[PHOTOGRAPHIC IMAGERY 'IS SOMETHING WRONG WITH C/M AND IF SO, WHAT?']

• Document Type: CREST
• Collection: General CIA Records
• Document Number (FOIA) /ESDN (CREST): CIA-RDP79B00314A000500040010-2
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 17
• Document Creation Date: December 19, 2016
• Document Release Date: December 13, 2005
• Sequence Number: 10
• Publication Date: January 13, 1964
• Content Type: REPORT

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I. INTRODUCTION
We were charged in essence with the problem "Is something wrong with
C/M and if so, what?"
The first step in coming to grips with this question is to agree to
methods for evaluating the system. Since the end result is a photographic
image we must construct an objective quantitative measure of image quality.
Against this standard the performance of the system must be measured and the
observed image compared with the one to which the system is designed - in-
cluding effects of atmosphere, image motion and film processing and
sensitivity in addition to the lens system.
If all of these factors are fully understood and the design performance
is achieved, then we conclude C/M is a satisfactory system in the sense we
have given it a test and it has passed. There is a big question of course:
have we given the right test, i.e., the most useful one from the viewpoint
of the mission we want C/M to accomplish? In more specific terms we speak of
the optical transfer function or the sine wave response curve t (k) as a
function of spatial frequency k as the most convenient meeting ground between
design and performance. In the engineering design of an optical system'one
seeks maximum resolution in lines/mm by keeping t (k) as large as possible in
the region of high k.
It is the primary concern of this Committee to determine to what extent
the design t (k) is achieved by the system in practice, On?the other hand,
there are users' criteria of quality and one might benefit for intelligence
purpose by trading off, for example, some resolution in order to achieve
higher contrast - this is a human factor involving the PI's. This question
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of the optimum design of a transfer function for the intelligence community
is a corollary and also vital problem.
The distinction between user criteria and engineering criteria
cannot be overstressed. In the first case on typically asks, "Is photo-
graphic sample A a better source of intelligence information than sample
B and if so by how much?" In the second case one asks, "Is the equipment
performing in actual use as it did under laboratory..test and if there is
a difference what is the magnitude of the difference?"'
We discuss first in this report the question of constructing an
objective measure of image quality that is both useful and experimentally
feasible. In practice, in the real world, there are many parameters affecting
the performance which cannot be precisely specified. The transfer function
t (k), is a product of four components:,
t (k) = t (k) t (k) t (k) t (k)
atmosphere image motion optics film,
and uncertainties in these individual factors make it impossible for us to
say that the system passes any test perfectly.
We also recognize that this characterization of performance by t (k)
is incomplete since granularity is not taken into account. In these
discussions we assume the slow, fine grained film Ii-IiO+ now in use is a fixed
parameter of the system.
Rather we must content ourselves by reporting it to perform within a
certain quality range. The more we can sharpen up the individual factors
the more precise will be our understanding-of the system. This calls for a
Measurement Program - which is the next main subject of discussion in this
report. Engineering passes over known design targets in known weather
conditions are one aspect. Another very important one is an in-flight
measurement program to determine, for example, what the effect of the in-flight
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environment is on the optical focus - one area of particular concern being
the possible focal errors introduced by thermal gradients and transients
in the camera barrel and lens system. We do not here attempt a detailed
design study but we indicate. the types of measurements felt to be most
desirable and which can be made on ground or in orbit without substantially
conflicting with the operational goals of the C/M missions.
As a general remark we add our very strong conviction of the need for
instituting with great urgency a program of mission measurements and analyses
to help identify the causes degrading most of the image quality obtained thus
far - or to verify by establishing a lack of correlation between the image
quality and the monitored parameters that the present quality is typical of
what is to be expected. The measurement programs proposed in this report
should be carefully prepared and not viewed as quick fixes.
II. SUMMARY AND RECOMMENDATIONS
A. Objective Measures of Image Quality
1. Edge measurement techniques for determining the optical transfer
function.
The aim here is to provide a reliable and reproducible
"canonical" technique for accurately measuring t (k). parti
cularly - for .high. spatial. frequencies (say 10 ft ground
resolution or 100 L/mm). We want to know t (k) for two
reasons. By comparing the measured t (k) with the value to
which the system is designed we can hope to answer whether
the photography obtained is all that can be expected from C/M
or whether there is a loss of resolution due to shortcomings
of the system. Since the atmosphere's transfer function enters
into this comparison it too must be measured or calculated
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In view of the extremely limited technical feed back as to the performance
of components in flight to the systems designers, it is amazing to those of us
on the "outside" how well C/M has done so far. Nevertheless, there are major
quality variations which follow.no understood pattern from one mission to
the next. In its best moments C/M has performed very well, indicating that
improvements to a higher level of relic"oility should be possible. The urgency
of a measurement program and of timely systematic performance analyses to
enable the designers to achieve possible improvements cannot, therefore,
be overemphasized.
