Measuring Albedo with ADI Morton M. Sternheim umassk12/digital June, 2012

1. Measuring Albedo with ADI Morton M. Sternheim www.umassk12.net/digital June, 2012

2. Objectives ADI Learn how to use Rectangle Tool to measure intensity (brightness) Learn how to use Line Tool Learn how to use File  Graph Colors Learn how to avoid over exposing photos Content Understand role of albedo in Polar climate change Understand how albedo depends on surface

3. Big Idea • Why are Polar Regions more affected by global warming than other parts of the globe? • One reason (there are others) is that as sea ice melts and more open water appears, more energy is absorbed, and warming accelerates. • This is a form of positive feedback and it makes the polar climate change faster than the climate in temperate areas. • Increasing vegetation on land also has a similar positive feedback effect.

4. Albedo • This effect is a change in the albedo – the fraction of the incident sunlight that is reflected back to space. • The albedo is much higher for snow and ice than for water or vegetation. http://www.energyeducation.tx.gov/environment/section_3/topics/predicting_change/img/albedo.gif

5. Measuring Albedo with ADI • Use Xerox paper as a standard; use 0.6 as its albedo • Avoid overexposure by having the paper fill • about half the image Xerox paper on grass

6. Click on Spatial Analysis, then open your image

7. Draw a Xerox Rectangle Average color 77.61

8. Draw a Sample Rectangle Average color 10.86

9. Result • Albedo = 0.6 x (sample value)/(Xerox value) • In this example, • Albedo of grass area = 0.6 (10.86/77.61) = 0.084 = 8.4% • .

10. Using the Line Tool to Measure Albedo

11. File  Graph Colors  Same Result ~75% ~10% Colors turned off

12. Comments This is a simple activity and does not depend on an understand of color basics, pixels, etc. Caution: If any intensity is 100% or close to that, the photo is overexposed and cannot be used to measure the albedo.