DTIC ADA430883: MightySat II.1 Hyperspectral Imager: Summary of On-Orbit Performance

13 Pages·0.97 MB·English

by  Defense Technical Information Center

Invited Paper
MightySat II.1 hyperspectral imager:
summary of on-orbit performance
2Lt SummerYarbrough,Thomas Caudill,Maj Eric Kouba,1Lt Victor Osweiler,
1Lt James Arnold,2Lt Rojan Quarles, andJim Russella
AirForceResearch Laboratory/VSSS
KirtlandAirForce Base,NM 87117
[phone], FAX[phone]
acurrentlywithBall Aerospaceand TechnologyCorporation
L.JohnOtten,B.Al Jones,AnaEdwards,JoshuaLane,AndrewMeigsb
Kestrel Corporation
3815OsunaRdNE
Albuquerque,NM 87109
[phone], FAX[phone]
bcurrentlywithRioGrandeMedical Technologies
Ronald LockwoodandPeteArmstrong
AirForceResearch Laboratory/VSBT
Hanscom Air ForceBase,MA01731
[phone], FAX[phone]
(AuthorContact: [email protected])
Keywords:Hyperspectralimager,spacebasedimager
ABSTRACT
The primary payload on a small-satellite, the Air Force Research Laboratory’s MightySat II.1, is a spatially modulated
Fourier TransformHyperspectral Imager (FTHSI) designed for terrain classification. The heart of this instrument is a solid
block Sagnac interferometer with 85cm-1 spectral resolution over the 475nm to 1050nm wavelength range and 30m spatial
resolution. Coupled with this hyperspectral imager is a Quad-C40 card, used for on-orbit processing. The satellite was
launchedon19July2000intoa575km,97.8degreeinclination,sun-synchronousorbit. The hyperspectralimager collected
its first data set on 1 August 2000. To the best of our knowledge, the MightySat II.1 sensor is the first true hyperspectral
earth-viewing imager to be successfully operated in space. The paper will describe the satellite and instrument, pre-launch
calibration results, on-orbit performance, and the calibration process used to characterize the sensor. We will also present
dataontheprojectedlifetimeofthesensoralongwithsamplesofthetypesofdatabeingcollected.
1. BACKGROUND:WHYHYPERSPECTRALINSPACE
Imageryfromspacehasbeenlimitedtoblackandwhitehighresolutionandmultispectralimagery. Blackandwhiteimagery
cannotdifferentiatebetweentypesofvegetationorroadmaterials. Multispectralimagerycandifferentiatetheseobjects, but
at a limited number of bands. To enhance the multispectral capability additional spectral bands need to be imaged.
Hyperspectralimageryexpandsthenumberofspectralbandsthatarecollected.
Previously, hyperspectral imagers have been mounted in light aircraft. These imagers are limited by flying conditions and
airspaceboundaries(i.e.nationalbordersandrestrictedflightareas). Whentheimagerisspace-based,however,theairspace
Imaging Spectrometry VII, Michael R. Descour, Sylvia S. Shen, Editors,
186 Proceedings of SPIE Vol. 4480 (2002) © 2002 SPIE · 0277-786X/02/$15.00
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1. REPORT DATE 3. DATES COVERED
2002 2. REPORT TYPE -
4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
MightySat II.1 hyperspectral imager: summary of on-orbit performance
5b. GRANT NUMBER
5c. PROGRAM ELEMENT NUMBER
6. AUTHOR(S) 5d. PROJECT NUMBER
Summer Yarbrough; Thomas Caudill; Eric Kouba; Victor Osweiler;
5e. TASK NUMBER
James Arnold
5f. WORK UNIT NUMBER
7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION
Air Force Research Laboratory/VS,3550 Aberdeen Ave SE,Kirtland REPORT NUMBER
AFB,NM,87117-5776
9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S)
11. SPONSOR/MONITOR’S REPORT
NUMBER(S)
12. DISTRIBUTION/AVAILABILITY STATEMENT
Approved for public release; distribution unlimited
13. SUPPLEMENTARY NOTES
The original document contains color images.
