Weather Calibration Efforts on the Advanced Technology Demonstrator

Polarimetric phased array radar (PPAR) technology is being considered as one of the candidate platforms for the next generation of weather radars. The unique electronic beam steering capability, inherent in PPAR, provides for the enhanced weather surveillance strategies that are envisioned to improve the weather radar products. However, one of the major technical issues related to the use of PPAR technology for weather surveillance is the calibration needed to produce the quality of measurements comparable to the parabolic-reflector antenna systems. Unlike the latter systems, PPARs are plagued with the existence of significant cross-polar antenna patterns which induce cross coupling between returns from the horizontally and vertically oriented fields resulting in the biases of polarimetric variable estimates. Furthermore, the antenna patterns which vary as horizontal and vertical beams are electronically steered in various directions, as consequence produce the scan-dependent measurement biases.

Through a joint collaboration of the National Oceanic and Atmospheric Administration and the Federal Aviation Administration, the Advanced Technology Demonstrator (ATD) was installed in Norman, OK in 2018. This state-of-the-art radar system will be used to evaluate the performance of PPAR for weather observations. It consists of an S-band planar PPAR that is being developed and integrated by the National Severe Storms Laboratory (NSSL), MIT Lincoln Laboratory, and General Dynamics.

The ATD calibration infrastructure includes a far-field calibration tower, located in the vicinity of the ATD site. Atop the tower is an S-band standard gain horn attached to a motorized platform that allows it to rotate about its axis and set the horn polarization in horizontal, vertical or any other desired position. For the purpose of weather calibration, this infrastructure is to be used to conduct accurate antenna beam-peak measurements of the fielded array. Accurate beam peak measurements of copolar patterns can be used to correct the scan-dependent measurement biases. Herein, we present the latest efforts aimed at the ATD weather calibration.