Remote SensingRemote Sensing
Energy Interactions with Energy Interactions with
Earth SystemsEarth Systems
Interactions with the Interactions with the AtmosphereAtmosphere
► Scattering, refraction, absorptionScattering, refraction, absorption
Interactions with the Interactions with the AtmosphereAtmosphere
► ScatteringScattering► Refraction Refraction ► Absorption Absorption
ScatteringScattering
► The redirection of EM energy by particles The redirection of EM energy by particles suspended in the atmosphere or large suspended in the atmosphere or large molecules of atmospheric gasesmolecules of atmospheric gases
► Rayleigh scattering Rayleigh scattering ► Mie scatteringMie scattering► Nonselective scatteringNonselective scattering
http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/opt/mch/sct.rxml
Rayleigh ScatteringRayleigh Scattering
► It occurs when atmospheric particles' It occurs when atmospheric particles' diameters are much smaller than the diameters are much smaller than the wavelength of the radiation d<<wavelength of the radiation d<<
► It is common high in the atmosphereIt is common high in the atmosphere
► Radiation with shorter wavelength is easier Radiation with shorter wavelength is easier to be scattered to be scattered
► Black vs. blue vs. red skies Black vs. blue vs. red skies
http://www-phys.llnl.gov/Research/scattering/RTAB.html
Mie ScatteringMie Scattering
► Particles' diameters are equivalent to the Particles' diameters are equivalent to the wavelength d ≈ wavelength d ≈
► It is common in lower atmosphere It is common in lower atmosphere
► It is wavelength dependentIt is wavelength dependent
Nonselective ScatteringNonselective Scattering
► Particles are much larger than the wavelength Particles are much larger than the wavelength d>>d>>
► All wavelength are scattered equallyAll wavelength are scattered equally
Effects of scatteringEffects of scattering► It causes haze in remotely sensed imagesIt causes haze in remotely sensed images► It decreases the spatial detail on the imagesIt decreases the spatial detail on the images► It also decreases the contrast of the imagesIt also decreases the contrast of the images
Refraction Refraction
► The bending of light rays at the contact The bending of light rays at the contact between two media that transmit light but between two media that transmit light but with different density; when light enters the with different density; when light enters the denser medium, it is defracted toward denser medium, it is defracted toward surface normal surface normal
AbsorptionAbsorption
► The atmosphere prevents, or strongly The atmosphere prevents, or strongly attenuates, transmission of radiation through the attenuates, transmission of radiation through the atmosphereatmosphere
► Three gases: Three gases: - Ozone (O3): absorbs ultraviolet radiation high in- Ozone (O3): absorbs ultraviolet radiation high in
atmosphere atmosphere - Carbon-dioxide (CO- Carbon-dioxide (CO22): absorbs mid and far): absorbs mid and far
infrared (13-17.5microm) in lower atmosphere infrared (13-17.5microm) in lower atmosphere - Water vapor (H- Water vapor (H22O): absorbs mid-far infrared O): absorbs mid-far infrared
(5.5-7.0, >27microm) in lower atmosphere (5.5-7.0, >27microm) in lower atmosphere
Atmospheric WindowsAtmospheric Windows
http://www.crisp.nus.edu.sg/~research/tutorial/atmoseff.htm#windows
► Those wavelengths that are relatively Those wavelengths that are relatively easily transmitted through the easily transmitted through the atmosphereatmosphere
Atmospheric WindowsAtmospheric Windows
Atmospheric WindowsAtmospheric Windows
► The windows: The windows: UV & visible: 0.30-0.75 UV & visible: 0.30-0.75m m Near infrared: 0.77-0.91 Near infrared: 0.77-0.91m m Mid infrared: 1.55-1.75 Mid infrared: 1.55-1.75m, 2.05-2.4m, 2.05-2.4m m Far infrared: 3.50-4.10 Far infrared: 3.50-4.10m, 8.00- 9.20m, 8.00- 9.20m, m,
10.2-12.410.2-12.4m m Microwave: 7.50-11.5mm, 20.0+mm Microwave: 7.50-11.5mm, 20.0+mm
► The atmospheric windows are important for The atmospheric windows are important for RS sensor design RS sensor design
Interaction with FeaturesInteraction with Features
Reflection, absorption, and transmission
Interactions with SurfaceInteractions with Surface
► All EM energy reaches earth's surface must All EM energy reaches earth's surface must be reflected, absorbed, or transmitted be reflected, absorbed, or transmitted
► Each is represented by a rate (%)Each is represented by a rate (%)
► Their rate depends on: Their rate depends on: type of features, wavelength, angle of type of features, wavelength, angle of illumination illumination