14. ABSTRACT
The primary payload on a small-satellite, the Air Force Research Laboratory’s MightySat II.1, is a
spatially modulated Fourier Transform Hyperspectral Imager (FTHSI) designed for terrain classification.
The heart of this instrument is a solid block Sagnac interferometer with 85cm-1 spectral resolution over
the 475nm to 1050nm wavelength range and 30m spatial resolution. Coupled with this hyperspectral
imager is a Quad-C40 card, used for on-orbit processing. The satellite was launched on 19 Jul 2000 into a
575km, 97.8 degree inclination, sun-synchronous orbit. The hyperspectral imager collected its first data set
on 1 Aug 2000. To the best of our knowledge, the MightSat II.1 sensor is the first true hyperspectral
earth-viewing imager to be successfully operated in space. The paper will describe the satellite and
instrument, pre-launch calibration results, on-orbit performance, and the calibration process used to
characterize the sensor. We will also present data on the projected lifetime of the sensor along with samples
of the types of data being collected.
15. SUBJECT TERMS
16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF
ABSTRACT OF PAGES RESPONSIBLE PERSON

a. REPORT b. ABSTRACT c. THIS PAGE 13
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boundary issues are eliminated. Space-based imagers can be affected by earth weather conditions and the satellite’s orbit,
however,theseeffectscanbeminimizedwithknowledgeoftheorbitandweatherreports.
The benefits of spaceborne hyperspectral imagery are numerous. The creation of spectral signature libraries can provide a
wealth of more specific global terrain data for agriculture, meteorology, rain forest management, geology, and urban
population studies. Seasonal weather conditions, biomass and insect infestation, mineral data, housing density, as well as
objectrecognitionareusefultoboththemilitaryandcivilianscientificcommunities.
2. MIGHTYSATII.1:BIGBANG,SMALLBUCKS
The MightySat mission is to provide a tailorable, affordable method to rapidly demonstrate the Air Force Research Lab’s
high payoff, enabling space technologies.1 The total cost of the MightySat II.1 satellite program was $38 million. The
Fourier TransformHyperspectralImager construction, testing, and integrationaccounts for $6 millionofthe total cost. The
adaptabilityofthe satellite isseeninthe amountand varietyofexperiments. Ten experiments are on board MightySat II.1,
consisting of Experimental Bus Components and Stand-Alone Experiments. There are five Experimental Bus Components
from solar array structures to the transponder. All of these components were unproven hardware. Two of the five Stand-
Alone Experiments are used in the collection of the hyperspectral image. The Fourier Transform Hyperspectral Imager
(FTHSI)istheprimarypayload,andtheQuad-C40(QC40)isutilizedforon-boardprocessing.
MightySatII.1buswasdesignedbySpectrumAstroIncorporatedtobeuniversalandadaptabletofitvariouspayloads. The
266-poundsatellitewaslaunchedat2:09PMMDTon19July2000fromVandenbergAFB,California.2 Thelaunchvehicle
was the Minotaur 2, the DoD-developed Orbital/Suborbital Program’s second launch vehicle. MightySat II.1 was inserted
intoasun-synchronousorbitat575kmand97.8degreeinclination.
3. PAYLOADDESIGN
Two components form the FTHSI payload. The hyperspectral instrument (HSI) is the imager, and the hyperspectral
instrumentinterface card (HII) allowsthe user to control the amount and parameters of the data collected. More discussion
oftheHSIandHIIcardwillfollowinlatersections. Inadditiontothepayload,FTHSIusestwootherVersaModuleEuropa
(VME)boardstocompletetheelectricalsystemoftheinstrument:thesolid-statememorycardandtheprocessorboard.
SpectrumAstro, Inc builtthe solid-state memory(SSM) card. The SSM contains 256 MB of RAM dedicated to FTHSI for
data storage.1 Data is written to the SSM and read out using normal VME protocols. This storage area is used for raw
FTHSIdata. TheSSM wasexpectedtolose4MBofmemoryper monthduetothe spaceenvironment. Todate there isno
evidencethatanymemoryhasbeenirreversiblycorrupted.
