Surface Albedo As a tool of Estimation of Temperature

Surface albedo as, i already mention in my recent post that it a measure of surface reflectivity over earth surface. It may give us and prediction about the future temperature changes over an area. 

Landsat

Surface albedo if correctly documented if may serve as an important tool of estimating surface energy balance which is helpful in understanding the temperature rise trends over a region. Although surface albedo itself, is a very difficult phenomena to measure because of variation in temporal and spatial context. Varying terrain profile like steep and multiple slopes and flat surfaces makes it is more complex, also the elevation of a region also alters reflectance due to associated atmospheric transmissivity characteristics than lower elevations. 

Yeah! In real words actually it is a very difficult task to estimate the surface albedo and to correlate it with the temperature rise. Here i am illustrating an estimation methodology which is based on the certain assumptions; they are

1. Assume the earth surface as "Lambertian surface" with equal reflectance of direct and diffuse irradiance 

2.  Vegetative cover over that study area should be same in nature (must have same vegetation canopy) 

Keeping above assumptions in mind if we proceed for estimation of surface albedo, then we have to necessary requirements 

1. Estimation data

2. Methodology 

Data required for estimation purpose are satellite imagery, and associated DEM for the same study area. By using the satellite image processing technique we can analyze the images to characterize the surface albedo. If we choose Landsat Thematic Mapper data for this purpose then we have two problems 

1. Sensor has only limited off-nadir pointing capability

2. It does not provide the continuous sensitivity to the entire solar spectrum.

When going for measurement of surface albedo one should keep in mind the some correction for topography and atmosphere. 

Procedure:

1. Geo-referencing of satellite images to the UTM using nearest neighbor technique. 

Original and supervised classified image

2. Classification of image (supervised or unsupervised)

3. Calculation of in band reflectivity  

4. Extrapolation of broad band albedo

After understanding the above method, one can calculate the surface albedo. The method includes procedure for atmospheric correction, topographic normalization, and extrapolation of broad band albedo from narrow band satellite measurements which is only mention above for detailed study one can refer various articles and literature. Above method cannot be applied for non Lambertian Surfaces. Angle of illumination effect on various vegetation canopies is different. And may or may not have pronouncing effect on a particular type of vegetation canopy. Like in comparison of alpine tundra vegetation, agriculture vegetation canopy have more pronounced effect. 

Estimation the surface albedo over a region and by calculating the changes in the different land cover uses over a particular area, we can also correlate the surface albedo to the changes in the temperature.