1. Report of the 3D RT working group of IRC Alexander Marshak & Jean-Luc Widlowski IRC business meeting, 26 th July 2009, Montreal, Canada

2. I3RC status (I3RC is an ongoing project initiated in the late 1990s) Objectives - comparing methods available for 3D atmospheric RT calculations - providing benchmark results for testing 3D RT codes - publishing an open source toolkit (community 3D MC code) - providing resources related to I3RC and 3D RT (codes, models, workshops, publications) Activities I3RC community code for 3D radiative transfer - A new version of the I3RC community MC model of 3D RT has been released in March, 2009; -The performance of the code is documented in the manuscript: "Computational cost and accuracy in calculating three-dimensional radiative transfer: Results for new implementations of MC and SHDOM” by R. Pincus and K.F. Evans (to appear in JAS); - The code has been beta-tested; - Over 30 downloads since March 2009; -Open Source Licensing to encourage further development and widest usage.

3. Plans - 3D RT Workshop 2011/2012; - I3RC involvement in possible model verification subgroup of CEOS/WGCV; - building an online 3D RT calculator for online comparisons with benchmark results; - creating an educational web pages on 3D RT; - adding k-distribution for gaseous absorption to the I3RC community code. Phase 3 of I3RC - Results from the 3 rd phase have been analyzed and documented on the I3RC homepage - A poster with results of I3RC Phase 3 was presented at IRS 2008 (Iguacu, Brazil). - A presentation on the Intercomparison of Lidar Simulation Models (I3RC Phase 3 Case 7) has been given on the International Conference on Mathematics, Computational Methods & Reactor Physics (Saratoga Springs, NY, 2009). An extended abstract has been published. - I3RC and 3DRT related resources ( codes, models, publications ) have been significantly expanded Lidar pulses in optically thick cloudsBroken Cu clouds observed by Terra over Brazil http://i3rc.gsfc.nasa.gov/

4. RAMI status (RAMI is an ongoing project initiated in the late 1990s) Objectives - to act as common platform for comparison efforts of canopy RT models - document uncertainties and errors among canopy RT models, - to establish protocols for the evaluation of RT models - to foster scientific debate Activities RAMI On-line Model Checker (ROMC) - web-based facility to provide quasi real time comparison results with respect to six ‘credible’ Monte Carlo models identified during RAMI-3 - over 30 canopy RT models registered; - ROMC graphs used as ‘proof of model quality’ in scientific publications. http://romc.jrc.it/

5. Plans - analyse RAMI4PILPS data (2009), writing of report/manuscript (2010) - conclusion of second part of RAMI-IV (end 2009), analysis of results (2010) - presentation of results in scientific meeting and publication online (2010); RAMI4PILPS (submission closed in May 2009) - addresses quality of Land surface schemes in SVATs, NWPMs & GCMs - supported by GLASS/GEWEX - deals only with shortwave fluxes - forward mode for 1D canopies - assimilation mode for 3D canopies - 9 groups have submitted results RAMI-IV (on-going until late 2009) - complete set of new test cases - increased realism of spectral and structural properties of test cases, - increased realism of simulated ‘data’ - 2 submission deadlines (mid/end 2009) - 10 groups submitted results http://rami-benchmark.jrc.it/

6.  intensify the collaboration between cloud and surface 3D RT modelling activities, possibly by setting up a field experiment where detailed measurements of canopy structure, its spectral properties and the incident radiation at the top-of-the-canopy are acquired concurrently with atmospheric composition measurements (ideally for known satellite overpass times) to constitute a possible test case for a future I3RC/RAMI phase.  space agencies and funding agencies to increase/standardise their quality requirements for cloud and surface RT models when used in operational algorithm development, scientific research proposals and future mission concept studies. A vehicle for this could be to make some sort of model grading or certification available via the IRC's 3D RT activities and to update these regularly (perhaps even through an automated web-based interface). Recommendations of the 3D RT working group