Abstract

IJJSS2014 :The6thIndonesiaJapan
JointScientificSymposium
Yogyakarta,28‐30October2014
Theme code: E5
Applicationofhyperspectralcameraforaerosol
characterization
NaohiroManago1*,HayatoSaito1,YoheiTakara2,MakotoSuzuki3,HiroakiKuze1
1CenterforEnvironmentalRemoteSensing,ChibaUniversity,1‐33Yayoi‐cho,Inage‐ku,
Chiba‐shi,Chiba,263‐8522,JAPAN
2EBAJapanCo.,Ltd.,#3012‐17‐12Takanawa,Minato‐ku,Tokyo,108‐0074,JAPAN
3InstituteofSpaceandAstronauticalScience,JapanAerospaceExplorationAgency,
3‐1‐1Yoshinodai,Chuo‐ku,Sagamihara,Kanagawa,252‐5210,JAPAN
Abstract
Optical observation of aerosol particles in the atmosphere is indispensable for various
purposessuchasatmosphericcorrectionofsatellitedata,basisforclimatechangestudies,
and air pollution monitoring. The progress in the remote sensing instrumentation has
madeitpossibletocarryoutaerosolstudiesonthebasisoftwo‐dimensionalimagery.As
comparedwithconventionalmethodologyusingaskyradiometerorasunphotometer,the
obvious advantage of the image formation is the elimination of necessity for precise
trackingofthesolarposition,inadditiontotheeaseofcloudrecognition.Inthisstudy,we
describethecharacterizationofanewlydevelopedhyperspectralcamerathatprovides
uswithimageswith752×480pixelsoverthewavelengthrangeof350‐1100nmwitha
typicalresolutionof6nm.Thewavelengthandradiancecalibrationandtheuniformity
checkoftheinstrumentaredescribedindetail.Wealsoreportonthepreliminaryresults
oftheaureoleandskylightanalysisconductedattheCenterforEnvironmentalRemote
Sensing, Chiba University. The present results have shown that the use of a compact
hyperspectralcameracanbepromisingfordetailedaerosolcharacterizationstudies.
Keywords
Hyperspectralimaging;Skylight;Troposphericaerosol;PM2.5;
1.Introduction
Recently, aerosol has become a popular concern because of the hazardous
concentrationof“PM2.5”occasionallyoccurringinlargecitiesworldwide.Sincephysical
andchemicalcharacteristicsofaerosolsvaryspatiallyandtemporallyinasignificantway,
aerosolcharacterizationisindispensabletounderstandingtheatmosphericenvironment
precisely.Skylightintensity(spectralradianceofscatteredsolarradiation)dependson
theseparationanglefromthesolarposition,andisstronglymodulatedbyintermediate
substancesintheatmosphere,especiallybytroposphericaerosols.
*Correspondingauthor.Tel.:+81‐43‐290‐3841;fax:+81‐43‐290‐3857.
E‐mailaddress:manago.naohiro@chiba‐u.jp
Inthisstudy,physicalandopticalpropertiesoftroposphericaerosols,suchassize
distribution and complex refractive index, are retrieved from the analysis of
hyperspectral (HS) imagery of skylight in conjunction with the information on the
wavelengthdependentaerosolopticaldepth(AOD)derivedfromdirectsolarirradiation.
Compared with conventional approaches such as those based on a sunphotometer
(Holbenetal.,1998)oraskyradiometer(Nakajimaetal.,1996),thepresentmethodis
advantageousbecauseofthefollowingfourreasons;1)usingaHScamera,skylightclose
totheSuncanpreciselybemeasuredwithagoodspatialcontext,whichresultsinbetter
determinationofsizedistribution;2)cloudypixelscanberejectedaccurately;3)column
amountofmoleculessuchaswatervaporcandirectlybemeasuredfromtheirabsorption
features;and4)simultaneousmeasurementofskylightintensitycanbemadewithinthe
view angel of the camera (ca. 20 deg). We explain the methodology for calibrating
instrumentsintermsofparameterssuchaswavelength,radiance,viewingangle,etc.Also,
wedescribetheformulationhowtheretrievalofaerosolpropertiesisimplemented,with
someexamplesshowingtheusefulnessofthepresentapproach.
