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How to calculate albedo yourself?

How to calculate albedo yourself?

The albedo value of different areas of the Earth surface is measured by observation satellites from the space or with pyranometers on ground. Obviously, these are rather expensive scientific equipment and not available for all. The data of MODIS – NASA’s observation instrument on board of two satellites on Earth orbit – is available online.

A simple way to measure albedo value and the value after making the surface lighter, is to use digital photography and some image editing software. Any camera can do this, also your mobile phone’s one.
An open source image editing software ImageJ is freely downloadable at
http://imagej.nih.gov/ij/index.html

The basics is the same with all the software – below it is explained with ImageJ.
You can also experiment with for example simple lightning meter.

1. Place a normal, white A4 paper on the surface that you want to measure. Take a picture with your camera of the paper in a way that the surface is seen as well. The white paper is your control area. Measure the light from the area you want to know the albedo (in the below example image, the grass). Don’t use flash and be careful with the shadows – other than that there’s no other things to worry about.
Example image

2. Download the image on your computer and open it in ImageJ. Choose Analyse → Histogram from the top menu. Select first area outside the paper in image. You’re interested in the Mean value visible then on the Histogram. It measures average brightness of each pixel in the selected area (normally 0-255). Write down the value. In this example case it’s 117,557.
Grass mean

3. Move the measurement area on the white paper and write down the Mean value of it, as well. In this case it’s 254,993.
Mean paper

4. The albedo is calculated as the ratio of the surface value divided by the control value (the white paper), and this answer multiplied by the correction term (white paper’s known albedo value).
In this case first:
117,557 / 254,993 = 0,461
The albedo value of 0.65 or 65% is carried forward as a known, standard albedo value for white printing paper. This is in close agreement with published figures for office paper. (Gorski, 2011 and National Printing Company, 2011)
To finish the calculation, multiply with standard paper value to get the final result:
0,65 x 0,461 = 0,29

After making the calculation, it’s good to check online what are the typical albedo values of the surface measured. In this example case, the surface was grass and typically albedo value for green grass is 0,25. This means that the example should be quite correct here as it is a little bit lighter than green grass, 0,29.

After you have made the surface lighter or whiter, you can repeat the same procedure and compare the values to know how much you’ve managed to change the albedo.

Change affect on climate

It would be of course interesting to then know what is the affects of the change in the albedo for the climate. For this one needs to know exactly these albedo values that was just calculated here but also for how long the lightening has been done and for how big area in square-meters. This information is maybe easily accessible. But what makes it trickier is that one would also need to know how much solar radiation comes to the surface exactly on that particular location. This is not the same amount everywhere as the amount changes in different parts of the Earth and in seasons. Also, the weather on the location has importance. Hopefully there will be examples of these values here later.

Still, the examples of this website give some idea of the affects and you can compare. The darker the surface one lightens the bigger the affect. In the examples, there are a description where the lightening has happened, for how long, for how big area in square meters, how much the change in albedo was in megajoules and the megajoules transferred into gasoline litres. One megajoule is 42,4 l of gasoline. For example, in Finland, when you drive a car with catalysator and using gasoline processed in the same country, it creates about 2,85 kg/l of greenhouse gas emissions.