Summary
The Federal Aviation Administration (FAA) is deploying a Weather Systems Processor (WSP) for the current-generation Airport Surveillance Radar - ASR-9. This modification exploits the coherency of the ASR-9 to perform Doppler wind measurement. Signature recognition algorithms then automatically detect low altitude wind shear phenomena, track thunderstorm motion and display appropriate graphical and alphanumeric alerts to air traffic control (ATC) personnel. The FAA and U.S. Air Force are now procuring an ASR-11 to replace older terminal surveillance radars at facilities that did not receive the ASR-9. Although the antenna pattern, scan rate and energy-on-target of the ASR-11 match the corresponding parameters of the ASR-9, two other characteristics are markedly different. It utilizes a low peak power solid state transmitter that requires transmission of long, coded waveforms and a pulse compression receiver. Secondly, its pulse transmission sequence consists of short (five-pulse) bursts at both different pulse-repetition frequencies (PRF) and different RF frequencies. In this report, we assess the technical and operational issues associated with adding a WSP to the ASR-11. The existing WSP data processing and display technology are largely re-usable for the ASR-11 based WSP. Ground clutter filter coefficients and the length and number of coherent processing intervals would need to be changed to conform to the ASR-11 pulse transmission strategy, and straightforward adaptations to the equations used in the pulse-pair weather reflectivity and Doppler velocity estimation would be required. With these changes, the ASR-11 could host the WSP, subject to performance degradations for low reflectivity wind shear phenomena such as dry microbursts and gust fronts. A benefits assessment waas performed to evaluate the operational requirements for an ASR-11 based WSP. Given that the FAA has already committed to deploy improved Low Level Wind Shear Alert Systems (LLWAS) at most ASR-11 airports, the incremental safety benefits for the ASR-11 WSP appear to be less than the cost of the equipment. A case can be made for deployment based on "situational awareness" benefits that the WSP has been demonstrated to provide to air traffic controllers. We estimate that the value to the public and airline industry of reductions in aircraft delay, and avoidance of unnecessary diversions, would be in excess of eight million dollars per year tallied across 18 of the larger ASR-11 equipped airports.