Fig. 1From: Geomagnetic Virtual Observatories: monitoring geomagnetic secular variation with the Swarm satellitesIllustration of the Geomagnetic Virtual Observatory concept; satellite magnetic measurements from within a target cylinder are used to infer field time series at the GVO location given by a red dot. Note the cylinder radius is not to scale, the actual cylinder footprints are shown in Fig. 3Back to article page