An Overview on the JCSDA Community Radiative Transfer Model (CRTM) Version 2

The community radiative transfer (RT) model (CRTM) is developed by the US Joint Center for Satellite Data Assimilation (JCSDA) for rapid satellite radiance simulations and radiance derivative calculations under various sky and surface conditions. It has been used in the Gridpoint Statistical Interpolation (GSI) data assimilation system at the NOAA National Center for the Environmental Prediction (NCEP) Environmental Modeling Center (EMC) and systems at other Numerical Weather Prediction (NWP) centers, as well as in many other satellite radiance data applications. The model was first released to the public in 2004, and has been substantially improved and expanded since then. It supports a large number of sensors, including the historical and near future sensors, covering the microwave, infrared and visible frequency regions.

The model comprises four major modules for calculations of the atmospheric transmittance, surface emissivity/reflectivity, cloud/aerosol optical property and RT solution, respectively. In the atmospheric transmittance module, on top is the multiple transmittance algorithm framework, which allows different transmittance algorithms to coexist. Within the framework, a new transmittance algorithm has been recently implemented, which combines the strengths of the OPTRAN algorithm (Optical Path TRANsmittance) and the ODPS algorithm (Optical Depth in Pressure Space), currently used in the RTTOV model. In addition, special algorithms are implemented to take into account the Non Local Thermodynamic Equilibrium (NLTE) effects for the IR hyper-spectral sensors, Zeeman-splitting effect for the SSMIS sensors and CO2 cell pressure leaking effect for the SSU sensors. The surface emissivity/reflectivity module consists of four sub-modules corresponds respectively to the ocean, land, snow and ice surface, which are further divided into small modules according to the frequency regions and surface sub-types. An array of physical and empirical models has been implemented into CRTM. For calculations of cloud and aerosol absorption and scattering, lookup tables of the optical properties of six cloud and eight aerosol types are included in the cloud/aerosol optical property module. Finally, the fast doubling-adding method, implemented in the RT solution module, solves the multi-stream RT equation. In this presentation, an overview of the model capabilities and applications will be provided.