Apollo 12 multispectral photography experimen

Goetz, A. F. H.

English

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BELLCOMM, INC.
955 L I ENFANT PLAZA NORTH, S.W., WASHINGTON, D.C.	 20024
COVER SHEET FOR TECHNICAL MEMORANDUM
TITLE- Apollo 12 Multispectral Photoqraphy 	 TM-70-2015-1
Experiment
DATE- February 20, 1970
FILING CASE NO(S)- 340
A LITHO R(S)- A. F. H. Goetz
FILING SUBJECT(S)(ASSIGNED BY AUTHOR(S))- Apollo 12 Photography
ABSTRACT
The Lunar Multispectral Photography Experiment,
S-158, was successfully carried out on Apollo 12. A number
of photographs were returned in the blue, green, red and
infrared portions of the optical spectrum. Preliminary data
analysis shows no color boundaries in the frame containing
the Fra Mauro formation and the Apollo 13 landing site. Color
differences were found in the frame containing Lalande n,
establishing the existence of small-scale color differences
on the lunar surface.
N 
IN U -^4
d	 (ACCESSION NUMBER)
	 (THRU)
(PAGE)	 (CODE)
SEE REVERSE SIDE FOR DISTR.BUTION LIST
BELLCOMM, INC.
955 L'ENFANT PLAZA NORTH, S.W.	 WASHINGTON, D. C. 20024
SUBJECT: Apollo 12 Multispectral Photography 	 DATE: February 20, 1970
Experiment - Case 340
FROM: A. F. H. Goetz
TM-70-2015-1
TECHNICAL MEMORANDUM
I PURPOSE OF THE EXPERIMENT
The goal of the Lunar Multispectral Photography
Experiment (5-158) was to obtain vertical strip photography
in three portions of the optical spectrum, blue, red and
infrared, at one to two orders of magnitude higher resolution
than obtainable from earth. A fourth camera, having a green
filter was added to the array for operational purposes.
However, for the sake of the following discussion it will be
considered part cf 5-158.
The further objectives of this experiment were to:
1. Photograph future Apollo landing sites so that
ground truth information provided by the returned samples may
be extrapolated to other points on the lunar surface.
2. Produce photometrically accurate, two and three
color images by photographic as well as computer processing
methods which will accurately delineate lunar color boundaries
and their magnitudes.
II LUNAR COLOR MEASUREMENT
Lunar color and its variation across the surface has
interested planetary astronomers for many years. This interest
has heightened with the growing weight of evidence, obtained
from accurate earth-}lased photoelectric photometry, which points
toward a positive correlation between color and compositional
differences (1) once we have obtained ground truth samples at
several sites of differing color, it may be possible to extrapolate
compositional color information to large areas of the moon which
will not be sampled in-situ.
In the present context color differences mean relative
differences in spectral reflectivity between points on the
surface. The general spectral reflectivity curve of the moon
shows a near linear increase in reflectivity from 400 nanometers (nm)
BELLCOMM, INC.	 - 2 -
to 800 nm (2)
	 Areas designated red or blue reflect more
energy in their respective wavelength regions than a standard
lunar area. In most cases the greater the separation in
wavelength, the greater the color difference obtained. The
differences between 400 nm E.nd 800 nm, among points on the
(1)
lunar surface, average 4-8%
Photographic (3) and photoelectric (1) methods have
been used in the past for the measurement of lunar color
variations. The best known photographic nethod used to date
is Whitaker's (3)
 sandwich printing tehhnic-ue in which a
negative UV and positive IR plate were sandwiched together and
printed. Color differences then show up as varying shades in
grey. The disadvantages of this method are that it is not
quantitative and that ' albedo changes can masgilerade as color
differences if the D log E curves of the two plates are not
extremely well matched. The advantage of the method lies in
the image form of data display.
