CARLTON E. MOLINEUX

.4 ir Force Cambridge Research Lab.Bedford, Mass.

Multiband Spectral Systemfor Reconnaissance *

INTRODUCTION

AN AIRBORNE spectral reconnaissance andr1.. data reduction system is being developedand tested for detecting, recording and dis­playing the surface manifestations of under­ground nuclear explosions and large magni­tude earthquakes. This work is being con­ducted by the I tek Corporation for the VELAProgram of the Advanced Research ProjectsAgency, Department of Defense, through theAir Force Cambridge Research Laboratories.

The basic concept of the system operationis that a subsurface disturbance (explosion orearthquakes of comparable seismic magni­tude) will produce physical manifestationsaffecting vegetation, terrain surface features.and terrain sub-surface features. Unique andspecific absorption, emission, scattering, orreflectance signatures can be established forall such objects and materials, using availablesensors, film and filters. The event will pro­duce changes in these signatures which can bedetected by airborne spectral reconnaissancein selected narrow bandwidths of the visibleand near-in frared.

The use of this system in civil aerial photog­raphy can provide much information to en­hance the photoin tprpreta tion of vegetation,soil, and geologic conditions.

SPECTRAL ENERGY CONSIDERATIONS

(Abstract on page 134)

A special nine lens camera (Figure 1)having different films and filters takessimultaneous photographs in several re­gions of the spectrum.

The airborne reconnaissance system is con­cerned with the remote sensing of reflectedenergy in the visible and near-infrared por­tion of the electro-magnetic spectrum or fromabout 0.35 to 5.0 microns. The airborne sys­tem depends on the sun as a source ofreflected energy, and near optimum illumina­tion is required because of the sensitivity ofthe photographic and spectrometer equip­ment. Reduced illumination due to cloudcover or low sun angle reduces the reflectedenergy below an acceptable level.

The solar energy spectrum expected on theground during a typical good weather flightis shown in Figure 2. The solar energy spec­trum rises to a peak in the visible and fallsoff beyond the near infrared to almost nothingbeyond four or five microns. The smoothcurve represents the energy distributionexcept for the sharper absorption bands.

Over half of the solar energy lies in theextended photographic region up to 0.9microns. Most of the remainder is within thesensitivity of the lead sulphide detectors.

* Presented at the 30th Annual Meeting of the Society in Washington, D. C, March 17-20, 1964.

131

132 PHOTOGRAMMETRIC ENGINEERING

FIG. 1. The Nine-lens Multiband Camera.

SYSTEM DESCRIPTION

The spectral reconnaissance system con­sists of airborne sensors and data handlingequipment. In addition, ground data collec­tion equipment has been developed to aid inthe collection of reliable ground data essentialto the evaluation of the data collected by theairborne system.

THE AIRBORNE SYSTEM

The airborne system consists of (1) a ninelens multiband camera, (2) two 70-millimeterframe cameras, (3) a skylight recordingcamera, (4) a cartographic camera (TypeKC-l), (5) a spectrometer system, and (6)control console. The airborne equipment isdesigned to be in a RC-130 aircraft. The air­borne sensors are operated in existing stabi­lized mounts in the RC-130 aircraft. Thespectrometers and color reference cameras areIMC integrated and synchronized with themultiband camera by a common intervalom­eter. This instrument also serves as the datalink with the spectrometer recordings per­mitting a synchronized signal to be recordedon the magnetic tape.

MULTlBAND CAMERA

The I tek nine-lens multiband camera, aunique research tool for obtaining spectralphotographic data, is shown in Figure 1.Camera data are presented in Table 1.

