What is Albedo?

By John Misachi on November 10 2017 in World Facts

Ice reflects 50% to 60% of incoming solar heat.

Albedo is part of the energy from the sunlight that casts back into the atmosphere. These rays have a significant effect on our climate. When the albedo rises, the universe reflects light more and consequently, higher levels of radiation are sent back to space so the Earth cools down. Albedo determines the level of heat on the Earth. It is now well known that most of the light from the sun moves up once it hits the Earth. Research has shown that water absorbs light more thereby reflecting less light. If there is more water compared to a hard surface, then there is less solar emission. The Earth, the moon, or any other planet has the ability to transmit albedo.

What is Albedo?

Albedo can be defined as a way of quantifying how much radiation is reflected from the surface. It is a comparison between the reflection radiation from the surface to the amount of radiation that hits it. This term also refers to the quantity of radiation generated by electromagnetic rays which consequently reflects away.

Seasonal Effects on Albedo

Summer

To understand albedo better, we look at two scenarios. One, if you walk barefoot on the black soil during summer, you will feel a lot of heat and can even get burnt because the surface is absorbing and retaining more heat. Another person walking on white soil during the same season will not be burnt. This is basically because white surface tends to reflect more heat and absorb very little of it. Equally, if you touch a black car in summer it will feel much hotter than touching a white car. This is because black absorbs and retains heat while white car surface will reflect back the solar rays.

Winter

During this season, it is generally wet with either water or ice. Water reflects approximately 6% of the light and absorbs the rest. Ice, on the other hand, reflects 50% to 60% of the incoming solar heat, thereby remaining cooler. A snow-covered area reflects a lot of radiation, which is why skiers having a risk of getting sunburns while on the slopes. Albedo diminishes when the snow-covered places start to warm up.

How is Albedo Quantified?

Albedo helps us to know how well a surface reflects solar energy. It is measured on a scale of zero to one (0-1). Surfaces differ in absorbent ability but will always be in the range of between 0-1.

Value “0” - If a score of zero is given, then the conclusion is that the surface is highly receptive to light, meaning that the surface takes in all the light that comes into contact with it. It is characterized by black surfaces.

Value “1” - This score is evidence that the surface does not absorb incoming light. It is characterized by white surfaces.

The albedo of our planet is 0.367, whereas that of the moon stands at 0.12, meaning the moon reflects 12% out of the radiation that falls on it. There are many satellites set up to monitor the planet's albedo by use of sensors which measure the light from the Earth that reflects on the surface of the moon. NASA has set out what is called Terra and Aqua Satellites to assist identify any changes in albedo.

Various Studies

A. Danjon Studies (1928- 1954)

André-Louis Danjon, a French national, conducted studies on Albedo. He used an approach known as “The eyes of a cat”. He used light to make a bio image of the moon, permitting the sight checking of similarity and differences of the degrees of two research specimens of the moon surfaces. Using this approach, he ceased some light from the part with sunlight to correspond with the sunlight of the other side.

The research led to what is known as Danjon scale astrolabe which also led to enhanced accuracy of major visual astrometry. He further came up with a five-point measuring parameter for assessing the visual appearance and brightness of the moon when there is a total eclipse. He used letter “L” to denote high darkness.

L-O: Moon cannot be seen. This is characterized by the total to the medium dimness.

L-1: The details are visible but with some difficulty.

L-2: The shadows at the middle are very dim but the outer edge is a bit bright.

L-3: The umbral shadow has yellow color around it.

L-4: There is a blue looking shiny color around the moon. It has shades of either red or orange. It illuminates a lot of light.

Earth Surface Albedo Variations 1998- 2014

These were the second studies done within a total of sixteen years. During this period, man tried to understand the ratio of earthshine as compared to lunar shine. This was assessed both from the aerial satellites and on the ground for a period of sixteen years. The moon was the focus of the study.

De Pater and Lissauer Table of Albedo

De Peter and Lissauer categorized albedo into two sets namely Geometric and Bond albedo Geometric albedo means the quantity of radiation in comparison to the frequency which the wave's shape repeats itself while Bond albedo highlights the total radiation reflected from an object in comparison to the total incident radiation from the solar planets.

Albedo Drivers

The Albedo Effect and Warming of the Universe

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