Abstract
A previous study has used the stable and peculiar echoes backscattered by a single “bright scatterer” (BS) during five winter days to characterize the hardware of C-band, the dual-polarization radar located at Monte Lema (1625 m altitude) in Southern Switzerland. The BS is the 90 m tall metallic tower on Cimetta (1633 m altitude, 18 km range). In this note, the statistics of the echoes from the BS were derived from other ten dry days with normal propagation conditions in winter 2015 and January 2019. The study confirms that spectral signatures, such as spectrum width, wideband noise and Doppler velocity, were persistently stable. Regarding the polarimetric signatures, the large values (with small dispersion) of the copolar correlation coefficient between horizontal and vertical polarization were also confirmed: the average value was 0.9961 (0.9982) in winter 2015 (January 2019); the daily standard deviations were very small, ranging from 0.0007 to 0.0030. The dispersion of the differential phase shift was also confirmed to be quite small: the daily standard deviation ranged from a minimum of 2.5° to a maximum of 5.3°. Radar reflectivities in both polarizations were typically around 80 dBz and were confirmed to be among the largest values observed in the surveillance volume of the Monte Lema radar. Finally, another recent 5-day data set from January 2020 was analyzed after the replacement of the radar calibration unit that includes low noise amplifiers: these five days show poorer characteristics of the polarimetric signatures and a few outliers affecting the spectral signatures. It was shown that the “historical” polarimetric and spectral signatures of a bright scatterer could represent a benchmark for an in-depth comparison after hardware replacements.
Highlights
Dual-polarization weather radars operating in mountainous terrains, such as the European Alps, are in charge of the surveillance of complex-orography regions
The rejection of ground clutter is critical since good radar visibility from a high site implies a very large number of ground clutter echoes
The Monte Lema radar, which is located at 1625 m altitude 10 km northwest of Lugano, is one of the five identical, dual-polarization, Doppler, C-band (5.5 GHz) systems operated by MeteoSwiss [6]
Summary
Dual-polarization weather radars operating in mountainous terrains, such as the European Alps, are in charge of the surveillance of complex-orography regions. In the operational radar processing chain of MeteoSwiss, ground clutter is automatically detected using well-consolidated algorithms and rejected so that only the radar echoes originated by the weather are retained. In this context, the use of high range resolution, Doppler and dual-polarization information maximizes the probability of having at least some clutter-free radar bins for each Cartesian pixel of the resampled operational product in the sampling volumes close to the terrain. During several years of operation at the end of the last century, the algorithm has been further improved [3]
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