The multiband camera obtains photo­graphic coverage from 0.4 to 0.9 microns. Thecoverage is subdivided by the use of ninematched lenses with different filters to takenine simultaneous exposures of the sameidentical ground area. Each of the resultantnine photographs taken during one exposureis of matched image size uniform with 0.001inch. Resolution is from 20 to 30 lines permillimeter. Six of the exposures are on tworolls of 70-0101. panchromatic film and threeexposures are on one roll of 70-0101. infraredfilm. Eight of the exposures represent signa­tures in eight different narrowband portionsof the spectrum. The ninth exposure is the fullsensitivity range of the IR film. The sensitiv­ity of panchromatic and infrared film plottedagainst the eight filter bands is shown inFigure 3. The fil ters used wi th each lens areshown in Table 2.

The camera body is a one-piece aluminum

MULTIBAND SPECTRAL SYSTEM FOR RECONNAISSANCE 133

FIG. 2. Solar energy expected on the ground.

TABLE 1

MULTJRAND CAMERA DATA

SEVENTY-MILLIMETER FRAME CAMEI{AS

The program also uses two 70-l11m. recon­naissance cameras wi th 100-foot magazi nes

numbers are located on each of the frames in astaggered manner so that each frame numberwill show when films are superimposed.

The nine 6-inch f/2.8 Schneider Xenotarmatched lenses are mounted to the camerabody casting with shims to adjust focal dis­tance.

The camera magazi ne is an A 9-B imagemotion compensation magazine modified topermit use of three 70-mm. films instead of9!-inch film.

The shutter is made up of three main andthree capping curtains operating as a singleunit. The camera is operated at a shutterspeed of 1/50 second because of the largeexposure factors necessary to obtain the sharpcutoffs between the eight filter bands.

Three parallel focal plane shuttersof three slits each so as to exposeall nine frames simultaneously

Modified A-9-B magazine with filmdrive image motion compensation.

Nine 6-inch f/2.8 Schneider Xenotarmatched lenses

Two rolls of 70 mm. Plus X Aero­graphic, one roll 70 mm. InfraredAerographic

Nine frames each 2t by 2t inchesThree exposures on each roll of film

IMC

Lens

Film Type

Frame formatExposure

TechniqueShutter

system

FIG. 3. Filter transmission and film sensitivityversus wavelength.

alloy sand casting with the external con­figuration designed to fit the ART-25 stabi­lized mount. The body is fitted with nine 6­inch lenses, light baffles, frame numbercounter, and magazine drive assembly.

The magazine drive assembly consists of aDC driven motor, a worm gear housing and acoupling to match the A 9-B magazine drivecoupling. Cycle time is 1~ to 2 seconds, de­pending on film load and supply voltage. Theframe counters are operated by an overheadrocker arm which is coupled to the magazinedrive motor. The count can be viewed fromoutside the camera body and can be reset tozero with a single stroke. Lucite tabs with

134 PHOTOGR.\lI1l11ETRIC ENGINEERING

to expose aerial Ektachrome and CamouflageDetection Film.

The Schneider Xenotar 6-inch f/2.8 lensesare used with these cameras to match themultiband camera. The first camera is astandard model with 1/500-sec. exposure foruse with Ektachrome film. The second camerawas modified to 1/300-sec. exposure to usecamouflage detection film. A third camerawith 1/S00-sec. exposure serves as a backupunit. A frame counter which was designed tofit on the back of each of the film magazinescan be reset from the control console and thecount can be checked visually.

corded and stored on magnetic tape, with abinary address corresponding to the multi­band exposure. These data are converted toX - Y graphic spectral plots by the use of asweeping wave analyzer. Development is nowunderway for analog to digital signal conver­sion and subsequent statistical correlationand automatic computing of spectral ratiosby a digital computer.

SKYLIGHT RECORDING CAMERA

An additional camera has been modified toprovide a means for making comparativeevaluation of light level and relative spectral

ABSTRACT: A unique airborne spectral camera and data reduction system hasbeen developed for reconnaissance of terrain surfaces and especially for detectingmanifestations of underground nuclear test activity. The system operates inthe 0.35 to 5.0 m'icron region of the visible and near-infrared spectrum. Theairborne system consists of a nine-lens multiband camera, associated colorreference cameras, a dual spectrometer system, cartographic camera, and sky­light recording camera, flown in a C-l30 aircraft. Specialized color enhance­ment and printing techniques emphasize the spectral reflectivity differenceson the film to enable analysis of surface e..ffects. Ground spectral data are col­lected to assist the interpretation of aerial imagery significance. Photointerpreta­tion of vegetation and geologic conditions by simultaneous photography innarrow spectral regions will be advanced by this system.

