An efficient radiative transfer model for hyperspectral IR radiance simulation and applications under cloudysky conditions

Abstract

An efficient radiative transfer model has been developed for hyperspectral infrared radiance simulation under both clear- and cloudy-sky conditions. The hyperspectral IR cloudy radiative transfer model (HIRTM) combines atmospheric transmittances due to molecular absorption and cloud absorption and scattering from cloud hydrometeors. An efficient analytical Jacobian methodology is also developed under both clear- and cloudy-sky conditions, which is needed both to assimilate cloudy radiances directly into numerical weather prediction models and to retrieve atmospheric soundings and cloud properties simultaneously from cloudy radiance measurements. In comparing HIRTM and its analytical Jacobian with the community radiative transfer model (CRTM), our research has shown that HIRTM’s Jacobian calculations are similar to those of CRTM. HIRTM and CRTM synthetic observations derived from model output are compared with corresponding real observations from Geostationary Operational Environmental Satellite 13 Imager observations, and both perform similarly under water clouds, while CRTM is colder than HIRTM for thick ice clouds.