NUMERICAL SENSITIVITY ANALYSIS OF PASSIVE EHF AND SMMW CHANNELS TO TROPOSPHERIC WATER-VAPOR, CLOUDS, AND PRECIPITATION

Potential uses of specific Extremely High Frequency (EHF) and Sub-Millimeter-Wave (SMMW) channels at 90, 166, 183, 220, 325, 340, and 410 GHz for passive spaceborne remote sensing of the troposphere and lower stratosphere are investigated using an iterative numerical radiative transfer model. Collectively, these channels offer potential for high spatial resolution imaging using diffraction-limited apertures of practical size, along with the ability to profile water vapor, map precipitation beneath optically opaque cloud cover, and to measure nonprecipitating cloud (e.g., cirrus) parameters. The numerical study, along with the results of previous passive microwave experiments, suggests that a widely-spaced set of EHF and SMMW channels can yield observable degrees of freedom related to clouds and precipitation not available by exclusively using the more thoroughly studied microwave channels below 183 GHz. A new passive airborne imaging instrument for tropospheric meteorological sensing at 90, 150, 183+/-1, 3, 7, 220, and 325+/-1, 3, 9 GHz, the Millimeter-wave Imaging Radiometer (MIR), is described.