The Next Generation of Airborne Polarimetric Doppler Weather Radar: NCAR/EOL Airborne Phased Array Radar (APAR) Development

The NCAR Earth Observing Laboratory (EOL) is entering the third year of preliminary system design studies, engineering prototype testing and project management plan preparation for the development of a novel Airborne Phased Array Radar (APAR).  We have proposed a phased development approach so that we take measured steps, perform a proper assessment, evaluate and mitigate risk, and move forward using project management best practices as prescribed by the National Science Foundation (NSF).

This system being designed by NCAR/EOL will be installed and operated on the NSF/NCAR C-130 aircraft. The APAR system will consist of four removable C-band Active Electronically Scanned Arrays (AESA) strategically placed on the fuselage of the aircraft.  Figure 1 is a schematic of APAR AESA placement on the fuselage.  Each AESA measures approximately 1.8 x 1.9 m and is composed of ~3000 active radiating elements arranged in an array of line replaceable units (LRU) to simplify maintenance. 

Results have recently been made available from the Computational Fluid Dynamics (CFD) studies organized by the EOL Research Aviation Facility (RAF).  The study results show that either of two proposed external antenna configurations (so called blister and pedestal mounts) can be flown on the C-130.  Details of the study will be shown during the presentation.

APAR, operating at C-band, allows the measurement of 3-D kinematics of the more intense portions of storms (e.g. thunderstorm dynamics and tornadic development, tropical cyclone rainband structure and evolution) with less attenuation compared with current airborne Doppler radar systems. The radar is sensitive enough to provide high resolution measurements of winter storm dynamics and microphysics.   Maximum radar range is expected to be ~75 km depending on the final AESA power and hydrometeor attenuation at C-band.

Polarimetric measurements are not available from current airborne tail Doppler radars. However, APAR, with dual-Doppler and dual polarization diversity, will further advance the understanding of the microphysical processes within a variety of precipitation systems. Figure 2 depicts the 4-AESA APAR scanning a single forward angle from all four AESA faces.  Such unprecedented observations, in conjunction with the advanced radar data assimilation schema, will be able to address the key science questions to improve understanding and predictability of significant weather.

NCAR/EOL is working on several focused efforts to answer key design questions as we formulate the project development plans.  A Technical Requirements Document (TRD) has been written.  It includes the scientific rationale for the radar, technical requirements (AESA hardware), system calibration protocols, aircraft structural specifications, electrical and environmental considerations, radar maintenance, concept of operations, as well as an overview of risk and project management. 

One of the key approaches for the APAR development is to take advantage of the technical experience offered by industry in the design and fabrication of AESA components.  Industry has received and responded to a Request for Information (RFI) released by the University Corporation for Atmospheric Research (UCAR) in late Spring 2016.   The information provided by vendors is being used by EOL to assess the technical viability of our approach and to get a better estimate of cost to develop and fabricate the AESA. This information will be vital to the final preparation of a technical proposal and project management plan.

A key challenge for the APAR development is settling on an optimum antenna aperture configuration that balances size, shape and performance.  Recently, published results from Vivekanandan, et al. 2016 examine alternate configurations and simulation results.  These outcomes will be briefly summarized for this presentation.

The planned APAR development that would bring the system to operational readiness for research community use aboard the C-130 is expected to take ~7 years once major funding support is realized.  Project management plans have been prepared for the first phase (development and testing of a partial panel) and a more general plan for the full development.  The APAR Team is actively seeking partners in industry and in the university community.  An APAR science and engineering advisory panel has been organized.

This presentation summarizes the latest information on the project now underway to provide the research community with advanced sensing capabilities of a C-band phased array radar system.   The authors will review the overall APAR design and provide new details of the system based on our TRD, airflow studies, antenna aperture simulations and general information from the RFI responses. We will further outline the next steps needed to bring this exceptional tool into full operation. 

Reference:

Vivekanandan, J., E. Loew, P. Tsai, W-C. Lee and J. Moore Airborne Polarimetric Doppler Weather Radar: Trade-offs Between Various Engineering Specifications. 2016 IEEE International Symposium on Phased Array Systems and Technology, 18 - 21 October 2016 Waltham, MA USA.