Measuring Albedo with ADI
Morton M. Sternheim
www.umassk12.net/digital
June, 2012
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
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.
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
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
Click on Spatial Analysis,
then open your image
Draw a Xerox Rectangle
Average
color
77.61
Draw a Sample Rectangle
Average
color
10.86
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%
.
Using the Line Tool to Measure Albedo
File  Graph Colors  Same Result
~75%
~10%
Colors
turned off
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.