Beam multiplexing of spaced pulse pairs at upper elevation scans for multifunction phased array radars

The use of spaced beam multiplexed pairs of pulses to increase speed of volume coverage has been previously proposed. It has been demonstrated that under certain conditions this technique reduces the time of volume coverage while preserving the accuracy of spectral moments (Yu et al. 2007). Herein this approach is reexamined and evaluated against the required accuracy of reflectivity and velocity estimates specified for the WSR-88D. Because of the stringent requirement on ground clutter filtering, this method is not suitable for lower elevation scans. Thus examined are the feasibility, accuracy, and clutter filtering in this mode at the upper elevation scans. To that end, the five upper elevations on the volume coverage pattern number 12 (VCP-12) are modified.

It is demonstrated that this beam multiplexing cannot satisfy the WSR-88D requirements on the velocity estimates if the MPAR has the same sensitivity as the WSR-88D and similar processing is applied. Use of both channels, one for the horizontally polarized returns and the other for vertically polarized returns, can produce an effective increase in signal-to-noise ratio of up to 3 dB. This is still not sufficient to tilt the scale in favor of beam multiplexing for measurement of velocities. If, in addition to processing the two signals, the sensitivity is increased by about 5 dB, then the PAR performance in beam multiplex mode would satisfy the error requirement wherever the WSR-88D does so.

It turns out that the estimates of reflectivity obtained from the proposed spaced pairs sequence exceed the WSR-88D requirement and thus need no special processing. The statistical errors in the polarimetric variables in the current specifications are subordinate to the errors in reflectivity and velocity. That is, the specifications are that, as long as the Doppler moment estimates meet error requirements, the corresponding errors in the polarimetric variables would be acceptable. Therefore the error in velocity estimates is the metric for gauging this technique. Various combinations of pulse compression, bandwidth extension, and sensitivity increase are investigated to evolve a strategy that decreases the volume coverage in beam multiplex mode. With conventional processing of contiguous pulses, the coverage of the five elevations is about one minute. By increasing sensitivity, beam multiplexing reduces this time to about half a minute. Further reduction to about 15 s is possible if modest pulse compression and bandwidth increase are employed. Recommendations on how to deal with ground clutter at these elevations in the beam multiplexing mode are given.

Reference: Tian-You Yu, M. B. Orescanin, C. D. Curtis, D. S. Zrnić, and D. E. Forsyth, 2007: Beam Multiplexing Using the Phased-Array Weather Radar, Jour. Atmos. Oceanic Tech. 24, 616-626.