SAIL (Scattering by Arbitrary Inclined Leaves) is one of the earliest canopy reflectance models (Verhoef, 1984, 1985) to simulate the bidirectional reflectance factor of turbid medium plant canopies, by solving the scattering and absorption of four upward/downward radiative fluxes.

ARTMO's  4SAIL input window.

The FLIGHT model (North, 1996) is based on Monte Carlo simulation of photon transport, and has been developed to simulate the observed reflectance response of three-dimensional vegetation canopies. 

ARTMO's  FLIGHT input window.

INFORM (Atzberger, 2000; Schlerf & Atzberger, 2006) is a SAIL-like canopy model modified to simulate forest canopies. The model considers tree geometry and density.

ARTMO's  INFORM input window.