Chapter 5Chapter 5
Multispectral, thermal and Multispectral, thermal and hyperspectral scanninghyperspectral scanning
Introduction to Remote SensingInstructor: Dr. Cheng-Chien Liu
Department of Earth Sciences
National Cheng-Kung University
Last updated: 7 May 2003
5.15.1 Introduction Introduction
MSS (multispectral scanning) vs. MCS MSS (multispectral scanning) vs. MCS (Multiband camera system)(Multiband camera system)• Fig 2.42, 2.43 (MCS)
• AdvantagesSpectral bands: 0.3~1.4 m with narrow band widthCollection: same optical system for all bands.Calibration: electronically rather than photochemically.Storage and transmission
5.2 Across-track multispectral 5.2 Across-track multispectral scanningscanning
Across-track (whiskbroom) scanner:Across-track (whiskbroom) scanner:• Fig 5.1: operation of a five-channels sensor flight line• Using a rotating or oscillating mirror (Fig 5.1b)• Contiguous strips 2D image• Dichroic grating two forms of energy
ThermalNonthermal prism UV, Vis and near-IR
• Detectors spectral sensitivity• Signal amplified recorded A-to-D View-in-
flight storage interpretation
5.2 Across-track multispectral 5.2 Across-track multispectral scanning (cont.)scanning (cont.)
An example of multispectral sensorAn example of multispectral sensor IFOV (instantaneous field of view)IFOV (instantaneous field of view)
• the cone angle with which incident energy is focused on the detector (see in Fig 5.1a)
• See “pure” and “mixed” pixels simultaneously.
ResolutionResolution• Spatial resolution: D=H΄ (Fig 5.2)• Ground resolution element (resolution cell)
Towards edge resolution cell (image distortion).For typical airborne MSS system: = 0.5 ~ 5 (mrad)
5.2 Across-track multispectral 5.2 Across-track multispectral scanning (cont.)scanning (cont.)
Trade-off between spatial resolution Trade-off between spatial resolution and radiometric resolution.and radiometric resolution.• IFOV
signal-to-noise ratio radiometric resolution spatial resolution
Fig 5.3: eleven-band digital across-Fig 5.3: eleven-band digital across-track MSS system.track MSS system.• 7 of them Landsat Thematic Mapper.
5.2 Across-track multispectral 5.2 Across-track multispectral scanning (cont.)scanning (cont.)
Fig 5.4: eleven-band MSS imagesFig 5.4: eleven-band MSS images• (A) street (B) grass:
clear contrast in all bandsTonal reversal: from band 8~10 (near-IR)
• (C) water (B) grass: difficult to differentiate in the Vis-band, but clean contrast
in near-IR bands.
• (D) cloud shadow:channel 1:somewhat illuminated by Rayleigh scatter near-IR low Rayleigh scatter darkest thermal no signal (moving clouds)
5.2 Across-track multispectral 5.2 Across-track multispectral scanning (cont.)scanning (cont.)
Fig 5.5: eight-band MSS imageFig 5.5: eight-band MSS image• Pavement grass:
clear in Vis-band(1~3)tones reverse in near-IR(4, 5) and mid-IR (6, 7)
• River plume: clear in thermal band (8)
• Dock: clear in band (6~8)
5.3 Along-track multispectral 5.3 Along-track multispectral scanningscanning
Along-track (pushbroom) scannerAlong-track (pushbroom) scanner• Fig 5.6
• A linear array of CCDs (charge-coupled device)
No scanning mirrorSize of detectors ground resolution
The smaller the better
Each band one array
5.3 Along-track multispectral 5.3 Along-track multispectral scanning (cont.)scanning (cont.)
Along-track (pushbroom) scanner (cont.)Along-track (pushbroom) scanner (cont.)• Pros:
Longer dwell time (residence time) Stronger and greater range of signal Better spatial and radiometric resolution
Fixed detector geometric integrity Size & weight & power No moving part reliability & life expectancy
• Cons:CalibrationLimited range of spectral sensitivity (<near –IR)
Underdeveloping
5.3 Along-track multispectral 5.3 Along-track multispectral scanning (cont.)scanning (cont.)
Fig 5.7 MEIS IIFig 5.7 MEIS II• the first airborne pushbroom scanner
• 1728-element linear arrays
• 8 spectral bands (0.39 m~1.1 m)
• IFOV 0.7 m rad
TFOV 400
• 8-bit (256 DN)
