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2024_RemoteSensing2-EMR (1).pptx
2024_RemoteSensing2-EMR (1).pptx
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slide-01
Introduction to Remote Sensing Electromagnetic radiation principles Electromagnetic radiation models Energy interactions in the atmosphere Energy interactions with Earth surface features Kin Ma, Wanxiao Sun: GVSU 1 Geography
slide-02
Introduction to Remote Sensing Energy recorded by remote sensors A: the energy source or A illumination (Electromagnetic radiation) D B: the Earth’s atmosphere B B C: the Earth’s surface D: the sensor C Kin Ma, Wanxiao Sun: GVSU 2 Geography
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Introduction to Remote Sensing Electromagnetic energy/radiation models Wave model Particle model Kin Ma, Wanxiao Sun: GVSU 3 Geography
slide-04
Wave model Electromagnetic radiation as an electromagnetic wave that travels through space at the speed of light. The electromagnetic wave consists of an electrical field (E) and a magnetic field (M). These two fields are orthogonal to one another Both fields are perpendicular to the direction of travel Kin Ma, Wanxiao Sun: GVSU 4 Geography
slide-05
Wave model (continued) Electromagnetic waves obey the basic equation: λ= c / v where • λ = wavelength: the distance from one wave peak to the next (µm) • c = speed of light (3 * 108 m/sec) • υ = frequency of waves: the number of wavelengths that pass a point per unit time (Hz) Kin Ma, Wanxiao Sun: GVSU 5 Geography
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Fig. 4.4--Electromagnetic Spectrum Gpy100, Physical Source: Hess, D. and McKnight, T. (2014)/ Hess_Chap4.ppt Geography, Chap.4 6
slide-07
Introduction to Remote Sensing Electromagnetic spectrum The Electromagnetic Spectrum is a continuous spectrum of all electromagnetic waves arranged according to frequency and wavelength. Kin Ma, Wanxiao Sun: GVSU 7 Geography
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Introduction to Remote Sensing Electromagnetic spectrum categories Light is a particular type of electromagnetic radiation that can be seen and sensed by the human eye (0.4 – 0.7 µm). Kin Ma, Wanxiao Sun: GVSU 8 Geography
slide-09
Particle theory (radiation) Suggests that EM radiation is composed of many discrete units called Quanta/Photons. The Energy of a quantum: where Q = hυ Q = Energy of quantum in Joules h = Planck’s Constant (6.626 * 10-34 J/sec) υ = frequency of waves But υ = c / λ (from c = υ λ) Therefore Q= hc λ Therefore, longer wavelength lower energy content Sensors operating at longer wavelengths must view large areas of the Earth to obtain detectable energy signal. Kin Ma, Wanxiao Sun: GVSU 9 Geography
slide-10
Stefan-Boltzmann Law (radiation) All objects at temperatures above absolute zero (-2730C or 0 Kelvin (K)) emit EM radiation/energy. (e.g. the Sun, terrestrial objects) How much energy an object radiates at certain wavelength is given by Stefan-Boltzmann Law: M λ = σT4 where M λ = total emitted radiation exiting from the object (in Watts per square meter) σ = 5.6697 * 10-8 W M-2 K –4 T = absolute temperature in degrees Kelvin (K) This law is expressed for an energy source that behaves as a blackbody. Blackbody: an ideal, hypothetical radiator that totally absorbs and subsequently re-emits (radiates) all energy incident upon it. Kin Ma, Wanxiao Sun: GVSU 10 Geography
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Wien’s Displacement Law Specifies the relationship between the peak wavelength (dominant wavelength) of emittance and the temperature of an object. λ max = 2897.8/T λ max : wavelength of the maximum emittance, (µm) T: temperature, K Sun: 0.483 µm Earth: 9.66 µm As the temperature of a blackbody gets higher, the wavelength at which the blackbody emits its maximum Blackbody radiation energy becomes shorter. Kin Ma, Wanxiao Sun: GVSU 11 Geography
slide-12
Energy interactions in the atmosphere Irrespective of its source, all radiation detected by remote sensors pass through some distance of atmosphere, or path length, of the atmosphere. Atmosphere causes: • Scattering • Absorption • Transmission Kin Ma, Wanxiao Sun: GVSU 12 Geography
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Scattering Unpredictable diffusion of radiation by particles or large gas molecules in the atmosphere. • Rayleigh Scattering Wavelength >> Particles Affects shorter wavelengths The sky appears blue Video Explanation https://www.youtube.com/watch?v=4HBuHX4-VU8 Short Summary section: 7:22-9:22 • Mie Scattering Wavelength = Particles Influences longer wavelengths • Non-selective Scattering Wavelength << Particles Affects all wavelengths Clouds appear white (B,R,G equally scattered) 13 Kin Ma, Wanxiao Sun: GVSU Geography
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Absorption Molecules in the atmosphere absorb radiant energy at various wavelengths with different intensity. Ozone: absorbs the harmful ultraviolet radiation Carbon dioxide: far infrared region Water vapour: longwave infrared and shortwave microwave radiation Kin Ma, Wanxiao Sun: GVSU 14 Geography
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Atmospheric windows Portions of the spectrum in which atmosphere transmits EM radiation particularly well. • visible, • near-infrared, • middle-infrared, • thermal-infrared, and • microwave Kin Ma, Wanxiao Sun: GVSU 15 Geography
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Energy Interactions with Earth’s features How can plants grow in the SHADE? Energy incident on a body is reflected, absorbed, or transmitted absorption: radiation is absorbed into the target transmission: radiation passes through a target reflection: radiation “bounces” off the target and is redirected Proportions of energy reflected, absorbed or transmitted vary for : • different features • different wavelengths Kin Ma, Wanxiao Sun: GVSU 16 Geography
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Active and passive remote sensing Kin Ma, Wanxiao Sun: GVSU 17 Geography
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Reflected energy Remote sensing systems depend on reflected energy • spectral reflectance or • reflectance or • spectral signature Where =the total amount radiant flux at specific wavelength incident to the Earth’s surface = the reflected energy = the transmitted energy = the absorbed energy Kin Ma, Wanxiao Sun: GVSU 18 Geography
slide-19
Types of reflections Specular (mirror-like): angle of incidence = angle of reflection Example? Lambertian (diffuse): reflects energy uniformly in all directions What is an example in the natural world? Regular case: most bodies behavior between the ideal specular and diffuse reflector Kin Ma, Wanxiao Sun: GVSU 19 Geography