2.Methodology
2.1Instrument
Inthisresearch,weuseaHScamera,NH‐2,manufacturedbyEBAJapanCo.,Ltd.(Takara
et al., 2012). Major specifications of the camera are listed in Table 1. It has a built‐in
scanningmechanism,sothatnootherexternaltranslationdeviceisrequiredtotakeHS
images,anditiscapableofscanning16º×10ºwideareain4seconds.Theopticsisbased
ontransmissiondiffractiongrating,andthereforelesssensitivetothepolarizationstate
ofincominglightcomparedwithanacousto‐optictunablefilter(AOTF)oraliquidcrystal
tunablefilter(LCTF).
Table1.SpecificationofEBAJapanNH‐2
Item
Value
SensorType
CMOS
Optics
Transmissiondiffractiongrating
Max.imagesize
752×480pixel
FieldofView
16º×10º
Spatialsamplinginterval
0.02º/pixel
Spatialresolution
0.07º
Max.wavelengthsize
480pixel
Wavelengthrange
350∼1100nm
Wavelengthsamplinginterval
1.6nm/pixel(minimum)
Wavelengthresolution
6nm(typical)
Colordepth
10bit(sensor),12bit(camera)
Dimension
76×62×193mm
Weight
850g
2.2Calibration
ThereareNx×Nw=752×480pixelsintheCMOSsensorarrayinsideNH‐2.Incidentlight
from an oblong light source is distributed into the x direction on the sensor, while
chromaticlightdispersedbythediffractiongratingisdistributedintothewdirection.In
addition,thebuilt‐inscannermovesthe“linesensor”verticallyinNy=480stepstoform
aHSimagewith2spatialdimensionsplus1wavelengthdimension.Thedataacquisition
software enables us to pick out wavelength pixels arbitrarily, and spatial pixels in a
2 rectangularregionofinterest.Themovingdistanceofthescanner’ssteppingmotorcan
bechangedbyreconfiguringthesettingssavedintheonboardROM.Thepixelnumbers
inxandydirectionsofaHSimage(pxandpy)arerelatedtohorizontalandverticalangle
(θx and θy), respectively, while the pixel number in w direction (pw) is related to
wavelength().
Similarly, the digital number output from the sensor (z) is related to spectral
radiance (L). In order to obtain coefficients to convert these instrumental values to
physical values, we have to perform viewing angle calibration, wavelength calibration,
andradiancecalibration.Wavelengthcalibrationandradiancecalibrationaredoneusing
calibrationcoefficientsderivedatthecentralregionofaHSimagefirst,thenuniformity
correction is performed to take the partial difference in an image into account. Also,
temperaturecorrectionsareneededtocompensatethetemperaturedependenceofthe
conversion coefficients. After proper calibrations and corrections, measured data are
comparedwithcalculateddatareproducedbyradiativetransfersimulationtoretrieve
aerosolproperties.Sinceinthisprocedure,thespatialresolutionandopticalresolution
ofthecalculateddatashouldbematchedwiththatofthemeasureddata,itisnecessary
toestimatetheseresolutionsbeforehand.Itisexpectedthatpolarizationdependenceof
NH‐2issmall,butitneedstobeconfirmedexperimentally.
Viewing angle calibration coefficients (Dx = dθx/dpx|r=0 and Dy = dθy/dpY|r=0) are
optimized so that the result of the simulation that modeled the optical system of the
camera can reproduce actual HS image. Here, we assume an image distortion model
expressedas
rd
 r (1  K1 r 2  K 2 r 4 ) ,
(1)
andoptimizethedistortioncorrectioncoefficients(K1andK2).Theparameters,randrd,
are the radial distance from the optical axis to image on the sensor before and after
correctingimagedistortion,respectively.Across‐sectionpaperonawallapartfromthe
cameralensisagoodtargetoftheHSimagefortheviewinganglecalibration.Oncewe
gettherelationshipbetweenpixelnumberandviewingangle,wecanestimatethespatial
resolutionoftheHScamerafromthespreadofanimageofapoint‐likelightsourceata
fardistance.
The relationship between wavelength pixel number (pw) and wavelength (λ) is
approximatedwithapolynomialfunctionas
  c0  c1 p w  c 2 p w 2  c3 p w 3  c 4 p w 4  c5 p w 5 .
(2) The coefficients (wavelength calibration coefficients) in eq.(2) are optimized using HS
imagesoflightsourceshavingnarrowemissionlineswithknownpeakwavelengths,such
asdischargelampsorlasers.
