P. M. MERIFIELD* (editor)J. M. SAARI

R. 'vV. SHORTIlILL

R. L. WlLDEY

D. E. 'vVILHELl\'lS

R. S. \VILLIAMS, JR.

Interpretation

ofExtraterrestrial

Imagery oI

- )

I I !

KILOMETERS

FRONTISPIECE. The multiringed basin of Mare Orientale.Lunar Orbiter IV moderate resolution photograph. Frameletwidth is about 90 km. Framelet orientation varies among thevarious Orbiter missions. (See page 489.) Note: Jorth is at thetop in this and succeeding lunar photographs. (NASA photo.)

Earth based telescopes; Photogeologic mapping of the Moon;Thermal mapping of the Moon; Lunar and planetary probes;Geologic interpretation of Lunar Orbiter photos; Photographicsensors for detecting extraterrestrial life.

(A bslract on next page)

TNTROD C'1'I0N

T HREE YEA RS HA VE elapsed si nce progressin the field of space imagery has been re­

ported on to the members of the society (VanLopik, Merifield, et at, 196.1), and a review of

* Chairman, Subcommittee V II, Photo Jnter­pretation Committee, American Society of Photo­grammetry, 1964-1967. Present address: EarthScience Research Corp., Santa iVlonica, Calif.90405. The authors are identified in their respectivesections.

477

478 PHOTOGRAMMETRIC ENGINEERING

some of the major projects that have beenundertaken is deemed appropriate. Terrestri­ally based telescopic photography and in­frared imagery are continuing to be utilized asfundamental tools in the study of celsetialbodies. Knowledge of the lunar and Martiansurfaces has been increased many fold byimagery returned from Ranger, Surveyor,Lunar Orbiter and Mariner spacecraft. Satel-

Ii te imagery of the earth is the su bj ect of asubsequent paper to be published in this jour­nal. Al though this paper is intended to encolll­pass the broad spectrum of the subject, it cannot be considered comprehensi\·e. Many proj­ects ha\·e been reported elsewhere, and in suchinstances, the reader is referred to the ap­propriate literature.

ABSTRACT: Imagery interpretation is playing an important role in the investi­gation of celestial bodies. Astronomers utilize terrestrially based photography inthe identification and mensuration of celestial objects such as galaxies, plane­tary nebulae, supernova remnants and sun spots. Telescopic photographs of theMoon are being used to construct 1: 1,OOO,OOO-scale maps of the lunar surface,and Earth-based infrared images of the Moon provide information on the dis­tribution of hot spots and aid in tlte analysis of thermal contour maps. Snrveyorphotography has yielded data 011 the size, shape and distribution of lunar sur­facefragments as well as the mechanical and photometric properties of lunar soil.Illterpretation of Lunar Orbiter photographs cOlltinnes to provide '/lew ill sightinto the origi'/l and history of lunar snrface feat ures.

TERRESTRIALLY BASED TELESCOPES

PHOTOGRAPHIC IMAGERY Dl CLASSICAL ASTRO:-,rOMY*

T HE CAMERA THAT provides the astronomerwith imagery is simply a large telescope inwhose focal plane is placed a photographicplate. The prj mary use categories of the de­veloped plate are: (1) recognition and classi­fication of particular forms in the image de­tail, (2) image photometry, and, the mosttime-honored of all, (3) the determination ofaccurate relative positions of objects on thecelestial sphere. The observational difficultieswhich confron t these endeavors are dom­inated by the principal problems of (1)resolution and (2) radiative signal-to-noiseratio. The nearer objects are sufficien tlybright that these two difficulties may beconsidered independently, but fainter objects,such as the ou ter regions of galaxies, presen t asituation in which the desired goals competewith one another in a direct trade-off, becausethe faster emulsion of a given type is alwaysthe grainier one.

Most of the well-known astronomicaltelescopes are sufficiently large that off-axisaberrations are of limited concern for thepractical sizes of photographic plates. Theclassical large refracting telescopes whose

* Contributed by Robert L. "Vildey, U. S. Geo­logical Survey, Flagstaff, Arizona. Publicationauthorized by the Director, U. S. Geological Sur­vey.

design culminated in the last century in theconstruction of the Yerkes 40-inch and Lick36-inch objective lenses, are usually mostaberrant in chromatism and sphericity, whileat sufficient distance from the optical axisastigmatism becomes importan t. Modern,large, fast reflecting telescopes have para­boloidal surfaces so that perfect imaging istheoretically possible until such distance fromthe optical axis is achieved as allows coma toquickly set in. Except for telescopes designedspecifically for wide-angle imagery, much useis made of the naturally OCCUlTing coma-freefield. 'v\Then the 200-inch Hale telescope wasbuilt, at f/3.3, the coma-free field was toosmall for adequately precise iris-diaphragmphotometry of stellar images, and a correctorlens was designed by Ross to enlarge this fIeld(Bowen, 1960a).

The epi tome of wide-angle telescopes is thetrue Schmidt camera, which makes use of thefact that a spherical mirror has no optical axisand cannot, therefore, if a concentricallycurved focal surface is used for the photo­sensitive surface, show coma or astigmatism(those aberrations which depend on size offield). Only spherical aberration is left, andthis can be removed by figuring a correctorplate, as an entrance pupil, as a figure ofrevolution based on a calculated fourth-

INTERPRETATION OF EXTRATERRESTRIAL IMAGERY 479

degree polynomial (Bowen, 1960b). Of course,the reA ector plate does have an axis, bu tbecause it is not a focusing de"ice its effectsare quite weak.

The angular resolution achievable inastronomy is usually limited by the turbu­lence in the atmosphere as a disturbance toits wa"e-propagating characteristics (Stockand Keller. 1960). The air ought to act,ideally, as an optically Aat filter p'"eceding theobjective. A Auctuation in density is a Auctua­tion in refractive index, however, and so thisis not the case. The average size of the seeingtremor disk might be 1 to 2 seconds of arc at areasonably good observatory site, while fromthree to seven nights a year it would becomeas small as 0.2 to 0.3 arc-sec in diameter.

