Interaction of EMR in Remote Sensing.ppt
- 1. Ch3: Energy Balance and Temperature Part 1
- 2. 1. Hand back, go over quizzes 2. Review of Solar Cycle
- 3. What happens to solar radiation as it travels through the atmosphere?
- 4. Energy Essentials Energy Essentials • Incoming solar rad’n (insolation) is the primary energy Incoming solar rad’n (insolation) is the primary energy source for the atmosphere source for the atmosphere • land, oceans, clouds, atmospheric gases and dust land, oceans, clouds, atmospheric gases and dust intercept insolation intercept insolation • Energy Pathways and Principles Energy Pathways and Principles – Input: shortwave energy from the Sun Input: shortwave energy from the Sun – Output: longwave energy from Earth’s surface Output: longwave energy from Earth’s surface • atmosphere and Earth’s surface heated by solar energy: atmosphere and Earth’s surface heated by solar energy: unevenly distributed by latitude and season unevenly distributed by latitude and season
- 5. Atmospheric Influences on Insolation Atmospheric Influences on Insolation 1. 1. Absorption Absorption 2. 2. Reflection and Scattering Reflection and Scattering 3. 3. Transmission Transmission
- 6. Absorption • absorption – transfers energy from radiation to absorber, absorber warms • gases, particulate matter, droplets absorb energy • radiation absorbed function of wavelength (not equal) • e.g. UV vs. visible light • near infrared rad’n absorbed by CO2 and H20v
- 7. Reflection and Scattering Reflection and Scattering • reflection reflection – redirection of energy w/o – redirection of energy w/o absorption absorption • all objects reflect visible light all objects reflect visible light effectiveness varies effectiveness varies • albedo – albedo – % of visible light reflected % of visible light reflected • There are two types of reflection (solid There are two types of reflection (solid surface: surface: – Specular Specular: light is reflected with equal : light is reflected with equal intensity (e.g. mirror) intensity (e.g. mirror) – Diffuse reflection Diffuse reflection OR OR scattering scattering: light : light is reflected in multiple directions, weakly is reflected in multiple directions, weakly (e.g. snow) (e.g. snow)
- 8. • Rad’n reaching Earth’s surface can be either: Rad’n reaching Earth’s surface can be either: – Diffuse rad’n (scattered) Diffuse rad’n (scattered) – Direct rad’n (unscattered) Direct rad’n (unscattered) • IMPORTANT: IMPORTANT: – Scattered energy is re-directed Scattered energy is re-directed NOT absorbed NOT absorbed – size of scattering agent relative to size of scattering agent relative to wavelength determines wavelength determines type of scattering type of scattering
- 9. 3 Types of Scattering: 3 Types of Scattering: 1. 1. Raleigh Raleigh 2. 2. Mie Mie 3. 3. Non-Selective Non-Selective A discussion of each type follows… A discussion of each type follows…
- 10. 1) Rayleigh scattering • involves gases, smaller than insolation wavelength • scatters light in all directions • most effective at short wavelengths (violet, blue)…hence, blue sky • explains reddish-orange sunsets when light travels through thick slice of atmosphere
- 11. 2. Mie scattering 2. Mie scattering – involves aerosols, larger than gas molecules involves aerosols, larger than gas molecules – forward scatter forward scatter – equally effective across visible spectrum equally effective across visible spectrum – explains hazy, gray days explains hazy, gray days – accentuates sunset/rise accentuates sunset/rise (e.g., in polluted areas) (e.g., in polluted areas)
- 12. 3) Non-selective scattering 3) Non-selective scattering – water droplets in clouds (larger than PM, gas molecules) water droplets in clouds (larger than PM, gas molecules) – Act like lenses; scatter all wavelengths equally Act like lenses; scatter all wavelengths equally – Why clouds appear grey or white Why clouds appear grey or white – Explains rainbows Explains rainbows when viewing rain when viewing rain in the distance (each in the distance (each wavelength bent a wavelength bent a different amount) different amount)
- 13. Transmission Transmission • percentage of energy passing through atmosphere and percentage of energy passing through atmosphere and reaching surface reaching surface • Amount reaching Earth surface is function of atmospheric Amount reaching Earth surface is function of atmospheric absorption, scatter, and reflection absorption, scatter, and reflection • Clear v. hazy, cloudy days Clear v. hazy, cloudy days
- 14. Fate of Solar Radiation what happens to it ??? • annual variation in insolation is ~ 7% (remember perihelion/aphelion • the insolation reaching top atmosphere can be • transmitted • absorbed (atmosphere and surface) • scattered/reflected back to space • assume 100 units (100%) of insolation reach top of atmosphere •Now What?
- 15. Earth’s Solar (“Shortwave”) Radiation Balance: 100% sunlight in at top of atmosphere 19 + 45 + 25 + 6 + 5 = 100% Q: Surface absorbs 45% - why doesn’t it become extremely hot?....
- 16. Answer – Other types of energy transfer also occur: 1. Longwave Radiation Transfer (mainly between earth & atmos.) • Sun heats earth surface, earth emits radiation (I=σT4 ) • Called “Longwave” because much longer wavelength than radiation emitted by sun due to cooler temp of earth 2. “Sensible” Heat Transfer (due to temperature gradients) 3. “Latent” Heat Transfer (evaporation, melting) A discussion of each follows…
- 17. 1. Longwave Radiation Balance So net surface loss due to longwave = 16% But there was an excess of 45% of solar radiation. Thus, we still have 45% -16% = 29% excess radiation at the surface…how do we get rid of it?
