VOL. 80, NO. 17 JOURNAL OF GEOPHYSICAL RESEARCH JUNE 10, 1975

Acquisition and Description of Television ScienceData at

G. EDWARD DANIELSON, JR., AND KENNETH P. KLAASEN

Jet PropulsionLaboratory, Pasadena,CalijCornia 91103

JAMES L. ANDERSON

California Institute of Technology,Pasadena, Calij•ornia 91125

The Mariner 10 televisionscience subsystem was an improved versionof the system,using 1500-ram-focal-lengthoptics. An elaboratepicture-taking sequence resulted in transmissionof over 4000 framesback to during two flyby encounterswith Mercury. Thesesequences utilized a real-timedata rate of 117.6 kbit/s, resultingin coverageof about 75% of the lightedportion of Mercury's surfaceat a resolutionof betterthan 2 kin. The completeset of usefulimages, which amounted to about 3000 frames, was processedwith three different types of digital image-processingenhancements.

INTRODUCTION in Figure 3. The relativefilter factors(ratio of integratedsys- tem spectralresponse without any filter to that with a given The Mariner 10 spacecraftencountered the Mercury filter) for each filter are listed in Table 1 for each camera,for for the first time on 29, 1974. Closest approach oc- input radianceswith both solar and mercurianspectra. curred on the dark side of the planet at an altitude of about A detailed summary of all of the functional characteristics 700 km. A secondencounter occurred on September21, 1974. of the cameras is given below. The aim point for thisflyby was chosen to be on the brightside at a range of about 50,000 km and about 45 ø south of the Characteristic Value equatorial plane. The spacecraftcarried twin, long focal length Focal length 1500mm television cameras to photograph the surface of Mercury. f/number f/8.4 About 3000 scientificallyuseful pictures were returnedfrom Field of view 0.36 ø X 0.48 ø both encounterswith surfaceresolution of up to 120 m. About Scanned area 9.6 X 12.35 mm 40% of the surface of Mercury was photographed at better Format 700 X 832 pixels than 2-km resolution. Encodinglevel 8 bits Frame time 42 s CAMERA CHARACTERISTICS Resolutionper TV line 9.5 X 10-6 rad

The Mariner 10 television sciencesubsystem is similar in PICTURE NUMBERING AND DATA many respectsto its predecessoron Mariner 9, which so suc- t TRANSMISSION cessfully mapped the surface of . One of the major differenceswas the optics. In order to increasethe high-resolu- Each Mariner 10 picture was assigneda unique identifica- tion coverageon the chosenflyby trajectory [Dunne, 1974] the tion number. The on-board electroniclogic in the flight data focal length of the Mariner 10 telescopewas increasedto 1500 subsystem(FDS) began numberingframes starting on the mm, 3 times that of the Mariner 9 high-resolution . launch pad about 6 hours before lift-off. The numbersin- An auxiliary, wide-angle (50-mm focal length) optical system, crementedby one for eachsuccessive 42-s frame.The FDS al- accessedthrough the filter wheel, was added as well. A de- waysassigned A camera frames odd numbers and B camera taileddescription ofthe optical design, illustrated inFigure 1, frameseven numbers. Several times in flight, is given by Larks [1974]. anomalies caused the counter in the FDS to reset itself to zero. The sensorwas an improved version of the seleniumsulfur (One resethappened just as the spacecraftwent into solar oc- photosurfaceslow-scan vidicon. The electronicdesign was im- cultation at Mercury encounter. Thus the incoming pictures proved to reduce the camera's susceptibilityto random elec- have been uniquely separatedfrom those taken on the out- tronic noise. A significantdesign change which resultedin an going leg of the trajectory at the first Mercury encounter. improvement over Mariner 9 was the incorporation of light Around closestapproach the numbersare 274XX on the in- flooding (F. Vescelus,unpublished data, 1975), which solved coming side and 40-200 on the outgoing side.) However, any the residual image problem that had plagued earlier Mariner picture can be uniquely identified (to the National Space television data reduction, especiallyon Mariner 6, 7, and 9 ScienceData Center, for example) by stating the major target [Young, 1974]. body along with the FDS number (e.g., earth FDS 14553 or The systemspectral transmission characteristics are shown Mercury FDS 48). in Figure 2. The opticsspectral transmission is plotted with the The Mariner 10 spacecraft could handle data in several spectraltransmission for eachfilter. The completesystem spec- modes. Data were recorded automatically on the on-board tral response(in amperesper unit area of vidicon surface)for tape recorderand playedback at a slowerrate (22.05 kbit/s) as each filter has been calcalatedfor an illuminating sourcewith much as possible.Since the tape recordertook 2.24 hours to Mercury's spectrum, as published by McCord and Adams play ba• 36 pictures at this rate and surface resolution [1972]. The responsecurves have beennormalized and plotted changedat a rate of about 0.8 kin/h, full-disk, high-resolution coveragenear Mercury encountercould not be accomplished Copyright¸ 1975by the AmericanGeophysical Union. by using this mode. Thus the pictures near closestapproach 2357 2358 DANIEL•ONETAL.: MARINER 10 MISSION