TheprocessorboardistheQC40andiscomposedoffourTMS320C40DSPchips.1 TheQC40wasoriginallydesignedasan
experiment to demonstrate the operation of the radiation hardened C40 chips and “smart-sensor” capabilities. The board is
configuredasatwo-slot,twoboardpackageandutilizesfourtantalumshieldedC40processors.1 Thefirstboardcontainsthe
C40andassociatedmemory,whilethesecondcardistheauxiliaryinterfacecard(QIB). TheQIBallowscameraimageryto
be routed directly from the camera to the processors. Each tile of the focal plane is hard wired to one processor, there are
four tiles and four processors. FTHSI planned to use the QC40 to do post-collection image processing and some real-time
imagerycollectionandprocessing.
4. IMAGERCHARACTERISTICS
FTHSIisaspatiallymodulatedFouriertransformbasedinstrumentthatencodeswavelengththroughaninterferometer. The
sensorisoperatedinapushbroommode,whichprovidesindividual1Dframesconsistingof1by1024spatialelementstrips.
Whentransformed these framesare collated into a contiguousswath with spatialdimensions up to n lines by1024 samples.
Once reassembled the pushbroom image consisting of x and y dimensions (comprising the spatial image) also possesses a
third dimension, z, that contains the spectral data information; approximately 142 discrete spectral bands from 475 nm to
1050nm.
TheinterferogramsareproducedbyamonolithicSagnacinterferometer.3,4 Thesceneisobservedthroughasetofforeoptics
thatimagesthesceneontoafieldstop. Theone-dimensionalimageisthenpassedthroughtheinterferometer wheretherays
Proc. SPIE Vol. 4480 187
are split, slightly sheared, and recombined to create an interference pattern in one dimension. From the interferometer, a
Fourier lens collimates the light and a cylindrical lens images the energy onto the detector, preserving the one by n spatial
dimensionandtheinterferencepattern. Acut-offfilterandCCDsensitivitypreventinterferencefromwavelengthsoutsideof
thespectralrangeofinterest.3
The purpose of the hyperspectral instrument is to demonstrate the utility of a Fourier transform imaging spectrometer
operatinginaspaceenvironment. Thedesignwasoptimizedfor measuringvegetationinthe visibletonearinfrared(600to
900nm)forterraincategorizationpurposes. Table1showsthedesignandactualpayloadcharacteristics.
Table1:FTHSIdesignandactualon-orbitcharacteristics.
PayloadCharacteristics Design Actual
SpectralRange 500-1050nm 475-1050nm
SpectralResolution/Accuracy 97cm-1/0.5cm-1 84.4cm-1/0.1cm-1
NumberofUsefulBands 146 146
FieldofView(FOV) 3degrees 3degrees
IFOV 0.0058degreesor0.0029degrees 0.0058degreesor0.0029degrees
SwathWidthat500kmAltitude 6.5kmto26km 7.5kmto30km
SwathLength 10kmto20.25km(nominal) 10kmto15.3km(nominal)
GSD 30m 30m
Pointing(Control/Knowledge) 0.15degrees/0.15degrees 0.15degrees/0.15degrees
SpatialCoverageTechnique Pushbroom Pushbroom
PayloadWeight 33kg 20.45kg
PowerRequirement(Peak/Steady) 66watts/60watts 55watts/47watts
PayloadVolume 17,045cubiccm 17,043cubiccm
RMSRadiometricCalibrationAccuracy 20% 10-15%
LifeSpan 90days >2years
5.IMAGERDESIGN
Theopticalsystemiscomposedofatelescopeandare-imagingsystem4(Figure1). Thetelescopeisa165mmclearaperture
Ritchey-Cretiendesign.3 ThesystemhasanF/#of3.4inthespatialdimensionandanF/# of5.3 inthe spectraldimension.2
Alignment of the lenses and interferometer in the system is maintained by using a solid-block interferometer. This design
uses no moving parts and helps to avoid alignment shifts during launch. The interferometer is composed of two glass
elementsthatarebothonehalfofthebeamsplitterandmirror. Theseglasspiecesarebondedtogetherandthenmountedinto
an aluminum housing. The pieces and housing are bolted together and then bolted to an aluminum base, resulting in the
abilitytoholdverytighttolerances.