AIRBORNE SPECTRO~IETER SYSTEM

The airborne spectrometer consists of tll'O

instruments, with a fifteen degree field of,·iew. One of the instruments uses a cadmiumselenide photoresistive detector with a usefulresponse in the spectral range of 0.35 to .94microns. The other instrument uses a leadsulfide detector with a useful response in thespectral range of 0.8 to 3.5 microns. Thecrown glass window in the RC-130 limits thelong wave response of this instrument toappmximately 2.8 microns.

The spectrometers use the Michelson In­terferometer principle to obtain much greatersensitivity than conventional rocking gratingspectrometers. They are small, light inweight, have rapid scan capability, and can beused with various detectors to cover a broadspectral range. Since the spectrometers arevery sensitive to vibration, the spectrometerheads are suspended in a rubber membranebasket to eliminate high frequency vibration,and padded to dampen the gross lateral andvertical movement. Image motion compensa­tion is provided by a rocking mirror. Thespectrometers are bore-sighted to coincidewith the optical axis of the camera system.

In flight the spectrometer data are re-

energy from film exposed on different daysand is used to calibrate signature and colortechnique. The camera fits into the RC-130sextant mount and incorporates an integrat­ing sphere and light pipe instead of a lens.The incident illumination is transmittedthmugh the eight multiband filters ontopanchromatic and I R film.

TAIlLE 2

MULTlIlAND CAMERA SPECTRAL BANDS

Lens Bandwidth Filters UsedNo. (m!")

1 400-500 Wratten 2B +35 +38A2 450-510 Wratten 3+473 520-550 \Vratten 15 +654 550-600 \\'ratten 57 + 12 + Balzers

155/1165 590-640 \\'ratten 90 + 24 +Optics

Tech. Interference6 670-720 Wratten 36+127 700-810 Wratten 89B+Balzers

455/1418 810-900 Wratten 87C9 Full Sensitivity

range of TRfilm

MULTIBAND SPECTRAL SYSTEM FOR RECONNAISSANCE 135

FIG. 4. Spectral system control console.

FIG. 5. Light table for viewing mllltiband film .

CONTROL CONSOLE AND SYSTE~f

The control console shown in Figure 4 con­tains equipment necessary for the manualcontrol and monitoring of the airborne sen­sors. A spectrometer moni tori ng scope, spec­trometer monitoring selecter, and an IMCmoni tor meter have been added to the con­trol panel in the console. The four channeltape recorder, spectrometer controls, binarycounter, all of which can be pre-set, arehoused in the rear of the console along wi ththe cable connectors.

The console, which weighs approximately500 pounds, is on casters and can be rolledinto the RC-130 and secured to the aircraftdeck.

DATA HANDLINC SYSTEM

The reflected energy from the earth's sur­face is recorded by the airborne photographicand spectrometer systems and techniqueshave been devised to systematically handlethe acquired flight data. The data that aresubject to analysis are: original color andblack and white photography, spectral signa­tures derived from the multiband photog­raphy, color derivatives and spectrograms.

PHOTOCRAPHIC ANALYSIS

The mul tiband photography is examined ona modified Richardson Light Table shown inFigure 5 so that the nine photographs fromone exposure can be examined together. Theaerial ektachrome and camouflage detectioncolor film are examined on light tables usingthe Bausch and Lomb Stereozoom Micro­scope. The color films are compared with theblack and white photography in performingphotoanalysis and selecting frames for color

••

FIG. 6. Block diagram of analog method used for production of spectrographs.

136 PHOTOGRAMMETRIC ENGINEERING

FIG. 7. Multiband panel showing wide tonal variation of crops in differing spectral regions.

