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Potential Applications of the Proposed Phased Array Doppler Radar on the NSF/NCAR C-130 in Hurricane Reconnaissance

Wen-Chau Lee, J. Vivekanandan, Eric Loew and Jim Moore wenchau@ucar.edu

National Center for Atmospheric Research Boulder, CO 80307-3000

The Earth Observing Laboratory of the National Center for Atmospheric Research proposes to develop the next generation of airborne remote sensing instrumentation suite called CAPRIS (Community Airborne Platform Remote-sensing Interdisciplinary Suite). CAPRIS includes a centimeter (C- or X-band) dual-Doppler radar, a millimeter wave cloud radar, and several lidars to be installed on the NSF/NCAR C-130. The purpose of this paper is to discuss the design concept of this new airborne dual-Doppler radar system and its potential applications to hurricane reconnaissance missions in the United States.

As a tail Doppler radar is not an option for a C-130 platform, the proposed the proposed radar takes advantages of a fuselage conformal phased array design that are composed of thousands of Active Element Scanning Array (AESA) elements. In order to support both surveillance and dual-Doppler coverages, four fuselage conformal phased array antennas will be installed. Two side looking antenna will be mounted on each side of the C-130 fuselage behind the rear door, one on top of the fuselage and one on the rear cargo door. Each antenna can form fore and aft beams and also electronically scan a 90 deg sector, a scanning geometry similar to the NOAA P3’s tail Doppler radar. A complete 360 deg scan can be achieved by combining data from these four antenna. Due to the large surface area of the C-130 fuselage, this radar system can be either C- or X- band. A C-band system will have a beamwidth ~2 deg, slightly wider than the current P3 tail radar system. A X-band system will have a beamwidth ~1.4 deg, narrower than the current P3 system. Either system will have the dual-Doppler radar capability to deduce 3- D air motions at a spatial sampling ~500 m. Lower attenuation at C-band would enable the radar to probe deeper into rain bands in a hurricane reconnaissance.

To improve the hurricane intensity forecasts, a better description of the hurricane inner core structure to initialize numerical model relies on Doppler radar observations and assimilating these data into hurricane models. Technical feasibility of installing these phased array radars on the C-130 hurricane hunters opens new avenues for continuous monitoring of tropical cyclones by Doppler radars. In order to improve radar data quality, retrieve cloud microphysics and also accurately estimate precipitation amount, Doppler radar is augmented with a dual-polarization capability. Hence, not only real-time dual- Doppler radar winds can be deduced during reconnaissance missions, the polarimetric radar capability can also provide microphysical properties within the precipitation system so that both kinematics and microphysics information can be assimilated to numerical models.

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