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I I I •- --__ I ! i I I I ! Fig. 1. Opticalschematic of Mariner 10 high-resolutiontelevision subsystem.

were sent back in real time at 117.6 kbit/s (i.e., one picture Far Encounter transmittedevery 42 s with no intermediatestorage) but with a The incomingfar-encounter sequence began as soonas Mer- correspondinglynoisier signal. During the missionthis trade cury could be viewed within the camera-pointingconstraints off betweendata rate and noisecould be madeindependently of the other sciencedata, since those data were telemetered in of the spacecraft.The primary objectivesof the far-encounter an independenttelemetry . A third modeof data return sequencewere (1) to obtain imagery of Mercury at pro- was transmissionin real time at 22.05 kbit/s. This slower, real- gressivelybetter resolutionwhile approachingthe planet and (2) to checkout and calibrate the televisionsubsystem and the time data rate allowedonly aboutone fifth of the total picture data to be returned for each frame. Two edit modes were avail- telemetry link. The intent of the initial sequence6 daysprior to encounter able to selectthe data to be returned.In one, only the center was to photographMercury through each spectralfilter at a strip (one quarter of the frame wide) was returned. In the minimum of two different exposurelevels (five levelsfor the other, calledthe skip-slidemode, only everyfourth pixel in a clearfilter) in orderto verify systemsensitivity as a functionof line was returned,with the first pixel returnedin a line being exposureover the dynamicrange of the instrument.Scan plat- shiftedover by two pixels from the previousline. In both of form pointing offsetsand motion of the spacecraftwithin its theseedit modesthe data were encodedwith only 6 bits. dead band resultedin obtainingonly about SEQUENCE one-half the desired number of exposure levels (Table 3). Therefore a completedetermination of the systemresponse A summaryof the imagingsequence for the first Mercury encounter is shown in Table 2. overthe entire dynamic range was not Possible. Enough data were obtained, however, to allow revised exposurecalcula- 1.0 I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I tions. The sequenceson subsequentdays consisted of imagery CLEAR through all filters at midscaleexposure levels and at pro- MINUSULTRAVIOL.E• gressivelybetter resolution.After flying by Mercury on the 0.8 - - BLU ' le0 --

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0.10 7/ 300 400 5•0 600 70• 0 300 400 500 600 700 WAVELENGTH, NM WAVELENGTH• nm Fig. 3. Integratedoptics, filters, and vidiconsystem response in- Fig. 2. Spectraltransmission of Mariner 10 televisionsubsystem op- dependentlynormalized for each spectralfilter on the basisof the ab- ticsand spectralfilters in percentplotted as a functionof wavelength. solute Mercury spectrumand plotted as a functionof wavelength. DANIELSONET AL.: MARINER I0 MISSION 2359

TABLE I. Mariner 10 Relative Filter Factors

Solar Radiance Mercurian Radiance

Filter A Camera B Camera A Camera B Camera

Clear (CLR) 1.08 1.08 1.08 1.08 Minus ultraviolet(MUV) 1.57 1.49 1.44 1.39 Ultraviolet polarizing(UVP) 43.93 54.23 60.25 75.02 Blue (BL) 2.64 2.46 2.66 2.48 Orange (OR) 5.37 5.66 4.17 4.47 Ultraviolet (UV) 11.63 13.70 16.01 19.05

