Lecture 4. Solar Radiation

1. Lecture 4.Solar Radiation

2. I. Solar Radiation • Radiation: transfer of energy as an electromagnetic wave i. Quantity - Solar constant: amount entering the atmosphere is fairly uniform. There are numerous factors that affect the amount that reach the different layers of vegetation. ii. Quality • Depend on type a. Ultra Violet b. Visible light c. Far red and infra-red

3. UV Visible Far-red Infra-red 10 1 intensity 0.1 0.01 0.4 0.7 0.1 1 10 100 wavelength (microns) Incoming Solar Radiation 9%, 41%, 50%

4. Types of Solar Radiation • The types are based on the length of the wavelength a. Ultraviolet • <0.4µm (wavelength) • Amount of UV reaching the surface is positively related to elevation • Approximately 10% of total incident radiation

5. Types of Solar Radiation b. visible light or photosynthetic active radiation (PAR) • 0.4-0.7µm (or 400-700nm) • Plants only use this portion of the spectrum in photosynthesis • About 50% of the light reaching the earth is in this spectrum • scientists can use the absorption of these different wavelengths to characterize land cover and canopy structure

6. Types of Solar Radiation c. Far-red and infra-red • >0.7µm (wavelength) • Not absorbed by vegetation • About 40% of incident radiation • Insects are able to use infra-red and far-red to detect trees that are stressed • Scientists use IR wavelength to characterize vegetation cover and canopy structure • HOW?????

7. UV visible infra-red Solar Radiation UV visible near infra-red (NIR) Remotely sensed vegetation indices: Simple ratio (SR): NIR/R Normalized Difference Vegeation Index (NDVI): NDVI = (NIR-R)/(NIR+R)

8. Local Classification of Vegetation

9. Solar Radiation LANDSAT ETM+ 30m June 2000 We can quantify disturbances Such as fire 10 km

10. Satellite of Roads and Deforestation 1985 1975 1992

11. ETM+ predictions of Aug. LAI Corn LAI=4.00+0.45*CCIca R2=0.63 Soy LAI=3.44+0.49*CCIsa R2=0.27 ETM+ predictions of July LAI Corn LAI=4.41+0.63*CCIcj R2=0.61 Soy LAI=1.54+0.49*CCIsj R2=0.58 Crop- and measurement date-specific indices derived from canonical correlation analyses of 4-date (April-September) ETM+ spectral trajectories 1:1 1:1 RMSE=0.45 Slope=0.99 Intercept=0.01 R=0.95 RMSE=0.71 Slope=0.92 Intercept=0.27 R=0.57

12. II. Energy Budget of Forest Ecosystems • S=R+C+G+LE+Ps • S=solar radiation • R=reflected solar radiation • C=convection • G=Conduction • LE=Latent heat of vaporization • PS=photosynthesis

13. II.Energy Budget i. Reflected Solar Radiation ( R ) • Amount of short wavelengths sent back to atmosphere plus long waves that are re-radiated • Albedo: • Reflectivity of a material summed over all its wavelenths (R = S x A)

14. Energy Budget: Albedo values for common land surfaces

15. II. Energy Budget iii. Convection ( C ) • heating of air, transfer of energy as air moves over a surface (leaf or canopy) • If leaf temp is greater than air temp then the rate of heat loss is roughly proportional to the square root of the leaf width. • Small leaves would be most advantageous in what climate? • What environmental condition(s) would cause high convection values for a forest?

16. II. Energy Budget v. Conduction (G) • Transfer of energy through a solid (i.e. movement of energy through the soil) Why do reptiles lay on roads at night in the fall?

17. II.Energy Budget iv. Latent Heat of Vaporization (LE) • the amount of energy required to vaporize water, approximately 580 cal per g of water at 28 oC • this process is important in transpiration when water undergoes a phase change (i.e. liquid to vapor) during transpiration. • What are ideal environmental conditions for trees to exhibit high rates of transpiration??

18. II.Energy Budget vi. Photosynthesis (PS) • A small component of energy balance at a site • Generally less than 1-2% Review • S = R + C + G + LE + Ps

19. Energy Budget of a Leaf

20. II. Energy Budgets • Bowen ratio: the ratio of convection (C) : (LE) latent heat of evaporation. • Ecologists use this ratio to characterize environmental conditions. It is useful because …. Why???

21. Bowen Ratios

22. Partition of energy budget for adjacent intact and clear cut forests

23. i)Latitude/geographic general decrease in solar radiation in areas from latitude of about 30o N and S of the equator. exception is areas supporting lowland tropical forests, where the tremendous transpiration results in greater cloud cover and water vapor is opaque to certain wavelengths of solar radiation III. Variations in Solar Radiation Quality

25. Global Net Radiation

26. Variations in Solar Radiation Quality (continued) ii) aspect • in the northern hemisphere, southerly and westerly aspects receive a greater amount of solar radiation than northern or eastern aspects. iii) altitude • higher elevation sites receive greater amounts of S than lower elevation sites iv) air pollution/wildfire • Heavily industrialized regions receive less amounts of S than pristine regions

27. forest clearcut Solar radiation effect v) adjacent vegetation -1 0 1 2 Distance from edge (tree heights)

28. IV. Light Attenuation in Forest Canopies • Beer-Lambert Law: IZ/I0 = exp (-k)(LAI) or calculation equation: ln(IZ/I0) = -(k)(LAI)

29. ii) Elevation i) Latitude a shorter path of solar radiation through the atmosphere results in a higher amount of UV-B input. Extreme UV exposure can result in degradation of the photosynthetic machinery, to protect this plants in environments where UV radiation is large generally have pigments in the foliage flavenoids and phenols that absorb the UV and minimize transmittance. high water content in the foliage is also an effective barrier to UV transmittance V. Variations in Solar Radiation Quality

30. V. Variations in Solar Radiation Quality iii) Vegetation • pigments in the foliage are responsible for absorbing or reflecting incoming radiation. • Chlorphyll absorbs violet, blue and red wavelengths and reflects green- hence the green appearance of foliage • Carotenoids-reflect yellow to orange and absorb blue to green wavelengths • Because vegetation absorbs almost all of the radiation in the visible spectrum, it is dark beneath the forest canopy.

31. Adaptations of Vegetation to Radiation Quantity • Sun leaves vs Shade leaves • Shade leaves are: • thinner • less deeply lobed • thinner epidermis • less palisade layers • fewer stomata • less supportive and conductive tissue

32. VI. Influences of Solar Radiation on Tree Growth i. Photosynthesis • The process of photosynthesis is light dependent. Plants typically “experience” 1-15% incident sunlight. • Photosynthesis is directly proportional to sunlight intensity when no other factors are limiting.

33. Influences of Solar Radiation on Tree Growth a. Light Compensation Point - amount of light (PAR) where photosynthesis=respiration - or, light intensity where the carbon balance = 0 b. Light Saturation Point - amount of light (PAR) where photosynthesis will not increase with increased levels of light - Photosynthetic machinery are saturated

34. Relationship between PAR and carbon balance Light saturation point Sun leaf or shade intolerant plant photosynthesis Shade leaf or shade tolerant plant Leaf or canopy carbon balance 0 Light compensation point respiration Photosynthetic active radiation (PAR)

35. ii. Photoperiod Mechanism Red light at 0.66um darkness Pred Pred Pfar-red Far-red light at 0.73um Pred = phytochrome red Pfar-red = phytochrome far-red Pfar-red is the biologically active phytochrome form