Multilag Estimators for the Alternating Mode of Dual-Polarimetric Weather Radar Operation

All National Weather Service weather surveillance radars are and will continue to be dual-polarimetric. Polarimetric weather radars measure the co-polar horizontally and vertically polarized returns from hydrometeors. This allows them to sense the size, shape, and state features of the hydrometeors, features the previous generation single-pol (usually horizontally polarized) weather radars could not sense, resulting in greatly improved quantitative precipitation estimation (QPE) and hydrometeor classification.

In polarimetric weather radar, multi-lag estimators allow for the estimation of signal powers (from which reflectivity and differential reflectivity are obtained) and co-polar cross-correlation coefficient without a need to first obtain estimates of the system noise powers. Having multi-lag estimators is useful, since accurate noise power estimates can be difficult or time consuming to obtain.

Thus far, the only multi-lag estimators that have been developed have been for the simultaneous mode of polarimetric weather radar operation, where the horizontal and vertical polarizations are transmitted and received simultaneously. This makes sense, since virtually all polarimetric weather radars today are mechanically scanned parabolic dish radars, and these almost always operate in the simultaneous mode (e.g., the WSR-88DP).

Future plans are considering replacing the nation’s current mechanically scanned weather and aircraft surveillance radars with a network of multifunctional phased-array radars (MPAR) that perform both tasks at the same time. Because it simplifies design complexity and reduces cost, these phased-array radars will likely operate in an alternating mode of polarimetric operation, whereby the radar alternates between the transmission and reception of the horizontally and vertically polarized beams.

To accommodate these phased-array radar systems, this paper develops multi-lag estimators for the alternating mode of polarimetric weather radar operation. The estimators are evaluated using simulated data and data from an X-band, polarimetric, phased-array radar.