Dual Frequency Millimeter-Wave Radar-Radiometer System for Volume Imaging of Clouds

The role of clouds in regulating fluxes of incoming solar radiation and upwelling infrared radiation is a poorly understood factor affecting global climate. In this project, a high-range-resolution (1m) scanning radar/radiometer system will be designed specifically to test cloud model predictions. The proposed radar will operate in the atmospheric transmission window centered at 35 GHz, which will provide high sensitivity and fine spatial resolution in a compact design. In addition, by adding a parallel radiometer channel at each frequency, the system will be able to estimate cloud liquid water content and correct the radar signal for attenuation. During Phase I, (1) the hardware needed to implement a parallel 35 GHz radiometer channel was developed and used to test the beam efficiency of a high performance 35 GHz Cassegrain antenna; (2) the mechanical design of a liquid cooled radar enclosure, suitable for all-weather operation, was completed; and (3) the feasibility of making high resolution millimeter-wave Doppler spectrum measurements in precipitation was demonstrated using a low power radar. Phase II will build a high power 35 GHz scanning cloud radar/radiometer with programmable range resolution as fine as 1.0 meter. The radar will employ the high performance Cassegrain antenna tested during Phase I, and the entire system will be mounted on a heavy duty elevation-over-azimuth pedestal. Commercial Applications and other Benefits as described by the awardee: Commercial sales of this system are anticipated for future ground-based and airborne atmospheric research radars applied to the study of cloud microphysics and fine-scale atmospheric turbulence, and for cloud model verification