- 18. Answer: “Sensible” and Answer: “Sensible” and “Latent” heat transfers. “Latent” heat transfers. 1. 1. Conduction Conduction – This is how excess heat in ground is This is how excess heat in ground is transferred to the atmosphere via an transferred to the atmosphere via an extremely thin layer of air in contact extremely thin layer of air in contact with the surface with the surface 2. 2. Convection Convection – Once the heat is transferred from Once the heat is transferred from the surface to the air via conduction, the surface to the air via conduction, convection takes over from here via convection takes over from here via “sensible” and “latent” heat transfers “sensible” and “latent” heat transfers First, recall 2 other methods of First, recall 2 other methods of energy transfer in addition to energy transfer in addition to radiation: radiation:
- 19. Free Convection (just like boiling water) Forced Convection (due to wind)
- 20. Sensible Heat Sensible Heat • Heat energy which is readily detected Heat energy which is readily detected • Magnitude is related to an object’s specific heat Magnitude is related to an object’s specific heat – The amount of energy needed to change the temperature of an The amount of energy needed to change the temperature of an object a particular amount in J/kg/K object a particular amount in J/kg/K • Related to mass Related to mass – Higher mass requires more energy for heating Higher mass requires more energy for heating • Sensible heat transfer occurs from warmer to cooler Sensible heat transfer occurs from warmer to cooler areas (i.e., from ground upward) areas (i.e., from ground upward) • Globally, about 8 units of energy are transferred to the Globally, about 8 units of energy are transferred to the atmosphere as sensible heat atmosphere as sensible heat
- 21. Latent Heat Latent Heat • Energy required to induce changes of state in a substance Energy required to induce changes of state in a substance • In atmospheric processes, invariably involves water In atmospheric processes, invariably involves water • When water is present, latent heat of evaporation redirects some energy When water is present, latent heat of evaporation redirects some energy which would be used for sensible heat which would be used for sensible heat – Wet environments are cooler relative to their insolation amounts Wet environments are cooler relative to their insolation amounts • Latent heat of evaporation is stored in water vapor Latent heat of evaporation is stored in water vapor – Released as latent heat of condensation when that change of state is Released as latent heat of condensation when that change of state is induced induced • Latent heat transfer occurs from regions of wetter-to-drier Latent heat transfer occurs from regions of wetter-to-drier • Globally, 21 units of energy are transferred to the atmosphere as latent Globally, 21 units of energy are transferred to the atmosphere as latent heat heat
- 22. Understanding Latent Understanding Latent heat: heat: • phase change requires +/- of energy • latent heat stored in H-bonds • latent heat of evaporation • latent of condensation • Energy absorbed S L V released V L S • Example - sweating Latent Heat
- 23. Summary : Total Energy Balance SW + LW +SH +LH = 0 for surface, atmos, top-of-atmos
- 24. Atmospheric Window • gases in atmosphere not effective at absorbing radiation between 8 – 11 μm Radiative properties of Atmospheric gases: Terrestrial Radiation Solar Radiation UV VIS IR
- 25. Radiative properties of gases Radiative properties of gases continued continued • When all gases are combined: When all gases are combined: – Atmos. fairly transparent to VIS (Shortwave) Atmos. fairly transparent to VIS (Shortwave) – Atmos. fairly opaque to IR (Longwave) Atmos. fairly opaque to IR (Longwave) • Exception atmos. window from ~8-12 Exception atmos. window from ~8-12 μ μm m • Increase/decrease concentration and changes Increase/decrease concentration and changes capacity radiation a gas can absorb (kind of like capacity radiation a gas can absorb (kind of like using a thicker blanket makes you warmer) using a thicker blanket makes you warmer) • The wildcard: clouds! These absorb just about all The wildcard: clouds! These absorb just about all longwave, including in atmos. window longwave, including in atmos. window – Will there be more clouds in a warming climate? Will there be more clouds in a warming climate?
- 26. Net Radiation and Net Radiation and Temperature Temperature • Earth’s radiation balance is a function of an Earth’s radiation balance is a function of an incoming and outgoing radiation equilibrium (SW incoming and outgoing radiation equilibrium (SW + LW = Net) + LW = Net) • If parameters were changed, a new equilibrium If parameters were changed, a new equilibrium would be achieved would be achieved • Balances occur on an annual global scale and Balances occur on an annual global scale and diurnally over local spatial scales diurnally over local spatial scales
- 27. Daily/Seasonal Radiation Patterns • insolation peak vs. temperature insolation peak vs. temperature • daily lag daily lag • seasonal lag seasonal lag •Lag is function of type of Lag is function of type of surface, wetness, wind, etc surface, wetness, wind, etc • Temperature increases when Temperature increases when input > output input > output • Temperature decreases when Temperature decreases when input < output input < output
- 28. • tropic-to-tropic – energy surplus • poles – energy deficits • ~ 38o N/S – balance • imbalance of net radiation at surface Equator/Tropics vs. high latitudes • drives global circulation • agents: wind, ocean currents, weather systems Latitudinal Variations in Net Radiation
- 29. Greenhouse Effect • relates to the trapping of terrestrial rad’n by gases in the atmosphere • major GH gases: CO2, H20(v), CH4 • imprecise analogy • the atmosphere/greenhouses are: • transparent to insolation (incoming) • opaque to longwave (outgoing) • greenhouses reduce the loss of energy by limiting convection (atm does not) • increase in GHG, increases counter-rad’n
- 30. Concepts Concepts • Fate of solar radiation (absorption, scattering, Fate of solar radiation (absorption, scattering, transmission transmission • Earth’s energy balance (SW + LW + SH + LH) Earth’s energy balance (SW + LW + SH + LH) • General radiative properties of gases and General radiative properties of gases and greenhouse effect greenhouse effect