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Measuring Albedo with ADIMorton M. Sternheim
www.umassk12.net/digital
June, 2012
ObjectivesADI
Learn how to use Rectangle Tool to measure intensity (brightness)
Learn how to use Line Tool Learn how to use File Graph ColorsLearn how to avoid over exposing photos
ContentUnderstand role of albedo in Polar climate changeUnderstand how albedo depends on surface
Big IdeaWhy 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.
AlbedoThis 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
Measuring Albedo with ADIUse 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
Click on Spatial Analysis, then open your image
Draw a Xerox Rectangle
Average color 77.61
Draw a Sample Rectangle
Average color 10.86
ResultAlbedo = 0.6 x (sample value)/(Xerox value)In this example,
Albedo of grass area = 0.6 (10.86/77.61) = 0.084 = 8.4%
.
Using the Line Tool to Measure Albedo
File Graph Colors Same Result
~75%
~10%
Colors turned off
CommentsThis 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.