Users' guide to WPL microwave radiative transfer software

This document describes a computer program that the NOAA Wave Propagation Laboratory (WPL) developed to simulate the brightness temperatures (Tb) observed by an upwardlooking microwave radiometer system along a vertical or slant path. FORTRAN source code listings are included as an appendix. WPL uses this software to calibrate radiometers, to simulate hypothetical radiometer systems, and to develop retrieval techniques. The program computes dear-sky Tb from radiosonde profiles of pressure, temperature, and humidity after extrapolating them to 0.1 mb and interpolating between levels where necessary to approximate a continuous atmosphere. Clear-sky attenuation is calculated from the Liebe and Layton water vapor and oxygen absorption model, which is valid for frequencies up to 1 THz. An optional doud-modeling scheme permits simulations under a variety of doud configurations. The Rayleigh approximation that underlies the doud absorption algorithm restrids its validity to nonpredpitating douds with partide radii less than about 100 pm; scattering is neglected. Hence, the cloudy Tb simulations are valid only for frequendes less than 100 GHz.