Vectorized CRTM for the Simulation and Direct Assimilation of Satellite Radiances

Abstract:

The Community Radiative Transfer Model (CRTM) is a fast radiative transfer model used for the direct assimilation of satellite radiances in support of weather forecasting as well as for the generation of satellite environmental data records and to support satellite instrument calibration. However, the CRTM (v2.3) employed in the current Gridpoint Statistical Interpolation (GSI) data assimilation system is a scalar radiative transfer model in which only microwave surface emissivity is polarized. Neglecting other Stokes components will cause significant errors in simulating or assimilating the radiances in many spectral regions including the ultraviolet (UV).

Supported by the Proving Ground and Risk Reduction (PGRR) program, a new and enhanced CRTM solver has been developed to solve this problem. In addition, more absorption gases are included, and wavelength-dependent surface reflectance is introduced. Rayleigh scattering optical depth and depolarization ratio are used in accurate calculations, and the effect of rotational Raman scattering will also be considered. The optical properties for aerosols and clouds are extended to the UV region. Major efforts are devoted to tangent linear (TL) and adjoint model programming. This new version of CRTM (currently v3.0 beta) is expected to greatly improve the radiance simulations at the Top of Atmosphere (TOA) observed by reflective solar bands of a variety of radiometers. This project will pave the way for the direct assimilation of Ozone Mapping and Profiler Suite (OMPS) radiance data in global and regional NWP models. The impacts on weather forecasting are expected to be positive. It may also have broader impacts on satellite radiance simulation and assimilation for other radiometers.