Plans for the polarimetric upgrade to the Shared Mobile Atmospheric Research and Teaching (SMART) radars

This paper will describe the planned polarimetric upgrade to one of the mobile C-band Doppler radars that is part of the SMART radar program. The most significant modification will be an antenna-mounted receiver with a four port dual-position waveguide switch that routes the transmitted pulse through a magic T to provide a dual-polarimetric simultaneous transmit and receive (STaR) capability. To ensure high signal quality at C-band on a mobile platform the existing 2.4 m diameter reflector will be replaced with a 3.1 m reflector that has high cross-polarimetric isolation and low sidelobe characteristics. Given highway clearance restrictions, the increased dimension of the antenna requires a vehicle with a lower deck than that on the existing SMART radar. When completed, the 1.2 degree beam-width C-band radar will measure differential radar reflectivity, differential phase, and cross-polarization correlation in addition to the normal spectral moments. We will also be able to record time series (inphase and quadrature components) to generate raw power spectra for each of the range bins in each beam.

The platform used for the existing C-band radar will become the platform for a new X-band polarimetric radar dubbed the NSSL-OU X-band Polarimetric (NO-XP) radar. The NO-XP design consists of a transmitter with a microwave signal splitter before the pedestal. This provides the STaR capability without using an antenna-mounted receiver. The completed X-band radar will be a 1.0° beamwidth dual-polarimetric radar capable of measuring the same suite of variables as the C-band polarimetric radar.

Mobility will enable the systems to be used in a wide range of studies including: quantitative rainfall estimation in land-falling hurricanes; hydrometeor classification in mesoscale convective systems and supercell thunderstorms; the relationships between cloud dynamics, microphysics, and electrification (making use of the complimentary 3-D lightning mapping system in central Oklahoma); the impact of assimilating polarimetric data in numerical weather prediction; and fundamental interpretation of polarimetric signatures at frequencies that are affected by resonance. In keeping with the collaborative nature of the SMART radar program, both of the new polarimetric radars will be made available to other users. Thus, these systems will become part of the national infrastructure for atmospheric science research and education.