Detector Configurations Used for Panchromatic, Multispectral and Hyperspectral Remote Sensing
Spectral unmixing of vegetation, soil and dry carbon cover in arid regions: comparing multispectral...
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Transcript of Spectral unmixing of vegetation, soil and dry carbon cover in arid regions: comparing multispectral...
Spectral unmixing of vegetation, soil Spectral unmixing of vegetation, soil and dry carbon cover in arid and dry carbon cover in arid regions: comparing multispectral regions: comparing multispectral and hyperspectral observationsand hyperspectral observations
G.P.Asner and G.P.Asner and K.B.HeidebrechtK.B.Heidebrecht
IntroductionIntroduction
Objective – Objective – comparison of multi- and hyper-spectral comparison of multi- and hyper-spectral observations to observations to
decompose remotely sensed datadecompose remotely sensed data Why Important? – Why Important? – Study of impacts ofStudy of impacts of climate variability and landclimate variability and land use on vegetation coveruse on vegetation cover
Difficulties – Difficulties – small individual canopiessmall individual canopies - phenological changes- phenological changes - separation of NPV and bare soil in NDVI- separation of NPV and bare soil in NDVI
ApproachesApproaches – correlation of NDVI – correlation of NDVI - Spectral Mixture Analysis- Spectral Mixture Analysis
SMASMA
Assumes linear combinationAssumes linear combination Two methods of reflectance Two methods of reflectance
coefficient selectioncoefficient selection
Image-basedImage-based reflectances used that are likely to exist in the areareflectances used that are likely to exist in the area
lack of pure pixelslack of pure pixels
Spectral LibrariesSpectral Libraries data readily collecteddata readily collected
lack of generability and scalabilitylack of generability and scalability
Data used – Image Data used – Image basedbased Landsat TM – Landsat TM – commonly availablecommonly available
Terra ASTER – Terra ASTER – dense 5-channel dense 5-channel sampling atsampling at
SWIR2SWIR2
Terra MODIS – Terra MODIS – available daily available daily
15-channel sampling of 15-channel sampling of
visible and NIR visible and NIR
The land under The land under researchresearch Chihuahuan Desert, New Chihuahuan Desert, New
MexicoMexico
- - 210mm ppt per year210mm ppt per year
- Long-term ecological- Long-term ecological
research siteresearch site
- mainly grassland and- mainly grassland and
shrubshrub RequirementsRequirements - low species diversity- low species diversity
- strong differences of PV- strong differences of PV
and NPV between sitesand NPV between sites
- nearly constant soil type- nearly constant soil type
- few soil crusts- few soil crusts
MeasurementsMeasurements
ADC camera for grasslandADC camera for grassland Ikonos camera for shrublandIkonos camera for shrubland Areas 8ha each, with 300m N-S Areas 8ha each, with 300m N-S transect established using GPStransect established using GPS Field SpectroradiometerField Spectroradiometer
- measurements every 5m along transects- measurements every 5m along transects
- all canopies within 5m of sampling pts - all canopies within 5m of sampling pts measuredmeasured
- conversion to reflectance using calibration - conversion to reflectance using calibration panelpanel
AVIRIS sensor – AVIRIS sensor – NASA ER-2 aircraft altitude 20kmNASA ER-2 aircraft altitude 20km - pixels 19m x 19m- pixels 19m x 19m
Model and AnalysisModel and Analysis
Auto MCUAuto MCU - Fully automated Monte Carlo based- Fully automated Monte Carlo based derivation of uncertainty of cover fractionsderivation of uncertainty of cover fractions
- - Code carried out on field spectra andCode carried out on field spectra and sub-sampled to satellite channelssub-sampled to satellite channels
AlgorithmsAlgorithms – – tiedtied SWIR2 PV, NPV, soil spectra ‘tied’ at 2.03SWIR2 PV, NPV, soil spectra ‘tied’ at 2.03μμmm Less dependent on biomass, architecture, Less dependent on biomass, architecture,
biochemistry biochemistry
- - divisiondivision divided spectral reflectance values by reflectance divided spectral reflectance values by reflectance
at first wavelength at first wavelength mathematically inappropriate for linear SMAmathematically inappropriate for linear SMA
ResultsResults
Landsat TM convolved dataLandsat TM convolved data - little difference - little difference between shrubland and grassland sitesbetween shrubland and grassland sites
MODIS and most of AVIRIS -MODIS and most of AVIRIS - spectrally spectrally indistinguishableindistinguishable
ASTER -ASTER - some differences some differences
AVIRIS AVIRIS – finds negative PV fractions– finds negative PV fractions
- bare soil overestimated by ~20% - bare soil overestimated by ~20% - NPV fractions good- NPV fractions good Tied SWIR2 – showed consistent accuracyTied SWIR2 – showed consistent accuracy - corroborated by previous work- corroborated by previous work
FutureFuture
Important to continue thisImportant to continue this
research for ecologicalresearch for ecological
monitoringmonitoring Further research into theFurther research into the
use of instruments such as use of instruments such as
AVIRIS (i.e. high SNRAVIRIS (i.e. high SNR
in SWIR2) in SWIR2)
for use in SMA methodsfor use in SMA methods