not necessary to an understanding of the basic operating 

principles of the device and will be ignored at this point in the discussion.) 

For any given scan line, the degree of high-frequency attenuation 

in the output signal, as that line is scanned, is dependent upon the amount 

of smear in the image along the line. This is a well-known result and is 

easily derived with an equivalent smear or dispersion transfer function. The 

amount of smear for the line is related to the distance along the line that the 

image was swept by the nutator since the line was last scanned. If the image 

displacement function (due to nutation alone) is A sin wt, then the line scanned 

r at times 0,— ' 2 ir ... will exhibit smear porportional to A. On the other 

co co co Tr 3Tr hand, the line scanned at 2— , 2 w will exhibit smear proportional to 

2A, and the corresponding signal will contain less high frequency energy. 

If the high frequency energy is isolated and filtered, the result is a second 

harmonic term (2 w) with no input rate, If now a linear input rate is superimposed upon the nutation oscillation, the smear characteristic will be 

different for positive and negative excursions of the image, and therefore the 

output signal will contain a fundamental frequency components more or less 

proportionalto the input rate. Further, the phase of the fundamental indicates 

the direction of the input rate. The output signals and of course dependent 

upon light level, and the Itek design intends to suppress this dependence by 

using the second harmonic term to drive an AGC network, This approach 

assumes the second harmonic is affected solely by light level, which is in fact 

not true, but becomes a better approximation as null rate error is approached. 
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Hycon 

3. The Hycon 'VS is essentially a phase-lock loop where the 

output signal (rate error) is derived from the amount of error signal required to drive two pulse trains of slightly different frequencies into 

coincidence. Figures A.-6 and A-7 present a pictorial schematic and a 

block diagram of the Hycon sensor. One of the pulse trains is obtained 

as the photodetector output of a stationary (with respect to the sensor) 

light source chopped by an intervening rotating slotted wheel. This is the 

reference signal and has a basic frequency equal to the number of slots 

in the wheel times the revolution frequency. The other pulse train is the 

output of another photodetector located at a fixed angle from the reference 

detector. The signal reaching this detector through the rotating slotted 

wheel is the focused image of the ground plane. At zero ground (input) 

rate, the basic frequency of this signal is the same as that of the reference, 

and comparison between them results in zero error signal. However, it 

is clear that if the image moves tangentially, the basic frequency will be 

altered by an amount proportional to the velocity. If the image moves in 

the direction of rotation, the frequency will be reduced by this amount; if 

it moves against the rotation, it will be so increased. Upon comparison 

of the two pulse trains, the phase-lock loop will attempt to restore coincidence, 

and the resulting feedback error signal is a measure of both rate error 

magnitude and direction. Amoung the advantages of such a system are 

simplicity in structure and the relative ease with which the system can be 

analyzed for error analysis and possible performance improvements. 
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APPENDIX B 

IVS SPECIFICATION 

A. The IVS specification lists the performance requirements necessary to 

meet the overall tracking mirror velocity error allocation. The sensor performance requirements have been developed as a part of the overall system error 

analysis for the GE AVE. The dynamic performance (frequency response), 

saturation, scale factor, noise, and threshold are requirements which are compatible with the tracking mirror settling time requirement and velocity error 

allocation. Table 8-1 presents a summary of the critical WS requirements, origin 

of requirement, and the effect of the requirement on other parameters. 

The operating light level and image contrast requirements as stated in the 

specification have been derived from data originally used in the G3 focus sensor 

design. The use of these data provides a definition of input light level modulation 

and average scene brightness. The specification provides a definition of scene 

brightness characteristics in terms of a two-dimensional Wiener spectrum. 

The Wiener spectrum data is used as being more meaningful than previous 

definitions of contrast ratio in that it is (I) less subject to different interpretations, 

(2) based on a logical description of scene content (spatial frequency), (3) relatable 

to contrast ratio if a spatial frequency bandwidth is defined, and (4) includes the 

factors the produce brightness variation with differing scene content. 

J. 