Camera
Telescope
LensAssembly
Interferometer
Figure1:ExplodedviewoftheFourierTransformHyperspectralInstrumenton-boardMightySatII.1.
188 Proc. SPIE Vol. 4480
Inordertoavoidvacuumqualifyingthecamera,thecameraishousedinsideofasealedcompartmentandtheopticalsystem
is vented locallyto vacuumconditions. The final lens in the system seals the camera compartment. A commercial Silicon
MountainDesign(Kodak)1M60-20 camera based ona 1024 x1024 frame-transfer detector builtbyThomson(7887A) was
modifiedbyKestrelforthisapplication.3 Theimageriscomposedoffourtiles(AtoD)eachwith256 x1024pixels. Each
tile hasitsownamplifier and RS422 digitaloutputdriver, butshare clockdriversand power supplyelectronics and was not
hardenedforspaceapplications. Usingthisconfiguration,thedatastreamisa48-bitwordat10or20MHzdependingonthe
binningmode. Dataratesfrom7.5framespersecondto110framespersecond,variousbinningcombinations,cameragains,
8 or 12 bit depths, and tile combinations can be used depending on the imaging requirements. This allows for the spectral
and spatial resolution and camera performance to be varied electronically. To protect the camera from radiation effects in
space,thehousingwallsweremade0.95cmthick.3
6.LIFETIMESTATISTICS
TheopticalsystemwasdesignedtomeetthesystemrequirementsinTable1,inthermalconditionsof–20to+20degreesC,
with the temperature band being determined bychanges in the index of refraction of the various refractive materials.5 This
temperature range is maintained through a cold biased design that uses thermal isolation, blankets, and heaters. Thermal
vacuum testing and on-orbit results have verified the abilityto maintain the temperature range. Figure 2 shows the value of
threeFTHSItemperaturesensorsduringthecollectssincelaunch.
2
1
0
-1
HSICT(avg)
-2 HSIIT(avg)
HSITT(avg)
-3
-4
-5
-6
7/18 8/12 9/6 10/1 10/26 11/20 12/15 1/9 2/3 2/28 3/25 4/19 5/14 6/8 7/3 7/28
Date
Figure2:FTHSIimagingtemperaturessincelaunch(asof2July2001).
Thetemperaturesensorsarelocatedonornearthetelescope (HSITT), interferometer (HSIIT),and the camera (HSICT). All
images have been taken within –5o and 2oC, which is well within the nominal operating range. The gradual decrease in
temperature continues at this slow rate until the heaters are triggered. Heater vents are programmed to open when the
temperaturesreachapproximately-5oC.
Thelargetemperaturevariationsthatoccurinthebeginningofthemissionareduetoattitudechangesofthesatelliteduringa
spacecraft anomaly. The central processing unit (CPU) experienced a gradual increase in the time it took to finish tasks
duringthe beginningofthe mission. The cause of the anomaly was found in a small section of code and has been fixed on
boardthesatellite. Beforetheanomalywasfixed,aVMEresetofthe satellite wasrequiredtoeliminateanytasksthat were
notresponding. WhenexecutingaVMEresetthesatellitewasorientedsothesolararrayswouldpointatthesun(SunPoint
Mode),andpowertothepayloadswasturnedoff. InthisconfigurationthetemperatureofFTHSIdecreaseduntilthepayload
Proc. SPIE Vol. 4480 189
power wasturned onand the low temperatures activated the HSI heaters. The heaters increased the FTHSI temperatures to
abovezeroandthendeactivated.
Since the camera is not qualified for vacuum conditions, the pressure in the compartment must be monitored. The
compartmentwasfilledwithdrynitrogengastoapproximately110kPapriortolaunch. Thedigitalpressuresensorhasrange
of0to103kPa. Figure3detailsthehighandlow-pressurereadingsatthetimeofeachcollect. Oncethepressurefallsbelow
690kPa,capacitorsintheopticalsystemshouldfail. Priortolaunch,itwasexpectedthatthepressure wouldbeapproaching
zerowithin12monthsafterlaunch. Fromthetrendsinthecamerapressuredata,thecriticalpressure willnotbereachedfor
another12years. Therefore,thesatellitewillre-entertheatmospherebeforethecriticalpressureisreached.
