DTIC ADA464621: The ISO Long-Wavelength Spectrometer

6 Pages·0.11 MB·English

by  Defense Technical Information Center

Astron.Astrophys.315,L38–L42(1996) ASTRONOMY
AND
ASTROPHYSICS
The ISO Long-Wavelength Spectrometer
?
P.E. Clegg1, P.A.R. Ade1, C. Armand2, J.-P.Baluteau34, M.J. Barlow5, M.A. Buckley6, J.-C.Berges3, M. Burgdorf2, E.
;
Caux7,C.Ceccarelli8,R.Cerulli8,S.E.Church9,F.Cotin7,P.Cox1019,P.Cruvellier3,J.L.Culhane11,G.R.Davis12,A.Di
;
Giorgio2, B.R. Diplock6, D.L. Drummond6, R.J. Emery6, J.D. Ewart2, J. Fischer13, I. Furniss5, W.M. Glencross5, M.A.
Greenhouse14, M.J. Griffin1,C. Gry23, A.S. Harwood6, A.S. Hazell1, M. Joubert315, K.J.King6, T.Lim2, R. Liseau816,
; ; ;
J.A.Long6,D.Lorenzetti17,S.Molinari2,A.G.Murray1,D.A.Naylor18,B.Nisini8,K.Norman11,A.Omont19,R.Orfei8,
T.J.Patrick11,D.Pe´quignot20,D.Pouliquen3,M.C.Price2,Nguyen-Q-Rieu21,A.J.Rogers6,F.D.Robinson22,M.Saisse3,P.
Saraceno8,G.Serra7,S.D.Sidher2,A.F.Smith6,H.A.Smith14,L.Spinoglio8,B.M.Swinyard6,D.Texier2,W.A.Towlson5,
N.R.Trams2,S.J.Unger6,andG.J.White1
1 QueenMaryandWestfieldCollege,UniversityofLondon,MileEndRoad,LondonE14NS,UK
2 TheLWSInstrument-DedicatedTeam,ISOScienceOperationsCentre,POBox50727,E-28080Madrid,Spain
3 Laboratoired’AstronomieSpatiale,CNRS,BP8,F-13376MarseilleCedex12,France
4 ObservatoiredeMarseille,2placedeVerrier,F-13248Marseille,France
5 DepartmentofPhysicsandAstronomy,UniversityCollegeLondon,GowerStreet,LondonWC1E6BT,UK
6 RutherfordAppletonLaboratory,Chilton,Didcot,OxonOX110QX,UK
7 Centred’EtudeSpatialedesRayonnements,CNRS,9avenuedeColonelRoche,F-31029Toulouse,France
8 CNR-IstitutodeFisicadelloSpazioInterplanetario,CP27,I-00044Frascati,Italy
9 ObservationalCosmology,MC59-33,CaliforniaInstituteofTechnology,Pasadena,CA91125,USA
10 Institutd’AstrophysiqueSpatiale,Ba^timent120,Universite´deParisXI,F-91405Orsay,France
11 MullardSpaceScienceLaboratory,UniversityCollegeLondon,HolmburyStMary,Dorking,SurreyRH56NT,UK
12 InstituteofSpaceandAtmosphericStudies,UniversityofSaskatchewan,Saskatoon,Saskatchewan,S7N5E2,Canada
13 NavalResearchLaboratory,RemoteSensingDivision,4555OverlookAvenueSW,Washington,DC20375,USA
14 NationalAirandSpaceMuseum,SmithsonianInstitution,LaboratoryforAstrophysics,Washington,DC20560,USA
15 CNES,2PlaceMauriceQuentin,F-75001Paris,France
16 StockholmObservatory,S-13336Saltsjo¨baden,Sweden
17 OsservatorioAstronomicodiRoma,I-00040MontePorzio,Italy
18 DepartmentofPhysics,UniversityofLethbridge,4401UniversityDrive,Lethbridge,Alberta,T1K3M4,Canada
19 Institutd’AstrophysiquedeParis,CNRS,98bisboulevardArago,F-75014Paris,France
20 ObservatoiredeParisMeudon,PlaceJanssen,F-92190Meudon,France
21 ObservatoiredeParis,61avenuedel’Observatoire,F-75014Paris,France
22 Code717.3,NASAGoddardSFC,Greenbelt,MD20771,USA
Received5August1996/Accepted22August1996
Abstract. TheLong-WavelengthSpectrometer(LWS)isoneof Keywords:artificialsatellites,spaceprobes–instrumentation:
twocomplementaryspectrometersaboardtheEuropeanSpace spectrographs–infrared:general
Agency’s Infrared Space Observatory1 (ISO) (Kessler et al.,
1996). It operates over the wavelength range 43 1969 m
at either medium (about 150 to 200) or high (68(cid:0)00 to:97(cid:22)00)
spectralresolvingpower.This Letterdescribestheinstrument
anditsmodesofoperation;acompanionpaper(Swinyardetal, 1.Introduction
1996)describesitsperformanceandcalibration.