WhenacquiringHSimages,atransmissivediffuserisplacedinfrontofthelensso
thattheincidentlightcanilluminatetheentiresensoroftheHScamera.First,weobtain
the spectral intensity (z) around an emission peak, as a function of wavelength pixel
number (pw), averaged in the central region of a HS image. Then, we find the peak
wavelengthpixelnumberandrelateittotheknownwavelength().Here,byusingspline
interpolation,thespectrumisinterpolatedonafinegridtoincreasetheprecision.After
pairingasufficientnumberofpwand,weobtainwavelengthcalibrationcoefficients(c0,
c1,etc.)byleastsquaresfitting.Next,wefindthepeakwavelengthpixelnumberinthe
entireregionoftheHSimageandcalculatethedifferencefromthecentralregionforeach
pixel.ThewavelengthresolutionoftheHScameracanbeestimatedfromthefullwidthat
halfmaximum(FWHM)ofintrinsicallynarrowemissionlines.
Radiance calibration coefficients (R=dz/dL) are obtained from a HS image of a
lightsourcewithknownspectralradiance(L)bycomparingsensoroutput(z)withL.The
spectral radiance of the light source can be evaluated if an already‐calibrated
spectroradiometerisavailable.Inthiscase,itisnecessarytomatchtheFOVbetweenthe
spectroradiometerandtheHScamera.Also,weneedtoconsiderthedifferenceofoptical
resolution, though it is not necessary to match the optical resolution if we use a light
source with smooth wavelength dependence like a halogen lamp. The linearity of the
sensoroutputcanbecheckedbycomparingradiancecalibrationcoefficientsobtainedat
variousinputlevelschangingeitherexposuretimeoftheHScameraortheintensityof
thelightsource.Inordertoobtainuniformitycorrectioncoefficients,alightsourcewith
uniformluminancedistribution(orknownluminancedistribution)withintheFOVofthe
HScameraisrequired.Integratingspheresandtwilightflat(skylightaroundthezenithin
cloudlessearlymorningorevening)areconsideredtobesuchlightsources.
TemperaturedependenceoftheHScameracanbeinvestigatedbyputtingitina
temperature‐controlled chamber and observing a light source outside the chamber,
changingtheinsidetemperaturestepbystep.Thefluctuationofthelightsourceintensity
should be monitored and corrected using a spectroradiometer. Apparent wavelengths
obtained by eq.(2) will change with temperature, and the difference of apparent
wavelengths()correspondingtotemperaturechange(t)canbemodeledas




  c0  c1  c22  c3  c4  c52 t  c6  c7 t 2 t .
(3)
A light source with some spectral features like a discharge lamp or a xenon lamp is
suitableforwavelengthcalibration.Asforsensoroutput(radiancecalibration),thedark
signal and dark‐subtracted signal have individual temperature dependence. It can be
considered that there is no wavelength dependence of dark signal itself, and it can be
modeled using a 5th order polynomial. The temperature dependence of the dark‐
subtractedsignalcanbemodeledusing2‐dimensional5thorderB‐splineinterpolation
based on measurements at several temperatures and wavelengths. A light source with
smoothwavelengthdependencelikeahalogenlampissuitableforradiancecalibration.
2.3Observation
The solar and sky radiation measurements were conducted at the Center for
EnvironmentalRemoteSensing(CEReS,35.62ºN,140.10ºE),ChibaUniversityunderclear
skyconditions.ThelocationoftheChibacityisabout30kmsouthofthecentralTokyo,
along the east coast of the Tokyo Bay. We pointed the HS camera toward the sun and
recordedHSimagesoftheaureole.Weputalightshield(steelbar)about2mapartfrom
the camera to block the direct sunlight. Almost at the same time, we measured solar
irradianceusingacalibratedspectroradiometer(EKO,MS‐720)withabaffletubelimiting
theFOVto5degrees(ManagoandKuze,2012).
2.4Analysis
Oncetheinstrumentsarecalibrated,wecancomparetheobservedspectrawith
simulatedones,andbyupdatingtheinputparametersofthesimulation(MODTRAN),we
can obtain optimal set of parameters describing tropospheric aerosols. The aerosol
properties that can be optimized by this method are AOD, extinction coefficient,
absorption coefficient, phase function, etc. Optimizing these parameters directly will
causeanill‐posedproblemsincetherearetoomanyunknownquantities,soweintroduce
three component aerosol model (Manago and Kuze, 2012). Especially for the test
observation,weusesimplifiedmodelswithoneortwocomponents.Inthesesimplified
models, we assume that aerosol shape is spherical, and the size distribution can be
describedbythelognormalmodel.Eachcomponenthasacomplexrefractiveindex(real
4 and imaginary part may be wavelength dependent, but must be controlled by two
parameters)andsizedistributionparameters(moderadiusandwidthofthedistribution).