A useful method of describing a random image process is by use of its meansquare amplitude spectrum. This statistic is equivalent to the autocorrelation 

function and. gives another measure of the separation at which fluctuations of 

the process may be expected in the plane of definition. The mean-square amplitude spectrum is usually referred to as a Wiener spectrttm. It is a two-dimensional analog of the noise power density spectrum used to describe the onedimensional noise processes in purely electronic fluctuations. The generic name, 

Wiener spectrum, is commonly used to eliminate the situation of a power spectrum 

having the dimensions of (power)2per unit bandwidth (i. e. , scenes reore- 
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The term contrast ratio, which is used widely, does not provide.an 

brightness 

adeqoate definition of input sceneAonaracteristics for a scene dependent sensor. 

Since all known scene dependent sensor mechanizations are spatial filters or 

possess some form of spatial filtering, the definition of contrast ratio must 

include a qualification with regard to a range of - spatial frequencies. If we 

assume the total scene brightness consists of an average or "DC" brightness 

term and an "AC'.' or brightness variation, the scene brightness can be expressed 

as: 

B=B

o 

-±o. 

Then an.expression of contrast ratio would be of the form: • 

B -a 

C o 

B

o 

- +a

It is obvious that the "AC" brightness terfn a) infers an•RMS brightness 

which can be - related to an integral of brightness variation per unit bandwidth 

over a 'selected bandwidth of spatial frequencies. Thus, to adequately use the 

term contrast ratio when defining typical scene characteristics, a spatial frequency bandwidth must also be defined. Thus, the definition of a Wiener spectrum 

and average scene brightness provides the required information and can be related 

or expressed in terms of contrast ratio over a specific spatial frequency bandwidth, 

if desired. 

Historically, the'development of the scene Wiener spectrum was initiated 

during the G3 focus sensor development. At the initiation of this development, the 

input scene ' light modulation characteristics were unknown. Previous 

brightness 

estimates or guesses had been made with regard to the scen.encharacteristics in 
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terms of a Wiener spectrum, but actual data was nonexistent. The use of a 

description in terms of a two-dimensional power or Wiener spectrum is mere! 

the application of communication theory to electro-optical sensor design. 

Initial studies involving the description of scene brightness content in terms 

of a Wiener spectrum used G photography, Initially, 76 microdensitometer tone 

traces of actual photography were obtained. These traces covered approximately 

One mile on the ground° Of the 76 tone traces, approximately 20 were of different 

scene character. The data obtained was converted to input scene brightness in 

foot-lamberts and processed via a digital computer program to obtain a onedimensional power spectrum of scene brightness versus spatial frequency. These 

one-dimensional power spectra possessed approximately the same character. That 

is, the input scene brightness power spectrum decreased with increasing frequency. 

Subsequent additional analyses by Eastman Kodak and Aerospace have demonstrated 

the same characteristics. These data were corrected to the extent possible for 

the optical system MTF, but were limited to a range (on the ground) of 1 cycle 

per 200 feet to 1 cycle per 10 feet. 

Using the above data, and assuming an isotropic process (i.e., circular 

symmetry), a two-dimensional Wiener spectrum can be obtained. These initial 

estimates of scene "modulation" were used to predict the G3 focus sensor signal 

levels. Subsequent flight data verified these estimates. 

At the initiation of the Dorian Program, the only data available were those 

developed for the G3 focus sensor design. This information was of limited quantity 

and did not contain a sun elevation angle condition below 250.. However, this information was used as the initial specification for IVS input scene brightness characteristics. Additional microdensitometer tone traces of G3 photography were requested; 
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ay 

- 

A 

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however, the time lag in obtaining such data is extremely long. It was then 

proposed to use the focus sensor telemetry data from G

3 flights to add additio 

data for the BIS input specification. The telemetry and calibration of the G

3 focus 

brightness 

sensor is such that the input sceneAmodulation over a narrow two-dimensional 

spatial frequency bandwidth can be obtained., since the transfer function of the 

focus sensor/optics is known at the operating spatial frequency of 1.cycle per 

30 .f eet on the ground, The data frOm Flights 8, 9, 10, 11, 12, and 13 have been. 

used to - obtain approximately 900 additional data points. Using these data, the 

input scene Wiener spectrum gain or level as a function of sun elevation angle 

has been obtained over the range of 5 to 90 degrees for an average Wiener spectrum 

shape determined from the analysis of microdensitometer- tone traces of actual 

photography. In addition, the average or "DC" scene brightness has been obtained 

for each of these measurements, and a plot of the Wiener spectrum gain versus 

average scene brightness has also been provided. These data were used as a 

requirement for IVS operation and as the ,basis for evaluating the three competitive 

Image Velocity Sensors. 