Apart from seeing, there is a fundamentalresolution limit imposed by the Fraunhoferdiffraction of the objective mirror, acting asan aperture stop. But this cannot be achie"edunless the primary mirror is precisely figured.And even a mirror which is initially correctcan be strongly disturbed by thermal shock­or flexure through improper support (Meinel,1960). The requisi te condi tions becomeharder to fulfill as the mirror diameter in­creases. Smaller mirrors can be figured toachieve consistently their diffraction limitunder normal nightti me operati ng condi tions.The diameter of diminishing returns begins toset in at about 30 inches, and a 6O-inch tele­scope which achieves its diffraction limit isquite rare. Although the diffraction limit ofthe 200-inch Hale is 0.035 arc-sec, its opti­mum figure limit is about 0.3, whereas theU. S. Geological Survey's 30-inch telescopehas a 0.18 arc-sec diffraction limit and 0.20has been achieved in practice.

In photographic imagery, the signal-to­noise ratio in brightness comparisons dependson quantum detectivity (essentially emulsiongraininess), the actual brightness level, andexposure time. Certainly a low f/ratio(usually implying a large mirror) improvesthe signal-to-noise '"atio achieved in a certainperiod of time, but because of the saturationphenomenon of a photographic emulsioncou pled wi th the importance of reci proci tyfailure at typical astronomical brightnesslevels, the fain test signal that can be detectedagainst the sky depends only on the effectivefocal length of the telescope and the emulsiontype itself, for a given sky background(Baum, 1962; Bowen, 1962). The f/ratioonly affects the time required to reach thislimit. Again because of the usual correlationwith graininess, a slow emulsion and not afast one is desirable if one can practically

afford the increased observing time requiredto reach the minimum detectable brightness(Sandage and I'd iller, 1966). A typical emul­sion used in o!Jsen'iug faint sources such asfaint stars, distant galaxies, and gaseousnebulae would be an Eastman '<odak type103a or lIa emulsion, whereas for brighterobjects like the :\loon, a much less grainyemulsion such as 649 or e,"en Panatomic Xcan be considered. One of the techniques ofavoidi ng the trade-off between the problem ofsignal-to-noise (speed) and resolu tion (grain­iness) is the use of an image tube (Kron, 1966;Kron and Papiashvili, 1962) which adopts anelectron-focu ed photo-emissi"e surface as anintermediary to improve the basic quantumefficiency of the photographic process.

Some of the uses of imagery for morpho­logical classification have been: classificationof galaxies into a supposed evolutionary se­quence (Sandage, 1961 a; Arp, 1966); di­tinction between distended gaseous nebulae,planetary nebulae, and supernova remnants(Abel et al., 1964); distinction between openstar clusters and globular clusters (\\'ildey,1961); classification of sunspot groups; dis­tinction bet"'een primary and secondaryimpact cra ters on the j\ loon (S hoe maker,1962); interpretation of lunar features, suchas volcanic craters, domes, sinuous rilles, andgarbens; geologic mapping by surficial expres­sion (Shoemaker and Hackman, 1962); andthe iden tification of i\ Iartian canali.

The second category-photographic pho­tometry of celestial imagery-is untrust­worthy unless great care is taken to ensureuniformity of exposure and de"elopment andpreferably to calibrate simultaneously withphotoelectric observations of detailed partsof the object. The photoelectric observationsare calibrated, in turn, to starts of constantluminosity, and when sufficiently compre­hensive they crosscheck the overall spa­tial uniformity in photometric responsivit)'.Lunar photometry may be used to determineconstraints for models of the lunar surfacestructure and as a lunar geologic mapping tool(Wildey and Pohn, 1964; Pohn and Wildey,1967). Similarly, an important constraint onatmospheric models is the predicted limb­darkening of the planet in question. Stellarphotometry constrains theories of stellarstructure and e"olution as well as the atmo­spheres of stars (Wildey, 1964).

The third category-astrometric photog­raphy-is responsible for both the establish­ment of the scale of the entire ni"erse out­side the solar system, "ia measurement ofst ellar parallaxes as t he Earl h t ra"els over

480 PHOTOGRAMMETRIC ENGINEERING

half an orbit about the Sun (Strand, 1963),and the determination of space motions ofstars through measuremen t of angular posi­tion changes (Dieck\'oss, 1963) over a periodof several decades (proper motions) in com­bination with spectroscopic Doppler radial"elocities. Although astrometric measure­men ts provide distances only out to abou t1015 km. (the radius of the Galaxy is of theorder 1018 km. and the radius of curvature ofthe geometry of the Universe is of the order1020 km.), all the myriad of distance-findingtechniques telescope together in calibration,with stellar parallaxes forming the ultimatebasis (Sandage, 1961b). The fundamentalassumptions in astrometry are that: (1) Thevery faintest stars form a fixed referencesystem which can be used to correct fielddistortions, whose parallaxes and proper

motions are immeasurably small because oftheir great distances; and (2) the center of astellar image repre en ts the posi tion of thestellar point source and hence reduction ofrandom error through many measurements isjustifLed. Astrometric techniques are used inEarth-based selenodesy, but the limitation ismuch more severe because of the lack ofjustifiable su bsti tu tes for the aforemen tionedassumptions (Arthur, 1962; Wildey et a.l.,1967) .

Al though the sophistication of instru men­tation placed at the focal planes of telescopeshas increased tremendously in the last 10years, the fundamental tool of observationalastronomy will continue to be for some time,as it has been for 7S years, the photographicplate.

* Contributed by Don E. \\"ilhelms, U. S. Geo­logical Survey, i\lenlo Park, California. Publica­tion authorized by the Director, U. S. GeologicalSurvey.

