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Understanding Radiation Models in Electronics and Remote Sensing

Learn about radiation properties, emissivity, heat transfer, and the greenhouse effect in electronics. Understand the impact of atmospheric and solar radiation on materials and the environment, and explore the importance of different surface finishes and coatings.

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Understanding Radiation Models in Electronics and Remote Sensing

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  1. CHE/ME 109 Heat Transfer in Electronics LECTURE 24 – RADIATION MODELS

  2. RADIATION PROPERTIES • EMISSIVITY FOR REAL MATERIALS CAN BE A FUNCTION OF WAVELENGTH AND DIRECTION • DIFFUSE EMITTERS ARE NOT DIRECTIONALLY DEPENDENT • GRAY BODIES ARE NOT WAVELENGTH DEPENDENT • EMISSIVITY IS RELATED TO THAT FOR A BLACKBODY, WHERE ε = 1 BY DEFINITION

  3. EMISSIVITY • THE SPECTRAL, DIRECTIONAL EMISSIVITY IS RELATED TO THE INTENSITY OF RADIATION EMITTED BY A BLACKBODY AT THE SAME WAVELENGTH BY: • .THE DIRECTIONAL EMISSIVITY IS DEFINED

  4. HEMISPHERICAL EMISSIVITY • THE SPECTRAL HEMISPHERICAL EMISSIVITY IS DEFINED: • .THE TOTAL HEMISPHERICAL EMISSIVITY IS THEN DEFINED AS

  5. GRAY BODY EMISSIVITY • REPRESENTED BY THE MATERIALS SHOWN IN FIGURE 12-28. • AVERAGED VALUES ARE USED FOR CALCULATIONS WHEN PRACTICAL, AS PER FIGURE 12-30 • MEASUREMENT OF THE AFFECT OF DIFFERENT SURFACE COATINGS CAN BE ANALYZED WITH THIS VARIABLE

  6. SURFACE FINISHES

  7. REFLECTIVITY, ABSORPTIVITY AND TRANSMISSIVITY • IRRADIATION ONTO A SURFACE CAN LEAD TO SEVERAL POSSIBLE RESULTS: • THE RESULTANTS ARE NORMALLY DEFINED WITH

  8. RADIATION PROPERTIES • ALL OF THESE PROPERTIES CAN BE SPECTRAL (BASED ON WAVELENGTH), SO THE PORTION IN EACH CATEGORY IS RELATED TO G BY:

  9. REFLECTION • REFLECTED IRRADIATION CAN BE DIRECTLY REFLECTED OR SCATTERED • IF THE REFLECTION IS AT THE SAME ANGLE AS THE INCIDENT RADIATION, THEN THIS IS REFERRED TO AS SPECULAR (MIRROR IMAGE) REFLECTION • DIFFUSE IS REFLECTED IN ALL DIRECTIONS

  10. OPAQUE SYSTEMS • THE RELATIONSHIP SIMPLIFIES TO α + ρ = 1 • THIS SITUATION CAN BE USED FOR REMOTE SENSING, SUCH AS BY SATELLITE • THE SPECTRUM OF THE REFLECTED RAYS PROVIDES AN INDICATION OF THE WAVELENGTHS THAT WERE ABSORBED • THE SOURCE OF THE INCIDENT RADIATION IS THE SUN, WHICH HAS A WELL DEFINED INTENSITY SPECTRUM