5.3 Along-track multispectral 5.3 Along-track multispectral scanning (cont.)scanning (cont.)
Fig 5.8: MEIS II in stereomode.Fig 5.8: MEIS II in stereomode.• External mirror forward-looking & aft-
looking
MOMS ( the 1MOMS ( the 1stst space borne space borne pushbroom scanner)pushbroom scanner)
5.4 Across-track thermal scanning5.4 Across-track thermal scanning
Thermal portion of the spectrumThermal portion of the spectrum• Atmospheric window two ranges (3~5m,
8~14 m)
Rapid response (<1-Rapid response (<1-sec)sec)• Photon electrical charge• Dewar cool detector
3 photon detectors in common use 3 photon detectors in common use todaytoday• Table 5.1: spectral sensitivity range
5.4 Across-track thermal scanning 5.4 Across-track thermal scanning (cont.)(cont.)
Fig 5.9Fig 5.9• Across-track thermal scanner schematic• Recording procedure:
1. Incoming energy2. Additional optics3. Focusing detector4. Detector (encased by a dewar) signal5. Amplify6. Display &record, amplified signal modulate tube7. Scan8. Record
• Platen• Film advanced rate = fn(V/H΄)• Fig 5.10: a typical thermal scanner system
5.5 Thermal radiation principles5.5 Thermal radiation principles
Radiant versus kinetic temperatureRadiant versus kinetic temperature• Kinetic temperature: contact internal
manifestation average translational energy of the molecules
• Radiant temperature: emitted energy external manifestation object’s energy state
Blackbody radiationBlackbody radiation• Fig 5.11: Spectral distribution of energy radiated
from blackbodies of various temperatures• Wien’s displacement law• Stefan-Boltzmann law
5.5 Thermal radiation principles 5.5 Thermal radiation principles (cont.)(cont.)
Radiation from real materialsRadiation from real materials• No perfect blackbody• Emissivity: (T) Mreal(T) / Mblack body(T)
0 < < 1fn(, viewing, T)
• Graybody fn(• Selective radiator = fn(
Fig 5.12 Fig 5.13: (6~14m)
Water ~ blackbody ( Quartz ~ selective radiator
5.5 Thermal radiation principles 5.5 Thermal radiation principles (cont.)(cont.)
Radiation from real materials (cont.)Radiation from real materials (cont.)• Importance of M( = 8~14 m) thermal sensing
Atmospheric windowM(T=300K) = 9.7 mFor broadband sensor treated as graybodyTable 5.2: typical values of emissivity over 8~14 m
Atmospheric effectsAtmospheric effects• Atmospheric windows: Fig 5.14
Thermal range : (3~5 m, 8~14 m)Atmospheric absorption & scattering colder objects.
Atmospheric emission warmer objectBiased sensor outputCompensation later this chapter
5.5 Thermal radiation principles 5.5 Thermal radiation principles (cont.)(cont.)
Interaction of thermal radiation with terrain Interaction of thermal radiation with terrain elements.elements.• EI=EA+ER+ET conservation of energy.
1 = ++ normalize1 = ++ Kirchhoff radiation law (good absorbersgood emitters)1= + assumption of opaque to thermal radiation.
• For real body:M= T4
Trad=Tkin
Table 5.3: typical valuesAlways underestimate T if neglect effect
• Surface T (<50m) internal bulk T
5.6 Interpreting thermal scanner 5.6 Interpreting thermal scanner imageryimagery
Successful interpretationsSuccessful interpretations• Rock type, structure• Locating geologic faults• Mapping soil type & moisture• Locating irrigation canal leaks.• Volcanoes.• Evapo-transpiration from vegetation.• Locating cold water springs.• Locating hot water springs & geysers.• Thermal plumes in lakes and rivers.• Natural circulation patterns in water bodies.• Forest fires.• Locating subsurface fires in landfills or coal refuse piles
5.6 Interpreting thermal scanner 5.6 Interpreting thermal scanner imagery (cont.)imagery (cont.)
Most application Most application qualitativequalitative
Some application Some application quantitative quantitative Considerations of the time for acquiring thermal Considerations of the time for acquiring thermal
datadata• Fig 5.15: generalized diurnal radiant T variations.