The total amount of aerosol is controlled by AOD and relative abundance of the two
componentsiscontrolledbyamixingparameter.Wemayfixsomeparametersifwedo
nothaveenoughinformation.
3.Resultsanddiscussion
3.1Wavelengthcalibration
Thewavelengthcalibrationcoefficientsweremeasuredusingdischargelampsof
mercury,cadmium,krypton,argon,etc.andaNd:YAGlaser.TheresultisshowninFigure
1.Weused14emissionlinesinthewavelengthrangebetween400and1064nm.The
errorofthe5thorderpolynomialapproximationtoconvertwavelengthpixelnumberto
wavelengthwas0.29nm(RMS,theerrorofthe1storderwas1.87nm).Weestimatedthe
opticalresolutionfromwidthsofseparatedemissionlinestobe5nmatwavelength470
nmand8nmatwavelength1064nm.
Figure1.Resultofwavelengthcalibrationusingvariouslamps.
3.2Radiancecalibration
The radiance calibration coefficients were measured by the following three
methods;i)Weusedhalogenlampsorskylightasalightsource,andcomparedoutput
fromtheHScameraandaspectroradiometer(EKO,MS‐720)calibratedbytheLangley
method. ii) We used halogen lamps and an integrating sphere as a light source, and
comparedoutputfromtheHScameraaswellasanotherHScamera(EBAJapan,NH‐7)
calibrated with the JAXA integrating sphere system (Yamamoto et al., 2002). iii) We
calibratedtheHScamerawiththeJAXAintegratingspheresystem(withhalogenlamps
asthelightsource).Theresultsexhibitgoodagreementsinthewavelengthrangebetween
450 and 700 nm. In the shorter wavelength, however, the results with halogen lamps
seemstooverestimatethesensitivityoftheHScamera,whileinthelongerwavelength
theskylightresultstendtooverestimatethesensitivity.Itturnsoutthattheinfluenceof
stray light increases for wavelengths  < 450 nm and  >700 nm, and the influence of
secondarylightappearsforwavelength>700nm.Sincehalogenlampsandskylightare
dimmerintheshorterandlongerwavelengths,respectively,largererrorsareexpected
for these wavelength ranges. A composite sensitivity curve made from the results of
halogenlampsinthelongerrangeandthatofskylightintheshorterrangeisshownin
Figure2.Theinfluenceofsecondarylightwillberemovedbyusingalongpassfilter.
Figure2.SensitivityoftheNH‐2hyperspectralcamera.
3.3Uniformitycheck
The wavelength calibration and sensitivity analysis were done using 10 × 10
pixelsaroundthecenteroftheFOV.Furthermore,weinvestigatedtheuniformityofthe
entire pixels. We measured the spectrum of a fluorescent lamp using NH‐2 with a
transmissivediffuserin frontofthelenssothatthewholesurface ofthe detectorwas
homogenouslyilluminated.Wesearchedtheapparentpeakwavelengthsaround620nm.
For each pixel, the spline interpolation was employed to derive the peak wavelength.
Judgingfromahistogramoftheapparentpeakwavelengthsforthewholeimage,theRMS
of the distribution is 0.41 nm, which is much smaller than the 1.6 nm width of each
wavelengthbin.
Next,toinvestigatetheuniformityoftheradiantvaluesmeasuredbyNH‐2,we
observedthetwilightflatbeforesunset.Sincewecannotignorethenon‐uniformityofthe
twilight flat in the FOV of NH‐2 (16º×10º), we rotated the camera horizontally, and
averaged4imagescorrespondingtotherotationanglesof0º,180º,90º,and270º.When
takingtheimageattherotationangleof0º,thedirectionoftherotationaxiswaschosen
soastomaketheimageasuniformaspossible.Sincethebuilt‐inscannerofthecamera
movesintheydirection,verticalstripes(fixedpatternnoise:FPN)canbeseenintheflat
imageduetothedifferentgainofindividualelementofthelinesensor.Toremovethe
noise,theflatimagewasdividedbytheFPN.Theremainingnon‐uniformityofthisimage
is presumably ascribable to the optical system itself and/or the non‐uniformity of the
twilightflat.TheRMSoftheradiantvaluedistributionis1.4%,anditis1.2%iftheFPNis
removed.
