An Improved Methodology for Ground Clutter Substitution Based on a Pre-Classification of Precipitation Types

Radar data contamination due to ground clutter is a common problem in any radar configuration, more so in mountainous areas. Addressing ground echoes contamination can be seen as a double task: first detection and elimination of contaminated areas, and second, substitution of removed contaminated values for a proper ones. Different algorithms have been developed to remove such contamination in an automatic manner, preserving the information due to precipitation. Most of these algorithms are based solely in the use of reflectivity information, or may include Doppler data.

The usual way to perform ground echoes substitution is the vertical extrapolation or the horizontal interpolation. The first one uses the shape of the vertical profile of reflectivity (VPR) to extrapolate non-contaminated values measured aloft, over the area affected by the ground clutter. The horizontal substitution interpolates into the ground echoes area those non-contaminated neighboring values located at the same height or elevation as the contaminated. The first option is limited by the variability of the VPR and the second by the size of the areas to be substituted.

The work developed proposes a substitution based on the type of precipitation. The idea of this new approach is to apply the horizontal option in those areas of precipitation with low reflectivity gradients (in general related with the stratiform precipitation). Vertical substitution is applied in areas with large reflectivity gradients (usually related with convective precipitation). In this latter case the VPR tends to have a uniform shape with height, that favors the vertical substitution, and the relation between the rain at a point and its surroundings is less clear (which invalidates the idea of horizontal interpolation).

This approach is evaluated in comparison of different options of substitution based on simple vertical or horizontal substitution. The different options are tested on selected events recorded by the C-band radar of the CMTC (Instituto Nacional de Meteorología, Barcelona). In addition, the dependence of their effectiveness on different conditions, such as the size of the clutter areas, the type of event, the distance to the radar of the clutters, etc., is evaluated.