PHOTOGEOLOGIC MAPPING OF THE MOON*

SYSTE~IATlC GEOLOGIC mapping of the Moon and crustal processes. The basic gross unitsfrom telescopic data has been carried out are (1) the dark, relatively smooth flat maresince 1960 by the U. S. Geological Survey. plains, and (2) the lighter rugged crateredConsiderable geologic information about the terra (also referred to as uplands or high-Moon has been accumulated, and the way lands). Almost any hypothesis of formationprepared for unmanned Surveyor and Lunar of these gross provinces and of craters leadsOrbiter spacecraft missions. The purpose of to the conclusion that the maria are youngerlunar geologic mapping is to determine and than the terrae; the maria filled depressionsmap the stratigraphy and structure of the in the terrae as coffee fills a cup and have hadMoon's crust, to work out from this the se- less time to become cratered than the terrae.quence of events that led to the present con- An extensive history has been worked outdi tion of the surface, and to discover the by application of such reasoning in theprocesses by which these events took place. Archimedes area (Figure 1) between theFifteen colored maps of the Moon's near side Apennine Ifountains (Montes Apenninus)at a scale of 1: 1,000,000 have been published and the main part of Mare Imbrium (Shoe-and an additional 31 are in preparation. maker, 1964). The oldest material forms the

Geologic investigations of both the Earth rugged mountains themselves, which are partand Moon are carried out by dividing the of a circular ring of mountains around acrust, which at first appears to be bewild- circular depression, the 1are Imbrium basin.eringly complex, into units. These units are Second in age is the light plains material thatrock bodies that seem to have a relatively fills in around the rugged material, and thirduniform character over a wide lateral range the crater Archimedes, whose rim materialand were probably laid down or emplaced in a and secondary craters are deposited on therelatively short period of time. Systematic light plains. Next youngest is mare material,geologic study of the Moon began when it was younger than Archimedes because a) therealized that rock units could be recognized mare fills Archimedes, and b) the extensiveon the Moon and placed in an age sequence fan of Archimedes rim material and secondarythrough the interpretation of photographs. craters present on the light plains are missingRecognition of age units is perhaps the most on the mare. Youngest are the craters Auto­noteworthy contribution of the geologist to Iycus and Aristillus, whose crater and raylunar studies, and has been the key to partly pattern, being completely developed on theunravelling the Moon's structure, history, mare and not filled or embayed like Archi-

medes, show that they are younger than themare; some rays are on the mare insideArchimedes. Thus we have five discrete rockunits in an ascending age (stratigraphic)column: rugged highlands, light plains,

I 'TEIU'RETATlON OF EXTR.\TERRESTRIAL lM.\GERY 481

FIG. 1. Archimedes region, illustrating age sequence of lunar geologic units. The dark smooth (mare)area (upper left-northwest) is part of Mare Imbrium; part of Apennine Mountains in lower right corner.Archimedes is the large (80 km) marc-ftlled crater. The other two large craters are Autolycus (top) andAristillus. One of the best Earth-based photographs ever made, taken by H. G. Herbig with the 120-inchreA ector, Lick Observatory.

Archimedes materials, mare materials, youngcrater materials. These relations demonstratethe important fact that the mare is not onlyyounger than the rugged terra but is enoughyounger to have given time for the light plainsand Archimedes to form before the mareformed.

Interpretations of the origin of the lunarmaterials have been made from their surfacecharacteristics and lateral distribu tion. Thesematerials are concluded to be complexlyinterbedded layers of volcanic and impactorigin. A fragmental layer forms on all ex­exposed surfaces, its depth varying with theage of the surface.

Craters, specifically, are doubtless of hothimpact and volcanic origin. The craters alongHyginus rille (Figure 2) are an example of thevolcanic; they are so regular in spacing andsize that they must have formed by volcanicaction localized along the rille (graben). Othervolcanic craters are those at the tops ofshieldlike domes.

The origin of craters by impact is deducedas follows: first, an explosive process is shownto have formed the craters, and second, im­pact is reasoned to be the explosive process.The explosive origin of Copernicus (90 km.

in diameter) was demonstrated beyondreasonable doubt by Shoemaker (1962), whoshowed that the pattern of secondary cratersaround Copernicus is accounted for to thelast detail by ejection of the secondary crater­producing fragments by energy from a pointsource within Copernicus. And in general, thelarge extent and radial symmetry of hum­mocky material (near the ri merest), radialgrooves and ridges (farther ou t), secondarycraters, and above all of the rays that extendgreat distances from large young cratersdemonstrate an explosive origin. That theexplosion was impact-produced can only bereasoned not proved, but it is difficult to con­ceive of the containment of sufficient volcanicenergy long enough to be released all at once.

The circular mare basins also are believedto be of impact origin, judging from theirgreat size and from resemblance of the ex­tcnsi\·e mantling deposits surrounding thehasins, such as the deposit on the ApennineMountains, to impact crater ejecta. However,the mare and light-plains materials that fillthe basi ns and other depressions are probablyvolcanic, judging from their great lateral ex­tent (and discounting unlikely origins such aswater-laid sediments). Moreover, many of

482 J'1I0TOGI{A~1 ~IETRlC ENG I NEEk[ NG

,FIG. 2. Hyginus rille (Rima Hyginus). The chart (by .. Air Force Aeronautical Chart and Informa­

tion Center) was compiled from many Earth-based photographs with critical detail added from visualtelescopic observations and shows the rille and its chain of craters hetter than any single Earth-basedphotograph. The inset is from a moderate-resolution (approximately 400 m) Lunar Orbiter IV photographand shows the rille approximately as it appears when observed visually with a large telescope on a goodnight. The chart and the inset include a field 175 km long.

these dark and light volcanics are believed tobe flows because they terminate abruptlyagainst higher topographic forms.

A considerable amount of informationabout the history and formation of the]\loon's surface thus has been gathered by

in terpretation of telescopic photographs.Spacecraft data have confirmed some obser­vations and interpretations and have modi­fied others, as discussed in another section(vVilhelms, this paper).

THER~IAL MAPPI:\G OF THE MOON*

THE CO:\TSTRUCTION OF an oscillographicthermal image of the ]\loon was first at­tempted by Sinton at the Lowell Observatory.Using a Golay cell as an infrared detectOl', hescanned the Moon with a resolution of 1/60the lunar diameter. The resulting image,however, lacked sufficient detail; his results\,"ere displayed as a series of isothermal con­tour charts (Geoffrion, et al., 1960). Recently,infrared images have been published for thefull Moon and for the penumbral and umbralphase of a lunar eclipse (Saari, et al., 1967)and for the third-quat'ter Moon (Salisburyand Hunt, 1967).