MULTIBAND SPECTRAL SYSTEM FOR RECONNAISSANCE 137

FIG. 8. Crown pattern details in the orchard are distinct in IR bands 7, 8 and 9, but less clear inbands J, 2. 3, 5 and 6. Human activity is evident in band 4 under the trees (less clearly in band 3 also)but not in the other bands.

138 PHOTOGRAMMETRIC ENGINEERING

FIG. 9. Several differences in appearance are evident between ponds and along a flowing stream.Shallow water and sessile vegetation shows at A in bands 3 and 4. The dark-toned "fingers" in TR bands7,8 and 9, extending from the ponds toward the LIpper right, indicate springs and seeps. (1/20,000 scale).

J\llJLTII:lAND SPECTRAL SYSTEM FOR RECONNAISSANCE 139

FIG. 10. Some details of bridge and highway construction are more evident in each of the nine frames.The old building foundation at the head of the arrow is more distinct in some frames than in others.

140 PHOTOGRAMMETRJC ENGINEERING

FIG. 11. Some agent, probably biological, reflects or emits photographic infrared from the beds oftrickling filters (secondary sewage treatment plants). This condition might possibly enable a rapid as­sessment of the operating efficiency of sewage treatment plants.

Ml'LTIBAND SPECTRAL S,STEM FOR RECONN,\ISSANCE 14J

FIG. 12. Distinct soil and vegetation variations shown in visible and infrared photographs.

142 PHOTOGRAMMETRIC ENGINEERING

FIG. 13. Optical unit for ground spectrometer use.

enhancement and for spectrometer datareduction.

The 70-mm. frame photography is alsouseful in photogeologic interpretation supple­menting the cartographic photography. TheIR (bands 7 and 8) is useful where moisturedifferences in soil are helpful in bringing outsurface features. Enlargements are made fromselected bands to aid interpretation.

The small frame format, limited area cover­age of each frame, and large number of framesof photography to be analyzed make the useof the nine-lens camera presently valuable toresearch programs and pilot studies. An oper­ational system might only require photog­raphy from a lesser number of selected bandwidths to provide the information and areacoverage required.

SPECTRAL SIGNATURE TECHNIQUE

The spectral signature techique is simplythat the calibrated data from the output ofthe spectral camera can be used to generate aspectrogram for any object photographed.The wavelength resolution is determined bythe bandwidth of the filters used. Data fromthe skylight recording camera is used to

FIG. 14. Boom-mirror mounting ofgrou nd spectrometer.

establish the relationship of object brightnessto density for each of the bands. Densitymeasurements are obtained from the filmwith the X-Y co-ordinate densitometer. Therelative brightness values for each band willbe used in drawing a spectogram for theselected object.

SPECTRAL DATA REDUCTION AND ANALYSIS

Figure 6 is a block diagram of the methodused for the prod uction of spectrographs. Anequipment design and computer program iscurrently under development to provide aneffective means of statistically reducing thelarge volume of data provided by the spec­trometers accurately and economically.

COLOR ENHANCEMENT

A color separation technique is used toenhance the tonal differences between objectsor areas imaged in the multiband photog­raphy. Selected frames from the eight bandsproduced in the multiband camera providethe tonal values necessary to employ a colorseparation system. Reflectance data from theground spectrometer system provide informa­tion on the spectral bands that can be used toenhance reflectance changes in plants or earth

TABLE 3THE COLOR ENHANCEMENT PIlOCESS

CameraNegatives

Film DuplicatePositives Negatives Intermediates

AdditivePrintingFilters

IntegralColorPrint

N1 ' P1~ 11 • G Color

N6 ---.-P6=:6:~12---- R?Derivative

Na 'Pa~I3 B

l\:liLTlBA~D SPECTRAL SYSTEM FOR RECON"AISSANCE 143

surface due to physical manifestations.Photographic methods are curren tly bei ng

used in performing color enhancement. Theprocess is difficult and time-consuming but isexpected to demonstrate the feasibility andusefulness of the technique. Applying colorenhancement in an operational system willutilize electronic techniques for rapid scan­ning and analysis and morc sophisticatedphotographic laboratory methods for theproduction of materials required for reportingpurposes.