Astronomical observations at far-infrared wavelengths, from
about20 mto300 m,arealmostimpossiblefromtheground
becauseo(cid:22)fatmosphe(cid:22)ricemissionandabsorption.Evenataero-
plane and balloon altitudes, spectroscopy is difficult because
Sendoffprintrequeststo:P.E.Clegg([email protected])
telluric lines obscure weaker and narrower extra-terrestrial
ISO is an ESA project with instruments funded by ESA Mem-
?
ber States(especiallythePIcountries: FranceGermany, theNether- lines.TheLWScoversthealmostunexploredwavelengthrange
landsandtheUnitedKingdom)andwiththeparticipationofISASand 43 1969 m:theshorterwavelengthend overlapswith the
NASA. 25(cid:0) 45: m(cid:22)rangeoftheShort-WavelengthSpectrometer(de
: (cid:0) (cid:22)
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1. REPORT DATE 3. DATES COVERED
1996 2. REPORT TYPE 00-00-1996 to 00-00-1996
4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
The ISO Long-Wavelength Spectrometer
5b. GRANT NUMBER
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6. AUTHOR(S) 5d. PROJECT NUMBER
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Naval Research Laboratory, ,4555 Overlook Avenue, REPORT NUMBER
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a. REPORT b. ABSTRACT c. THIS PAGE 5
unclassified unclassified unclassified
Standard Form 298 (Rev. 8-98)
Prescribed by ANSI Std Z39-18
P.E.Cleggetal.:TheISOLong-WavelengthSpectrometer L39
Graauwetal.,1996)whilstthe longestwavelengthiscloseto
thecurrentlimitforphotoconductivedetectors.
TheLWSwasdesignedtoachievethetwomainobjectives
ofastronomicalspectroscopy:thedetectionandidentificationof
dust(orsolidstate)featuresandlines-togetherwithadetermi-
nationoftheirstrengthsandratios-forwhichmoderatespectral
resolvingpoweroftensuffices;and thestudy of theshapesof
linesforkinematicpurposes,forwhichhighresolvingpoweris
needed.[Highresolvingpowerisalsoneededtodetectveryfaint
linessittingonastrongcontinuum.]Wethereforechosetode-
signtheLWStooperateintwomodes.Initsmoderate-resolution
mode,itsspectralresolutionelementis029 mbetween43 m
and946 mand060 mbetween946: m(cid:22)and1969 m(cid:22).In
high-re:so(cid:22)lutionmo:de,i(cid:22)tsresolvingpow:er(cid:22)variesbetw:een(cid:22)8100
and8500,forthewavelengthrange47 70 m,andbetween
6800and9700forthewavelengthrange(cid:0)70 (cid:22)1966 m.