Recent advances in photoelectric instrumentation
allow ground-based relative color measurements to be made to
t0.1% accuracy (4). However, point-by-point measurement is a
time consuming process and not suited for image display. Work
now in progress with electronic imaging systems will incorporate
the advantages of both methods.
Computer image processing (5) of photographs combines
the advantages of photo graphic image display and provides
quantitative color information for the entire picture, albeit
at accuracies less than obtainable from photoelectric photometry.
III EQUIPITNT AND OPERATION
The 5-158 array consisted of four 70mm Hasselblad
cameras with 80mm lenses. The filter — black and white film
combinations were: blue, 47B/3401; green, 58/3401; red, 29+0.6ND/
3401; IR, 87C/SO246. Type 3401 is a plus-X, aerial-film and
50246 is 5424 infrared aerographic film coated on a 4 mil base.
The center wavelength of each filter-film combination is: blue,
430 nm; green, 540nm; red, 660 nm; IR, 860 nm.
An intervalometer tripped all shutters simultaneously
at 20 second intervals. For operational purposes the shutter
speed on all four cameras was fixed at 1/60 second. Focus
settings were fixed at 44 feet for the IR camera and - for the
other three. In order to facilitate f-stop changes, the vertical
strip photography was broken into three segments. During rev 27
I
ii
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the blue, green and IR cameras were cet at f-5.6 and the red
camera at f-4.0. Photography was taken between longitudes 120°E
and 90°E and between 54°E and 15'W. The minimum sun angle was
approximately 25°. The remainder of the vertical photography was
carried out on rev 28 at f-8/5.6. The off-vertical targets of
opportunity were exposed at f-5.6/4.0 for Theophilus and Descartes
and f-2.8/2.8 for Fra Mauro. Figures 1 and 2 show the photography
ground track.
IV FILM CALIBRATION AND PROCESSING
All flight film calibration and processing was
carried out b y the MSC Photo-Technology Laboratory (PTL).
Pre-flight calibration was accomplished by applying a 21-step
gray wedge to the film in a 1-B sensitometer. For 5-158 a
special step tablet was constructed to provide 4 21-step wedges
arranged to fit in a 60 x 60mm format to facilitate film scanning
procedures. In addition, a pre-flight standard wedge and a
post-flight special tablet were applied to the leader of the
film.
Pre-flight process controls were established to
develop the films to the following gammas: blue, 1.7; green,
1.65; red, 1.6; IP, 1.5. The different gammas were chosen to
compensate for the increasing transmission of the standard
wedge toward longer wavelengths. In other words, the absolute
gamma should be 1.7 for each film. The relatively high gammas
were chosen to Qive the maximum exposure differentiation com-
mensurate with the required dynamic range on the film. The
gammas obtained were: blue-1.68, green-1.48, red-1.42, IR-1.44.
The reasons for the discrepancy among control and flight film
gammas are not completely understood but, most likely, they can
be attributed to radiation fogging and latent image decay. PTL
is investigating this effect.
V FILM RETURN
Each of the blue, green and red cameras returned 142
frames while the IR camera in which the film had been rationed,
returned 105 frames.
The resolution in the 3401 returned film is about 30 meters.
This limit is approximately the motion resulting from the shutter
speed of 1/60 second. The densities on all frames fell within
the approximate straight line portion of the respective D log E
curves shown in Figure 3. This wasa necessary requirement for
data reduction by photographic methods. For reasons not under-
stood at this time all IR frames have a 4mm wide underexposed
stripe at the leading and trailing edges of each frame. The IR
frames are not in focus and will not be usable for color difference
analysis.
BELLCOMM, INC.
	 - 4 -
VI DATA REDUCTION AND ANALYSIS
The color or spectral reflectivity differences
sought in this study are not detectable by eye or on normal
color film. The eye is very sensitive to small color variations
under controlled laboratory conditions, in particular when the
objects have the same brightness and are juxtaposed. However,
the eye is incapable of reliably detecting small differences in
spectral reflectivity in conjunction with brightness differences
such as in a lunar surface scene. Normal color additive
techniques using color separation photographs also fail to show
up differences even at high saturation.
