Center for Earth Observation

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How to convert Landsat DNs to albedo

Albedo is an important property of the Earth surface heat budget. A simple definition of albedo (a) is the average reflectance of the sun’s spectrum. This unitless quantity has values ranging from 0 to 1.0 and will vary based on the land cover. For example snow would have a high value and coniferous forests a low value.

The input to the albedo calculation will be a Landsat image that has been converted from digital numbers to Top of Atmosphere (TOA) reflectance. Please refer to the FAQ Converting Digital Numbers to Top of Atmosphere Reflectance on this site for detailed instructions on how to accomplish this.

Liang (2000) developed a series of algorithms for calculating albedo from various satellite sensors. His Landsat formula to calculate Landsat shortwave albedo was normalized by Smith (2010) and is presented below.

    Where ρ represents Landsat bands 1,3,4,5, and 7. Note that Landsat band 2 (green) is not used.

This formula can be implemented in ENVI using Band Math as:

((0.356*B1) + (0.130*B2) + (0.373*B3) + (0.085*B4) + (0.072*B5) -0.018) / 1.016

Note: If you have areas outside of the image scene or mask area with values of 0.0 these will have a negative value. You should apply a mask to convert these fill values to NaN (Not a Number) before or after calculating albedo.

References

Liang, S. 2000. “Narrowband to broadband conversions of land surface albedo I algorithms.” Remote Sensing of Environment 76, 213-238.

Smith, R.B. 2010. “The heat budget of the earth’s surface deduced from space” available on this site

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