Polarized Radiative Transfer in the CRTM

An important goal of this JCSDA-funded project is to compute the Stokes parameters (i.e., I, Q, U, and V) within the Community Radiative Transfer Model (CRTM), which will have important applications in cloud retrievals and in data assimilation by improved use of satellite instruments that measure partially or fully polarized radiation. For example, it has been shown that not accounting for polarization generated by clouds, atmospheric molecules and the ocean/land surface in retrieving cloud properties from reflected solar radiation can produce errors as large as 15% in the retrieved properties. Also, having the ability to compute polarized radiances will allow satellite instruments like WindSat, which measures fully polarized (Stokes vector) radiation at select microwave frequencies for observing the near-surface wind vector over the oceans, to be fully exploited in radiance data assimilation.

Our main effort will involve integrating an advanced vector adding-doubling RT model for solar wavelengths into the CRTM. At infrared and microwave wavelengths, there will also be an effort to utilize existing polarized (I, Q) 2-stream and 4-stream models as well as to develop a new vector Eddington RT model. The accuracy of these models will be evaluated under different conditions as compared to benchmark calculations made by the vector version of the discrete ordinate RT model (VDISORT).