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in principle. As discussed further in Section D the only
significant effect of atmospheric haze on C/M photography
a.d tie f' c. resolwl-o' aIfi&o. kc.. c(r.. f
is a DC reduction of contrast t (k) is independent of
this and therefore of the atmosphere.
The practicability of microdensitometric edge measure-
ments for a routine evaluation of photography at high
resolution in order to determine t (k) must still be
established. As a relatively new technique it is still
fraught with practical di:ficulties and potential dangers.,.
It presents no theoretical problems, however. Suitable
edges for the scale of C/ICI photography are found in nature
in the form of large airfield landing strips and for special
tests can be conveniently provided by a target,layout
on the ground.
In order to demonstrate practicability of edge measure-
ments for 100 Lines/mm analysis a long-range industrial
program is in progress and full support to continue and
expand it is recommended. Its developm ent goals should be
1) Establish reliability by comparing recent measure-
ments of t (k) f.rom edge scans to results from
sine wave targets. The resulting modulation trans-
fer function should be combined with a film modula-
tion threshold curve to predict the resolution in
Lines/mm for direct experimental comparison.
Compare and standardize different p-densitometer
slits, determining optimal dimensions and data
handling methods..
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3) Determine pract::cability of the method in terms of
number of man-hours involved per edge.for a reliable
scan.
Toward these ends we recommend that there be
1) Initiated both at Westover and NPIC a program of
selecting and measuring edge on new mission
material (and on past material if warranted by
success of the above program) both to advance the
confidence in and reliability of edge measurements
and to accumulated data on C/M performance.
At this time we do not believe the edge scan
method is ready for production use; and
2) Constituted a working group including representatives
of principal laboratories to carry out a
standardization study on edge measurement techniques.
This activity should not be bound by security re-
strictions but should operate as an industrial
cooperation oriented by a work statement for such
a study for this Committee.
2. Visual comparison of photography of unknown quality with photo-
graphy of known quality as obtained by the same optical system.
This technique of subjective quality comparators or "GENES"
(Graded Estimated Measuring Samples) for judging image quality
is of interest and potential value because there are no standard
resolution targets in operational photography and the edge scan
measurements are still of uncertain merit. Moreover comparative
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analysis of properly prepared GEMS may provide some valuable
input into a human equation for the optimum photography for
use of the intelligence community.
F--' Both the flexibility and quantitative value of GEMS
are uncertain at this moment and experience in working with
them will be important in evaluating this technique.
The first use of such photographic comparators is for
engineering evaluation. They will be designed with the aim
of permitting the observer to identify the main characteristics
of quality degradation in the actual picture - whether due to
reduction of t (k) for high k leading to fuzzy edges of high
contrast, or non-optimal processing to high or low average
densities which affects graininess, or loss of contrast (due
Su~~1
to the s of the effects of corona discharge, light leaks,
haze, and thin clouds) but with edges remaining sharp. The
observer will identify these quality characteristics by
comparison with a library series of GEMS that can be brought to
adjacent positions in sequence by a comparison eyepiece. He
can also rate the photography by a resolution level in L/mm
for 2:1 contrast targets as imaged in the GEMS.
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The second use would be to determine the effects of the
variables introduced into the GEMS on the value of photographic
material for intelligence purposes. To reiterate an earlier
point - our primary Committee concern is to determine how well
the system produces its design transfer function, but the
question of what the transer function to which the system is
to be optimally designed is a longer-ranged and corollary
question, and is discussed in the technical sections.
A comparison technique: for assessing the photographic
quality is presented and the basic elements of a GEM library
are discussed in this report. As a first step.in implementing
this program a simple dual microscope system with a comparison
eyepiece and a small library of GEMS with varying resolutions
has been prepared.
3. First results of Edge Scan Measurements and visual photographic
comparators applied to operational photography.
Edge scan measurement: on mission photography have been
made with the Eastman Kodak; -densitometer as summarized in
Figures 1, 2, and 3 where the resolution in L/mm is computed from
the measured transfer function for 2:1 contrast targets.
GEM measurements of the limiting resolutions of scenes in
the close vicinity of these edge scans were made and the corre-
lation with the edge scan results shown in Figure 4. That no
better than a moderate degree of correlation was found indicates
the extreme caution with which these first results must be viewed.
SPECIAL- HAN DLI NG
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The 77 frames of Mission 9056 which were given subjective
MIP (Mission Information Potential) rating at NPIC and as
discussed and plotted by
caused very STAT
great concern, were compared with the GEMS as shown on
Figure 5. A lack of correlation is evident - as it is also
with the RES (Reciprocal Edge Spread)measurements made at
Westover (Figure 6). Furthermore, these two different
subjective measures of quality, RES and MIP, fail to correlate
with each other as shown by Figure 7. The conclusion from
this is that-both MIP and RES measurements have a presently
uncertain, if indeed any, quantitative value.
