An Advanced Multi-Frequency Radar for Atmospheric Research

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This is a Major Research Instrumentation award that supports the development of a portable, three-wavelength scanning radar designed for meteorological research. Called the Advanced Multi-Frequency Radar (AMFR), it consists of a single antenna capable of transmitting and receiving frequencies in the Ku-band (13 GHZ), Ka-band (33 GHz), and W-band (95 GHz). (These frequencies correspond respectively to wavelengths of 2.2, 0.91, and 0.32 cm.) Each of the three radar systems will be capable of both Doppler and polarization measurements. The PI has already developed a dual-wavelength radar called the Cloud Profiling Radar System (CPRS), which operates at 0.9 and 0.3 cm. This award enables the addition of the third radar having 2.2 cm wavelength, the construction of a new antenna, and improvement of the sensitivity of the existing systems at 0.9 and 0.3 cm. A unique feature of the radar is a system of feeds designed to insure that the single antenna produces collocated, matched beams for the three wavelengths. Measurements at all wavelengths will thus be from the same volume of cloud. The AMFR will be highly portable and relatively inexpensive to deploy. Applications will be primarily to cloud microphysics. Initial emphasis will be on layer clouds and precipitation processes in winter storms. The radar will be able to detect some precipitation-free clouds, at least at the shorter wavelengths. Moreover, rain and snow, when present, give different signals at the three receivers because the polarization characteristics of precipitation and the deviations from Rayleigh scattering both depend on wavelength. These signals can be employed in various ways to distinguish rain from snow and to give information on the shape of ice-phase precipitation particles, the drop-size distribution in rain, and the variation of these quantities with height and time. Measurements of this kind will give new insight on the formation and evolution of precipitation, contributing fundamentally to cloud physics and providing information needed to improve the treatment of precipitation in mesoscale and climate models.