The two methods mentioned in Section II, the
photographic sandwich and computer image processing techniques,
are basically techniques for ratioing two pictures. Ratioing
is necessary to remove the brightness variations due to general
albedo and slope differences. Because the film density is a
function of the log of the exposure, ratios are formed by taking
differences in densities between two pictures, Such difference
pictures for two colors have been produceO by photographic (3) and
computer methods (5). Data reduction for S-158 will be carried
out in three colors using extensions of both methods. Details
of these procedures will be the subject of later publications.
Figure 4 shows frame 8438, a view of the Fra Mauro
Formation and the Apollo 13 landing site, taken with the blue,
green, and red filtered cameras. The dark corner in each picture
is due to obscuration by the edge of the hatch window. No
noticeable density variations, other than an overall brightness
difference, are visible.
A two color computer difference picture was constructed
from the center portion of the frame, including the Apollo 13
landing site. A blue and a .red frame were digitized and, through
use of the calibration wedges, each point in the picture was
converted into the log exposure domain. A total of approximately
two million points were measured in each picture. The pictures
were registered, subtracted from another point for point, and
contrast stretched. An arbitrary location was chosen to be gray.
Preliminary data reduction shows no significant color variations
within the frame, suggesting that the area is uniform in composi-
tion.
A two color difference picture of frame 8392,
Figure 5, covering a portion of Mare Nubium and Lalande n was
constructed. Figure 6 is a contrast stretched red minus blue
print of 8392 in which dark areas are bluer and light areas
are redder than an arbitrary point which was chosen to be gray.
BELLCOMM, INC.
	 - 5 -
Distinct color differences are evident particularly between
Lalande n and the surrounding mare and between what appears to
be secondary impact ejecta rays and the surrounding mare.
Although the frames have not been calibrated for camera vignetting
or adjusted to a lunar standard by earth-based photometry, there
is now clear evidence for local, small scale color variations on
the lunar surface. Further discussion of this result must await
the analysis of other frames.
VII SUMMARY
The Lunar Multispectral Photography Experiment has
yielded a large number of black and white photographs in the
four colors. Preliminary inspection has shown evidence of a
wide variety of surface features which may or may not exhibit
color differences. Two existing image data reduction methods
are being expanded to produce images which display greatly
enhanced three color contrast. Two color difference pictures
have been produced, one of which establishes the existence of
small scale color differences on the lunar surface.
ACKNOWLEDGMENTS
The author is indebted to his co-investigators
Mr. F. C. Billingsley, Jet Propulsion Laboratory, Prof. E. Yost,
Long Island University, and Prof. T. B. McCord, Massachusetts
Institute of Technology, for their 
-
continuing upport in this
project.
2015-AFHG-gmr	 A. F. H. G
Attachments
References
Figures 1-4
BELLCOMM, INC.
REFERENCES
1. McCord, T. B., Color Differences on the Lunar Surface,
J. Geoph. Res., 74 3131-3142, 1969.
2. McCord, T. B., Color Differences on the Lunar Surface,
Ph.D. Dissertation, California Institute of Technology,
1968.
3. Heacock, R. L., G. P. Kuiper, E. M. Shoemaker, H. C. Urey,
and E. A. Whitaker, Interpretation of Ranger VII Records,
Ranger VII, Part II, Experimenter's Analyses and Interpreta-
tions, TR 32-700, Jet Propulsion Laboratory, California
Institute of Technology, 1964.
4. McCord, T. B., A Double-Beam Astronomical. Photometer,
Applied Optics, 7, 475-478, 1968.
5. Billingsley, F. C., A. F. H. Goetz, J. N. Lindsley, Color
Differentiation by Computer Image Processing, Photographic
Science and Engineering, 14, 28-35, 1970.
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