The lack of correlation of RES with edge scan measurements
can in part be attributE:d to the sensitivity of the RES
results with the average density of exposure. At this time
we see no quantitative -value to RES and therefore no reason
for continuing a program of measuring RES values.
In.assessing image quality by subjective standards we
believe that variations in the illumination conditions contri-
bute significantly to the observed spread of quality although
we have not assessed the significance of these variations
quantitatively. Figures 8 and 9 show two striking examples of
this effect in technically equivalent pairs of photographs.
Only the angle of solar illumination is different in Figures 8
and the angle between viewing directions and illumination in
Figures 9. The actual shadows are the same in :Figs 9 which
show two successive frames 10 seconds apart along a flight
line but the extent to which they are viewed depends strikingly
in the camera's angle of view.
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It is also clear that, factors which reduce the relative
brightness of the shadows such as haze and scattered clouds
will tend to dilute the above effects, so as to make the
photography generally drift in quality toward the low contrast
of the subsolar point seen in Fig. 9. Indeed the---..i'i'___
moderate haze in scattering light into the shadows has
a xgWe significant effect on overall quality 11vgft the DC
back-scattering of light into the lens. Clouds can produce
a similar effect even though a ground target is directly
illuminated by the sun and directly visible by the camera.
These factors which play an important role in subjective
evaluations are not relevant in an engineering analysis
of a system in terms of limiting resolution in L/mm. If one
is to compare objective and subjective measure5of image quality
such as NIP values then a way must be found to take into
account the effect of variability of subject matter.
The GEM and edge scan measures show some promise but
conclusions at this time would be premature and the-question
of C/M's performance is still to be decided by continued
analyses by edges and scans and GEMS. Mission-9062 is now being
analyzed by edge scan and GEM ratings and results obtained so
far are summarized in Figures 10 and 11.
Beyond determining a level of average performance in terms
of limiting resolution in L/mm for 2:1 contrast targets we
would like to determine :a mean spread in performance. about this
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average. Neither the edge scan nor GEM measurements have
advanced yet to the level that we can with any confidence
deduce this spread from observations. Moreover in the
absence of a detailed measurement program on-in-orbit
physical parameters the anticipated spread in performance
cannot be computed accurately.
The potential values of GEMS for relating the physical
characteristics of the photographic image with its intelli-
gence value to the PI remains to be explored and further
work in this direction is recoimnended.
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B. Measurement Program
1. In-flight measurements for obtaining engineering data to check
on system performance in the operational environment and to
correlate with image quality.
The C/M system is subjected to extensive laboratory tests
on the ground in Boston, Palo Alto, and Vandenberg to check its
operation both before and after thermal and .pressure changes,
in different gravity orientations, and after vibrations. These
tests are designed to cover the range of parameters anticipated
during launch and orbital. phases and focal settings must still
be within tolerances.
There is no way of knowing, however, that focal errors
resulting from thermal gradients and transients do not degrate
actual system performance in flight. No in-flight measurement
program exists for determining the temperature inhomogeneities
during flight due to variable sun angles and camera barrel ex=
posure to space, and furthermore, there is no in-flight
verification that the focal point is at the film. Remedies
for these deficiencies are proposed.. They require a continuing
in-flight measurement program not seriously interfering with
operational activities and designed to:
a) locate the focal point relative to the film and
b) measure local temperatures of the level.
Furthermore, a vigorous and more thorough laboratory study with
a theoretical model is encouraged to complement this program,
providing more details as to where to put temperature 'sensors
on board and pointing the way toward improved thermal control.
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Additional ground tests over a broader range of
parameters for checking f:Llm.flatness are suggested. These-
should include a broad temperature range and should be de-
signed to test vibration and post acceleration effects.
Another recurring plague of C/M photography is corona
discharge. Laboratory tests suggest that if the film were
maintain at a pressure of 20 to 100 instead of at ambient
this condition would be controlled. Work is in progress to
develop a light weight pressure system and should be pressed
with full support. In view of the recurring serious corona
problem a suitable system for maintaining pressures above 20
even if not at optimal on, should be introduced in C/M as
soon as possible, along with periodic pressure monitoring.
Direct tests on film properties and sensitometry are
discussed in Section C.
2. Engineering passes with daylight photography of design aerial
targets.
It is recommended that these be carried out and the present
program extended until one is driven to the conclusion that the
system is.working up to its design potential. Simultaneous re-
cording of component perfonnance in the measurement program
described in the preceding section is necessary to permit degraded
imagery to be correlated with faulty components. The resulting
loss of operational coverage resulting from such a program
i' is
is 1 ~rtsignificant andaa very worthy investment.