TABLE 2. First Mercury Encounter Sequence

Resolution, Phase Range, km km Frames FDS N umbers

Incomingfar encounter,-6 to - 1 5,700,000-800,000 280-20 546 14339-25728 Incomingcolor mosaicking,- 16 to 635,000-100,000 14-3 162 25927-27104 -4 hour Close encounter, -4 to -I-4 hours 100,000- 5500 3-0.12 592 27207-27477 0-392 Outgoingcolor mosaicking,-I-4 to 100,000-635,000 3-14 144 494-1354 q- 16 hours Outgoing far encounter,q- 1 to q-3days 800,000-2,800,000 20-60 108 2055-2590 5996-6049 search,+ l to q-3 days 1,000,000-3,500,000 627 3932-5418 8045-8106 Total 2179 dark side a similar type of far-encountersequence was per- The 117.6-kbit/s data rate was used,yielding full-frame, full- formed,beginning about 1 day after closestapproach. Both in- resolutionpictures at an averagebit error rate of about 1 in 40 coming and outgoing data were played back from the space- [Clarke and Evanchuk, 1974]. Figure 6 shows the planned craft tape recorder at 22.05 kbit/s and had a bit error rate of mosaic patterns and the resolution ranges for the first four lessthan I in 1000 bits. Figure 4 showsexamples of the view of real-time mosaics.The actual coveragewas similar to the plan Mercury 2 days before and 3 days after encounter. exceptthat motion of the spacecraftwithin its attitude control dead band and scan platform pointing errors caused some Color Mosaicking gaps in the coverage,especially near the bright limb. The ac- Between4 and 16 hours beforeand after encounter,higher- tual footprints of the two highest-resolutioninbound and the resolutioncolor photography of Mercury was obtained. Be- two highest-resolutionoutbound mosaicsare shown in Figure sidesobtaining higher-resolution coverage at lessthan full disk 7. The resolutionsrange from about 900 m (FDS 27415and the intent of this sequencewas to isolate color differences 125) down to 120 m for the first outboundpicture (FDS 42). (which suggestcompositional differences)by using widely Eighteen of the highest-resolution inbound frames (FDS separatedspectral filters (UV and orange (OR)) and to mea- 27458-27475) and the 17 highest-resolutionoutbound frames sure the degree of polarization of the reflected light (which (FDS 42-58) were recorded for later playback at very low bit givesinformation on soil particle sizes)using the UV and UVP error rates. Table 5 summarizes the pertinent geometric (ultraviolet polarizing) filters. These data were also played parametersassociated with thosepictures with a resolutionof back from the tape recorderat 22.05 kbit/s at the correspond- about 500 m or better. Figure 8 showsthe planned coverage ingly low bit error rate. Table 4 lists the best-resolutioncover- and resolution ranges for the last five real-time outbound ageof the entiredisk and the best-resolutionphotograph of mosaics.Again, the actual coverageresembled the plan except some part of the disk obtained through each color filter for for a few gaps. both the incomingand the outgoingviews of Mercury. Figure At about 1 day and 22 hoursafter closestapproach a search 5 showsthe 8.9-km-reSolutionincoming view taken through for a satellite of Mercury was begun. Additional searchdata the OR filter and the 10.6-km outgoingview taken throughthe were taken around 2 days and 12 hours and 3 days and 22 UV filter.

Close Encounter TABLE 3. Numberof ExposureLevels Obtained During Mercury I Calibration Sequence Within about 4 hoursof closestapproach, continuous, real- time imagingof Mercurywas achieved except for a 30-mingap Camera Camera around encounter,when the spacecraftwas on the dark sideof Filter A B the planet.The objectiveof this portion of the sequencewas to CLR 2 2 obtain the highest'resolutioncoverage of as much of Mercury MUV 2 3 as possible,including photography of the entire visiblepor- UVP 0 1 tion of the planet at a resolutionof 1 km or better.The images BL 4 2 OR I 1 were all taken through the CLR (clear) filter to minimize the UV 2 0 requiredexposure time and therebythe smearin the pictures. 2360 DANIELSON ET AL..' MARINER 10 MISSION

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Fig. 4b

Fig. 4a

Fig. 4. The (right) incomingand (left) outgoingfar-encounter views of Mercury.

