The sensitivity of polarimetric quantities on ground clutter and melting layer contamination is investigated by using in-phase (I) and quadrature (Q) components of signals measured by the Météo-France C-band polarimetric Doppler radar at Trappes located about 30 km southwest Paris, France. In a first step, I and Q components of various types of ground clutter (i.e., point targets to more complex settings) and various locations within the melting layer are examined. In a second step, I and Q time series from these contaminations are added to I and Q observed within rain. In order to determine the critical level when the superposition of rain and contamination exceeds the measurement accuracy required for polarimetric parameters and rainfall rate, the intensity of the added contamination varies from being 30 dB lower to 30 dB larger than that of rain. This presentation shows the differences in Zh, Zdr, ρhv, φdp, specific differential phase (Kdp) and polarimetric rainfall rates R(Zh), R(Zh, Zdr), R(Kdp), R(Kdp, Zdr) between the control run using I and Q measurements within rain and the simulated superposition of rain and contamination.
Sensitivity studies of radar reflectivity on ground clutter contamination showed that a measurement accuracy of 1 dB is exceeded when the clutter intensity is ~10 dB larger than Zh in rain. Polarimetric quantities showed a stronger response to ground clutter contamination. The measurement accuracy was on average exceeded when the ground clutter intensity was ~5 dB larger than the rain intensity. Ground clutter starts to influence considerably the accuracy when the ground clutter contamination is >7 dB for Zh, >1 dB for Zdr, and when rain and ground clutter have the same intensity for ρhv and φdp. As a consequence, rainfall rate estimations using polarimetric quantities tend to be very sensitive to ground clutter contamination compared to R(Zh). Also, sensitivity studies on temporal and spatial resolution showed high resolution polarimetric quantities tend to be very noisy. In order to maintain the measurement accuracy for polarimetric parameters longer dwell times compared to radar reflectivity are required. This can only be achieved by reducing rotation speed, reducing spatial resolution, or increasing high pulse repetition frequencies.