NPOL : The NASA transportable S-band dual-polarimetric Radar. Antenna system upgrades, performance and deployment during MC3E

In 2000, NASA designed a new dual polarization portable S-band weather research radar using commercially available components except for the antenna system. Specifications for the antenna and pedestal performance were taken from those used for the NSF CHILL radar. The winning bidder proposed an innovative antenna design (FLAPS) using crossed dipoles and a mesh structure. The result was light weight, easy to assemble and economical to deploy. Unfortunately the design had a fundamental flaw and the polarimetric performance did not meet research quality standards. Because the NPOL serves as a critical tool for NASA precipitation research and in particular, ground validation activities, the NASA Precipitation Science Program recently replaced the antenna and pedestal systems with a larger reflector (8.5 m diameter, 0.9 degree beam width) using a conventional center fed parabolic dish.

The system transmit, receive and antenna performance were all recently evaluated by operating and calibrating the radar on site next to the CSU-CHILL radar in Greely, Colorado. The results of these tests followed by subsequent testing and calibration checks in Oklahoma during a first deployment are very encouraging.

The first field campaign deployment for the modified NPOL system supported ground validation research for the NASA Global Precipitation Measurement (GPM) mission was during the Mid-Latitude Continental Convective Clouds Experiment (MC3E) held in northern Oklahoma. This paper describes the new NPOL system, its performance, and presents preliminary results from the MC3E deployment.