(cid:0) : (cid:22)
2.DescriptionoftheInstrument
Fig.1.TheopticaltrainoftheLWS
2.1.Overalldesign
tionisfocusedbymirror(8)ontothecylindricalsurfaceofthe
The LWS consists of three main components, the focal plane
detectorblock.
unit (FPU), operating at liquid-helium temperatures, and two
warmunits:theanalogueprocessingunit(APU)-whichdrives Theopticalsubsystem isdesignedto satisfy theJacquinot
thevariousmechanismsandpowersthe detectorsin theFPU, criterionfortheresolutionoftheinstrument,tooptimisethecol-
aswellasprocessingtheresultingsignals-andthedigitalpro- limationofthebeamatthepositionoftheFabry-Perotetalons,
cessing unit (DPU), which commands the LWS via the APU andtomatchthespectralresolutionachievedbytheinstrument
andinterfaceswiththespacecraftdata-handlingsystem. ingratingmodetotheorder-sortingneedsoftheFPs.
TheFPUitselfconsistsofthreesubsystems:theopticalsub- Thegratingisruledwith7.9linespermillimetreatablaze
system,thedetectorsubsystemandtheFabry-Perotsubsystem. angleof30 onarotationally-symmetricSchmidtprofile.Itis
o
Theopticalsubsystemcomprisesacollimator,agrating,andre- mountedona scanningmechanismsimilar to thatused in the
focusingopticswhichfeedthedetectorsubsystem.TheFabry- SWSanddescribedbydeGraauwetal.(1996).Withthegrating
Perotsubsystem,whichissituatedinthecollimatedpartofthe initsrestposition,theradiationisincidentatannominalangleof
beam,consistsofawheelcarryingtwoFabry-Perotinterferom- 60 .Thegratingisusedinsecondorderforthewavelengthrange
o
eters.Thewheelcanbesetinanyoffourpositions:inoneof 43 946 mandinfirstorderforthewavelengthrange946
these,thebeampassesstraightthroughthesubsystemwhilstin 196(cid:0)9 :m.(cid:22)It can be scanned, by means of a servo-contro:lle(cid:0)d
another,thebeamiscompletelyobscured.Intheremainingtwo driv:e m(cid:22)echanism, through 70 . The grating was originally
positions, one or other Fabry-Perotis placed in the beam and intended to scan through (cid:6)35: oin normal operation, a range
modulatesitspectrally. chosensothatthenominal(cid:6)ran:geoofwavelengthscoveredbyone
detectorchanneloverlappedthatof theadjacentdetectorbya
fewmicrometers.Theextendedscanningrangeof 70 allows
2.2.OpticalDesign(SaisseandRabou,1988) -atthecostofasmallincreaseinpowerdissipate(cid:6)din:tohefocal
plane-thenominalwavelengthrangeofanydetectorchannelto
Figure1 showstheopticaltrainof theLWS superimposedon
becoveredbyitstwoneighbours,thusprovidingredundancyin
aphotographoftheinstrumenttakenbeforetheintegrationof
thecaseofafaileddetector.Thisincreaseofthescanningrange
theFabry-Perotsubsystem.Thef/15beamfromthetelescope
also extends the long-wavelength coverage out to 1969 m.
isfoldedbymirror(1)andcomestoafocusonthemirror(2),
In order to maximise the sensitivity of the instrument:at(cid:22)all
which was designed to restrict thefield of view on the sky to
wavelengths, however, the grating is now scanned more than
1.65arcmin-thediffractionlimitofthetelescopeat118 m.
Inpractice,thebeamissomewhatnarrowerthanthis(Swiny(cid:22)ard (cid:6)3:5oinnormaloperation.
et al., 1996). The field mirror is surrounded by a concentric
out-of-fieldrejectionmirrortoavoidproblemswithstraylight.
2.3.DetectorsandColdElectronics(Churchetal.,1993)
Frommirror(2),thebeampassestothemirrors(3)and(4)be-
forereachingtheFabry-Perotsubsystemviathemirror(5).The Figure 2 is a drawing of the detector block, which contains
beam is then reflected by plane mirrors (6) and (7) on to the ten detectors: five of these cover the short-wavelength range
grating,whichhasanoff-centreSchmidtprofiletocorrectfor 43 90 m in nominally 10 m-wide channels while the
sphericalaberration.Finally,onleavingthegrating,theradia- (cid:24)others(cid:0)cover(cid:22)the long-wavelength(cid:22)90 197 m in nominally
(cid:0) (cid:22)
L40 P.E.Cleggetal.:TheISOLong-WavelengthSpectrometer
ror(8)infigure1.Thestressonthelong-wavelengthdetectors,
whichisappliedwithamechanicalscrew,reducesthegapbe-
tween the acceptors and the valence band, thus reducing the
energyneededforexcitationofcarriersintotheband.Thisre-
duction in energy-gap, however, also allows more carriers to
bethermallyexcitedintotheband;inordertokeeptheirdark-
currentstoacceptablelevels,therefore,thestresseddetectorsare
operatedatthelowesttemperatureavailable,thatofthehelium
tank at 1.8 K. The unstressed detectors in contrast, are found
tobehavepoorlyat1.8Kandarethereforeoperatedat3.0K.
