Usually, when we talk about remote sensing we’re talking about how features reflect energy onto the electromagnetic spectrum. All but one of the public/commercially available satellites currently in orbit use this kind of information. I’m looking at you, GRACE, and your wonderful wobbles.
But there’s other ways to go about measuring and identifying stuff from a distance. Here’s a cool map of the quietest places in the US that was recently published in Science. To create the map, acoustics were measured at many points across the US over sustained periods of time. It looks like that point data was then interpolated (along with ancillart datasets) to create this final map.