Fig. 1.From: Determining field-aligned currents with the Swarm constellation mission(a) Sketch of a quad of 4 measurements points needed for the calculation of FAC density at the centre. Points Q1, …, Q4 are positions on the orbit tracks of satellites SwA and SwB connected by route elements dℓ. (b) Measurement points on SwB orbit are selected at slightly shifted times with respect to SwA, so that a symmetric quad is achieved.Back to article page