Operating the two types of detector at different temperatures
isachievedbymountingthemonthermally-separatebars.The
unstresseddetectorsaremountedontheupperoftwobarsinthe
detector block. This bar, which accommodatesa heater and a
thermometeroperatinginaservoloop,hasaweakthermallink
to the lower bar. The lower bar, accommodating the stressed
detectors(shaded)isthermallyshortedtotheheliumtankwith
ahigh-conductancecopperstrap.
Thephoto-currentinadetectorelementisaccumulatedon
theinputcapacitanceofanFETinaJF-4integratingamplifiers
suppliedbyInfraredLaboratories,Inc.TheseFETsareoperated
atabout60KwithintheirTO5cans,whicharecarefullyshielded
toavoidstraythermalemission.Theamplifiersarereadoutat
88 Hz and are re-set at pre-set intervals, usually 0.25 or 0.5
seconds.
Fig.2.DrawingoftheLWSdetectorblock.
Fiveinfraredilluminators,alsoprovidedbyInfraredLabo-
ratories,Inc.,areusedtomonitorandcalibratethestabilityof
responseofthedetectors.
20 m-widechannels.Radiationinthelong-wavelengthrange
- co(cid:22)ming from the grating in first order of diffraction - is, of
course,focusedontothesamerangeofpositionsonthedetector 2.4.Fabry-Perots(Davisetal.,1995)
blockasisradiationintheshort-wavelengthrangecomingfrom
Foruseinhigh-resolutionmode,theLWScontainstwoFabry-
thegratinginthesecondorderofdiffraction.Alternatedetectors
Perot interferometersmounted on a wheel driven by a pinion
arethereforedesignedtorespondtolongandshortwavelengths
engaging gear-teeth on the rim of the wheel: a new type of
respectively.Consequently,eachdetectorreceivesnotonlyits
cryogenicmotorwasespeciallydeveloped(Davisetal.,1991)
“own" wavelengthbutalsoothermultiplesofthiswavelength
to drive the wheel. The short-wavelength Fabry-Perot covers
inotherordersandmustbepreventedfromrespondingtothese
thewavelengthrange47 70 mwhilstthelong-wavelength
extraneousordersbybandpassfilters.Thisbecomesverycritical Fabry-Perotdealswiththe(cid:0)rema(cid:22)ining70 1966 m.Rotation
at the shortest wavelengths and makes high demands on the of the wheel brings successively into th(cid:0)e para:lle(cid:22)l part of the
designofthefilters.
beam(betweenmirrors(5)and(6)offigure1):anopenaper-
Threedifferenttypesofphotoconductivedetectorareused ture,sothattheLWScanbeusedinmoderate-resolutionmode
tocovertherequiredrangeofwavelengths.Theshortestwave- asagratingspectrometer;theshort-wavelengthFabry-Perot;a
lengthchannelSW1(nominally43 50 m)usesaberyllium- blankingplateformeasurementofthedetectors’dark-currents;
dopedgermanium(Ge:Be)detector(cid:0).The(cid:22)nextfivechannelsin and the long-wavelength Fabry-Perot. [In practice, the dark-
wavelength-space(SW2:50 60 mSW3:60 70 m,SW4: currentismeasuredwithoneoftheFPsinthebeam,itsetalon
70 80 m,SW5:80 90(cid:0)ma(cid:22)ndLW1:90(cid:0) 110(cid:22) m)use beingdeliberatelymadenon-paralleltoreflectbackallradiation
gall(cid:0)ium-d(cid:22)oped germani(cid:0)um (G(cid:22)e:Ga) detectors(cid:0)whilst(cid:22)stressed arrivingviatheopticalpathoftheinstrument.]