It should be noted that there are many assumptions associated with the 

adopted model of scene characteristics, but the assumptions and/or weaknesses . 

are known. This model at least provides a uniform and understandable definition 

which can be used by all contractors in their design and subsequent evaluation. 

Historically, numerous philosophical discussions involvipg input material were 

held with the various IVS contractors, and the only real information generated 

brishtness 

during these meetings was that a scientific definition of sceneAcharacteristics 

was lacking. As a. result of these discussions, it was apparent that a consistent 

definition should be made or an unbiased comparison of the proposed sensors 

would be impossible. 
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APPENDIX C 

IVS TEST PLANS 

The GE test program to date has served to evaluate the performance of the competitive IVS units and aid in the selection of a unit for 

prime use. This portion of a comprehensive over-all IVS test program 

has been referred to by GE as the Evaluation Test Program. This Evaluation 

Test Program has consisted of tests of the breadboard IVS units on a 

Bench Tester and Open Loop Tester. A briel summary of these test 

configurations is presented below and an evaluation test program schedule 

is presented in Table C-1. The detailed test procedures associated with 

these test configurations and the specific IVS units are presented in 

References 2 through 7. 

1. Bench Tester - The primary purpose of the Bench Tester 

was the functional checkout of each breadboard IVS unit prior to formal 

tests in the Open Loop Tester. Secondary tasks were those of obtaining 

quantitative operational data to supplement those which would be obtained 

from the open loop tests so as to provide a check of critical parameters. 

Upgrading of the tester also permitted additional tests such as image 

rotation. The Bench Tester was composed of the following items: 

a. Sensor Mount - A K&E instrument stand with height and 

rotation adjustments was used for sensor mounting. A compound table 

with two-axis translation as well as rotation was also mounted to the 

instrument stand. This assembly permitted alignment of a telecentric 

lens system and also permitted focus adjustment. 

b. Optical System - The optical system consisted of a telecentric lens system which duplicated the performance of the Open Loop 

Tester optical system and that of the optical system in the MOL vehicle. 

The rnMin difference was that the target scene was placed at approximately 
.1 I L . 

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22, inches from the front element of the collimator section, and a 5-inch 

diameter portion of the scene was reduced to 2. 8 inches in the image 

plane of the sensor. A light shield was constructed to fit over the optical 

system to eliminate stray light. 

c. Target and Target Motion - A photograph was taken of the 

high contrast urban scene at a reduced scale of 5.6 so that the spatial 

• frequencies in the Bench Tester, image plane would be consistent with 

those of the Open Loop Tester (OLT). An x-y plotter was used to drive 

the scene target. The target was mounted to the pen carriage of the 

plotter. For scene rotation tests, a separate variable speed drive 

assembly was used to rotate the target material. 

d. Illumination - Scene or target illumination was provided by 

four floodlights illuminating:the target material. A DC power source was 

used to control these lights. A calibration of average scene illumination at 

the 2. 8 inch IVS interface versus the supply voltage to the lights was made. 

The AC modulation signal or Wiener Spectrum for the scene used was calibrated from previous data obtained on the OLT. 

The Bench Test Plan for each IVS breadboard unit (See Ref. 2 

through 4) called for the functional verification of the following• common 

parameters: 

(1) Illumination threshold and saturation levels at zero velocity. 

(2) Null threshold velocity 

(3) Linearity and saturation velocity 

(4) Frequency respopie 

(5) Effects of voltage variation upon parameter values. 