Two examples of our lunar infrared imageswill be presented here, one of the full Moon,and one during totality of a lunar eclipse. The

* Contributed by J. 1\1. Saari and R. W. Short­hill, Boeing Scientific Research Laboratories,Seattle, Washington.

measurements, made in 1963, used a mercury­doped germani u m photodetector wi th a 10 to12 micron filter. The Moon was scanned in arastel' fashion with a resolution of about1/200th of its diameter and the infrared signalrecorded on magnetic tape (Saari and Short­hill, 1967). These measurements were madeat 23 different phases through a lunation. Asimilar set of measurements were made duringthe lunar eclipse of 19 December 1964. Theobjective of this infrared research is to studythe thermophysical properties of the lunarsurface. Much of the data reduction has beendone with the aid of computers; large iso­thermal contour charts were drawn and usedfor detailed quantitative analysis (Shorthilland Saari, 1965). I mages reconstructed fromthe line-scan data were found to be usefuladj uncts to our analysis because they werehelpful in visualizing the global thermalpatterns on the Moon.

INTERPRETATION OF EXTR.\TERRESTR1AJ. 1~IAGERY 483

FJG. 3. An enhanced infrared image of the full Moon at 23 1134.3 MUT, 18 December 1964 (phase angle2°16'). North is inclined at 30° to the left of vertical in both figures.

Full N[oon: The infrared images were con­structed by intensity modulating an oscil­loscope using the recorded analog signalwhile applying the proper horizontal andvertical defection voltages (. aari, etal., 1966).An image of the full Moon is shown in Figure3. The variation in brightness temperatureon this image can be understood in terms ofthe solar radiation falling on the surface, thelocal inclination of the surface and its visiblealbedo. The incident solar radiation, which isalmost completely absorbed, is reradiated atinfrared wavelengths. Thus, at full :vroon thebrightness temperature of the subsolar poin tis abou t 398° K and decreases to approxi­mately 3200K at the limb. Variations in localslope and changes in the visible albedo ac­count for small differential' in brightnesstemperatures of the order of lOOK O\'er thedisk. Because of the large signal difference(~800K) between ~hc subsoJar point (center)and the limb, the image was electronicallyenhanced to bring out these small brightnesstemperature differences presel~t over thesurface. The low-frequency conlponent wasremoved wi th an appropriate fil ter and high­frequen.:y emphasis was employed, so that a

flat image similar to a visible photograph wasobtained. This filtering technique, however,produced a deficiency in the image, in thatthe limbs were made over-bright.

The brighter circular regions on this imageare the maria (visible albedo~0.06), whichare warmer since they absorb more of theincident solar radiation. The uplands (visiblealbedo~0.12), darker on the infrared image,are cooler, as are the bright ray craters (someshow up as small black dots). To the left ofcenter and about ten scan lines in diameter isthe ray crater Copernicus. I ts system ofbright rays is observed to be cooler than thesurrounding mare material. The large circularfeature (about 1/5 the lunar diameter) in theupper-left quadrant is J\lare Imbrium. Varia­tion in contrast within Imbrium may indicatedifferent stages of lava flow as some observershave suggested. The dark outline around theright edge of Imbrium is caused by the highvisible albedo of the mountains, combinedwith the low inclination of the Sun on theinward slopes. This same effect can be seen onseveral of the large craters (i.e., Copernicus).

Eclipsed Jlroon: The most interesting imagerevealed by the data is shown in Figure 4.

484 PllOTOGI{'\~I~IETl{IC ENGINEEIUNG

FIG. 4. An infrared image of the eclipsed moon at 2H I8.8M UT, 19 December 1964. The bright circularfeature centered 30 scan lines from the bottom is the ray crater Tycho, a major hot spot. In the lower leftcorner the bright region in the sky is caused by thermal radiation from the telescope.

This vividly presents the heterogeneity in thethermophysical properties of the lunar sur­face and was obtained during the totality ofthe lunar eclipse. No image enhancement wasneeded because of the relatively large changesin signal obtained over the lunar disk. Thehundreds of "hot spots" (white dots in theimage) have been for the most part identifiedas visibly bright craters, many of which areassociated wi th craters smaller than theresol u tion of the instru men t (Shorthill andSaari, 1965). The image shows that the hotspots are non-uniformly distributed on thelunar hemisphere with a concentration in

are Tranquillitatis (in the upper right

quadrant on the image). In addition to the1,000 hot spots found, portions of or all ofcertain maria are also observed to be therm­ally enhanced during the eclipse.

In conclusion, it must be stated that in­frared images of the Moon furnish onlyqualitative information. For studying thethermophysical properties of the surface, it isnecessary to do precision radiometry to ob­tain reliable brightness temperatures. How­ever, infrared images, two of which have beenpresented here, are useful as an aid in theanalysis of our large thermal con tour mapsand in visualizing the distribution of the hotspots.

LUNAR AND PLANETARY PROBES

SURVEYOR SPACECRAFT*

SURVEYOR I WAS successfully soft-landed onthe lunar surface June 2, 1966 and returnedover 11,000 television pictures to Earth.

* Summarized from Vrebalovich and Jaffe(1967), Shoemaker et at. (1967a, 1967b) and Jaffeet at. (1967).

Analysis of these pictures has been describedrecen tly in this journal by HoI t and Morris(1976) and Batson (1967). Surveyor II,launched September 20, 1966, crashed intothe Moon on September 23, 1966.

Surveyor III soft-landed on the Moon on

I TERPRETATlO OF EXTRATERRESTRIAL IMAGERY 485

April 19, 1967, and returned 6,315 televisionpictures. The distribution of craters and rock­like features near Surveyor II [ was found tobe similar to that observed by Surveyor 1.Blocks up to 4 m. long were visible from thespacecraft. Some of these were angular orflat; others were more rounded. Sizes ofindividual visible particles extended down tothe 1.0 mm. resolution limit of the camera;over 85% of the exposed surface consisted ofunresolved ftner material. As in the SurveyorI photos, no examples were found in which afragment seemed perched on a pedestal, asreported from the Luna IX pictures. It isbelieved that the pedestals reportedly ob­served in Luna IX pictures are illusions thatare, in part, due to the lower resolution of theLuna IX pictures and to the particular con­ditions of illumination under which they weretaken.