  11. REMOTE SENSING EXAMPLE • LEAF REFLECTION COMPONENTS http://geog.hkbu.edu.hk/geog3610/lect-06.pdf

  12. REMOTE SENSING EXAMPLE • LEAF REFLECTION COMPONENTS http://geog.hkbu.edu.hk/geog3610/lect-06.pdf

  13. REMOTE SENSING EXAMPLE • LEAF REFLECTION COMPONENTS http://geog.hkbu.edu.hk/geog3610/lect-06.pdf

  14. REMOTE SENSING EXAMPLE • LEAF REFLECTION COMPONENTS http://geog.hkbu.edu.hk/geog3610/lect-06.pdf

  15. REMOTE SENSING EXAMPLE • LEAF REFLECTION COMPONENTS http://geog.hkbu.edu.hk/geog3610/lect-06.pdf

  16. REMOTE SENSING EXAMPLE • LEAF REFLECTION COMPONENTS http://geog.hkbu.edu.hk/geog3610/lect-06.pdf

  17. REMOTE SCAN OF OTHER MATERIALS • SOIL BY TYPE • PRESENCE OF MINERALS • PRESENCE OF MOISTURE IN ALL THREE PHASES

  18. KIRCHHOFF’S LAW • AT THERMAL EQUILIBRIUM, ENERGY INPUT IS EQUAL TO ENERGY OUTPUT • CONSIDERING A SMALL BODY IN AN ISOTHERMAL ENCLOSURE (FIGURE 12-35) • AN ENERGY BALANCE ON THE BODY REQUIRES THAT INCIDENT RADIATION IS EQUAL TO EMITTED RADIATION • WHICH LEADS TO

  19. GREENHOUSE EFFECT • THE GREENHOUSE EFFECT RESULTS BECAUSE GASES HAVE WAVELENGTHS AT WHICH THEY SELECTIVELY ABSORB RADIATION • IF THERE WERE NO ATMOSPHERE, THE EQUILIBRIUM TEMPERATURE OF THE EARTH WOULD BE ABOUT 33 C COLDER THAN THE CURRENTLY VALUES • WHEN THE CONCENTRATION OF CERTAIN GASES ABSORB CHANGE, THE AMOUNT OF REFLECTED RADIATION WILL CHANGE

  20. GREENHOUSE EFFECT H • THE GASES OF INTEREST ARE: WATER, CO2, METHANE, NITROUS OXIDE. • NASA • THERE HAVE BEEN CYCLES OF THESE CONCENTRATIONS BASED ON ICE CORES FROM ANTARCTICA THAT GO BACK AS FAR AS 200,000 YEARS

  21. GREENHOUSE EFFECT

  22. GREENHOUSE EFFECT • THE CURRENT CONCERN IS BASED ON A RECOGNITION THAT IN THE LAST 200 YEARS OF THE INDUSTRIAL REVOLUTION THE CONCENTRATIONS HAVE BEEN CONTINUOUSLY INCREASING • THE CURRENT CONCENTRATIONS ARE NEAR OR ABOVE HISTORICAL HIGHS • AVERAGE TEMPERATURES ARE ALSO INCREASING • ANTHROPOGENIC CONTRIBUTIONS CONTINUE TO INCREASE AS MORE OF THE WORLD BECOMES INDUSTRIALIZED

  23. GREENHOUSE EFFECT

  24. ATMOSPHERIC & SOLAR RADIATION • OZONE, O3, HAS A SIGNIFICANT IMPACT ON THE AMOUNT OF ULTRAVIOLET RADIATION THAT IS INCIDENT ON THE EARTH • THE OZONE REACTION WITH THE UV PHOTON IS: O3 + Photon → O2 + O + heat • .AND THERE IS NORMALLY AN EQUILIBRIUM ESTABLISHED. O + O2→ O3 • THE OZONE CONCENTRATION AND TEMPERATURE VARY WITH ALTITUDE

  25. OZONE CONCENTRATIONS http://www.epa.gov/ozone/science/sc_fact.html

  26. OZONE CONCENTRATIONS • 90% OF THE OZONE IS ABOVE 15 km IN THE STRATOSPHERE • THE REACTIONS ARE RELATIVELY SLOW BECAUSE GAS DENSITY IS LOW • WHEN OZONE GETS IN THE LOWER ELEVATIONS, IT CAN HAVE TOXIC EFFECTS • DEPLETION OCCURS WHEN HALOGENS BUILD UP IN THE STRATOSPHERE AND DEACTIVATE THE OZONE CYCLE • NET REDUCTIONS IN STRATOSPHERIC OZONE CONCENTRATIONS WILL RESULT IN MORE UV LIGHT GETTING TO THE SURFACE OF THE EARTH • UV SEEMS TO CONTRIBUTE TO SKIN CANCER • UV CAUSES FAILURES IN SOME MATERIALS.

  27. MONTREAL PROTOCOL IN 1992 • HAS RESULTED IN A REDUCTION IN THE USE OF CFC’S AND OTHER HALOGEN CONTAINING MATERIALS • HAS SHOWN A DECREASE IN THESE COMPONENTS IN THE STRATOSPHERE • EQUILIBRIUM COULD BE REESTABLISHED WITHIN 50 YEARS

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