SPECKS IN NOWHERE. “The magnetosphere-ionosphere system has been explored by a multitude of Earth-orbiting spacecrafts, but still the sparsity of the satellite fleet and the vast regions to be covered means that, at any given time, direct measurements of the magnetospheric processes are limited to only a few points in space.”
https://link.springer.com/article/10.12942/lrsp-2007-1