Albedo is the term that describes the reflectance of sunlight onto Earth's surface. For different surfaces its value vary from 0 – 1, where a value of 0 indicates that 100 % of the light is absorbed while a value of 1 means that all of the light is instead reflected.
It is considered a fundamental atmospheric parameter that has deep implications on temperature and therefore, climate change. The heat energy budget is directly affected by the albedo, as it holds a key role in the process by which our planet achieves an equilibrium between the solar radiation which enters the atmosphere and is afterwards emitted as heat radiation into space, in considerably longer wavelengths.
By designing and building a suitable apparatus IRIS wishes to examine the reflectance of the surfaces found in the ground and atmosphere of the polar region; to perform measurements in the infrared (IR) and visible (VIS) spectrum. There are several factors that determine the albedo:
· Microphysics and type of clouds
· Solar Zenith Angle (SZA)
· Species, health and quality of vegetation also known as Red-edge
· Type of ground
One large difficulty in measuring surface albedo is the fact that atmospheric scattering affects the obtained values, even at relatively low altitudes, and correcting this effect requires a vast knowledge about the atmospheric composition at the measurement site. This information may not always be available, especially if one considers that the various layers of the atmosphere are very different to each other.
The SZA is an essential parameter to be studied in order to correctly calculate the local albedo of an area, since it affects the albedo in a deterministic way. It is the angle formed between the zenith and the midpoint of the sun disk. It portrays the amount of radiation received from the sun on a horizontal surface, and therefore the influence of the sun’s angle with the reflectance of surfaces. The SZA is calculated as a function of time, day number and latitude. Most surfaces reflect more light the lower the sun is on the horizon, but studies show that snow appears to be an exception to this case; showing almost no variation and in some cases even a decreasing albedo for larger SZA.
Effects of the Solar Zenith Angle
The importance of clouds
Depending on their height, temperature, thickness and composition clouds play a major role to radiation scattering. This is because they consist of various droplet formations which size of effective radius has different scattering properties. Along with the anthropogenic aerosol particles and their absorption properties, these characteristics greatly affect their albedo and radiation scattering.
Cold cloud and snow albedo vary significantly in their absorption and reflectance properties, regardless of the fact that they are both white and have a very low temperature. IRIS wishes to differentiate between cold clouds and snow on the ground.
The Red Edge
The “red edge” is a spectral signature characteristic of terrestrial vegetation. This is due to the strong absorption by chlorophyll in the red region, in contrast with a strong reflectance in the near-infrared. IRIS will use this property to observe vegetation and distinguish between living and dead plants in order to detect and describe the anomalies in the terrestrial albedo.
As the albedo reflection indirectly affects vegetation, and therefore the climate circle of the next year, we would like to combine our data with albedo measurements of previous years and see its connection and effects of climate change in the arctic.