sail_BDRF: The SAIL BDRF function
In ccrtm: Coupled Chain Radiative Transfer Models

The SAIL BDRF function

1 2	sail_BDRF(w, lai, sumint, tsstoo, rsoil, rdd, tdd, tsd, rsd, tdo, rdo, tss, too, rsod)

`w`	goemeric reflectance parameter
`lai`	leaf area index
`sumint`	exp int
`tsstoo`	Bi-directional gap fraction
`rsoil`	background reflectance
`rdd`	Bi-hemispherical reflectance over all in & outgoing directions (white-sky albedo).
`tdd`	Bi-hemispherical transmittance (diffuse transmittance in all directions)
`tsd`	Directional hemispherical transmittance for solar flux
`rsd`	Directional hemispherical reflectance for solar flux (diffuse solar angle)
`tdo`	Directional hemispherical transmittance (diffuse in viewing direction)
`rdo`	Directional hemispherical reflectance in viewing direction
`tss`	Direct transmittance of solar flux
`too`	Direct transmittance in viewing direction
`rsod`	Multi scattering contribution

spectra matrixwith 4 reflectance factors and canopy transmission for wavelengths 400 to 2500nm:

[1] = bi-hemispherical reflectance (rddt). White-sky albedo: the reflectance of the canopy under diffuse illumination. The BRDF integrated over all viewing and illumination directions.
[2] = hemispherical directional reflectance (rsdt). Black-sky albedo: reflectance of a surface under direct light without a diffuse component. It is the integral of the BRDF over all viewing directions.
[3] = directional hemispherical reflectance (rdot). Diffuse reflectance in the vieweing direction.
[4] = bi-directional reflectance (rsot). The ratio of reflected radiance in the viewing direction to the incoming radiant flux in the solar direction.
[5] = Canopy transmission of diffuse light through the canopy (taud).
[6] = transmission of direct light through the canopy (taus).