3.4Darknoise
Whentheobservationtargetisnotbrightenough,thedarknoiseofthecamera
becomesrelativelyimportant.Weobtainedadarkimagebyaveragingimagestakenwith
thetypicalsettingsforskylightmeasurements.ThemeanandRMSofthedarkimagewere
estimatedtobe70±15count.ThedarkimageiscontaminatedbytheFPNarisingfrom
theoffsetvaluesofthesensorelements,andaftersubtractingtheFPN,theresultingvalue
was0±5count.Notethatalthoughthecolordepthofthesensoris10bits,themaximum
signalofthecamerais4095counts(i.e.theunitcountis4).
3.5Viewingangle
TheviewinganglewasestimatedfromaHSimageofa1cm‐griddedcross‐section
paperonawalllocated1.2mapartfromthecameralens.Bycomparingtheimagewith
optical simulation results, the viewing angles in x and y directions are estimated to be
0.022 deg/pixel and 0.020 deg/pixel, respectively. The viewing angle in x direction is
determinedbythepixelsizeoftheCMOSsensor,whiletheviewingangleinydirectionis
determinedbythemovingdistanceofthescanner’ssteppingmotor.Thedistortionatthe
6 outersideoftheimagewasnegligiblysmallcomparedwiththemeasurementerror.From
a HS image of distant streetlights taken at night‐time, the spatial resolution of the HS
camerawasestimatedtobe0.07deg.
3.6Temperaturedependence
TemperaturedependenceoftheHScamerawasmeasuredusingatemperature‐
controlledchamber(Espec,MC‐710T).Wechangedthetemperatureinsidethechamber
between 0 and 40ºC by 10 K step. We waited at least 150 min after changing the
temperaturetoobtainHSimages.ThetemperatureoftheHScamerawasmeasuredbya
hygrothermal sensor (Sensirion, SHT21) installed inside the camera, and it was
approximately2Khigherthanchambertemperaturewhenitreachedequilibrium.The
lightsourcewasplacedoutsidethechamberwherethetemperaturewascontrolledtobe
22±1ºCbyanairconditioner,andthelightenteredinsidethechamberthroughaglass
window.Weusedamercurydischargelamptomeasurethetemperaturedependenceof
apparentwavelength.Withareferencetemperatureof22ºC,thedifferenceofapparent
wavelengths is less than 1 nm below 32ºC. However, the higher the temperature, the
larger the difference, which becomes as large as 2 nm at 42ºC. The fitting error of the
polynomialmodelis0.1nm(RMS).
Formeasuringthetemperaturedependenceofsensoroutput,weusedahalogen
lamp. The dark signal increases monotonically as temperature rises. The temperature
correctionfactorofdark‐subtractedsignalissmall(lessthan5%)between500and900
nm.Outsidethiswavelengthregion,however,thefactorcanbeaslargeas30%.Thefitting
errorofthe2‐dimensionalB‐splinemodelis2%(RMS,0.7%at<40ºC).
From measurements with polarized filters, we confirmed that polarization
dependenceoftheHScamera(NH‐2)isnegligiblysmall(lessthen±1∼2%).
3.7Aerosolcharacterization
We conducted test observations using NH‐2 under clear sky conditions at the
CEReSsiteseveraltimessinceApril,2013.Throughtheanalysis,ithasbeenfoundthat
theuseofaonecomponentaerosolmodelbasedonasetofcomplexrefractiveindexand
sizedistributionparameterswasgenerallyinsufficientforreproducingtheobserveddata
(radiancedistribution).Thisisduetothesteepincreaseoftheaureoleintensitynearthe
sun:intheregionwithseparationanglessmallerthan3deg.Recently,ithasbeenfound
that the separation angle dependence can be reproduced by introducing the two
component aerosol model with different particle sizes. An example of observation and
analysis results is shown in Fig. 3. In Fig. 3(a), the contour plot depicts the aureole
intensityat550nm.Thesunwaslocatedattheupperrightpositionindicatedbytheblack
star.Thus,thisimagerepresentsthelowerleftquadrantregionaroundthesun.There
wasasteelbaratthesolarpositiontoblockthedirectsolarradiation,butitwaserased
byimageprocessingandshadedwithcrosssigns.