Reflection Absorption Transmission
ReflectionReflection
► Light ray is redirected as it strikes a Light ray is redirected as it strikes a nontransparent surface nontransparent surface
► Spectral reflectance Spectral reflectance ==RRII = (E of wavelength = (E of wavelength reflected from the object)/ reflected from the object)/
(E of wavelength (E of wavelength incident upon the object) incident upon the object)
ReflectionReflection
► Specular reflectionSpecular reflection When surface is smooth relative to the When surface is smooth relative to the
wavelength, incident radiation is reflected in a wavelength, incident radiation is reflected in a single direction single direction
► incidence angle = reflection angle incidence angle = reflection angle
► Diffuse (isotropic) ReflectionDiffuse (isotropic) Reflection► When surface is rough relative to the When surface is rough relative to the
wavelength, energy is scattered equally in all wavelength, energy is scattered equally in all directions directions
► Lambertian surface Lambertian surface
Transmission Transmission
► Radiation passes through a substance Radiation passes through a substance without significant attenuation without significant attenuation
► Transmittance (t): Transmittance (t): transmitted radiation transmitted radiation t = --------------------------- t = --------------------------- incident radiation incident radiation
AbsorptionAbsorption
absorbed radiation absorbed radiation t = --------------------------- t = --------------------------- incident radiation incident radiation
InteractionsInteractions
All features at the earth’s surface interact with All features at the earth’s surface interact with EM energy all three ways but with different EM energy all three ways but with different proportionsproportions
Reflection + Transmission + Absorption = Reflection + Transmission + Absorption = 100%100%
EmissionEmission
http://www.crisp.nus.edu.sg/~research/tutorial/infrared.htm
Spectral Characteristics of Spectral Characteristics of FeaturesFeatures
http://www.crisp.nus.edu.sg/~research/tutorial/infrared.htm
Spectral Reflectance CurveSpectral Reflectance Curve
VegetationVegetation
► Chlorophyll absorbs blue and red, reflects Chlorophyll absorbs blue and red, reflects green green
► Vegetation has a high reflection and Vegetation has a high reflection and transmission at NIR wavelength rangetransmission at NIR wavelength range
► Reflection or absorption at MIR range, Reflection or absorption at MIR range, the water absorption bands the water absorption bands
From http://rst.gsfc.nasa.gov/Intro/nicktutor_I-From http://rst.gsfc.nasa.gov/Intro/nicktutor_I-3.html3.html
Vegetation Vegetation
► The palisade cells absorb blue and red light and The palisade cells absorb blue and red light and reflect green light at a peak of 0.54mm reflect green light at a peak of 0.54mm
► The spongy mesophyll cells reflect near infrared The spongy mesophyll cells reflect near infrared light that is related to vegetation biomass light that is related to vegetation biomass because because the intercellular air space of spongy mesophyll the intercellular air space of spongy mesophyll layer is where photosynthesis and respiration layer is where photosynthesis and respiration occur occur
► Vegetation moisture content absorbs mid Vegetation moisture content absorbs mid infrared energy infrared energy
► Jensen, J. R. "Biophysical Remote Sensing." Annals, 73:(1),111-132. Jensen, J. R. "Biophysical Remote Sensing." Annals, 73:(1),111-132.
Biophysical Sensitivity of Biophysical Sensitivity of Spectrums ..Spectrums ..
Upper epidermis
Palisade
Spongy mesophyll
Lower epidermishttp://www.cstars.ucdavis.edu/projects/modeling/
SoilsSoils
► Soil moisture decreases reflectanceSoil moisture decreases reflectance► Coarse soil (dry) has relatively high Coarse soil (dry) has relatively high
reflectancereflectance► Surface roughness, organic matter, iron Surface roughness, organic matter, iron
oxide affect reflectanceoxide affect reflectance
WaterWater
► Transmission at visible bands and a strong Transmission at visible bands and a strong absorption at NIR bandsabsorption at NIR bands
► Water surface, suspended material, and Water surface, suspended material, and bottom of water body can affect the spectral bottom of water body can affect the spectral responseresponse
ReadingsReadings
► Chapter 1Chapter 1
AbsorptionAbsorption
From http://rst.gsfc.nasa.gov/Intro/nicktutor_I-From http://rst.gsfc.nasa.gov/Intro/nicktutor_I-3.html3.html
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