The following discussion describes the colorenhancement process, illustrated in Table 3.The multiband exposure is examined to selectthree frames as inputs for color enhancement.In this illustration, frames 1 (band 400-450mM), 6 (band 650-700 mM), and 8 (band 800­900 mM) were selected because of greatestvisual differences.

The process is carried out as follows:

Step 1. Film chip positives are exposed by con­tact on the RolI-To-Chip printer, and de­veloped to a gamma of 0.7.

Step 2. These positives are registered andpunched in the Registration Punch.

Step 3. The positi'"es of bands 1 and 8 arcprinted by contact into pre-punched film inthe Registration Printer, and developed to agamma of 1.0, to produce duplicate negatives.

Step 4. The positives and negatives are printedsubtractively (superimposed) in registrationonto prepunched film in the RegistrationPrinter to form intermediates. Each inter­mediate is made from the superimposition ofone positive and one negative each from adifferent band. One intermediate is printedfrom each of the following combinations:

I, from N,'+P612 from N 8'+PII, from N,'+P8

Step 5. The intermediates made in Step 4 arensed in making the f,nal integral print onEktacolor Print film. Each intermediate isprinted additively in the registration printerso that the image of each is transferred to onlyone of the color controlling layers of theColor Print.

I, is printed from a green filter to form an imagein the magenta layer

I" is printed with a blue filter to form an imagein the yellow layer

13 is printed with a red filter to form an imagein the cyan layer.

These images, when printed on a single tri­pack film constitute the final color enhance­ment, which, being a transparency, can beused for viewing or reproduction.

The intermediates represent differences ofreRectance between bands, so these colordifferences are what is represented. v,"here nocolor differences occur, the negatives andpositives cancel, so no color shows on the finalenhancement. Increases in the original tonal

contrast of 10 per cent for normal color filmto 60 per cent in the final color derivativeproduct of the multiband camera have beenproduced.

Representative samples of multiband pho­tography are given in Figures 7 through 12.

GROUND SPECTROMETER DATA COLLECTION

A supplementary system of portable, self­contained ground spectral reRectance measur­ing instruments has been developed to pro­vide useful data to enhance the interpretationof the airborne spectral imagery. The systemconsists of the same pair of spectrometer unitsas used in the aircraft wi th battery-poweredphotographic and electronic recording equip­ment.

An optical unit shown in Figure 13 wasdesigned to allow the two spectrometer headsand an associated recording camera to viewalong the same optical axis. The spectru m tobe measured can be sequentially viewed byeach of the two spectrometer heads and thecamera by rotating mirrors in the optical unit.

Standardization of solar light intensity andcalibration is accomplished before each read­ing by a spectrometer reading of a vapor­deposited aluminized glass cloth reRectancestandard panel.

Present mounting configuration shown inFigure 14 uses a 10 foot aluminum boom witha mirror mounted at the top end. The mirroris adj usted to allow the spectrometer to lookat the ground area directly below. In thismanner vegetation up to 10 feet in height canbe viewed at rates up to 60 points per 5 hourday.

Surface effects of changes in moisture con­tent, vegetation conditions, soil density, sub­sidence, deposition of dust, etc. can thus bedetected by skilled photoi n terpreters fromthe relative brightness and color difference ofany such natural or artificial anomalies ap­pearing on the resulting imagery. \Vith testflights over areas having detailed groundproperty knowledge a catalog of "keys" canreadily be developed for use in remote areas.

The application of multiband spectralreconnaissance has obvious advantages O\'erblack-and-white or color aerial photographyin detecting and recording the more subtlechanges of surface conditions occurringseasonally in nature or as a result of militaryor cultural activity. The present system hasbeen used at altitudes below 10,000 feet, butthere is no theoretical limit to its altitudeeffectiveness.

E D.