All pixel values except the shaded region were plotted against the separation
angle in Fig. 3(b). It can be seen that pixel values at the same separation angle are
distributedinaverynarrowregion.Inthisfigure,thesimulationresultsusingthetwo
componentaerosolmodelareshownwithadashedline.Thesimulationresultsreproduce
theobserveddataevenatthesmallestseparationangle,assmallas1deg.
(a)
(b)
Figure3.(a)2‐dimensionalaureoleintensitydistributionaroundthesunmeasuredwiththeNH‐2HScamera.
(b)Separationangledependenceoftheaureoleintensity.
Theparametersofthetwocomponentaerosolmodelandtheiroptimizedvalues
arelistedinTable2.Thevaluesinsidebracketswerefixedduringthefittingprocedure.
In addition, we optimized AOD and water scale factor (WSF) using the direct sunlight
spectrum observed with MS‐720. Then, the imaginary part of the refractive index was
optimizedusingtheskylightspectrum.Finally,themoderadiusofthecomponent1and
the mixing ratio (weighted by extinction coefficient) were simultaneously optimized
usingtheaureoleintensitydistribution.Wefedbacktheresultstore‐optimizethevalues
ofAODetc.andthewholeprocedurewasrepeatedseveraltimes.Themoderadiusofthe
component2waschosenfromthefollowingsetofvalues:0.01,0.05,0.1,or0.5m:after
optimizingotherparameters,thevaluewiththesmallestresidualwaschosen.
Table2.Parametersofthe2componentaerosolmodel
Parameter
Value
Aerosolopticaldepth
0.17
Realpartofcomplexrefractiveindex
(1.53)
Imaginarypartofcomplexrefractive
index
8.8×10‐5
Moderadius
2.61mand0.5m
Sizedistributionwidth
(0.26)
Mixingratio*
1:5.32
Waterscalefactor**
0.25
*Mixingratioweightedbyextinctioncoefficientat550nm
**Scalefactortothedefaultwatercolumnamount(2.92g/cm2).
4.Conclusion
WehavedescribedtheresultsofourrecentmeasurementsconductedwithNH‐2
hyperspectralcameradevelopedforvariousremotesensingpurposes.Sinceonlyaslight
changeintheskyspectracanleadtoconsiderabledifferenceintheaerosolpropertyin
the atmosphere,careful calibrationisneededbeforeapplyingthecamera totheactual
solar radiance measurements. Thus, we have conducted calibration measurements in
termsofthewavelengthreadout,radiancestability,uniformity,darknoise,viewingangle,
andtemperaturedependenceoftheoutputofNH‐2.Apreliminaryanalysisoftheaureole
andskyradiancedatahasindicatedthatbyusingatwo‐componentaerosolmodel,theill‐
posednatureoftheaerosolretrievalcansuccessfullybecircumventedandtheobserved
imagery was well fitted to the simulation result based on detailed radiative transfer
calculation.Inthefuture,wewillapplythemethodologyforaerosolmeasurementsunder
8 various conditions, with detailed comparison with collocated measurements with a
sunphotometerandaskyradiometer.
Acknowledgements
ThisworkwasfinanciallysupportedbyJSPSKAKENHIGrantNumber13401088.
References
Holben, B. N., et al. (1998), AERONET – A Federated Instrument Network and Data Archive for
AerosolCharacterization,RemoteSensingofEnvironment,Vol.66,No.1,pp.1–16,Elsevier
Publishing.
ManagoN.,andH.Kuze(2012).Determinationoftroposphericaerosolcharacteristicsbyspectral
measurements of solar radiation using a compact, stand‐alone spectroradiometer, Appl.
Opt.,Vol.49,No.8,pp.1446‐1458,TheOpticalSocietyofAmerica.
Nakajima,T.,etal.(1996),Useofskybrightnessmeasurementsfromgroundforremotesensingof
particulatepolydispersions,Appl.Opt.,Vol.35,No.15,pp.2672‐2686,TheOpticalSocietyof
America.
Takara,Y.,etal.(2012),RemotesensingapplicationswithNHhyperspectralportablevideocamera.
In Proceedings of SPIE 8527, Multispectral, Hyperspectral, and Ultraspectral Remote
SensingTechnology,TechniquesandApplicationsIV.
Yamamoto, Y., et al. (2002), Development of a calibration standard of the spectral radiance for
opticalsensors,In:Proc.ofthe41stSICEAnnualConferenceVol.3,pp.1885‐1890.

Download Report