In 2007, IRCTR (Delft University of Technology) installed a new polarimetric X-band LFMCW radar (IDRA) at the meteorological observation site of Cabauw, The Netherlands. It provides plan position indicators (PPI) at a fixed elevation with a high range resolution of either 3 m or 30 m at a maximum observation range of 1.5 km and 15 km, respectively. IDRA aims to monitor precipitation events for the long-term analysis of the hydrological cycle. Due to the specifications of IDRA, the spatial and temporal variability of a large range of rainfall intensities (from drizzle to heavy convective rain) can be studied. Even though the usual observation range of IDRA is limited to 15 km, attenuation due to precipitation can be large enough to seriously affect the measurements. In this contribution we evaluate the application of a combined method to correct for the specific and the differential attenuation, and in the same vein estimate the parameters of the raindrop-size distribution. The estimated attenuations are compared to a phase constraint attenuation correction method.@en

At X-band, the propagation effects such as attenuation and differential phase are more pronounced than at S- or C-band. Furthermore, already in moderate rain the scattering regime is not exclusively Rayleigh which leads to the presence of the differential backscatter phase. Particularly the stronger attenuation but also the differential backscatter phase at X-band are usually regarded as deteriorating effects. However, we can also change our perspective, and see them as a valuable carrier of microphysical information. In this contribution we introduce a new method to estimate the raindrop-size distribution from polarimetric X-band weather radar measurements using the specific differential phase and the differential backscatter phase. This new method is successfully applied to data from IDRA, the polarimetric X-band weather radar of IRCTR, TU Delft, that provides continuously since three years measurements from the top of the 213 m high tower at the meteorological observatory at Cabauw, The Netherlands.@en

In 2007, IRCTR (Delft University of Technology) installed a new polarimetric X-band drizzle radar (IDRA) at the meteorological observation site of Cabauw, Netherlands. It provides plan position indicators (PPI) with a high range resolution of either 3 m or 30 m. IDRA aims to monitor any precipitation events for the long-term analysis of the hydrological cycle. Due to the specifications of IDRA the spatial variability of a large range of rainfall intensities (from drizzle to heavy convective rain) can be studied. This also permits the assessment of mesoscale changes in the precipitation pattern due to aerosols (second aerosol indirect effect). As a first step in order to achieve these aims, we present the results of an exponential drop-size distribution retrieval using the conventional algorithm that is based on the radar reflectivity Z and the differential reflectivity Zdr. We will exploit the boundaries of applicability of this drop-size distribution retrieval algorithm for light precipitation. Thereby, we will focus on the limits for the extraction of the median drop diameter using the differential reflectivity. We will discuss potential sensor synergies to extract the median drop diameter even in light precipitation.@en

Polarisation diversity in radar remote sensing proved to be very successful in a variety of applications. Hydrometeors as raindrops or ice crystals are anisotropic radar targets giving rise to the use of polarisation diversity in weather radars. One advanced polarimetric weather radar is DLR's POLDIRAD in Oberpfaffenhofen. The huge data archive of this radar consists mainly of power measurements at diverse polarisation bases. This study investigates the possibility to apply the polarisation basis transformation directly on power measurements. As a result, empirical transfer functions for the change of the polarisation basis of radar reflectivities are derived. To check their validity they are applied to appropriate polarimetric radar data from the POLDIRAD.@en

For studying atmospheric phenomena and monitoring climate change, radar has been proven to be an indispensable and dependable tool. A Doppler radar also allows for the observation of particle velocities and filtering of the received signal in the frequency domain. A polarimetric radar exploits the anisotropy of the precipitation medium by employing pulses of different polarizations. A Doppler polarimetric radar not only combines both aforementioned advantages, but also offers the possibility to interpret the radar observables as functions of the particle velocities instead of single, integrated values. This option of finely partitioning the radar resolution volume results in abounding information which seems attractive; however, careful consideration should be placed on how to process it in order to access its content and avoid pitfalls. This paper presents rain measurements carried out by the IDRA X-band Doppler polarimetric radar located in Cabauw, the Netherlands. The focus is on the estimation of differential phase (¿dp) and specific differential phase (Kdp), from a spectral polarimetric point of view. With an adequate spectral polarimetric processing, it is expected to improve the estimates of ¿dp and Kdp. Comparison with the established, time-domain technique will be carried out. Kdp is challenging to estimate because it is a phase-related observable and the phase of radar signal presents rapid variations, necessitating careful processing and filtering. Yet, it is valuable, as it has been sufficiently supported in literature that it results in advantageous rain rate retrieval and classification algorithms.@en