Remote Sensing Energy Interactions with Earth Systems

Interactions with the Atmosphere ► Scattering, refraction, absorption

Interactions with the Atmosphere ► Scattering ► Refraction ► Absorption

Scattering ► The redirection of EM energy by particles suspended in the atmosphere or large molecules of atmospheric gases ► Rayleigh scattering ► Mie scattering ► Nonselective scattering

Rayleigh Scattering ► It occurs when atmospheric particles' diameters are much smaller than the wavelength of the radiation d<< ► It occurs when atmospheric particles' diameters are much smaller than the wavelength of the radiation d<< ► It is common high in the atmosphere ► Radiation with shorter wavelength is easier to be scattered ► Black vs. blue vs. red skies

Mie Scattering ► Particles' diameters are equivalent to the wavelength d ≈ ► Particles' diameters are equivalent to the wavelength d ≈ ► It is common in lower atmosphere ► It is wavelength dependent

Nonselective Scattering ► Particles are much larger than the wavelength d>> d>> ► All wavelength are scattered equally Effects of scattering ► It causes haze in remotely sensed images ► It decreases the spatial detail on the images ► It also decreases the contrast of the images

Refraction ► The bending of light rays at the contact between two media that transmit light but with different density; when light enters the denser medium, it is defracted toward surface normal

Absorption ► The atmosphere prevents, or strongly attenuates, transmission of radiation through the atmosphere ► Three gases: - Ozone (O3): absorbs ultraviolet radiation high in atmosphere - Carbon-dioxide (CO 2 ): absorbs mid and far atmosphere - Carbon-dioxide (CO 2 ): absorbs mid and far infrared ( microm) in lower atmosphere - Water vapor (H 2 O): absorbs mid-far infrared infrared ( microm) in lower atmosphere - Water vapor (H 2 O): absorbs mid-far infrared ( , >27microm) in lower atmosphere ( , >27microm) in lower atmosphere

Atmospheric Windows ► Those wavelengths that are relatively easily transmitted through the atmosphere

Atmospheric Windows

► The windows: UV & visible:  m Near infrared:  m Mid infrared:  m,  m Far infrared:  m,  m, ► The windows: UV & visible:  m Near infrared:  m Mid infrared:  m,  m Far infrared:  m,  m,  m Microwave: mm, 20.0+mm  m Microwave: mm, 20.0+mm ► The atmospheric windows are important for RS sensor design

Interaction with Features Reflection, absorption, and transmission

Interactions with Surface ► All EM energy reaches earth's surface must be reflected, absorbed, or transmitted ► Each is represented by a rate (%) ► Their rate depends on: type of features, wavelength, angle of illumination ReflectionAbsorptionTransmission

Reflection ► Light ray is redirected as it strikes a nontransparent surface ► Spectral reflectance   =  R  I  = (E of wavelength reflected from the object)/ (E of wavelength incident upon the object) (E of wavelength incident upon the object)

Reflection ► Specular reflection When surface is smooth relative to the wavelength, incident radiation is reflected in a single direction When surface is smooth relative to the wavelength, incident radiation is reflected in a single direction ► incidence angle = reflection angle ► Diffuse (isotropic) Reflection ► When surface is rough relative to the wavelength, energy is scattered equally in all directions ► Lambertian surface

Transmission ► Radiation passes through a substance without significant attenuation ► Transmittance (t): transmitted radiation t = incident radiation

Absorption absorbed radiation t = incident radiation absorbed radiation t = incident radiation

Interactions All features at the earth’s surface interact with EM energy all three ways but with different proportions Reflection + Transmission + Absorption = 100%

Emission

Spectral Characteristics of Features

Spectral Reflectance Curve

Vegetation ► Chlorophyll absorbs blue and red, reflects green ► Vegetation has a high reflection and transmission at NIR wavelength range ► Reflection or absorption at MIR range, the water absorption bands From

Vegetation ► The palisade cells absorb blue and red light and reflect green light at a peak of 0.54mm ► The spongy mesophyll cells reflect near infrared light that is related to vegetation biomass because the intercellular air space of spongy mesophyll layer is where photosynthesis and respiration occur ► Vegetation moisture content absorbs mid infrared energy ► Jensen, J. R. "Biophysical Remote Sensing." Annals, 73:(1),

Biophysical Sensitivity of Spectrums.. Upper epidermis Palisade Spongy mesophyll Lower epidermis

Soils ► Soil moisture decreases reflectance ► Coarse soil (dry) has relatively high reflectance ► Surface roughness, organic matter, iron oxide affect reflectance

Water ► Transmission at visible bands and a strong absorption at NIR bands ► Water surface, suspended material, and bottom of water body can affect the spectral response

Readings ► Chapter 1

Absorption From