Third Radiation Transfer Model Intercomparison (RAMI) exercise: Documenting progress in canopy reflectance models

• Published in: Journal of Geophysical Research 2007-05, Vol.112 (D9), p.D09111:1-n/a
• Main Authors: Widlowski, J.-L., Taberner, M., Pinty, B., Bruniquel-Pinel, V., Disney, M., Fernandes, R., Gastellu-Etchegorry, J.-P., Gobron, N., Kuusk, A., Lavergne, T., Leblanc, S., Lewis, P. E., Martin, E., Mõttus, M., North, P. R. J., Qin, W., Robustelli, M., Rochdi, N., Ruiloba, R., Soler, C., Thompson, R., Verhoef, W., Verstraete, M. M., Xie, D.
• Format: Article
• Language: English
• Subjects: absorption; digital hemispherical photography; Earth sciences; Earth, ocean, space; Ecology, environment; Ecosystems; Exact sciences and technology; leaf orientation; Life Sciences; model intercomparison; plant canopies; project; radiative transfer; scattering; solar-radiation; surface; validation; vegetation canopies; vegetation canopy
• ISSN: 0148-0227; 2169-897X; 2156-2202; 2169-8996
• DOI: 10.1029/2006JD007821

The Radiation Transfer Model Intercomparison (RAMI) initiative benchmarks canopy reflectance models under well‐controlled experimental conditions. Launched for the first time in 1999, this triennial community exercise encourages the systematic evaluation of canopy reflectance models on a voluntary basis. The first phase of RAMI focused on documenting the spread among radiative transfer (RT) simulations over a small set of primarily 1‐D canopies. The second phase expanded the scope to include structurally complex 3‐D plant architectures with and without background topography. Here sometimes significant discrepancies were noted which effectively prevented the definition of a reliable “surrogate truth,” over heterogeneous vegetation canopies, against which other RT models could then be compared. The present paper documents the outcome of the third phase of RAMI, highlighting both the significant progress that has been made in terms of model agreement since RAMI‐2 and the capability of/need for RT models to accurately reproduce local estimates of radiative quantities under conditions that are reminiscent of in situ measurements. Our assessment of the self‐consistency and the relative and absolute performance of 3‐D Monte Carlo models in RAMI‐3 supports their usage in the generation of a “surrogate truth” for all RAMI test cases. This development then leads (1) to the presentation of the “RAMI Online Model Checker” (ROMC), an open‐access web‐based interface to evaluate RT models automatically, and (2) to a reassessment of the role, scope, and opportunities of the RAMI project in the future.