Range Extension of Doppler Radar by Combined Use of Low-PRF and Phase Diversity Processed Dual-PRF Observations

A strategy to extend observation range of Doppler radar is proposed and tested with real data.

Both low pulse reputation frequency (low-PRF) and phase diversity processed dual-PRF (PDP) can be used to extend observation range of Doppler radar. However, the former suffers from small unambiguous velocity limit and the latter suffers from frequent data missing in second-trip echo region.

The strategy is to apply the Hybrid Multi-PRI dealiasing (HMP) method (Yamauchi, et al. 2006) to two scans of Doppler velocity data that observed with low-PRF and observed with PDP. The HMP developed by the authors is an accurate and robust method to derive a higher unambiguous Doppler velocity field from one or more scans of Doppler velocity data observed with two or more PRFs. By applying the HMP, both low-PRF and PDP data are dealiased with higher unambiguous velocity limit of PDP data. Using both low-PRF and PDP data dealiased by HMP solves aforementioned shortages of low-PRF and PDP.

The strategy is tested with the dataset of the typhoon DANAS observed by the Meteorological Research Institute C-band Doppler radar on September 11, 2001. Doppler velocity data were collected with two scan modes, low-PRF (600/480 Hz) and phase diversity processed dual-PRF (940/752 Hz). Unambiguous velocities of the modes are 33 m/s and 53 m/s, respectively. Observation ranges of the both modes are 250 km. 96% of Doppler velocities are correctly dealiased by HMP. Strong wind of 40 m/s near the typhoon center which located 240 km away from the radar is also correctly dialiased. Velocities are not determined for the rest of the data which corresponds to small isolated echos only observed with low-PRF. The processing time for a set of PPI is approximately 10 seconds using Pentium 4 workstation. The results demonstrate the strategy practically succeeded to extend observation range of Doppler radar with high unambiguous velocity limit.