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A minimal aerial tarE;et is designed which permits determination
of the transfer function t (k) from edge measurements on the scale
of C/M photography as well as for any system of comparable or
superior resolution. This determination is independent of any
DC reductions of contrast such as may be caused by light leaks,
corona fogging, or atmospheric haze. Deployment and use of standard
resolution targets is also encouraged.
In order to determine the loss of contrast in C/M mission
photography due to recurring serious corona difficulties and of
other unwanted film expovre, it is desirable to remove the con-
trast reduction due to atmospheric haze alone. This is best done
by flying a calibrated camera, using identical film and pro-
cessing, in an aircraft at high altitudes over targets of known
ground contrast at approximately the same time as the satellite
engineering pass. This is not envisaged as a continuing test
program but one to be terminated as confidence is gained that
extraneous light is not fogging the film. Relative merits of
different filters and slit widths could also be assessed.by such
a program once the airplane is flying.
C. Film Processing and Sensitometric Strips
1. Film Processing
No appreciable degradation of limiting resolution in the
C/M photography was found to result from film processing.
It does appear, however, that the processing has frequently
been to a fuller level than that to which the mission is de-
signed.
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The exposure criteria are based on two series of experimental
data collected from aircraft and aerial reconnaissance cameras.
These data are further reviewed in the light of analysis of current
operational results. We recommend resumption of a program to
review exposure criteria and chemical processing.and modification
of procedures as found appropriate to maximize the final product
quality. The exposure latitude of the film (higher D max). should
be extended without adverse effect.
,2. Sensitometric Strips
Sensitometric strips are controlled exposures which provide
a calibration of the characteristics curve (density vs. log
exposure) of the mission film. If desired as a monitor of film'
processing uniformity throughout 'a mission sensitometric
exposures should be placed frequently along the edges. This is
done most conveniently after flight exposure and just prior to
processing. At present in view of corona and other non-image
forming light problems, sensitometric strips are of uncertain
value for this monitoring function. However, they appear to be
attractive as an adjunct for edge measurements since sensitometric
step wedges on each frame can be. used conveniently f`or calibrating
the microdensitometer and. film combination out of the edge trace.
In view of present uncertainties in high resolution-edge scanning
techniques and reliability, their trial evaluation is. recommended.
D. Atmospherics
1. Calculation of Weather Effects
The transfer function of the atmosphere plays an important
role in the considerations of each of the three preceding sections.
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For example, in designing: to a transfer function thereA~p
limited value striving for a lens transfer function which
achievesa resolution suxstantially dulled by turbulence.
Likewise if the DC haze filtering presents only objects. of
low contrast to the lens it is for such objects and not for high
contrast ones that it is desirable to optimize the resolution.
The effect of turbulence on the transfer function is
.negligible on the scale cf 10 ft. ground resolution photography
(2 x 10-5 rad angle). Hcwever, there is appreciable contrast
reduction as a DC effect of haze. This is very sensitively
dependent on local weather and its degree of preditability
over hostile territory is undetermined. There are suggestions
that it may be correlated usefully with atmospheric humidity,
which can--be predicted with a measure-of reliability and this
F
study now in progress at Wright ield deserves ^,g sup-
port and encouragement. Analysis. of atmospheric parameters in
conjunction with the overflights discussed in B.2 will be useful
in this study. Once it has been ascertained that the image con-
trast is determined primarily by haze and not by corona or light
leaks, GEMS as discussed in A.2 w ae-of value for somoting a
measurr ' loss of contrast or modulation resulting from haze.
2. Prediction of Weather
The extent to which world-wide weather data as available from
Program 417 can be integrated into the mission orbit selection to
reduce-, the present average of roughly 50% cloud cover in the photo-
graphy is explored but no conclusion reached.
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 1. Sine Wave Targets
2. Photometric Edge
and Microdensitometers
3. Three Bar targets
4. RES
Photographic comparitors
GEMS
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. COMPARISON OF VARIOUS METHOD OF IMAGE QUALITY MEASUREMENT
Static
Laboratory
Test of
Instrument
Dynamic
Laboratory Test
of Instrument
Operational
Evaluation of
Technical
Performance
Less Convenient
and precise but
related to (1)
and (3)
Too much data
compared to (3)
Less convenient
and precise but
related to (1)
and (3)
Targets too
large
Good, more
available than (3)
But Less Precise
Good but limited
by available
targets
requires photo-
metric data
Convenient but
MlleUlua aiiu accuracy
not validated
Possibly good
Precision not
validated
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Operational
Evaluation
of Quality For
Photo. Interpretation
Value because
Relationship
to PI
usefulness not
known
May be of use as
experience is gained.
Good Subjective
Judgment includes
scale, haze, subject
matter, illumination,