hours after encounter. The l d 22h sequenceconsisted of 521 brate the instrument further. One day before and I day after frames taken with an 11.7-s exposuretime and sent back in closestapproach, pictureswere taken through each filter at a real time at 22.05 kbit/s, some being in the skip-slide edit midscaleexposure level and were transmitted in real time at mode and others in quarter-framestrips. The 2d 12h sequence 117.6 kbit/s. At these times the planet Mercury nearly filled contained70 taped frameswith 8.4-sexposures, and the 3d 22h the camera field of view. At about 3 hours before encounter, sequencecontained 35 taped frames with 11.7-s exposures. real-time imaging at 117.6 kbit/s began again and continued Each of thesesequences covered an area out to about 36 Mer- until about 3 hours after encounter. Photomosaics of the im- cury radii on either sideof the planet in the eclipticplane and agestaken during the Mercury 2 closeencounter are shownin 12 Mercury radii above and below the plane. Pre- Figure 9 along with the areas of the planet planned to be liminary analysisof thesedata revealedno satellitelarger than coveredby each mosaic.The intent of the close-encounterse- 5 km in diameter with an similar to that of Mercury. quencewas to cover the areas in the south polar and bright limb regionsnot photographedon Mercury 1. The Mercury 2 Second Mercury Encounter photography would then provide both a geologicand a carto- A summary of the imaging sequencefor the secondMer- graphic tie betweenthe two quadrantsphotographed on Mer- cury encounteris shownin Table 6. Imaging beganwhen Mer- cury 1 and would yield a more representativesample of the cury could first be viewedby the camera.The main purposeof surface morphology upon which to base scientific con- the far-encountersequence was to checkout and calibrate the clusions.The imageswere all taken throughthe CLR filter ex- television subsystemafter its 6-month rest. The sequence4 cept for one wide-angle-filter(WAF) frame taken near closest days prior to encounterincluded picturesof Mercury taken through each spectralfilter of each camera at a midscaleex- TABLE 4. Best Resolution of Color Mosaics posure level and sent back at 22.05 kbit/s in the skip-slide mode. The sequence3 days before encounterwas a rather ex- Incoming Outgoing tensive instrument calibration with several exposure levels through each filter spread over the dynamic range of each Full Partial Full Partial camera (Table 7). Since the television optics heaters were Coverage, Coverage, Coverage, Coverage, Filter km km km km shorted out by a power systemanomaly soon after Mercury 1 encounter,the camera operating temperaturewas much lower, OR 8.9 4.7 21.0 5.3 and a recalibration of the instrumentwas required to verily ex- UV 7.8 7.8 10.6 6.3 posuresettings and for usein photometricanalysis. Two days UVP 21.0 7.8 21.0 7.4 BL 41.0 10.0 8.5 8.5 before encounter, images of were taken at severalex- MUV 8.9 8.9 8.5 8.5 posure levelsthrough the CLR filter to photometricallycali- DANIELSON ET AL.: MARINER 10 MISSION 2361 approachand the two frameson either sideof the WAF frame, age processingare describedby Rindfieischet al. [1971] and duringwhich the filter wheelwas stepping from CLR to WAF Dunne et al. [1971] in the context of . An and back to CLR. The averagebit error rate achievedwas image-processingsystem was developedat the Jet Propulsion about I in 35 Resolution was between 1 and 2 km for the real- Laboratory for Mariner 9, the principal features of which time images.Failure of the tape recorderprior to the en- are elucidatedby Cutts [1974]. This existing'MTC/MTVS' counter sequenceprecluded its use. image-processingand hard-copy production facility was A third passon the dark side of Mercury is scheduledfor chosen by the Mariner 10 project to perform the standard March 16, 1975.Although the dark sideaim point waschosen processing of all pictures. The standard processing for to maximizethe sciencereturn from the particlesand fieldsex- Mariner 10 was a two-part operation,consisting of 'real-time' periments, valuable imaging data can also be ob- processingand 'systematic' processing. tained. The planned imaging sequenceconsists of a far-en- In real-time processing,about half of the images were re- countercalibration and a check-outsequence followed by a constructedimmediately upon receiptof the data in both vola- close-encountersequence of high-resolutionphotography tile and hard-copyforms to supportengineering and pressre- aimedat targetsof interestselected from earlierphotography. lease requirements.The volatile display was converted to Frameswith resolutionas high as 60 m are anticipated. standard 525-1inetelevision and distributed by video cable to monitors used by engineersand scientistsand to other moni- DATA PROCESSING tors for NASA guestsin Pasadena,California, and Greenbelt, Standard computerdigital image processingof all useful Maryland. Since this real-time processingsystem could not re- imagingdata wasperformed by softwaredeveloped for pre- construct the images as fast as data were received from the vious Mariner imaging subsystemswith some modifications Goldstone tracking station and because overseas stations necessitatedby hardware and picture-taking sequence could not relay the data to Pasadenaas fast as the spacecraft differences.Some aspects of the developmentof Mariner im- could sendthem, a secondpass of all the data through the sys-

