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