A C implementation of the Geometric Optic Radiative Transfer model as described in Ni et al. (1999). Models the BRDF of forests at optical wavelengths by calculating the viewed proportions of illuminated and shaded crown and ground, and their reflectance factors, for randomly located ellipsoids.
This version of the model was originally used as the forward operator for data assimilation experiments described by Quaife et al. (2008).
- Calculates BRDFs for arbitrary view-illumination geometry and from 400nm to 2500nm.
- Calculates spectral albedo and absorption by the forest (e.g. fAPAR).
- Coupled to PROSPECT-D to (optionally) provide leaf optical properties.
- Soil reflectance using EOFs from Price (1990).
- Reads/writes LUTs of key intermediate variables to speed up some applications.
Dr Tristan Quaife & Dr Wenge Ni-Meister
With the exception of the contents of the PROSPECT-D directory all code was written by Tristan based on the equations described in Ni et al. (1999) or, in the case of the KOpen probability routines, translated directly from Wenge's code.
Information about PROSPECT authorship can be found at http://teledetection.ipgp.jussieu.fr/prosail/
usage: gortt [options] < angles.dat > output.dat
A list of [options] and brief description of the format of the angles.dat file can be found by typing:
gortt -u
The following example calculates the reflectance for a forest with an LAI of 4.0 at wavelengths of 450nm, 600nm and 1000nm for a view zenith of 10 degrees, solar zenith of 30 degrees and relative azimuth of 20 degrees.
echo -en "1 4 450 600 800 1000\n10 0 30 20\n"|./gortt -LAI 4.0
I have only ever tried installing on Linux platforms. As long as you have the standard development tools installed (specifically gcc, gfortran and make) it should just be a case of typing make. Note that currently the C bindings for the PROSPECT are throwing a number of warnings. As far as I can tell these are harmless.
Ni, W., Li, X., Woodcock, C. E., Caetano, M. R., & Strahler, A. H. (1999). An analytical hybrid GORT model for bidirectional reflectance over discontinuous plant canopies. IEEE Transactions on Geoscience and Remote Sensing, 37(2), 987-999.
Price, J. C. (1990). On the information content of soil reflectance spectra. Remote Sensing of Environment, 33(2), 113-121.
Quaife, T., Lewis, P., De Kauwe, M., Williams, M., Law, B. E., Disney, M., & Bowyer, P. (2008). Assimilating canopy reflectance data into an ecosystem model with an Ensemble Kalman Filter. Remote Sensing of Environment, 112(4), 1347-1364.