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Fig. 5 The (right) incomingphotomosaic of Mercury taken through the orangelilter at a resolutionol'about 8.9 kill and the (left) outgoingphotomosaic taken at ultravioletwavelengths with a resolutiono1' about 10.6 kin. 2362 DANIELSONET AL.' MARINER10 MISSION

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tern was necessarysubsequent to the initial receipt.This pass justedby a functionof the pictureelements above the onebe- wascalled systematic processing. In the processof production ing adjusted. of the TV experimenters'data record(a reformattedmagnetic The softwaresystem developed for Mariner 9 wasmodified tape versionof the video data) a histogramof the distribution principallyto accommodateMariner 10 data systemhard- of raw brightnessvalues in each frame was produced.Inspec- ware changes.The major changesfrom Mariner 9 to Mariner tion of thesehistograms before reconstructionof the images 10 were a reductionfrom 9 to 8 bits per pictureelement and in systematicprocessing permitted many framesshowing only the introduction of edited data modes for major parts of the sky or unilluminatedplanet to be excludedfrom re- mission.Changes in the text accompanyingeach image were construction. necessitatedby an inability to obtain timely target intercept Three versionsof each frame were producedin systematic informationand a requirementto displayengineering data for processing:a contrast-enhanced'raw' versionand two spa- system test purposes. tially filteredversions designated 'high-pass-filtered' and 'ver- Improvementswere madein the limb-ringingsuppression tical AGC,' the filtered versionsdiffering the directionin the and reseausuppression algorithms used in the filteredver- frame in which the filter was operating. sions.The bright limb of a planetrepresents the extremecase A 'filter'in image-processingterminology isthe emphasis of of highspatial frequency information and completely disrupts somespatial frequencycomponents of an imagewith respect the operationof simplefilters in its vicinity.To avoid this to others.Most commonly,as is true in thiscase, the high-fre- problem,which also occurs at frameedges, a routineis writ- quencycomponents, which contain the fine detail of the image, ten that locateshigh-brightness edges at eitherside of eachline are retained, while the lower-frequencycomponents are sup- and replacesvalues outside those edges with the averageof a pressed.In the high-pass-filteredversion the brightnessvalue few pictureelements just insidethe edges. The reseaus,a grid of each pictureelement is adjustedby removinga fractionof of reflectivespots on the vidicon faceplatefor geometric the averageof pictureelements nearby in the horizontaldirec- calibrationpurposes, appear as very dark spotsin the image tion. In the vertical A GC version, picture elementsare ad- and producea similarproblem for simplefilter routines.After DANIELSON ET AL.: MARINER i0 MISSION 2363

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Fig. 7. Footprintsof thehighest-resolution (a, b) inboundand (c, d) outboundframes actually obtained. The FDS number for eachframe is alsoshown. The footprintshave been plotted on high-resolution(2 kin) photomosaicsof Mercury. 2364 DANIELSON ET AL.: MARINER 10 MISSION

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Fig. 7c 2366 DANIELSONET AL.: MARINER 10 MISSION

Fig. 7d DANIELSON ET AL.: MARINER 10 MISSION 2367

TABLE 5. Geometric Parametersfor High-Resolution Frames

Frame Dimension, km Lati- Longi- Slant Incident Emission Phase Resolu- FDS tude, tude, Range, Angle, Angle, Angle, Hori- tion,* No. deg deg km deg deg deg zontal Vertical m

