Definition: dual-polarization

In general, weather radars send and receive microwaves at one polarization, usually horizontal. By transmitting and/or receiving radar waves at more than one polarization, additional information can be obtained on the nature of the targets.

The most common dual-polarization scheme is the transmission and reception of horizontally and vertically polarized waves. As a first approximation, horizontally polarized waves are sensitive to the horizontal dimension of the targets while vertically polarized waves are sensitive to the vertical dimension of the targets. So by comparing the relative strength of the two returns for example, one can determine whether the targets have no preferred orientation (or are round) like snowflakes or hailstones, or if they are somewhat flat like raindrops.

Other parameters that can be measured include the cross-corelation of the two signals (indicative of the regularity or irregularity of the targets), and the relative delay between the two waves (a potentially promissing parameter for quantifying rainfall more accurately).

In the McGill system, only the S-band radar is set-up for dual-polarization. In our set-up, the transmission and reception of horizontally and vertically polarized waves is simultaneous, which allows us to obtain reasonably accurate data despite our very fast scanning rate (6 rotations per minute).