The librat model is the 'forward' version of the drat model, that is, within librat the rays are traced from the source to the viewer. librat features the same capabilities as the drat model.
The model is now written as a stand-alone library now, so the core function calls can be incorporated into any code quickly and easily.
Huang, H., M. Chen, and Q. Liu,
Three-dimensional plant modelling for remote sensing simulation studies using the botanical plant modelling system,
Agronomie - Agriculture and Environment, 19,1689 185-210.
Disney, M. I., Lewis, P., Bouvet, M., Prieto-Blanco, A. and Hancock, S.,
Quantifying surface reflectivity for spaceborne lidar via two independent methods,
IEEE Transactions on Geoscience and Remote Sensing, 47(10), doi: 10.1109/TGRS.2009.2019268.