...
The radar data which are provided at a given hour include a mask, which shows locations within the European domain (Figure 1) with no valid data from the radar observation network. Radar data can be missing for reasons including: the area not being covered by the existing radar network, the radar at a particular location being offline at that particular time, or errors with the data provided by a particular radar location. To prevent discontinuities at the edge of the radar coverage, an inverse distance the inverse of a hyperbolic tangent weighting function is applied, this produces a smooth transition from areas with valid radar coverage to those without radar coverage (shown in grey in Figure 1).
...