1 1 4
1 1 2
1 1 0
1 0 8
1 0 6
1 0 4
1 0 2
1 0 0
7 /2 8 8 /2 2 9 /1 6 1 0 /1 1 1 1 /5 1 1 /3 0 1 2 /2 5 1 /1 9 2 /1 3 3 /1 0 4 /4 4 /2 9 5 /2 4 6 /1 8
D a y
M in im u m R e a d in g M a xim u m R e a d in g
Figure3:FTHSIcamerapressuresincelaunch(asof2July2001).
7.SENSORCALIBRATION
CalibrationoftheFTHSI wasoriginallygoingto be accomplished usingtwo techniques. The first used a pair offiber optic
feedsthatdirectsunlightontotheedgesofthedetectoratthetimeofeachcollect. AttheoutsideedgesoftilesAandD,ten
pixels are dedicated to calibration. The tile D edge fiber feed contains an Erbium dope with known spectral absorption
values. Thisstrip would thenbe compared withthe tile A edge, whichisexposed to sunlight, to see if the absorption value
hasshifted. Thismethodofcalibrationcouldnotbeusedduetoinsufficientsignal. Thesecondcalibrationtechniqueapplies
a vicariouscalibrationthatdependson knowingthe reflectance and radiance ofa targetatthe time of the collect. Since the
beginningof 2001, we have successfullycollected the same ground area with the satellite, AVIRIS, and ground truth teams
overanumberofsites. Inaddition,co-collectswithNASA’sHyperionimagerhavebeenperformed.
High
response
Mean
response
Low
response
Figure4:Calibrationresponsegraphwithstandardradianceusingdatafrom5January2001.
190 Proc. SPIE Vol. 4480
AsampleofthetypeofcalibrationbeingappliedisshowninFigure4. These werethe firstsuccessfulradiometricvicarious
calibrations obtained in early January 2001. The data shows well collapsed calibration curves over the designed optimal
operatingbandofthesensor(550nmto900nm). Thevariationsatthelongandshorterextremesarerelatedtothedecreased
quantumefficiencyofthesilicondetectorattheseextremes.
Spectral Calibration
2nd Order Poly Fit =(3.41478E-6)*(N2)-(0.0051064)*(N)+157.957
84.6
84.4
n
bi 84.2 CurveFit
1/
m- 84
c FromIvanpau,15fps,1by2
n, binned
o 83.8
uti FromIRAN1014,7.5fps,1by2
ol 83.6 binned
s
e
R
83.4
83.2
0 200 400 600 800 1000
SpatialPixelNumber(N)
Figure5:CalibrationcurvefortheFTHSIsensorbasedon16December2000data.
Original Uncorrected 760 nm absorption band, Ivanpau, 0351
10000
9000
8000
7000
Row140,TileA
6000 Row372,TileB
Row676,TileC
U5000
D
Row811,TileD
4000
3000
2000
1000
0
152 153 154 155 156 157 158 159 160 161 162
Bin#
Figure6:Spectralshiftinthe16December2000collect.
Proc. SPIE Vol. 4480 191
Thespectralcalibrationcurve,Figure5,showshowthespectralresolutionofthesensorchangesoverthefocalplane. The
sourceofthis0.05%variationinthespectralresolutionisan8-micronshiftintheoffsetintheSagnacinterferometeroverits
10cmlength. Uncorrected,thespectralvariationproducesaspectralshiftinthedata(Figure6). Figure6detailstheshiftof
theO absorptionbandatdifferentlocationsonthefocalplane. Thisdifferencecanbeadjustedbyapplyingthecalibration
2
notedinFigure5.
S/N = Mean/Stdv, 24a, 5 frames, Row 150
1k by 1k, 1/125 sec gate, Average S/N =41.1
350
300
250
200
N
/
S 150
100
50
0
1 9 7 5 3 1 9 7 5 3 1 9 7 5 3 1 9 7 5
1 2 3 4 4 5 6 7 8 8 9 0 1 2 2 3 4
1 1 1 1 1 1
Freq,1050nm to455nm (85cm-1per bin)
Figure7:Prelaunchsignaltonoiseratio(SNR)ofthesensor.