(6) Special features of each sensor 
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t 

Additional quantitative tests which were performed upon the 

Bench Tester were: 

(1) Effects of illumination leyels upon sensor parameters 

(2) Image rotation effects 

(3) Effects of power interrupt upon performance 

These tests were conducted in conjunction with the Open Loop 

Test Program described later. . 

Each vendor was notified when the bench tests were scheduled 

to begin. Vendor representatives were present during the initial alignment, 

power application and testing of each sensor. Their presence assured that 

any early malfunctions or deviation in sensor performance would be noted 

or corrected. 

All tests performed on the Bench Tester were formally conducted 

and documented. In addition, a specific detailed test procedure was written 

for each sensor and for any subsequent special testing. A summary of the 

Bench Tester results can be found in Reference 8. Many of the sensor 

anomalies observed on the Open Loop Tester were first observed during the 

Bench Tester Evaluation. 

2. Open Loop Tester - The purpose of the Open Loop Tester 

(OLT) was to formally, evaluate the performance of the three contending IVS 

units with a realistic simulation of the orbital operating conditions expected. 

Secondary tasks were to evaluate any observed anomalies and attempt to 

determine the cause of these anomalies. 

A complete design, Xalysis, and experimental program was 

conducted to verify the adequacy of the OLT for IVS evaluation. (See Ref. 9 

through 11). In the OLT, the scene dynamics were provided by using a 
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lens system were driven on a earriagc,and the carriage motion with respect 

to the fixed photographic scene simulated the relative motion of the vehicle 

passing over a target. The object material which was located on the platen 

contains scene characteristics which were consistent with real-world 

targets (e. g. , contrast, spatial frequency distribution, and geometrical 

shapes). Image motion was generated by controlling the relative position 

of two lenses mounted on axes which were mutually perpendicular (Dynalens). 

The two axes of the Dynalens were controlled and commanded separately to 

induce image motion to the IVS.• 

The principal optical elements of the OLT consisted of a collimator 

telecentric lens system and deviating prism (Dynalens)using a variable prism 

technique to deflect the line of sight (LOS).from the target material in amplitude 

and rate. 

During typical sensor evaluation testing, the IVS was moved in a 

straight path first towards an object (simulated target) and then away from this 

object in a path parallel to the object platen gimbal axis. (See Figure C-1.) 

This motion was scaled to simulate the change in range between the IVS (orbital 

vehicle) and the object (target) as the orbital vehicle tracked a target. The 

object material was held on a platen that was supported by a single-axis gimbal. 

The angle of the platen gimbal was preset to position the IVS with respect to 

the platen. This axis generated the correct geometry for the obliquity. 

A complete simulated tracking run of a target (e.g., from a forward 

to an aft locking stereo half angle) using the simulator started with the IVS 

approaching the object platen wi.fh the platen initially position so that an oblique 

angle was formed between the IVS line of sight and platen. As the IVS approached 
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the target platen, the IVS mounting pla.Lform rotated to continually point at 

the center of the target or• the platen. At nadir, the IVS moved away from the 

platen as the IVS mounting platform continued to rotate to angular positions 

corresponding to aft-looking•stereo angles. 

When different roll angle positions of a target were being simulate& 

the gimbal axis of the target platen was preset to an angle that corresponded 

to the desired roll angle, The roll axis or target platen gimbal zo-rairwa tied 

during any one target pass. 

The previous description provided the means by which the orbital 

changing geometric conditions were simulated for IVS testing. The addition of 

intentional image velocity with respect to the IVS was provided via a Dynalens. 

The Dynalens was located behind the collimator lens. When-the. Dynalens was 

in the neutral position, light passed- through it without deflection. When the 

Dynalens system was commanded to deflect the line of sight, one of its two plates 

was tilted with respect to the other one. This caused a proportional deflection 

of the light rays entering the Dynalens. Each Dynalens plate was. one-axis 

actuated; the two axes were mutually perpendicular. This permitted the generation 

of complex line-of•-sight deflections in response to smear motion commands. The 

light then passed through a telecentric lens assembly which fodused an image at 

the optical interface with the IVS being tested. 

