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Albedo

Albedo extended definition

Albedo (al-bee-doh) is a measure of how much light that hits a surface is reflected without being absorbed.  Something that appears white reflects most of the light that hits it and has a high albedo, while something that looks dark absorbs most of the light that hits it, indicating a low albedo.

Albedo why do i care ag/K-12

Why do I care? Albedo is another name for reflectivity. The albedo of a surface determines how much sunlight will be absorbed and warm the surface compared to another surface that reflects most of the light and does not change temperature.

Albedo prerequisites

I should already be familiar with: Radiation

Albedo body

 

A high albedo surface reflects 80% of incoming radiation. The low albedo surface reflects only 10% of incoming radiation.
Figure A

The amount of energy that is reflected by a surface is determined by the reflectivity of that surface, called the albedo.  A high albedo means the surface reflects the majority of the radiation that hits it and absorbs the rest.  A low albedo means a surface reflects a small amount of the incoming radiation and absorbs the rest.  For instance, fresh snow reflects up to 95% of the incoming radiation.  Therefore, fresh snow has a high albedo of .95.  By contrast, water reflects about 10% of the incoming radiation, resulting in a low albedo of .10.  Since 30% of the sun’s energy is reflected by the entire earth, the earth has an average albedo of .30.  Generally, dark surfaces have a low albedo and light surfaces have a high albedo.  For example, in summer the black asphalt road is scorching hot. This is because much of the heat is absorbed by the asphalt allowing the asphalt to burn your feet as you walk on it. When it’s hot outside, lighter clothing keeps you cooler because it reflects most of the sunlight that hits it, keeping you cool. Keep in mind that it is still possible to get sunburnt while wearing a light colored shirt with no sunscreen underneath. Although much of the incoming radiation is reflected, there is still quite a bit that is absorbed by the shirt.

Albedo relation to agriculture/K-12

How does this relate to agriculture?

Have you ever wondered why it helps to put black tarp under your crops during cool weather?  This black tarp absorbs the heat from the day and emits it all through the night and keeps your plants from dying during a light freeze.  There are also special ground coverings that can be used to absorb more sunlight and conduct the energy into the soil, which raises the soil temperature and allows quicker germination and growth of plants like tomatoes.  Use of these ground covers can effectively lengthen the growing season by warming up the soil more quickly than it would on its own.  In contrast, painting whitewash over greenhouse glass in summer can reflect sunlight before it gets into the greenhouse, keeping the temperatures inside cooler.

All Activities Opening

Activities to further explain this module:

What Factors Impact a Greenhouse? Activity

Activity: What Factors Impact a Greenhouse?  (You will be re-directed to the UCAR website to an activity shared by the owners of the site.)

Description: This activity focuses on the factors that affect the heating in a greenhouse. Students will develop their own model using 2-liter bottles and measure how each bottle warms up and retains heat.

All modules using this activity: Albedo, How Clouds Form

Last modified date: Monday, June 25, 2012 - 12:31pm