Television observations with color filtersindicated that the Moon is gray. The localalbedo of the fine-grained undisturbed surfacewas estimated to be 8.5%± .2% (Vrebalovichand Jaffe, 1967).

urveyor III landed in a crater about200 m. in diameter and 15 m. deep in OceanusProcellarum. By close comparison of theSurveyor III pictures with a Lunar OrbiterIII photograph of the Surveyor III landingsite, it is possible to identify more than 100craters and large blocks that are recognizablein both the Surveyor and Lunar Orbiterpictures. Because the number of these is solarge, it was possible to use the informationobtained from the two different sets ofpictures to produce a topographic map of thecrater by methods analogous to ordinary fieldsurveying, after a solution was obtained ofthe orien tation of the Surveyor I II camera(Shoemaker, et al., 1967a).

Surveyor IV, launched July 14, 1967, wasunsuccessful in making a soft-landing; itsretro motor exploded shortly before lunartouchdown.

Surveyor V, which soft-landed on the 1\1 oonon Septem ber 11, 1967, has retu rned over19,000 pictures. The area of southwesternMare Tranquillitatis in which Surveyor Vlanded appears generally similar to the sites inOceanus Procellarum observed by SurveyorsJ and III (FigUl'e 5). All three areas are faidylevel, dark maria with rather similar distribu­tions of craters and rocks. A surface layer ofweakly cohesive fine particles, aggregates,and rocks is present in 1are Tranquillitatis

and Oceanus Procellarum. Differences be­tween surface layers in these maria a,'e rela­tively small.

Surveyor V landed in a dimple-shaped, 9­by 12-meter rimless crater, which is thelargest member of a small chain of rimlesscraters; a parallel row of very small cratersalso occurs within the large crater. On thebasis of its shape and the alinement of smallassociated craters, the crater in which Sur­veyor V landed may have been formed bydrainage of surficial fragmental debris into anorth west- trendi ng fissure.

Observations of block-ri mmed craters,,'elatively nearby, indicate that the localthickness of the layer of fragmen tal debriswi th low cohesion is not more than 5 meters.The walls of the Surveyor V crater provideexposures of the upper meter of this debrislayer. Di fferen t types of fragmen ts are re­vealed in the pictures of the debris dislodgedfrom these walls during the spacecraft land­ing and in the pictures of the undisturbedparts of the walls. The types of fragmentsinclude (1) bright, angular objects, which areinferred to be pieces of dense rocky material;(2) dark, rounded objects, which are probablyaggregates of very fine-grained particles; and(3) dark, lumpy objects, which appear to beaggregates of aggregates. The aggregatecharacter of some of the loose, ejected frag­men ts is well demonstrated by the presence ofbright, angular chips set in a dark, fine­grained matrix.

The estimated normal albedo (normalluminance factor) of the undisturbed parts ofthe lunar surface near Surveyor V is 7.9± 1.0percent, somewhat lower than that observedat the Surveyor III landing site. Debrisejected on the lunar surface in front of thefootpads has a normal albedo of 7.5± 1.0percent, which is only about one-twentiethlower than the albedo of the undisturbedsurface, bu t is si milar to the al bedo of thematerial disturbed by the footpads at theSurveyor III landing site (Jaffe, et al., 1967,Shoemaker, et aZ., 1967b).

Surveyors VI and VII, the final twoSurveyor spacecraft, ha\'e made successfulsoft landings on the Moon and ha\'e returnedhigh q uali ty television pictures as well asinformation about the composition of thelunar surface from magnetic and alpha back­scattering experiments. Analysis of the datafrom these most recent flights is currently inprogress.

486 PHOTOGRAMMETRIC ENGINEERING

FIG. 5. Mosaic of narrow-angle pictures from Surveyor V showing the northwest wall of the craterin which the spacecraft is located and the far field beyond the rim of the crater extending to the horizon.(NASA photo.)

GEOLOGIC I~TERPRETATION OF LUKAR ORBITER PHOTOGRAPHS*

T HE EXTRAORDINARILY successful LunarOrbiter project has produced a rich photo­graphic data bank that is greatly increasinggeologic knowledge of the Moon and willcontinue to do so for years to come. Becauseof the wide areal coverage-nearly completefor the whole Moon at 500 meters resolutionor better, nearly complete for the Earth­facing side at 70 to 200 meters and veryextensive at 1 to 20 meters-Orbi ter photosserve as the con text in which to place datafrom spacecraft missions such as the Surveyorand the projected manned Apollo missions.This discussion will briefly show how Orbiterrefines the basic geological framework inter­preted by Earth-based telescopic means,mainly by the U. S. Geological Survey, dis­cussed in an earlier section (vVilhelms, thisarticle). Quantitative photogrammetdc re­sults, still preliminary, will not be discussed.

* Contributed by Don E. Wilhelms, U. S. Geo­logical Survey, Menlo Park, California. Publica­tion authorized by the Director, U_ S. GeologicalSurvey.

Fh-e Lunar Orbi ter missions flew success­fully out of five attempted, a remarkablerecord, especially since they flew nearly onschedule. Lunar Orbiter I (August 1966)photographed 9 potential Apollo landing sitesselected on the basis of Earth-based photo­graphs and telescopic observations in theequatorial belt; it also photographed a num­ber of supplementary sites. During thephotographic portion of the mission, periapsis(nearest approach) fell near the Apollo bel tand a\-eraged 52 km. altitude, and apoapsis(highest point of orbit) came on the far sideand averaged 1,850 km. altitude. Resolutionof abou t 8 meters was achie\'ed on the Earth­side medium resolution photographs, but thefailure to achieve the proper image-motioncompensation for the high-resolution systemcaused unacceptable smear of the high­resolution frames-the only significant failureof the en tire program. However, excellen tphotographs were obtained of the far side,including the famous frames with the Earthin the background. Lunar Orbiter II (Novem-

INTERPRETATIO T OF EXTRATERRESTRIAL IMAGERY 487

ber 1966), a similar mission, was almostcompletely successful and contributed themost of all missions to speci fication of Apollosites,S of the 13 photographed becomingprime sites. It also contributed the famousoblique photograph of the crater Copernicus.NIission III (February 1967) differed slightlyfrom the first two in that the orbit was in­clined 21° to the equator in order to exploreadditional sites, including several photo­graphed at an oblique angle because of thesuccess of the Mission II Copernicus oblique.Mission III added 3 prime Apollo sites andmany other sites of scientific interest; its onlyfailure was in lost frames in some of theeastern si tes.

