Airborne Doppler Radar Measurements - Development of the University of Wyoming Next Generation King Air and Examples from CAESAR

Airborne radars provide a beneficial perspective when researching clouds and precipitation. Vertically pointing antennas provide estimates of hydrometeor vertical velocity along the entire flight track. Furthermore, Reflectivity and velocity cross-sections have superior resolution; the observable range is small compared to horizontal scans and the moving platform doesn’t suffer from large contributing volumes like with RHIs. The greatest advantage is the ability to target clouds of interest, but a moving platform also introduces complexities. Space and power limitations require airborne systems to be smaller, transmit less, and use smaller wavelengths, but aircraft can fly close to cloud-top, improving detection of weaker reflectivity regions and avoiding rapid attenuation from low-level precipitation.

The University of Wyoming (UW) supports two mm-wavelength, airborne profiling radars, the Wyoming Cloud Radar (WCR) and the Ka-band Profiling Radar (KPR). The WCR can operate up to four narrow-beamwidth antennas (~0.7°) and uses a klystron amplifier for greater transmit power. The KPR is a 35 GHz Doppler radar with a 2.1° beamwidth that operates a nadir and zenith antenna simultaneously. It utilizes advanced pulse-compression techniques such as linear frequency modulation (chirp) and quadratic phase coding (QPC) to improve sensitivity while using a solid-state amplifier that fits in an under-wing PMS-style canister. Both radars were built, and recently upgraded, by ProSensing Inc in collaboration with the UW team and will be supported on the UW Next Generation King Air (UWKA). Airframe modifications to the new UWKA were completed in July 2024, including WCR ports that will allow up to four antennas for full-vertical profile, Dual-Doppler synthesis. In addition, a dual-polarization antenna is available for installation in the forward of zenith pointing direction for enhanced hydrometeor characterization. Together, with the suite of available microphysics instrumentation, the UWKA is an optimal platform for investigating cloud and precipitation physics and their underlying processes. The facility aircraft and instrumentation are available through the NSF Facility and Instrumentation Request Process (FIRP).

The WCR and KPR were recently installed on the NSF/NCAR C-130 as part of the Cold Air outbreak Experiment in the Sub-Arctic Region (CAESAR) based out of Kiruna, Sweden. In the early Spring, over the Norwegian Sea, the radars observed mixed-phase, shallow-convection driven by extreme heat and moisture fluxes into the arctic-sourced air. WCR operated three antennas: zenith, nadir, and aft-nadir (for below aircraft dual-Doppler), while KPR operated the nadir antenna only (i.e., dual-frequency observations exist below the aircraft). This presentation will use data collected during CAESAR to demonstrate the radars’ capabilities and expected performance on the NSF/UW new King Air research aircraft.