Legislación Comparada

Graphical Reflectivity MeasurementsMeasurements

Very precise measurements can be made of the reflectivity of materials Very precise measurements can be made of the reflectivity of materials that more easily reveal their subtle differences. Above is a plot of the reflectivities that more easily reveal their subtle differences. Above is a plot of the reflectivities of green vegetation, dry vegetation and soil between wavelengths of 0.4 and 2.5 of green vegetation, dry vegetation and soil between wavelengths of 0.4 and 2.5 micrometers (400 to 2500 nm). Scientists use graphs such as these to design micrometers (400 to 2500 nm). Scientists use graphs such as these to design instruments that help them discriminate between a variety of interesting materials instruments that help them discriminate between a variety of interesting materials and mineral deposits.

and mineral deposits.

Problem 1

Problem 1 _{- An astronomer wants to map the surface of Mars with telescopes on- An astronomer wants to map the surface of Mars with telescopes on}

Earth to search for plant life. What wavelength range would help her more easily Earth to search for plant life. What wavelength range would help her more easily discriminate between the martian soil and living vegetation?

discriminate between the martian soil and living vegetation?

Problem 2

Problem 2 _{- An earth scientist measures the intensity of light between two- An earth scientist measures the intensity of light between two}

neighboring land areas at a wavelength of 2.0 microns and 0.7 microns. Spot A neighboring land areas at a wavelength of 2.0 microns and 0.7 microns. Spot A appears to be 5 times brighter than Spot B in the longer wavelength band, but appears to be 5 times brighter than Spot B in the longer wavelength band, but nearly equal in brightness in the shorter-wavelength band. What may be the nearly equal in brightness in the shorter-wavelength band. What may be the difference in substances between the two spots?

difference in substances between the two spots?

Problem 3

Problem 3 _{- The difference in the vegetation reflectivity between green- The difference in the vegetation reflectivity between green}

vegetation and dry vegetation is that green vegetation still contains the molecule vegetation and dry vegetation is that green vegetation still contains the molecule chlorophyll. What is the difference in absorption by chlorophyll molecules at a chlorophyll. What is the difference in absorption by chlorophyll molecules at a wavelength of 0.6 microns?

Answer Key

Answer Key

₁₁₁₁

Problem 1

Problem 1 _{- An astronomer wants to map the surface of Mars with telescopes on- An astronomer wants to map the surface of Mars with telescopes on}

Earth to search for plant life. What wavelength range would help her more easily Earth to search for plant life. What wavelength range would help her more easily discriminate between the martian soil and living vegetation?

discriminate between the martian soil and living vegetation?

Answer: The graph shows that the reflectivity of green vegetation is substantially Answer: The graph shows that the reflectivity of green vegetation is substantially brighter than soil between wavelengths of 0.7 to 1.4 microns. At 0.9 microns, the brighter than soil between wavelengths of 0.7 to 1.4 microns. At 0.9 microns, the reflectivity

reflectivity of green of green vegetation ivegetation is about s about 0.7 or 0.7 or 70%, whil70%, while soil e soil is is only only about 0.25 about 0.25 (( 25%) at the same wavelength,

25%) at the same wavelength, so green vegetation is nearly three times as bright asso green vegetation is nearly three times as bright as

bare soil at 0.7 microns.

bare soil at 0.7 microns.

Problem 2

Problem 2 _{- An earth scientist measures the intensity of light between two neighboring- An earth scientist measures the intensity of light between two neighboring}

land areas at a wavelength of 2.0 microns and 0.7 microns. Spot A appears to be 5 land areas at a wavelength of 2.0 microns and 0.7 microns. Spot A appears to be 5 times brighter than Spot B in the longer wavelength band, but nearly equal in times brighter than Spot B in the longer wavelength band, but nearly equal in brightness in the shorter-wavelength band. What may be the difference in substances brightness in the shorter-wavelength band. What may be the difference in substances between the two spots?

between the two spots? Answer:

Answer: The graph shows that The graph shows that at 0.7 miat 0.7 microns, the reflectance crons, the reflectance curves for greencurves for green

vegetation and dry vegetation cross, which means they are of equal reflectivity at this vegetation and dry vegetation cross, which means they are of equal reflectivity at this wavelength.

wavelength. At 2.0 microns, the At 2.0 microns, the reflectivity of dry vegetation reflectivity of dry vegetation is about 0.25 or 25%,is about 0.25 or 25%, while green vegetation is much darker and only 0.05 or 5% reflective.

while green vegetation is much darker and only 0.05 or 5% reflective. Spot B appearsSpot B appears

to be 5 times brighter than Spot A so that suggests that Spot A consists of green

to be 5 times brighter than Spot A so that suggests that Spot A consists of green

vegetation and Spot B consists of dry vegetation.

vegetation and Spot B consists of dry vegetation.

Problem 3

Problem 3 _{- - The difference in The difference in the vegetation reflectithe vegetation reflectivity between green vegetation vity between green vegetation andand}

dry vegetation is that green vegetation still contains the molecule chlorophyll. What is dry vegetation is that green vegetation still contains the molecule chlorophyll. What is the difference in absorption by chlorophyll molecules at a wavelength of 0.6 microns? the difference in absorption by chlorophyll molecules at a wavelength of 0.6 microns?

Answer: From the graph, green vegetation has

Answer: From the graph, green vegetation has a reflectivity of a reflectivity of about 5% while dryabout 5% while dry vegetation has

vegetation has a reflectivita reflectivity of y of about 18%. about 18%. Because %emission Because %emission + %absorption + %absorption == 100%, the absorption of green vegetat

100%, the absorption of green vegetation is ion is 95% while dry vegetation absorbs only95% while dry vegetation absorbs only 82% of the light at this wavelength.

82% of the light at this wavelength. The difference in absorption is 13%.The difference in absorption is 13%.

Note: Student’s answers may vary in percentage depending on the graph estimation Note: Student’s answers may vary in percentage depending on the graph estimation method used.

12

12