Water range of T is small
Water Tmax(water) Tmax(rock)+1~2Crossovers
• Thermal conductivity• Thermal capacity• Thermal inertia ( conductivity)
• Predawn imagery preferred but difficult
5.6 Interpreting thermal scanner 5.6 Interpreting thermal scanner imagery (cont.)imagery (cont.)
Fig 5.16: day time and night time imageryFig 5.16: day time and night time imagery• Water
• Land
• Trees
• Paved area
Fig 5.17: day time thermal imageryFig 5.17: day time thermal imagery• Beach ridge(B)
• Lakebed soil(A)
• Trees( C )
• Bare soil (D)
• Mowed grass (E)
5.6 Interpreting thermal scanner 5.6 Interpreting thermal scanner imagery (cont.)imagery (cont.)
Fig 5.18: night time thermal imageryFig 5.18: night time thermal imagery• Cows• Deers• Metal roof
Fig 5.19: high resolution daytime thermal Fig 5.19: high resolution daytime thermal imageimage• Helicopter shadows
Fig 5.20: Daytime thermal imageryFig 5.20: Daytime thermal imagery• Hot water• Circulations
5.6 Interpreting thermal scanner 5.6 Interpreting thermal scanner imagery (cont.)imagery (cont.)
Fig 5.21 nighttime thermal image depicting Fig 5.21 nighttime thermal image depicting building heat loss.building heat loss.
Fig 5.22 Thermovision camera and display Fig 5.22 Thermovision camera and display unitunit
Fig 5.23 Thermal images showing Fig 5.23 Thermal images showing streamline heat loss.streamline heat loss.
NASA’s Thermal infrared Multispectral NASA’s Thermal infrared Multispectral Scanner (TIMS).Scanner (TIMS).• Plate 10(a). TIMS image• Plate 10(b). A generalized lithologic map
5.7 Geometric characteristics of 5.7 Geometric characteristics of across-track scanner imageryacross-track scanner imagery
Along-track scanner Along-track scanner no mirror, fixed no mirror, fixed geometric relationshipgeometric relationship
Across-track scanner Across-track scanner systematic and systematic and random geometric variationsrandom geometric variations• Spatial resolution and ground coverage
Table 5.4W= 2H΄tan
5.7 Geometric characteristics of 5.7 Geometric characteristics of across-track scanner imagery (cont.)across-track scanner imagery (cont.)
Tangential scale distortion (TSD)Tangential scale distortion (TSD)• Fig 5.24: Source of tangential scale distortion
d/dt=const doesn't mean dx/dt=const
• Fig 5.25: the effect of tangential distortionConstant longitudinal scale & varying lateral scale
S-shaped sigmoid curvature
• Fig5.26: Comparison of aerial photo & across-track thermal scanner image
• Fig 5.27: tangential scale distortioncompression near the top-bottom edge
5.7 Geometric characteristics of 5.7 Geometric characteristics of across-track scanner imagery (cont.)across-track scanner imagery (cont.)
Tangential scale distortion (cont.)Tangential scale distortion (cont.)• Fig 5.28 correction of TSD
p= ypmax/ymax
Yp= H΄tanp
• Electronically or digitally correct TSD rectilinearized images
5.7 Geometric characteristics of 5.7 Geometric characteristics of across-track scanner imagery (cont.)across-track scanner imagery (cont.)
Resolution cell size (RCS) variationsResolution cell size (RCS) variations• Fig 5.29
// fight direction H΄ H΄ =H΄sec flight direction H΄ H΄sec=H΄ sec=H΄sec2Response time: time that a scanner takes to respond
electronically to a change in ground reflected or emitted energy
Variations of RCS can be 3~4 times along a scan line
• Limitation of RCS to the image analysisObject>pixel(RCS) representative analysis
• Compensation of irradiance fall-off due to RCS
5.7 Geometric characteristics of 5.7 Geometric characteristics of across-track scanner imagery (cont.)across-track scanner imagery (cont.)
1-D relief displacement (RD)1-D relief displacement (RD)• Fig 5.30: RD in a vertical aerial photo vs an
across-track scanner image
• Dynamic continuous process sensitive to the aircraft attitude deviations (Fig 5.34)
• Fig 5.31: across-truck thermal scanner image illustrating 1-D RD.
5.7 Geometric characteristics of 5.7 Geometric characteristics of across-track scanner imagery (cont.)across-track scanner imagery (cont.)
1-D relief displacement (RD)1-D relief displacement (RD)• Fig 5.32: 1-D RD and TSD
• Fig 5.33: Effect of nonsynchronized image recording rate and V/H΄ ratio
• Fig 5.34: distortions induced by aircraft attitude deviations
• Fig 5.35: effect of roll compensation
5.8 Radiometric calibration of 5.8 Radiometric calibration of thermal scannersthermal scanners
Thermal scanner image Thermal scanner image lack of lack of geometric integrity geometric integrity • Take photo simultaneously
• Night time use daytime photo (even old photos will do)