27458 10.0 23.7 20,213 76 50 Ill 172 133 449 27459 -0.22 19.4 19,774 80 39 Ill 169 130 439 27460 -8.6 17.8 19,334 82 33 Ill 165 127 429 27461 -15.9 17.8 18,895 82 30 111 161 124 419 27462 -23.2 17.2 18,456 83 29 111 157 121 410 27463 -30.5 17.1 18,018 83 30 112 153 118 400 27464 -37.7 17.2 17,579 84 33 112 150 116 390 27465 -44.5 18.6 17,140 84 38 112 146 113 381 27466 -51.4 19.9 16,702 84 44 112 143 110 371 27467 -43.0 29.8 16,264 75 46 114 139 107 361 27468 -37.3 28.4 15,826 75 44 114 135 104 351 27469 -33.0 27.5 15,389 74 43 115 132 101 342 27470 -26.5 27.7 14,952 73 43 115 128 99 332 27471 -21.2 28.8 14,515 72 44 116 124 96 322 27472 -16.0 28.5 14,078 72 45 117 121 93 313 27473 -11.0 28.5 13,642 71 48 117 117 90 303 27474 -6.9 27.8 13,206 71 50 118 113 87 293 27475 -3.5 27.2 12,770 70 53 118 110 85 283 27476 -15.0 49.2 12,800 52 69 121 107 83 284 27477 -18.0 40.0 12,100 61 60 121 101 81 269 1048575 -21.5 15.9 11,500 84 37 121 96 79 255 000 -20.0 11.9 11,000 88 33 121 92 77 244 42 31.5 166.0 5,468 70 45 110 43 33 121 43 31.8 160.5 5,873 66 48 109 46 36 130 44 30.2 158.5 6,276 64 48 107 50 38 139 45 29.0 156.8 6,696 62 47 106 53 41 149 46 28.0 156.0 7,119 61 46 104 57 44 158 47 26.0 155.0 7,545 59 46 103 60 46 167 48 22.8 155.5 7,959 59 44 102 64 49 177 49 19.8 156.0 8,385 59 42 100 67 52 186 50 16.5 156.5 8,822 59 41 99 71 55 196 51 12.8 157. 9,273 58 40 98 74 57 206 52 10.5 157.4 9,724 58 40 97 78 60 216 53 7.7 160.0 10,163 61 37 96 82 63 226 54 3.5 162.5 10,633 63 37 94 85 66 236 55 0.8 164.5 11,098 65 36 93 89 68 246 56 -4.0 168.0 11,607 68 37 92 92 71 258 57 -8.0 171.8 12,121 72 38 90 96 74 269 58 -7.9 171.5 12,554 72 38 90 100 77 279 59 -6.6 171.0 12,960 72 36 89 103 80 288 -5.8 171.0 13,378 72 35 89 107 82 297 61 -4.7 169.8 13,796 70 34 89 111 85 306 62 -4.0 169.7 14,300 70 34 88 114 88 317 63 -1.3 169.6 14,694 69 31 88 118 91 326 2.2 169.1 15,074 69 28 88 122 94 335 65 5.6 167.8 15,258 68 25 88 125 97 339 8.2 167.1 15,874 68 24 87 129 99 352 67 10.9 167.1 16,289 68 22 87 133 102 362 68 14.3 167.4 16,686 69 19 86 136 105 370 69 16.9 167.1 17,113 69 18 8:6 140 108 380 70 19.7 167.5 17,536 69 17 86 144 111 389 71 22.0 168.3 17,962 70 15 85 147 114 399 72 25.5 169.0 18,398 72 15 85 150 116 408 73 27.2 169.2 18,839 72 15 85 154 119 418 74 31.1 169.3 19,300 73 17 84 158 122 428 75 33.6 170.1 19,755 74 18 84 162 125 439 76 37.1 171.3 20,223 76 21 84 166 128 449 77 40.8 172.5 20,707 77 24 83 170 131 460 78 46.0 172.8 21,235 78 29 83 172 133 471 79 49.7 175.9 21,738 81 32 82 176 136 483 80 57.7 178.2 22,374 84 41 82 180 139 497 81 64.9 181.3 23,024 87 48 82 184 142 511

Geometric parametershave been referencedto center of frame. * Has been defined to be 2.2 TV lines. 2368 DANIELSONET AL.' MARINER 10 MISSION

MERCURY MERCURY MERCURY

1 l'••••••""•"••••'" .....••' 1 '" • "p 'i • .X[

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RESOLUTION 2.5 TO 2.9 KM

MERCURY ....•jj•j'••,,,,?, IXl ' I• ß ! IN. •1• I ß IIL '11 Ii II IIII II .Xll .M i II.Xl

RESOLUTION 3.2 TO 3.6 KM

Fig. 8. Plannedcoverage of the lastfive real-time mosaics at the firstMercury encounter. The rangeof surfaceresolution is shown for each mosaic.