These three missions ftlled most of thedirect Apollo requirements and left the re­maining two largely for scien tifLc purposes(which of course also apply to Apollo).Mission IV (May 1967) was of a type en­tirely different from the first tht-ee and unfore­seen in the design of the spacecraft. Tts al­ti tude (approxi mately 2,700 km. periapsis,6,100 km. apoapsis) and orbit inclination(85°) allowed it to survey the entire front sideof the Moon, which it did with stunningsuccess, except for a fogged strip 10° wide inthe east, in the face of greater difficulties thanfaced in any other mission. This is the si nglemission that, because of its wide cO"erage, willprobably prove to have the greatest ultimatevalue to lunar studies, although its yaluewould have been greatly reduced without theearlier and later high-resolution missions. Thegreatest achievement of Mission IV was per­haps the photograph of the Orientale basin(Fron tispiece), taken near the end of thephoto mission. Mission V (August 1967-onlya year after Mission 1) was another largelyscien tific mission and an extraordi narilyproductive and successful one, the mostnearly flawless of all Lunar Orbiter missionsdespite the fact that it, too, flew an 85° orbit,which the spacecraft was not designed for. r tsupple men ted the other Apollo-orien ted mis­sions by adding another possible site and byproviding high-resolution stereoscopic co,-­erage for four prime Apollo sites selected byearlier missions.

Cross geologic (rock or age) units arerecognized on Earth-based photographs andfiner-scale ones on Orbiter photographs. TheOrbiter-deri"ed units commonly are com­posed of surficial materials that show agerelations opposi te to those among the grossunits on which they are developed. For ex­ample, telescopic studies of the Flamsteedregion, landing site of Surveyor T, clearly

indicated age relations like those at Archi­medes, where young mare material embaysand fills an old crater, but Orbiter photo­graphs of the Flamsteed ring (Flamsteed P)prod uced a surprise that led to new knowl­edge of lunar surface processes. Orbiter Ishowed a com'ex moulding all around theFlamsteed ring that is clearly superposed onthe mare and so is younger (Figure 6). Thisrelation could be interpreted to mean that thering itself was younger than the mare andtherefore was some sort of volcanic extrusiveoverlying a ring dike (O'Keefe, 1967); butsince such mOll/dings are also present aroundmany contacts of mare with rugged objects,including many diverse forms difficult toexplain by volcanism, the more reasonablehypothesis is that the surface material on oldterrain is a mobile fragmental layer thatmigrates downslope through the effects ofgravity in a lunar manifestation of the processcalled mass wasting. Such mass wastingprobably explains the relati"e paucity ofsmall craters on slopes relative to plains, alsothe re,-erse of what is expected from the grossage relations. Thcse obseryations (1) setlimits on the engineering properties of lunarsurface materials, and (2) show that astro­nauts will seldom find in-place rock outct"Opsto sample in old terrain but will easily be ableto sample the a,-erage composition of a ruggedterra by sampling the float at its base.

Ft"Om the apparen t abrupt termination ofmare material against terra observed tele­scopically, it was early reasoned that the mareconsisted of yolcanic flows and the wide arealextent of the presumed fIo,,'s suggested,through analogy "'i th terrestrial rocks, ei therbasalt or ash-flow tuff. Surveyor V and VIobservations apparently indicate a basalticcomposition for the maria, and Orbiters IVand V have conflrmed that flows are presentby photographs of very clear flow fronts in1'Iare Imbrium (Figure 7) (previously indi­cated but not prm'ed in excellent telescopicphotographs). The presence of more than oneflow indicates an extended and complicatedhistory of marc emplaccment, as expectedfrom the delayed filling of 1'Iare Imbrium de­duced telescupically and from experience 011Earth, "'herc "cry little happcns cataclysmic­ally.

1'lany c"cnts 011 the 1'100n do happcncataclysmically, in particular the formationof many craters, as discussed in an earliersection (\\"ilhelms, this paper). ]\[any geo­logists, howe"er, ha,-e resisted this fact,presumably because of their experience withEarth geology-or "'hat seemed to be their

488 PHOTOGRAMMETRIC ENGINEERING

FIG. 6. Part of the Flamsteed ring, showing convex moltldings at base of slopes. Lunar Orbiter II Imoderate resolution photograph; site was also photographed by Orbiter I and the ring appears in thedistance in Surveyor I photographs. Framelet width is about 1.8 km (NASA photo.)

experience. As the impact origin of manylunar craters is being demonstrated, moreand more impact craters are being found onEarth as well. The 1\Toon, however, is stillwhere the big ones are found. I mpact cratersrange in size from tiny ones observed on high­resolution Orbiter photographs through tele­scopically observed craters such as Coper­nicus to mare basins such as Imbrium andOrientale (to be discussed below).

I t must be emphasized that many of thesmaller craters have long been believed by all

but the most fanatic impact proponents to bevolcanic (or more generally, internal) inorigin, and this belief has been confirmedbeyond a shadow of a doubt by Orbiterphotographs. An example is the craters alongHyginus rille, discussed in the section onmapping (\\'ilhelms, this paper), known andinterpreted as volcanic in origin beforeOrbiter; this origin was only confirmed byOrbi ter.

Other fascinating features of internalorigin are sinuous rilles, river-like objects

FIG. 7. Lobate flows in 1\Iare Imbrium. Lunar Orbiter V moderate resolution photograph.Framelet width is abollt 5 km. (NASA photo.)

1NTERf'RETATJON OF L\.TRATERRESTI<I.\L I~I.\GI·:RY 489

FIG. 8. Sinuous rilles near the parLly buried crater Prinz. Lunar Orbiter IV high resolution photograph.Framelet width is about 14 km. (NASA photo.)

