Effects of propagation conditions on radar beam-ground interaction: impact on data quality

Abstract

Abstract. A large part of the research in the radar meteorology is devoted to the evaluation of the radar data quality and to the radar data processing. Even when, a set of absolute quality indexes can be produced (like as ground clutter presence, beam blockage rate, distance from radar, etc.), the final product quality has to be determined as a function of the task and of all the processing steps. In this paper the emphasis lies on the estimate of the rainfall at the ground level taking extra care for the correction for ground clutter and beam blockage, that are two main problems affecting radar reflectivity data in complex orography. In this work a combined algorithm is presented that avoids and/or corrects for these two effects. To achieve this existing methods are modified and integrated with the analysis of radar signal propagation in different atmospheric conditions. The atmospheric refractivity profile is retrieved from the nearest in space and time radiosounding. This measured profile is then used to define the `dynamic map' used as a declutter base-field. Then beam blockage correction is applied to the data at the scan elevations computed from this map. Two case studies are used to illustrate the proposed algorithm. One is a summer event with anomalous propagation conditions and the other one is a winter event. The new algorithm is compared to a previous method of clutter removal based only on static maps of clear air and vertical reflectivity continuity test. The improvement in rain estimate is evaluated applying statistical analysis and using rain gauges data. The better scores are related mostly to the ``optimum" choice of the elevation maps, introduced by the more accurate description of the signal propagation. Finally, a data quality indicator is introduced as an output of this scheme. This indicator has been obtained from the general scheme, which takes into account all radar data processing steps.

Enhanced radar precipitation estimates using a combined clutter and beam blockage correction technique

“…The correction for residual anaprop clutter is performed with the method of Alberoni et al (2001) modified by Fornasiero et al (2005). This method compares, for each range-bin, the reflectivity value at the dynamic elevation map with those observed at the successive elevation scans at the same location.…”

“…This map is built resuming different information: the static map of precipitation-free echoes, the beam blocking rates and the heights, relative to the ground, of the 3-dB beam lower limit. The last two parameters are obtained simulating the beam path through a multi-layer model (Fornasiero et al, 2005(Fornasiero et al, , 2006, where the refractivity gradient profile is retrieved from a linear weighted combination of the two nearest (in time) radiosoundings profile, collected by a station that is co-located with the radar. The resulting profile is then interpolated at vertical steps of 0.2 km.…”

Quality-based generation of weather radar Cartesian products

“…Having determined a set of quality indices, a total QI field describing overall data quality can be computed, most often by using a multiplicative scheme (e.g. Fornasiero et al, 2005;Germann et al, 2009;Ośródka et al, 2014).…”

Quality Control Algorithms Applied on Weather Radar Reflectivity Data

“…There are not many papers focused on quality characterization of such data. Fornasiero et al (2005) presented a scheme employed in ARPA Bologna (Italy) for quality evaluation of radar data both raw and processed. The scheme developed in Institute of Meteorology and Water Management in Poland (IMGW) in the frame of BALTRAD project was described by Ośródka et al (2010Ośródka et al ( , 2012.…”