Dear Firyal Latrache ,

The albedo by definition is the reflection coefficient of the incident solar radiation.

It depends on the properties of the land surface. So, if the land surface does not change, one can assume that the albedo is consatnt with time.

So, you can assume the albedo consatnt with time if the surface does not change.

Best wishes

Thank you very much Dear Abdelhalim abdelnaby Zekry , your response helped me.

best wihes

If the land surface of the selected location changes then the albedo value will also change. But I think it is not possible in every hour.

Dear Firyal Latrache

During a day the albedo value changes, even when the material is the same. It is because that albedo is function of three things: (1) material, (2) light source condition, (3) geometry of the environment and the material itself (roughness).

To give you an example, for a single day, when the sky cloudiness changes the albedo also changes. Basically albedo is different for a clear and cloudy sky conditions. Also albedo is a function of Sun zenith angle, which changes over the course of the day. There are several literatures that confirm that albedo is a function of several parameters and changes over the course of a day. For instance, see the graph below, which shows a value of local albedo for fixed spot (for two days), see how it changes over the course the day.

I strongly recommend reading the attached article, in which all the albedo models are reviewed and a comprehensive albedo model was introduced. In the paper, you will also find a mathematical proof on the albedo variation over a course of day.

I hope that helps and let me know if you have further questions.

Best regards,

Hesan