\\'hich, with few exceptions, had been loapoorly seen before Orbiter to establish theirmode of formation, now known to be by someflow mechanism still not understood in detail,and not by faulting (Figure 8).

Another way in which Orbiter photo­graphs help interpret Earth-based observa­tions should be mentioned. Several craters,crater chains and other objects were selectedto be photographed by Orbi ter partly becausethey show an anomalously high signal in thethermal region of the infrared at eclipse. Oneinterpretation of this anomalous signal wasthat an insulating layer apparen tly presen tover most of the Moon was lacki ng and freshrock might be exposed, and indeed high­resolution Orbiter photographs show manylarge fresh rock fragmen ts at every suchinfrared anomaly photographed. Such freshrock was sought by Orbi ter because it willprovide valuable samples to be collected byastronau ts.

A final lunar feature to be discu sed here isperhaps the most spectacular of all photo­graphed by Lunar Orbiter, the Mare Orien­tale basin (Frontispc.), barely reae-hed byLunar Orbiter IV before its picture-takingability gave out. The importance of Orientalein lunar geologic studies is that it is the fresh­est object at the upper end of the impact sizescal a mare basin, that is, a large circularcrater surrounded by multiple rings andpartly filled by mare material. (Orbi terphotographs of the far side of the ]\\ oon show

structural basins that are similar but lackmare filling.) Fresh exposures in Orientale ofstructures and geologic units that are erodedand cO\'ered in older basins show what is to beexpected in lhe other basins, such as Im­brium. Four rings of peaks surround Ori­entale, and intcrestingly similar but moresubdued and more deeply co\'ered ones occurin the other basins-in about the samespacing. The inner ring of islands in Imbriumwas once thought to ring an inner deep basinlike, say, the cratel' Copernicus; now it is seenthat the inner basin probably lies somewhatinside this ring and is relatively shallow. Thethird ring corresponds to peaks covered byArchimedes rim material, as discussed in anearlier section (Wilhelms, this paper).

The continuity and regularity of the ringsof Orientale and therefore Imbrium show thateach of the e craters is a unified structurcwhose origin centered about a point-anorigin easily explained by impact (of anobject only a few miles in diameter) butdifficult to explain by an internal mechanism;a pre-caldera dome, for example, would haveto have been of enormous height to collapseand form the present ring structure. Thesurface materials also suggest impact origin.Most interesting is the outer ridged andgrooved material first seen in Orientale(McCauley, 1967b). Comparison of ringstructures between basins shows that thiscorresponds in position to material on theflanks of the Apcnnine Mountains, long

490 1'.1I0TOGR.\1I1111ETRIC ENGINEEI{1NG

FIG. 9. Floor of Orientale basin including youngprobable volcanic crater (lower right quadrant)and part of young probable impact crater (upperleft). Lunar Orbiter IV moderate resolution photo­graph. Framelet \\-idth is about 12 km. (NASAphoto.)

believed to be impact ejecta from the giantI mbri u m basi n-crater. The Orien tale ma­terial, to have such streaked texture, musthave been emplaced by a great outward rushof material such that could hardly have beenproduced by volcanism; even though thedetails of texture around the older erodedImbriUIll are not clear, the analogy with

Orien tale su pports the impact origi n ofImbrium.

Orientale's freshness provides an additionalopportunity to interpret origins from photo­graphs. Since the features superposed on theyoung Orientale are known to be young, thecrater shown in lower right of Figure 9 mustbe young; but it lacks the hummocky ter­races, radial ridges and grOO\'es, and secon­dary craters of the large craters discussedabove and of the crater near it (upper leftcorner of photograph). Therefore, wi th thevariable of age better known than for othercraters, a caldera origin is here very stronglysupported and criteria for recognition of othercalderas can be developed (McCauley,1967b).

In summary, it should be clear from theforegoing discussion that no single, simpleorigin of lunar features can be invoked toexplain all lunar features; volcanism andimpact have both played a role. This factshould always have been assumed, and waswell demonstrated by Earth-based means,but it has been spectacularly confirmed bythe highly successful Lunar Orbiter program.I t remains to establish the relative propor­tions of impact and volcanic features and todetermine exactly how these two processes,along with mass wasting, radiation, tecton­ism, and other processes, have shaped thesurface of the Moon and at what time in thehistory of the Earth-Moon system it all tookplace. Photographs from Lunar Orbiter andthose to be taken by future orbiting space­craft will be the principal tool for doing this.Data acquired by other means can be fitted tothe framework provided by the Orbi tel'missions, and Orbiter will show the way formanned exploration to sample localities likelyto yield diagnostic material.

PHOTOGRAPHIC SENSORS FOR THE DETECTION OL' PAST ANDPRESENT EXTRATERRESTRIAL LIFE*

PRELIMINARY WORK BY Air Force CambridgeResearch Laboratories' Terre trial SciencesLaboratory in the continuing investigation ofthe application of remote sensors for geolog­ical research has suggested two films andspectral regions amenable for the possibledetection of past and presen t life on otherplanetary surfaces. The two types of photog­raphy are ultraviolet and false color (colorinfrared, camouflage detection).

* Contributed by R. S. Williams, JL, Air ForceCambridge Research Laboratories, Bedford, Mas­sachusetts.

VI traviolet photography in the 3,90oA-­4450A spectral region is accomplished byusing Kodak 5424 film with Wratten 36 and47 B fi! tel's. Carbonates (limestones, etc.)have a higher reflectivi ty in this spectralregion than any other common rock. OnEarth, carbonates are a ubiquitous sedi­men tary rock. Large deposits al most in­variably contain fossils of marine organisms,and most large carbonate deposits wereformed in a marine environment. Extensiveareas of carbonate exposure on other plane­tary surfaces would strongly suggest former

Il\TERPRETATJON OF EXTRATERRESTRIAL J:I/.\l";ERY 491

oceans and the presence of aqueous organ­Isms.

