r_foursail {ccrtm}

R implementation of foursail (pure R)

Description

The pure R version of foursail is included in the package as an easy way to review the code, and to check more optimized versions against. Model originally developed by Wout Verhoef.

Usage

r_foursail(rho, tau, bgr, param)

Arguments

rho

input leaf reflectance from 400-2500nm (can be measured or modeled)

tau

input leaf transmittance from 400-2500nm (can be measured or modeled)

bgr

background reflectance. Usual input is soil reflectance spectra from 400-2500nm (can be measured or modeled)

param

A named vector of SAIL parameter values (note: program ignores case):

• [1] = Leaf angle distribution function parameter a (LIDFa)

• [2] = Leaf angle distribution function parameter b (LIDFb)

• [3] = Leaf angle distribution function type (see ?lidfFun)

• [4] = Leaf area index (LAI)

• [5] = Hot spot effect parameter (hspot) - The foliage hot spot size parameter is equal to the ratio of the correlation length of leaf projections in the horizontal plane and the canopy height (Verhoef & Bach 2007).

• [6] = Solar zenith angle (tts)

• [7] = Observer zenith angle (tto)

• [8] = Sun-sensor azimuth angle (psi)

Value

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).

Author(s)

Marco D. Visser (R implementation)