Albedo vs Reflectance
Albedo and reflectance are two important concepts discussed in reflection of electromagnetic waves. These two concepts hold a great significance in fields such as astronomy, chemistry, geology and even biology. It is crucial to have a clear understanding of these two concepts in order to excel in such fields. In this article, we are going to discuss what albedo and reflectance are, definitions of albedo and reflectance, their applications in the relevant fields, their similarities, and finally the difference between albedo and reflectance.
What is Reflectance?
Reflectance is defined as the fraction of incident electromagnetic power that is reflected at an interface. This must not be confused with the electric field reflected at the interface. The term “reflection coefficient” describes the fraction of electric field that is reflected at an interface. However, this “reflection coefficient” is also connected to the reflectance. This reflection coefficient can be determined using the Fresnel’s equation. It can take either real or complex value. The reflectance of a surface is the magnitude of the square of the reflection coefficient. The reflectance of a surface is always positive. If the reflectance of an object is zero, it means that the object does not reflect any of the electromagnetic waves, which are incident on the object. All this EM waves are absorbed, and the object cannot be seen using any optical or electromagnetic method. If the reflectance of an object is 100%, it means the object does not absorb any electromagnetic wave falling on the object. Such objects are perfect reflectors. Reflectance and reflectivity are two different concepts; reflectivity is a property of thick objects. It can be defined as the highest value the reflectance can get. As the object gets thicker, the reflectance value becomes more independent of the nature of the back surface. The reflectance of an object with a large thickness would only depend on the nature of the interface.
What is Albedo?
Albedo is defined as the ratio of reflected radiation from the surface to incident radiation upon it. The albedo of an object depends on the frequency of the incident wave. This is also known as reflection coefficient and diffuse reflectivity. The albedo of an object is a property of the surface. When the albedo of an object is given without the frequency, it generally means the albedo of the visible range is averaged to get the value. Albedo is a very important property in astronomy. The albedo values of the objects in the solar system determine their visibility. This is because they do not generate any power. What we see is the reflected light from the sun.
What is the difference between albedo and reflectance?
• Reflectance is defined for an interface of two media while albedo is defined for a surface.
• Reflectance depends on the medium of the incident wave, but albedo does not depend on the medium of the incident ray.
• The reflectance may depend on the depth of the surface but albedo does not.