# Roujean BRDF¶

The BRDF object that implements the algorithm developed by Roujean et al. 1992. The algorithm is suitable for surface reflectance from a variety of terrains and is based upon three parameters, k0, k1 and k2 which the user must know a-priori or derive from measurements. The reader is referred to their paper for complete details.

## Example¶

import sasktranif.sasktranif as skif
import math

brdf = skif.ISKBrdf('Roujean')
brdf.SetProperty('SetPredefinedParameters', 8);
mjd            = 52393.3792987115;
location       = [0.0, 0.0, 25000.0, mjd];
mu_in          = math.cos( math.radians( 30.0 ) )
mu_out         = math.cos( math.radians( 60.0 ) )
cosdphi        = math.cos( mat.radians( 150.0 ) )
[ok,brdfvalue] = brdf.BRDF( 600.0, location, 0.6, 0.7, -0.8)


## Properties¶

BRDFParameters( param:array)

A 3 element array containing the 3 parameters of the Roujean distribution. For examples see Table 1 of Roujean et al. 1992.

n Setting
parameters[0] k0
parameters[1] k1
parameters[2] k2
SetPredefinedParameters( code: int )

An integer value that loads the Roujean BRDF parameters from an internal table of values. The table replicates the values published in Table 1 of Roujean et al. 1992. The table provides a visible setting (580 nm to 680 nm) and a near infra-red (NIR) setting (730 nm to 1100 nm). Pass in the appropriate code from the table below to select the appropriate BRDF setting

Terrain Visible Code NIR Code
PLOWED FIELD 1 21
ANNUAL GRASS 2 22
HARD WHEAT 3 23
STEPPE 4 24
CORN 5 25
ORCHARD GRASS 6 26
IRRIGATED WHEAT 7 27
PINEFOREST 8 28
DECIDUOUS FOREST 9 29
SOYBEAN 10 30
GRASS LAWN 11 31

## References¶

 [Roujean1992] Roujean, J.L., M. Leroy, and P.Y. Deschamps, “A bidirectional reflectance model of the Earth’s surface for the correction of remote sensing data”, J. Geophys. Res., 97(D18), 20455-20468, 1992, doi:10.1029/92JD01411.