r_foursail: R implementation of foursail (pure R)

In MarcoDVisser/ccrtm: Coupled Chain Radiative Transfer Models

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)

MarcoDVisser/ccrtm documentation built on Feb. 19, 2025, 1:15 p.m.