ABSTRACT
A radio wave in the microwave/millimeter-wave band strongly interacts with ambient atmospheric particles like water vapor, oxygen, and hydrometeors. The effects of interaction are twofold. On the one hand, the atmospheric absorption, scattering, and refraction limit the performance of the microwave/millimeter-wave system, and on the other hand, this interaction allows the propagated wave to be used as the diagnostic tool for probing the lower atmospheric structure. Water vapor is perhaps the most important minor constituent that can affect the thermodynamic balance, photochemistry of the atmosphere, sun-weather relationship, and biosphere. The vertical and horizontal distribution of water vapor, as well as its temporal variation, is essential for probing into the mysteries of several effects. In fact, this triggered the need for the measurement of ambient water vapor for numerical weather prediction, short-term as well as severe storm forecasting. On the other hand, liquid water content measurement of clouds also provides very important input to the global circulation model (GCM).
