At this picture, captured from the Buienradar.nl real-time dynamic visualization, you can see the precipitating area above the Netherlands and North Sea (January 15, 2008). As soon as the cloud layer and precipitations have been quite homogenous, the symmetrical figures at this picture show, actually, the antenna patterns of two weather radars - in De Bilt (at the center of lower circuit) and in Den Helder (at the center of upper circuit).
Brookner, E., 2008: Phased-array Radars: Past, Astounding Breakthroughs and Future Trends, Microwave Journal, 51(1) - pp. 30
In-depth look at the advanced development and proliferation of phased-array radars over the last five decades...
FGAN/FHR (Forschungsgesellschaft für Angewandte Naturwissenschaften/ Forschungsinstitut für Hochfrequenzphysik und Radartechnik - Defense Research Facility for Applied Science/Research, Institute for High-frequency Physics and Radar Techniques), Wachtberg near Bonn, Germany.