Ge:Gaisusedforthefourlongest-wavelengthchannels(LW2: TheconstructionoftheFabry-Perotetalonsisshowninfig-
110 130 m, LW3: 130 150 m, LW4: 150 170 m ure 3. The moving plate (4) is suspended on leaf-springs (8)
andL(cid:0)W5:17(cid:22)0 190 m).[(cid:0)Thesea(cid:22)rethenominalw(cid:0)avelen(cid:22)gth between the back plate (1) and the fixed plate (9). Each cor-
ranges;theactu(cid:0)alrang(cid:22)eofwavelengthscoveredbyeachchan- nerofthemovingplatecarriesaloudspeaker-likedrivecoil(3)
nelisadjustedtooptimisethesensitivityoftheinstrumentatall whichoperatesinagapsurroundingapermanentmagnetinthe
wavelengths(Swinyardetal.,1996).] backplate(2).Thepositionofeachcorner,relativetothefixed
Detectors are mounted in integrating cavities to increase plate,isdeterminedbymeasuringthechargeonthecapacitance
their absorption efficiency and are fed by a horn designed to micrometer(6),formedbypadsonthemovingandfixedplates.
coupleefficientlywiththeradiationleavingthesphericalmir- Thesepositionsarecontrolledbyaservosystemwhichsupplies
P.E.Cleggetal.:TheISOLong-WavelengthSpectrometer L41
software used to implementthe AOTs, however,make use of
thismultiplexingwherepossibletominimisethelengthofscan
andthereforethetimeneededtocarryoutanobservation.The
spectralresolutionelementsingratingmodeare029 minthe
short-wavelength channels (SW1 - SW5) and 0:60 (cid:22)m in the
long-wavelengthchannels(LW1-LW5).Theser:esol(cid:22)utionele-
mentscorrespondtoaresolvingpowerrangingbetweenabout
150and300.
3.2.2.Fabry-PerotMode
InFabry-Perotmode,thegratingismovedsoastomaximisethe
powerfallingonthedetectoratthewavelengthunderinvestiga-
tionandtheappropriateFabry-Perotisusedtoscanaboutthat
wavelength.Ifarangeofwavelengthsistobestudied,thegrat-
ingwillbemovedperiodicallysoastokeepthegratingtrans-
missionasnearmaximumaspossible.Althoughmultiplexing
betweendetectorsstilloccurs-radiationindifferentordersof
Fig.3.TheconstructionofaFabry-Perotetalon. theFabry-Perotwillbefallingondetectorsotherthantheone
selectedforthewavelengthofinterest-itisunlikelythatanyof
thesedatawillbeuseful.Therearetworeasonsforthis.First,
sufficientcurrenttothedrivecoiltomakethemeasuredcharge
there may not be spectral lines in the other orders. Secondly,
equaltoacontrolvalue.Thetwoplatesarescannedparallelto
andmoreimportantly,thegratingwillbesetsothatithaspeak
eachotherbyapplyingappropriatesignalstothethreecoils.
transmissionattheFabry-Perotorderofinterest.Otherorders
Thefixed and movingplates carry the reflecting elements
will fall on the (uncalibrated) wings of the grating’s spectral
(5),madeoffree-standingnickelmeshessuppliedbyHeiden-
responsefunction.
hain;thesemeshesareaffixedtothemesh-mountingrings(7)
whichareattachedtotheplates.Themeshesconsistofarectan- Theresolvingpowerachievedin Fabry-Perotmodevaries
gulargridofrectangularsection:thethicknessofthemeshesis between 6800 and 9700. The free spectral range of a Fabry-
3 m,thewidthofthe“bars"ofwhichthemeshesarecomposed Perot is given by , where is the order of interference.
