The accurate and rapid computation of the infrared emission of the Earth's atmosphere at high spectral resolution is important to the development of algorithms for retrieving geophysical quantities from hyperspectral satellite observations. Variations in the microphysical properties of clouds, in terms of the phase, size distribution, number density, and vertical distribution, make the inclusion of clouds less than straightforward.

The influence of clouds on the top-of-atmosphere radiance is parameterized into cloud transmittance and reflectance functions with the aid of a well tested multiple scattering code (DISORT). Computations are performed for both ice and liquid clouds for a range of effective droplet diameters, cloud optical depths and observation zenith angles at 201 wavenumbers covering the spectral range from 500 to 2500 wavenumbers. Coupled with a clear sky fast model, the resulting database of polynomial fitting coefficients enables the rapid simulation of hyperspectral observations of top-of-atmosphere radiance in the presence of clouds.

The fidelity of this approach to modeling cloudy radiances is verified by taking simulations from a fast model configured for the Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS)instrument channels and comparing with equivalent simulations from a line-by-line radiative transfer code coupled with DISORT. Initially developed to simulate single phase clouds of one layer, this approach is now being tested on multi-layer, mixed phase clouds. We present our findings on the speed and accuracy of our approach for a range of observation scenarios.