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.