What does dual-polarization weather radar provide that enhances precipitation measurements?

• A. Differential reflectivity Z_DR and differential phase Z_DP, enabling estimates of drop shapes, sizes, and phases.
• B. Only increases the maximum detectable reflectivity.
• C. It eliminates the need for calibration.
• D. It measures wind speed using Doppler alone.

Answer: (A)

Dual-polarization radar sends and receives both horizontal and vertical waves, giving access to polarimetric parameters that reveal microphysics of precipitation. The differential reflectivity, Z_DR, measures how much the radar returns differ between horizontal and vertical polarizations. This difference is sensitive to particle shape: as drops grow larger and become more oblate, Z_DR increases, so we can infer drop shapes and estimate sizes, helping distinguish between different kinds of precipitation (for example, rain vs hail). The differential phase, Z_DP, tracks the phase shift between the two polarizations as the wave travels, which accumulates with distance and depends on the size distribution and phase (liquid or ice) of the hydrometeors. Together, Z_DR and Z_DP provide direct information about drop shapes, sizes, and whether the precipitation is liquid or frozen, leading to more accurate rain-rate estimates and better precipitation typing. The other options don’t capture this added polarimetric information.