Simultaneous wind velocity estimation and dual-polarization measurements of precipitation and clouds by an S-band profiler

The Transportable Atmospheric RAdar (TARA) is an S-band FM-CW profiler that is located at Cabauw, the Netherlands. It is a part of European Union sponsored meteorological measurement site.

The TARA measurements can be carried out in single polarization mode, alternating polarization mode and/or wind measurement mode, that employs two offset beams. Simultaneous use of alternating polarization and wind measurement modes can provide a unique opportunity for studying both dynamical and microphysical properties of precipitation and clouds. However, the use of these two modes simultaneously reduces the maximum unambiguous velocity and therefore impairs the wind measurements. Generally four to five sweeps are necessary to collect both dual-polarization and two offset beam measurements. In this article a method that would mitigate this effect and therefore allows for accurate wind and dual-polarization observations is presented.

A retrieval method of the three dimensional wind velocity is based on processing of Doppler spectra. Because it makes use of three beam observations carried out on sweep to sweep basis, aliasing problem appears as the main drawback of this technique. This limitation is further enhanced by adding dual-polarization measurements. As the maximum unambiguous measurable velocity decreases dramatically (its maximum value was around 4.5 m/s), a very important effort has been dedicated to palliate this important limitation. Therefore, a successful dual-polarization technique has been employed for the main beam dealiasing, while a more classical one was used for the other beams with good results, as well.

The results show the good behaviour of this wind velocity retrieval method. Different measurements have demonstrated how this technique behaves in different meteorological conditions, with or without precipitation.