is(cid:22)6 m, and the periods of the grid are 19 m for the long- Its resolvingpowe(cid:21)r,=onn theothenr hand is givenby , where
wave(cid:22)lengthFabry-Perotand155 mforthe(cid:22)short-wavelength is its finesse. In order to achieve a resolving ponwFer of 104
Fabry-Perot.Thenarrowtoleran:ce(cid:22)allowedonthesedimensions Fwiththeavailablefinessesofabout100,weneedtooperatein
iscriticaltotheperformanceoftheinstrument. orders of around 100; the ratio of the wavelength to the free
spectralrangeisthenalsoabout100.Ifthegratingistoavoid
spectralcontamination,bypreventingadjacentspectralorders
3.UsingtheLWSInstrument(Cleggetal.,1994)
of the Fabry-Perots from reaching the detectors, its resolving
3.1.Summary powermustthereforealsobeabout100.Itwastheneedforthe
gratingtoorder-sortfortheFabry-Perotwhichsettherequire-
The LWS has two operational modes: grating (medium-
mentontheresolvingpowerofthegrating.Inbothgratingand
resolution) mode and Fabry-Perot (high-resolution) mode. It
Fabry-Perotmodes,observationsarecarriedoutwithoneoftwo
has six different observational modes which can be accessed
standardlengthsofdetectorintegrationramps,0.25sand0.5s.
viafour AstronomicalObservationTemplates(AOTs, cf. sec-
Thetotalintegrationtimeperspectralpointisthenachievedby
tion3.3).
varyingthenumberoftheseramps.Itwasoriginallyintended
thatspectrabeobtainedbycarryingoutanumberofintegrations
3.2.OperationalModesoftheInstrument at each setting ofthegratingor Fabry-Perotuntilthetotalre-
quiredintegrationtimehadbeenbuiltup.Inordertominimise
3.2.1.GratingMode
the low-frequency end of 1/f noise, however, a fast-scanning
Ingratingmode,theFabry-Perotwheelisturnedtoitsopenpo- modewasalsoimplemented.Inthismode,onlyoneintegration
sitionandthegratingisscannedovertherangeofangleneeded isperformedateachpositionofthegratingorFabry-Perot,the
tocoverthedesiredwavelengthrange.Notethat,alldetectors totalintegrationtimebeingbuiltupbyrepeatedscanning.This
arereceivingradiationallthetimeandthecorrespondingdata method is now recommended for all observations because it
arebeingreadout.Whetherornotthesedataareusefultothe avoidssuccessiveintegrationrampsbeingaffectedbythesame
observerdependsupontherangeofwavelengthsselected.The particlehit(cf.Swinyardetal.,1996).
L42 P.E.Cleggetal.:TheISOLong-WavelengthSpectrometer
3.3.ObservationalModesoftheInstrument isnoneoftheusualmonitoringofchangesindetectorrespon-
sivityordark-current(cf.Swinyardetal.,1996),theaccuracy
3.3.1.Medium-ResolutionWavelengthRangeLWS01
with which the signals are extracted is significantly reduced.
This grating-modeAOT results in a medium-resolutionspec- Lastly,thedatacannotbeprocessedbystandardmethods.For
trum covering a wavelength range, specified by the user, up allthesereasons,themodeisavailableonlytomembersofthe
to the full range of the LWS in medium-resolution mode LWSConsortium.
(430 1969 m).Thereisaminimumtotherangecovered,
corr:es(cid:0)pondin:g(cid:22)to 125 m for the short-wavelength channels 4.Conclusion
(SW1 - SW5) and:25(cid:22)m for the long-wavelength channels
(LW1 - LW5). Data a:re(cid:22)recordedfrom all ten detectorswhile The Long-Wavelength Spectrometer was designed to provide
astronomerswith a spectroscopictoolin a region of the elec-
thespecifiedrangeisbeingscanned.Theobserverhasachoice
tromagnetic spectrum largely inaccessible hitherto. It is fully
ofsamplingthespectrumat1,1/2or1/4ofaresolutionelement.
functioninginorbitandisproducingspectrafromavarietyof
astronomicalobjects:otherpapersin thevolumeillustratethe
3.3.2.Medium-ResolutionLineSpectrumLWS02
resultsbeingachieved.
