Energy Interaction in the Atmosphere

8/11/2019 Energy Interaction in the Atmosphere

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PROCESS OF REMOTE SENSING

Energy Source or Illumination (A) - The firstrequirement for remote sensing is to have anenergy source which illuminates or provideselectromagnetic energy to the target ofinterest.


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Interaction with the Target (C) - Once theenergy makes its way to the through theatmosphere, it interacts with the targetdepending on the properties of both thetarget and the radiation.


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Recording of Energy by the Sensor (D) -After the energy has been scattered by, oremitted from the target, we require a sensor(remote - not in contact with the target) tocollect and record the electromagneticradiation.


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Transmission, Reception, and Processing(E) - The energy recorded by the sensor has tobe transmitted, often in electronic form, to areceiving and processing station where thedata are processed.


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Interpretation and Analysis (F) - Theprocessed image is interpreted, visuallyand/or digitally or electronically, to extractinformation about the target, which wasilluminated.


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Application (G) - The final element of theremote sensing process is achieved when weapply the information we have been able toextract from the imagery about the target inorder to better understand it, reveal somenew information, or assist in solving a

particular problem.


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Radiation and the Atmosphere (B)

What are the factors that affect the intensityand spectral composition of radiation?


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1. ScatteringScattering occurs when particles or large gasmolecules present in the atmosphere interactwith and cause the electromagnetic radiationto be redirected from its original path.


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a. Rayleigh Scatteringoccurs when particles are very smallcompared to the wavelength of the radiation.These could be particles such as small specksof dust or nitrogen and oxygen molecules.Rayleigh scattering causes shorter

wavelengths of energy to be scattered muchmore than longer wavelengths.


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b. Mie Scattering occurs when the particlesare just about the same size as thewavelength of the radiation. Dust, pollen,smoke and water vapour are common causesof Mie scattering which tends to affect longerwavelengths than those affected by Rayleigh

scattering.


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c. non selective Scattering. This occurs whenthe particles are much larger than thewavelength of the radiation. Water dropletsand large dust particles can cause this type ofscattering. Nonselective scattering gets itsname from the fact that all wavelengths are

scattered about equally.


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2. AbsorptionIn contrast to scattering, this phenomenon

causes molecules in the atmosphere to absorbenergy at various wavelengths.

Some radiation is absorbed through electronor molecular reactions within the mediumencountered; a portion of the energyincorporated can then be re-emitted (asemittance), largely at longer wavelengths, sothat some of the sun's radiant energy engages inheating the target giving rise then to a thermalresponse.


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Interaction with the Target (C)

Energy interactions with earth surfacefeatures.

When solar radiation hits a target surface, itmay be transmitted, absorbed or reflected.Different materials reflect and absorb

differently at different wavelengths.


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Ei() = Er() + Ea() + Et()

Ei- incident energyEr- reflected energy

Ea- absorbed energyEt- transmitted energy


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the reflectance characteristics of earthsurface features may be quantified., and thisis measured as a function of wavelength andis called spectral reflectance .

= Er() / Ei() *100


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Recording of Energy by the Sensor(D)

Remote Sensing Systems

1- Visual remote sensing system The humanvisual system is an example of a remotesensing system in the general sense.


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Remote Sensing Systems

2- Optical Remote Sensing In OpticalRemote Sensing, optical sensors detect solarradiation reflected or scattered from the

earth, forming images resemblingphotographs taken by a camera high up inspace.


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Energy Interaction in the Atmosphere