Lesson 3: Background

Interpreting Satellite Visible Images

Imagine two layers, one of which overlies the other. The upper layer has flux transmittance and reflectance T₁ and R₁, and the lower layer T₂ and R₂. How much total flux R_T is reflected from the combination of layers? Some flux is reflected from the first layer (R₁); some of the flux transmitted through the first layer is reflected from the second layer and transmitted through the first layer (T₁R₂T₁); some of this flux reflected from the second layer is reflected back downwards, where some portion is reflected back up (T₁R₂R₁R₂T₁), and so on. Because reflection and transmission are both less than one, we can use the summation formula for geometric series to compute the total reflection is:

where the term in square brackets accounts for the multiple reflections between the layers. There is a similar relation for transmission.