DLM considers the asymmetric distribution of pigments, water and dry matter. The differences in light diffusion between adaxially and abaxially incident collimated light are modeled by introducing an abaxial diffusion parameter. Both adaxial and abaxial reflectance and transmittance of a wide variety of leaves can be accurately simulated with good precision.
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Reference:
Stuckens, J., Verstraeten, W.W., Delalieux, S., Swennen, R., & Coppin, P. (2009). A dorsiventral leaf radiative transfer model: Development, validation and improved model inversion techniques. Remote Sensing of Environment, 113, 2560-2573.