SignaltonoisedatawastakenusingLabsphereasanextendeduniformsourcepriortolaunch(Figure7).Thisdataisfor
1/124thsecondgatingand1x1binnedparameters. Toconvertthistothemorenormaloperatingmodeof15framesper
second(fps)with1x2binning,theSNRvaluesshouldbemultipliedby14. Thisgivesanaveragesignaltonoiseratioof
575. Bestopticalperformanceisobtainedwithaslowerframerate. However,thisslowerframeraterequiressatelliteroll
backratetoincrease,whichdecreasesthetimebeforetheeffectsoftheearth’srotationarenoticeable,evenwithatwo-axis
maneuver. Acompromiseof15fpsisnowusedformostobservations.
8.SENSORSTATUS
The sensor is surviving well in space. Dark current collects are used to determine bad pixels on the focal plane. On every
nominal collect, three dark current frames are taken looking into deep space. In addition, about once a month a larger dark
current collect is taken over an ocean at night. Dark current collects will show “hot” pixels on the focal plane. To find
“cold” pixels, an image of a bright scene is taken. Most recently, ice fields in Canada have been imaged to find any cold
pixels. Thesecollectsallowthechangesinthebadpixelmaptobetracked,andimagestobecorrectedforbadpixelsduring
processing. Overthecourseofthemission,thefocalplanehasshownonlyaveryslowincreaseinthenumberofpixelswith
non-standardresponse(Figure8). Thecoldpixelcomparison,Figure8,detailshowfewadditionalcoldpixelscanbeseenon
thefocalplane. Compensationforcoldorhotpixelsiseasilyaccomplished,usingtherawdata,bytakingadvantageofhow
aFouriertransformsensormultiplexesthespectraldataovertheentireinterferencepatternandinterferogramsymmetry. We
areabletocompensateforbadpixeleffects,evenwhentheyappearasacluster.
192 Proc. SPIE Vol. 4480
512
256 Prelaunch
1088
0
0 256 512 768 1024
Figure8:Comparisonoffocalplanecoldpixelsfromprelaunchto29March2001.
Throughoutthemissionaghostimageinthedatahasbeennoticed. Originally,thiswasnotrecognizedduetothealongtrack
spatialresolutionbeinguptotwicethedesignedvaluesandtheuseofthetwocentertileswhichexhibitlessghosting. As
themissionprogressedthealongtrackresolutiondecreasedto30mandimagesstartedtoincludetileD,makingtheghosting
moreprevalent. TheghostingoftheimageisleastnoticeableontileAwherethereisfromzeroto3pixelimagedifference
andgraduallybecomesmorenoticeableuntiltileDwherethereisa12pixelshift(Figure9). Theexactcauseoftheghosting
isstillbeinginvestigatedalthoughitappearstoberelatedtothelackofanARcoatedcoveroverthedetector. Whiletheuse
ofacoverisnominallyusedinasiliconcharge-coupleddevice(CCD)device,itwasremovedduetoconcernsonthevacuum
compatibilityofthebandingagentandconcernovermechanicalsurvivability. Throughgroundprocessingwehavebeen
abletoapplyalinearversionofamaximumexpectedvaluealgorithmtothedatathatshouldremovemostoftheghost.
MoreworktorefinethealgorithmisbeingcompletedatKestrelCorporation.
Figure9:ImageoficeflowsintheBeringStraitdetailingghosting.
9.ON-BOARDPROCESSING
FTHSI uses the QC40 processor to run a variety of processing options. The most successful of the options is the Cyclical
Redundancy Check (CRC).1 For everycollect, a CRC is performed on the data in the SSM. Then both the CRC and SSM
dataaredownloadedtotheground. OnceongroundanotherCRCiscreatedfortheSSMdataandthenthe groundCRCand
satelliteCRCarecompared. ThisallowsfortheSSMdatatobecheckedfordataerrorsduetotransmission.
