GEOG/GEOL 4093 Remote Sensing of the Environment Lecture 4 EMR Interaction With Mater Outline of today’s lecture • Review • Atmospheric Effects -Scattering • Atmospheric Effects -Absorption • AttenuationReview (Basic Laws) Planck’s law (Spectral Radiance) Stefan-Bolzmann law (TIR) • The total emitted energy over the whole spectrum is proportional the physical temperature M = esT4 M = sT4 Blackbody GraybodyBasic Laws Blackbody - Object that absorbs and emits 100 % of radiation - Does not exist in nature - Emissivity would equal one Graybody - Object that reflects part of the incident radiation - Emissivity is smaller than one Emissivity • Describes the actual absorption and emission properties of real objects (“gray bodies”) • Is wavelength dependent • Is equal to (graybody emittance)/(blackbody emittance) • Establishes an object’s radiant temperature (Trad ) or brightness temperature Trad = ε1/4Tkin ε = ( Trad / Tkin)4Emissivity Basic Laws Two objects can have the same kinematic temperature, but different temperatures radian• Sun’s temperature = 6000 K the wavelength of peak emittance = 2898 mm K/6000 K = 0.48 mm • Earth’s temperature = 300 K the wavelength of peak emittance = 2898 mm K/300 K = 9.6 mm Wien’s displacement low : lmax = k/T Basic Laws k = 2898 mm K Source:Chuvieco and Huete 2010Sun’s Radiant Energy Distribution For terrestrial remote sensing the most important source is the sun • EM from ultraviolet – visible – infrared • (max) = 0.47 µm The surface temperature of the earth is 300 K • (max) shifted to longer wavelengths (9.7 µm) In remote sensing • 2.5 µm upper limit for reflected solar energy • 6 µm lower limit for self-emitted energy from the earthEMR Interaction With Matter Radiative properties of a natural surface • Radiation incident upon a surface must either be transmitted (t) through it, reflected (a) from the surface or be absorbed (z). • For solar radiation, a is referred to as the surface albedo • If we consider only part of the EM spectrum, a is referred to as the spectral albedo • Albedo is the percent of incident solar energy that is reflected from a surface Transmissivity + Reflectivity + Absorptivity = 1Albedo (reflectivity) of various surfaceAttenuation The reduction of Intensity of EMR as it passes through a medium. Sometimes called extinction (Combination of absorption and scattering) EMR Interaction With MatterAtmospheric Scattering Types of scattering encountered in the atmosphere. The type of scattering is a function of 1) wavelength, 2) size of the gas molecule, dust particle, and/or water vapor droplet encounteredAtmospheric ScatteringA Clear Blue Sky Blue radiation (l = 0.46 mm) Red radiation (l = 0.66 mm) (0.66mm/0.46mm)4 = 4.24 Blue light is scattered 4x more than red lightAtmospheric ScatteringAt sunset, solar radiation must traverse a longer path through the atmosphere. Viewing a setting sun, the energy reaching the observer is largely depleted of blue radiation, leaving mostly red wavelengths (Rayleigh). Dust and smoke add additional scattering with a wavelength dependence that increases the red-sky effect (Mie) Red Sky at NightNon SelectiveAtmospheric Effects - ScatteringPhoto by Pitan S, GISTDAPhoto by Pitan S, GISTDAALOS AVNIR-2 - Fukuoka, Kyu-shu, Japan Data Courtesy JAXA/RESTEC - Processed by ESRI Japan Image containing substantial scattering Image after atmospheric correction Source http://www.geosystems.delImage containing substantial scattering Image after atmospheric correction IKONOS - Dresden, Germany Credit: Space Imaging Source http://www.geosystems.delAsymmetric OH Stretch Symmetric OH Stretch HOH Bend Atmospheric Absorption This absorption is the transfer of electromagnetic energy to the molecules with which the EMR comes in contact with.Atmospheric AbsorptionAtmospheric AbsorptionAttenuation CoefficientAtmospheric Windows • Regions in the EM spectrum where energy can be fully transmitted • 0.3-0.7 mm UV and visible light • 3-5 mm emitted thermal energy from Earth • 8-11 mm emitted thermal energy from Earth • 1 mm-1 m radar and microwave
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