01-Introduction

01-Introduction - 3/31/2008 Remote Sensing: The Major...

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3/31/2008 ESM 266 1 Remote Sensing: The Major Source for Large Scale Environmental Information Jeff Dozier • Emphasis: understand the principles of acquiring and interpreting data from satellite-based remote sensing systems Basic physics Available sensors and products Environmental applications through image analysis Observations from space • Sun-synchronous polar orbits – Global coverage, fixed crossing, repeat sampling – Typical altitude 500-1,500 km •Low-inclination, non-Sun-synchronous orbits – Tropics, mid-latitudes, varying sampling – Typical altitude 200-2,000 km • Geostationary orbits – Regional views of full Earth disk, continuous coverage – Over Equator only, altitude 35,000 km Observations from aircraft and ground • Aircraft – Regional and local, any sampling times – Repeat sampling – In situ atmospheric chemistry, clouds and aerosols, heat and vapor fluxes – Sparse coverage • Ground – Repeat or continuous sampling – Sparse coverage Radiation • A body radiates energy when electrons in its atoms receive or generate so much energy that they release a small packet of energy (photon) • If the atoms are receiving or generating a lot of energy (i.e. they are hot) they emit photons in large numbers and frequently. Thus, both the intensity (energy per unit time) and the frequency of emission are high. • Since energy ( E ) travels through a vacuum at a constant speed ( c, the speed of light), if the frequency ( ν ) of particle (wave) emission is high, the wavelength ( λ ) is short: • Planck’s law: energy per photon λ ν c = h h = = h is Planck’s constant 4 There is a spectrum (range) of wavelengths of electromagnetic radiation Wavelength ( λ ) For remote sensing, we usually use μm (micrometer, 10 –6 m) or nm (nanometer, 10 –9 m) to measure wavelength, except in microwave. http://www.yorku.ca/eye/spectrum.gif 5 Two rules describing radiation were derived from this simple postulate Planck’s equation • At a given temperature a body emits a spectrum of wavelengths and the () 2 5 2 , where 1 x hc hc Lx kT e == Peak radiation for hotter intensity of radiation varies with the wavelength wavelength energy Peak radiation for hotter object is higher and at shorter wavelength Hotter object radiates more at all wavelengths c = speed of light = 3.0 x 10 8 ms –1 h = Planck’s constant = 6.63 x 10 –34 Js k = Boltzmann’s constant = 1.38 x 10 –23 JK –1 6
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3/31/2008 ESM 266 2 So, total energy at Sun = E × 4 π R 2 Watts That same amount of energy spreads out over the surface of a sphere Intensity of solar radiation ( Intensity of solar radiation (Wm –2 ) is reduced at Earth’s orbital at Earth’s orbital distance, from ~10 distance, from ~10 8 to ~10 3 Wm –2 R = Sun’s radius P = radius of Earth’s orbit 2 m W Let E = Energy generated at Sun at a distance of Earth’s radius (4 π P 2 ) So, energy at Earth is At upper edge of Earth’s atmosphere S 0 = 1370 W m –2 : the ‘solar constant’ P R 2 2 2 2 0 m W 4 4 = = P R E P R E S π 7 Planck equation for Sun and Earth 10
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This note was uploaded on 08/06/2008 for the course ESM 266 taught by Professor Dozier during the Spring '08 term at UCSB.

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01-Introduction - 3/31/2008 Remote Sensing: The Major...

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