Theabilitytoprocessthedatawhileon-orbitwasagoaloftheprogram. ThroughtheutilizationoftheQC40processors,the
algorithms for processing data on the ground were also put on-board the satellite. The QC40 could be electronically set to
process the data using various settings. Algorithms for performing apodization, spectral filtering, and the Fast Fourier
Proc. SPIE Vol. 4480 193
Transform (FFT) are examples of the code that was available for on-board processing. Results of the first attempts to
performon-boardprocessingwerenotencouraging. AllprocessingwastakinglongerthanexpectedduetheCPUslowdown
satelliteanomaly. Inadditiontheresultsoftheprocessingwereproducingunrealisticresults.
Aftergroundtestingwiththeengineeringmodel,thecauseswerefound. Amisunderstandingofhowthedata waswrittenin
the SSM during a collect resulted in the bits being read into the QC40 backward. This caused the initial problem. It was
further found that the spectral filter and magnitude codes were not functioning correctly. The final problem was the
conversion from floating point value to integer value. The QC40 EEPROM write pin was disabled prior to launch, so a
permanent fix to on-board the satellite processing will not occur. There is a possibility that some of the code could be
patchedforoneprocessingrun,butthischanceisunlikelytohappenduetotimeconstraints. Ultimately,thismeansthatthe
rawSSMdatamustbedownloadedandprocessedontheground.
The primary objective of the QC40 experiment was to show that the C40 processors could operate in space. Original
estimatesexpectedthatatleastoneprocessorwouldhavebeenlostbythispointinthemission. Currentlyallfourprocessors
arestillinnominalworkingcondition. ThereforetheQC40hasexceededitsdesignexpectations.
10.IMAGINGPARAMETERS
Several imaging modes are available using variable camera and imaging parameters and the ability to reorient the satellite.
Since the lenses and mirrors cannot move, a data collection requires the satellite to maneuver. In a nominal collect, the
satellitefirstyaws90degreestoorienttheapertureperpendiculartothe satellitevelocityvector. Onceoriented,thesatellite
then performs a roll to slow the satellite ground track speed to a speed that sets the desired along track spatial resolution.
Thisallowsforcontiguouspushbroomswathstobecollectedwiththespacebetweenthestripsbeinglessthanacentimeter.6
The maneuvering commands along with imaging parameters are sent to the satellite 24 to 48 hours prior to the time of the
collect. Imageparametersallowtheusertoconfigurethe camera to bestsuitthe type ofground that willbe imaged. These
parameters are changed electronically in the HII card as a result of the upload. The HII controls the camera and routes the
data stream from the HSI into the SSM. The HII is controlled by a single Field Programmable Gate Array (FPGA)
respondingto commands sent to it from the spacecraft control computer (RAD6000). The commands that that programthe
HII to select the data to be saved include: desired tiles to collect, line length, lines per frame, bit depth, start of data collect
(GMT), and starting and ending memory addresses. Commands that initialize the camera are passed directly between the
FPGAandtheHSI.Table2outlinesthepossiblecameraconfigurations,nominalconfigurationbeforelaunch,andthecurrent
nominalconfiguration.
Table2:HIIcardfunctionsandnominalsettings.
PriortoLaunch
Function SelectionsAvailable CurrentSettings
NominalSettings
CameraFrameRate 7.5,15,30,60,110fps 30fps 15fps
1/fps,1/125,1/250,1/500,
CameraGatingTime 1/fps 1/fps
1/1000sec
CameraBinningMode 1x1,1x2,2x1,2x2 1x2 1x2
CameraGain 1or4 1 1
DataBitDepth 12or8bit 12bits 12bits
NumberofImagingTilestoRecord 1,2,3,or4 2(BC) 2(AB)
11.HYPERSPECTRALIMAGESFROMSPACE
On1August2000 at18:47:51 GMT,the first hyperspectralimage wastaken froma space-based platformand subsequently
downloaded. The target was the Denver International Airport (DIA) region in Denver, Colorado. Although the image was
taken slightly north of the aim point, several geographical land features allowed the Horse Creek Reservoir, just north of
DIA,tobelocated(Figure10).
194 Proc. SPIE Vol. 4480