TABLE 6. SecondMercury EncounterSequence Phase Range,km Resolution Frames FDS Numbers Incomingfar encounter, 3,800,000-900,000 160-20 433 158495-160760 -4 to - 1 day 164607-164734 Jupiter calibration photog- 7.1 X 108 16,000 44 162632-162677 raphy, -2 day Close encounter, 120,000-50,000 2.6-1.1 360 166471-167033 -3 to +3 hours Outgoing far encounter, 900,000 20 72 168765-168848 +l day Total 909

dark areasat the edgesof lines are replacedfor limb-ringing TABLE 7. Numberof ExposureLevels Obtained During Mercury 2 suppression,reseaus are suppressedby replacing remaining Calibration Sequence low-brightnessvalues with the averageof those near them. Filter Camera A Camera B Significantchanges for Mariner 10 included disablingthe CLR 6 7 limb-ringing suppressionalgorithm on the dark sideof frames MUV 4 2 containing a significant fraction of near- scene UVP 2 2 information and modifying the automatic contrast enhance- BL 4 4 ment of the raw versionof the sameframes to avoid suppress- OR 5 2 UV 2 5 ing useful low-brightnessscene information. The result of DANIELSON ET AL.' MARINER 10 MISSION 2369

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-.;.Z . ""•'TM •'•;•::"-'•...... DANIELSON ET AL.: MARINER 10 MISSION 2393 these changeswas that much less information near planet productsfor the mosaics.This paper representsthe resultsof one limbs and frame sides or of low exposure values was de- phaseof researchconducted at the Jet PropulsionLaboratory under NASA contract NAS 7-100. Division of Geological and Planetary stroyed by the automatic algorithmsthan would otherwise ,California Institute of Technology,contribution 2573. have been the case. Examplesof the processingdescribed are shownin Figure 10. The frame shown coversmuch of the outgoing aspectof REFERENCES Mercury, from the limb in the lower left corner to very near Clarke, V. C., Jr., and V. L. Evanchuk, 117.6 kilobit telemetry from the terminator in the lower right corner. Becauseof space- Mercury, paper presented at 1974 International Telemetering Conference, Int. Found. for Telem., Instrum. Soc. of Amer., and craft-pointinggeometry, north is down in framestaken after Electron. Ind. Ass., Los Angeles, Calif., Oct. 15-17, 1974. closestapproach. The real-time and systematiccontrast-en- Cutts, J. A., Mariner Mars 1971 television picture catalog, vol. l, hanced raw pictures(Figures 10a and 10b) include a histo- Experiment design and picture data, Tech. Memo. 33-385, pp. gram of receiveddata numberslabeled 'data input.' The histo- 63-77, Jet Propul. Lab., Pasadena,Calif., 1974. gram showsa wide range of valuesresulting from large light- Dunne, J. A., Mariner 10 Mercury encounter,Science, 185, 141-142, 1974. ing anglevariations and significantalbedo contrasts. This wide Dunne, J. A., W. D. Stromberg,R. M. Ruiz, S. A. Collins, and T. E. range of input values limits the degree of contrast en- Thorpe, Maximum discriminabilityversions of the near-encounter hancementpossible without exceedingthe dynamic range of Mariner pictures,J. Geophys.Res., 76, 438-472, 1971. the printing process.In this casethe processingof these two Larks, L., The narrow-angletelescope for the visual imaging sub- raw versionsdiffers only in details.High-pass-filte. red and ver- systemof the Mariner /Mercury (1973) spacecraft,Proc. SPIE Instrum. Astron., 44, 35, 1974. tical AGC versions(Figures 10cand 10d) reduceregional con- McCord, T., and J. Adams, Mercury: Surface compositionfrom the trast rangewhile retaininglocal variations,thereby narrowing reflectionspectrum, Science, 178, 745-746, 1972. the width of the data input histogram and allowing a more Rindfieisch,T. C., J. A. Dunne, H. N. Frieden, W. D. Stromberg, and effective contrast enhancement of fine details. R. M. Ruiz, Digital processingof the Mariner 6 and 7 pictures,J. Geophys.Res., 76, 394-416, 197I. Acknowledgments.We are indebted to Nancy Evans, Patsy Young, A. T., Television photometry:The Mariner 9 experience, Conklin, and IsabelLopez for their assistancein the preparationof the Icarus, 21, 262-282, 1974. many piecesof art work and data tables.The planningand execution of the actual sequencewere aided by software developedby Robert (Received February 12, 1975; Toombs. We also thank Dave TheiSsenand the MVM '73 personnelin revised February 27, 1975; the Image ProcessingLaboratory at JPL for providing the photo acceptedMarch 3, 1975.)