Cooperatively cleansing cross-correlations

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In 2015 we used LOFAR station RS509, close to the Eemshaven, to investigate the effect of windmills on LOFAR data. We observed radio frequency interference (RFI) associated with TenneT's 380 kV Eemshaven-Oudeschip facility. Most of the signal was direct, but some of it was scattered by the rotors of nearby wind turbines, picking up their time modulation. Agentschap Telecom measured that the RFI was too severe, and TenneT engineered a solution.

Because one does not simply decouple more than a GigaWatt from the national grid, it took from July 4 until end of September to upgrade the entire installation. The horizon images show that the 380 kV station (right white bar) has improved already after the first modifications on the LOFAR-facing side, and is now no longer detectable in one second of single sub band data. The remaining intermittent RFI comes from the direction of RWE's Eemshavencentrale (left white bar). This does not necessarily mean that it is the interference's source: it might just be reflecting signals from the environment, or the RFI may even belong to a wind turbine in between the powerplant and the LOFAR station. We currently do not know. In any case, the excessive interference's disappearance enables further research into windturbine-caused RFI at the Eemshaven wind farm.