The simulated targets or test scenes used during the evaluation of the 

• 

IVS units were consistent and based upon the definition of input scene conditions 

presented in the IVS specification. Three different two-dimensional scenes 

-At 

were used. Scene content conisted of (1) a high detail city scene, (2) a low 

detail rural scene, and (3) a random dot target. The average scene brighness 
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was measured at the IVS interface, and the sCe.710 modulation was measured 

by taking high resolution photographs through the optics at the WS image plane. 

These photographs were then scanned with a microdensitometer and processed 

via a computer program to obtain a Wiener spectrum of the scene 'statistics. 

These data were then correlated (see Ref. 11) with the specification levels, and. 

a calibration was made of illumination level and Wiener spectrum level (modulation). In addition to the scene average illumination and modulation calibration) 

a "haze" generator was used to increase the average illumination level at the 

IVS interface without increasing the modulation. This "liate" generator was . 

included in an overall calibration of input scene illumination. 

Prior to initiation of IVS testing, a design effort was carried on at • 

GE to develop the OLT for IVS evaluation. A detail OLT specification was 

written (See Ref. 9). Subsequently,, a. detailed evaluation of the OLT was performed and the results are documented in Ref. 11. This OLT design included 

such features as the automatic refocus of the image in.real time during dynamic 

testing to compensate for slant range changes, an optical system MTF which 

matched the actual MOL optics to 50 1/mm over typical operating conditions, 

aperture variation during testing to simulate the vignetting Of the actual orbital 

system and a maximum vibration or noise image rate of 0.0025 inch/sec. 

(IVS threshold specification = .01 inch/sec). 

The detailed tests performed on the candidate IVS units are defined 

in References 5 through 7. The results of these tests are documented in 

References 12 through 14. The overall summary covering the IVS evaluation 

tests is presented in Reference". 
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Testing was conducted in an extremely formal manner and fully 

documented. Vendor representatirc.res were present during a major .portion 

of the tests associated with their units. Additional. tests were performed at 

the request of and under the direction of the various IVS vendors. 

3. Closed Loop Tester - The purpose of the closed loop tester is 

to evaluate the performance of the IVS units using a realistic simulation of 

orbital operating conditions and the TM (tracking mirror) drive dynamics. The 

closed loop tester uses the open loop tester hardWare together with an analog 

computer simulation of the TM drive dynamics and disturbances. The actual 

TM drive dynamics are provided by analog computer simulation driving the 

Dynalens system to control the image motion in two axes. 
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REFETUF.NCF.S 

) Performance/Design and Product Ccmfiguration Requirements for 

Image Velocity Sensor Specification No. EC 701A, Rev. 5, 4 Dec. . 

1967 DIN 3701-236-5 

2) Beta Bench Test Procedure (Paul) = Goodyear, March 5, 1968 

DIN 3808-212-1 

Beta Bench Test Procedure (Peter) = Itek, March 11, 1968 

DIN 3808-220, 5 

4) Beta Bench Test Procedure (Mary) = Hycon, March 21, 1968 

DIN 3808-2Z4-3 

5) Beta Subsystem Evaluation Test Procedure (Peter) = It.ek 

DIN 3808-208-6 

6) Beta Subsystem Evaluation Test Procedure (Mary) = Hycon 

DIN 3808-226-3- 

7) Beta Subsystem Evaluation Test Procedure (Paul) = Goodyear 

Revision I DIN 3808-226-04 

8) Beta TestEvaluation Report to be released 15 May 1968 by G. E. 

9) Beta Tester Specification, 10 November 1967, DIN 50102-32-3 

10) Beta Tester Readiness Test Plan, 20 November 1967 

DIN 50102-34-1 

11) Beta Tester ReadinesS Report, DIN 5p102-42-1, 7 March 1968 

12) Beta Subsystem Test Data (Mary), DIN 3808-210-4 (Hycon) 

13) Beta Subsystem Test Data (Peter), DIN 3808-208-6 (Itek) 

14) Beta SubSystem Test Data (Paul), DIN 3808-210-4 (Goodyear)