False color photography was speciallydeveloped to differentiate, by color change,between living Rora and ersatz Rora (camou­Rage). False color photography is obtainedwith Kodak 8443 film with a \\'ratten 12 filterplus an emulsion balance filter. The spectralregion covered lies between approximately

50001\ and 8500A. Nonhing matter onEarth is recorded as a bluish green color.Living Rora from higher order vascular plantsto lower order lichens and algae are recordedas a reddish-orange color. False color photog­raphy is an accurate diagnostic tool in dif­ferentiating between living and non-livingmatter on the Earth's surface.

BIBLIOGRAPHY

Abel, G. 0., Aller, L.H., Czyzak, S., Ilenize, K. G.,Kaler,]. B., Liller, W., Minkowski, R., Munch,G., O'dell, C. R., 1964, "Planetry Nebulae-ASymposium in Honor of Dr. Ira S. Bowen, May25, 1964," Publications of the Astronomical Soci­ety of the Pa.cific, Vol. 76-77, No. 451-454.

Arp, H. c., 1966, "Atlas of Peculiar Galaxies,"Astroph:ys1:cal Journal Supple'ments, Vol. XIV,No. 123.

Arthur, D. \V. G., 1962, "On the Problems ofSelenodetic Photogrammetry," International A s­tronomical Union Symposium No. 14, Chapter12, Academic Press, New York.

Batson, R M., 1967, "Surveyor Spacecraft Tele­vision Photogrammetry," PHOTOGRAMMETRICEl\GINEERI:"G, Vol. XXX[II, p. 1365-1372.

Baum, W. A., 1962, "The Detection and \[easure­111ent of Faint Astronomical Sources," Astro­nomical Techniques (Ed. W. A. Hiltner) Chap­ter 1, University of Chicago Press, Chicago.

Bowen, I. S., 1960a, "The 200-lnch Hale Tele­scope," Telescopes, (Ed. G. P. Kuiper andB. M. l\liddlehurst), Chapter 1, l niversit)' ofChicago Press, Chicago.

Bowen, I. S., 196/1b, "Schmidt Cameras," Tele­scopes, (Ed. G. P. Kuiper and B. M. l\liddle­hurst), Chapt~r -±, niversity of Chicago Press,Chicago.

Bowen, IS., 1962, "Spectrr>graphs." AstronomicalTechniques, (Ed. W. .'\. H:ltner), Chapter 2,University of Chicago Press, Chicago.

Dieckvoss, W., 1963, "Photographic Proper Mo­tions," Basic Astronomical Data, (Ed. K. A.Strand). Chapter 4, U ni versi ty of Chicago Press,Chicago.

Geoffrion, A. R., Korner, M., and Sinton, 'vV. M.,1960, "Isothennal Contours of the Moon,"Lowett Obs. Butt. 5,1-15.

Holt, I-l. E. and E. C. Morris, 1967, "Interpreta­tion of Surveyor I Lunar Photos," Photogram­metric Engineering, Vol. XXXIII, p. 1352-1362.

Jaffe, L. D. et ai, 1967, "Principal Scientific Re­sults, Surveyor V, A Preliminary Report," Na­tional Aeron. and Space Admin., NASA SP-163,p. 1-2.

Kron, G. E., and Papiashvili, 1. 1., 1962, "Progresson the Lick-Stromolo Image Tube," Publica­tions of the A stronomical Society of the Pacific,Vol. 74, No. 441, p. 404.

Kron, G. E., 1966, "Image Tubes," Advances inElectronics and Electron Physics, Vol. 22A, (Ed.]. D. 'IcGee, E. Mullan, and E. Kahan), p. 59,Academic Press, New York.

Levin, Viele and Eldrenkamp, "The Lunar OrbiterMissions to the l\[oon," Scientific American,May, 1968.

McCauley, J. P., 1967a, "The j ature of the LunarSurface as Determined by Systematic Geologic

Mapping," ill l11alltles of the Earth and TerrestrialPlanets, New York and London, .I ohn Wiley &Sons, p. 431-460.

McCanley, J. F., 1967b, "Geologic Results fromthe Lunar Precursor Probes," Am. Inst. Aero­nautics and Astronautics, AIAA Paper No. 67­862, 8 p.

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\\'ildey, R. L., 1964, "The Stellar Content of handchi Persei-Cluster and Association," Astrophysi­cal Journal Supplements, Vol. VJ II, No. 84.

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Wildey, R. L., Schlier, R. E., Hull, ]. A., audLarsen, G., 1967, "An Operational Theory ofLaser Radar Selenodesy," Icarus, Vol. 6, No.3,in press.

Bibliography of Computer ProgramsThe ASP bibliography of computer pro­

grams has been updated by the Committeeon Compu tational Photogram metry, and alisting of the contents is available at theAmerican Society of Photogrammett·y, 105N. Virginia Ave., Falls Church, Va. 22046.

When it was originally compiled, this bibli­ography was limited strictly to those com­puter programs involving photogrammetry.However, in updating the contents, theCommittee has broadened the scope to in­clude many programs which might be usedin support of photogrammetric programs. Asan example, programs have been includedwhich convert latitudes and longitudes intogrid coordinates, and vice versa.

The bibliography has been compiled with

the intent of reducing computer programmingcosts and man-hours by keeping photogram­metrists informed of existing programs. Thelisting reveals that considerable amounts ofti me and money are lost each year throughduplication of efforts. The enthusiasticresponse and assistance which the Committeehas received in updating the list (as com­pared with the response during the originalcompilation) indicate that photogramme­trists are becoming aware of the savings pos­sible.

If you have computer programs which youwould like to include in this bibliography, orif you would like additional information con­cerning it, please contact the Society.

Articles for Next MonthDr. J. M. Anderson, Block Triangulation by ISP Commission III.Dr. Sidney Bertram, The Dr AMACE and the Automatic Photomap per.J. M. Burnham and P. R. Josephson, Color Plate Metric Stability.C. E. Olson, L. W. Tombough, H. C. Davis, Inventory of Recreation Sites.J. T. Parry, W. R. Cowan, J. A. Heginbottom, Color for Coniferous Forest Species.F. B. Silvestro, Object Detection Enhancement.Dr. B. Shmulter, Triangulation with Independent Models.Prof. J. Vlcek, Systematic Errors of rmage Coordi nates.Paul R. Wolf, Trilaterated Photo Coordinates.