5.8 Radiometric calibration of 5.8 Radiometric calibration of thermal scanners (cont.)thermal scanners (cont.)
Two methods of radiometric calibrationTwo methods of radiometric calibration• Internal blackbody source referencing
Two controlled sources: cold & hotView the sources during every scan lineFig 5.36: configurationA typical mission: height 600m 0.30C but atmospheric condition can
be 20C
• Air-to-ground correlation:Account for atmospheric effectsTheoretical approachEmpirical approach the general approach
Fig 5.37 a sample of calibration curve Fig 5.38 a thermal radiometer used for air-to-ground correlation measurements
5.9 Temperature mapping with 5.9 Temperature mapping with thermal scanner datathermal scanner data
Many applications Many applications MapMap Two proceduresTwo procedures
• Image-basedCrude form: qualitative depiction low geometric and radiometric
integritySuffice for many applicationTonal levels densitometric analysis rectilinerarized imagery.
• Numerically basedN=A+BM=A+BT4
N: DN A, B : to be determined : emissivity T: kinetic temperature
Two unknown (A, B) two equations (data)
5.10 FLIR systems5.10 FLIR systems
Forward-looking infrared (FLIR) Forward-looking infrared (FLIR) system system oblique views of the terrain oblique views of the terrain ahead of an aircraftahead of an aircraft• Fig 5.39
• Point forward sweep across the scene of interest
• Military applications
5.11 Imaging spectrometry5.11 Imaging spectrometry
Hyperspectral Hyperspectral multispectral multispectral• Fig 5.40• Fig 5.41: Selected laboratory spectra of minerals• Hyperspectral data detailed identification of
materials and quantification of their abundance
Airborne Imaging Spectrometer (AIS)Airborne Imaging Spectrometer (AIS)• 128 channel from 1.2~2.4 m with 9.3 nm band width• 1.9 mrad, 4200m high, resolution 8x8m, swath 32 pixel
5.11 Imaging spectrometry (cont.)5.11 Imaging spectrometry (cont.)
Airborne Imaging Spectrometer (cont.)Airborne Imaging Spectrometer (cont.)• Fig 5.42: AIS images
Condominium complexa: schoolb: field
Loss of detail in the atmospheric water absorption band (1.4m) Watered courtyard lawn a (compared to unwatered field b)
Water vapor absorption bands 0.94, 1.14, 1.4, 1.88 m
5.11 Imaging spectrometry (cont.)5.11 Imaging spectrometry (cont.)
Fig 5.43: selected laboratory spectra of Fig 5.43: selected laboratory spectra of green leavesgreen leaves• Main components: chlorophyll and water• Shape + peak+valley species
Fig 5.44: same as Fig 5.43 but single speciesFig 5.44: same as Fig 5.43 but single species• Main components: lignin & holocellulose• Difference green or dry holocellulose
Assessing biomassVegetation stressCarbon cycleDiscriminating plant communitiesPhenological conditions
5.11 Imaging spectrometry (cont.)5.11 Imaging spectrometry (cont.)
Airborne Visible-Infrared Imaging Airborne Visible-Infrared Imaging Spectrometer (AVIRIS)Spectrometer (AVIRIS)• 224 channels, 0.4~2.45 m with bandwidth 9.6nm• Altitude: 20km, resolution 20m, swath: 10km
• Plate 11: hyperspectral image cubeA common way to display hyperspectral dataColor composite: 0.557(b), 0.815(g), 2.209(r) m
• Fig 5.45Three stages: green leaf initiation development change in plant
pigment proportions flowering domancy leaf loss senescence
• ApplicationsAVIRIS data spectra matching library mineral typeAn export system-based analysis approach
5.11 Imaging spectrometry (cont.)5.11 Imaging spectrometry (cont.)
Compact Airborne Spectrographic Compact Airborne Spectrographic Imager (CASI)Imager (CASI)• Commercial, programmable
• 288 channels from 0.4~0.9m with bandwidth 1.8 nm
• IFOV= 1.2 mrad
5.11 Imaging spectrometry (cont.)5.11 Imaging spectrometry (cont.)
Geophysical and Environmental Research Geophysical and Environmental Research Imaging Airborne Spectrometer (GERAIS)Imaging Airborne Spectrometer (GERAIS)• 63 channels, 0.4~2.48 m• Fig 5.46: GERAIS Image for identifying minerals
Label A in channel 41 dark spot aluniteAlunite dark from 41~44 absorption light from 49~52 reflection
Red edgeRed edge• The slope of a reflectance spectrum from 0.68~0.76
m• Shift change in the chemical and morphological
status heavy metals in the soil
5.11 Imaging spectrometry (cont.)5.11 Imaging spectrometry (cont.)
DIAS-7915DIAS-7915 ASDIS-204ASDIS-204
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