Quality index scheme for 3D radar data volumes

Quality of ground precipitation estimated from radar data can be characterized basing on comparison with rain gauge measurements. A quality index scheme taking into consideration sources of radar data errors can be employed for this purpose. Analogous work on assessment of quality of 3D radar reflectivity volume is more difficult due to lack of such a benchmark.

Technique of quality characterization for 3D volume of radar data proposed in the presentation consists in estimation of quality for each data measurement point defined by radar scan strategy, not for volumetric pixel (voxel).

A concept of quality index (QI) as a unitless quantity with values from 0 (bad quality) to 1 (excellent quality) is proposed. The algorithm consists of the following steps:

(1) Selection of the most significant error sources – set of quality parameters.

(2) Estimation of particular radar data errors as functions of the parameters.

(3) Calculation of particular quality indexes.

(4) Determination of an averaged quality index.

The following quality factors are preliminarily selected as important sources of errors:

- Extension of a radar beam. Parameters: surface areas of both horizontal and vertical cuts of the radar beam (sq. km).

- Attenuation of radar beam in meteorological targets. Parameter: attenuation in precipitation (mm).

- Radar beam shielding by ground targets. Parameter: shielding of radar beam in percentage.

- Vertical profile of reflectivity and related phenomena (melting layer). Parameter: four flags related to altitude: above melting layer, within melting layer, under melting layer, and no melting layer.

An example of the quality index calculation for volume data generated by Polish weather radar network POLRAD is presented.