Radiation transfer model intercomparison (RAMI) exercise

TLDR

The study focuses on terrestrial radiation transfer, using abstractions of typical homogeneous and heterogeneous scenes. The paper presents the rationale, protocol, and evaluation procedures of RAMI, proposes quantitative assessment of model discrepancies, and outlines future expansion to more complex systems and inverse problems. The first‑phase RAMI intercomparison involved eight one‑ and three‑dimensional models simulating radiation for defined terrestrial scenes and illumination conditions, with the resulting fields compared, documented, and analyzed according to a newly proposed protocol and evaluation procedures. The intercomparison showed that, despite diverse models, the community can generate comparable radiation fields, and the analysis identified outliers and their key deficiencies.

Abstract

The community involved in modeling radiation transfer over terrestrial surfaces designed and implemented the first phase of a radiation transfer model intercomparison (RAMI) exercise. This paper discusses the rationale and motivation for this endeavor, presents the intercomparison protocol as well as the evaluation procedures, and describes the principal results. Participants were asked to simulate the transfer of radiation for a variety of precisely defined terrestrial environments and illumination conditions. These were abstractions of typical terrestrial systems and included both homogeneous and heterogeneous scenes. The differences between the results generated by eight different models, including both one‐dimensional and three‐dimensional approaches, were then documented and analyzed. RAMI proposed a protocol to quantitatively assess the consequences of the model discrepancies with respect to application, such as those motivating the development of physically based inversion procedures. This first phase of model intercomparison has already proved useful in assessing the ability of the modeling community to generate similar radiation fields despite the large panoply of models that were tested. A detailed analysis of the results also permitted to identify apparent “outliers” and their main deficiencies. Future undertakings in this intercomparison framework must be oriented toward an expansion of RAMI into other and more complex geophysical systems as well as the focusing on actual inverse problems.