ThisAOTproducesmedium-resolutionspectraaroundupto10
Acknowledgements. TheLWSwasdesignedandbuiltbyaconsortium
wavelengths,specifiedbytheobserver.Dataarerecordedfrom
of scientists and engineers from Canada, France, Italy, the UK and
alltendetectorswhilethespecifiedrangesarebeingscanned.
theUSA.Hardwareandsoftwarewereprovided by: Centred’Etude
Theobserverhasachoice,infractionsofaresolutionelement, SpatialedesRayonnements,Toulouse,France;IstitutodeFisicadello
ofthespectralsamplinginterval. Spazio Interplanetario, Frascati, Italy; Laboratoire Astronomie Spa-
tiale,Marseille,France;MullardSpaceScienceLaboratory,University
CollegeLondon,HolmburyStMary,UK;RutherfordAppletonLabo-
3.3.3.High-ResolutionWavelengthRangeLWS03
ratory,Chilton,UK;QueenMaryandWestfieldCollege,London,UK;
ThisAOTresultsinahigh-resolutionspectrumcoveringawave- UniversityCollegeLondon, London, UK.Theauthorsgratefullyac-
knowledgefundingbythefollowingnationalagencies:CNES,CNR,
length range,specified by the user, up to the fullrangeof the
NASA,NSERCandPPARC.
LWS(470 1966 m)inhigh-resolutionmode.Usefuldata
arerecord:ed(cid:0)from:on(cid:22)lyonedetectoratatime.Theobserverhas
achoiceofsamplingthespectrumat1,1/2or1/4ofaresolution References
element.
Church,S.E.,Griffin,M.J.,Ade,P.A.R.,Price,M.C.,Emery,R.J.and
Swinyard,B.M.,1996,InfraredPhysics34,389
Clegg,P.E.,Heske,A.andTrams,N.R.,1994.LWS/PEC/2039.01“Ob-
3.3.4.High-ResolutionLineSpectrumLWS04
servers’sManual",Issue1
This AOT produces high-resolution spectra around up to 10 Davis,G.R.,Furniss,I.,Towlson,W.A.,Ade,P.A.R.,Emery,R.J.,Glen-
wavelengths,specifiedbytheobserver.Usefuldataarerecorded cross,W.M.,Naylor,D.A.,Patrick,T.J.,Sidey,R.CandSwinyard,
fromonlyonedetectoratatime.Theobserverhasachoiceof B.M.,1995,Appl.Optics,34,92
deGraauw,Th,etal.,1996.Thisissue.
samplingthespectrumat1,1/2or1/4ofaresolutionelement.
Kessler,M.F.etal.,1996.Thisissue.
Davis,G.R., Furniss,I., Patrick,T.J., Sidey.R.C. and Towlson,W.A.
3.3.5.Narrow-BandPhotometryLWS02 1991.In25thAerospaceMechanismsSymposium,Pasadena,May.
NASAconferencepublication3113
In this mode, the grating is not scanned but kept at a fixed
Saisse, M. and Rabou, P. 1998. In SPIE vol. 1013, “Opitcal Design
position by a special choice of a parameter in AOT LWS02. MethodsandLargeOptics",pp66-73.
The resultis narrow-bandphotometryat ten wavelengths,de- Swinyardetal.,1996.Thisissue.
terminedbythechoiceofasinglewavelength,withintherange
43 1969 m.Thespectralresolutionelementis029 min
the(cid:0)short-:wa(cid:22)velength channels (SW1 - SW5) and 0:60 (cid:22)m in
thelong-wavelengthchannels(LW1-LW5). : (cid:22)
3.3.6.SerendipitouslyParallelMode
Longafterthedesignoftheinstrumentanditsobservingmodes
wascomplete,itwasrealisedthatalimitednumberofastronom-
icallyusefuldatacouldbetransmittedinhousekeepingchannels
whilethesatellitewasslewingorotherinstrumentswerebeing
used.Inthismode,theslopeoftheintegrationrampsissimply
estimatedonboardbytakingthedifferencebetweenasample
atthebeginningandendoftheramp.Moreover,becausethere