Rapid Calculation of Microwave Opacity and Transmittance for Water-Vapor Atmospheric-Sounding Channels

By approximating a line-by-line calculation of atmospheric transmittance with simplified analytical expressions for effective opacity, upwelling brightness temperatures for five passbands in the 183-GHz water-vapor line are obtained with the fidelity of 0.04 K or better in the mean and 0.06 K or better standard deviation. The effect of weak ozone lines in or near the passbands is included by calculating their passband-average opacity. The passband-average opacity due to the water line is corrected to passband-average transmittance by a linear adjustment.