Between 1997-2001 the ground around the Three Sisters Volcanoes in Oregon bulged indicating magma was rising. This bulge was detected using InSAR.
InSAR stands for Interferometric Synthetic Aperture Radar. Satellites record images of the Earth's surface, and these images can be combined to show subtle movements of the ground surface, called deformation. InSAR is a proven technique for mapping ground deformation using radar images from Earth-orbiting satellites. InSAR greatly extends the ability of scientists to monitor volcanoes because, unlike other techniques that rely on measurements at a few points, InSAR produces a spatially complete map of ground deformation with centimeter-scale accuracy without subjecting field crews to hazardous conditions on the ground.
[Description from USGS's https://volcanoes.usgs.gov/activity/methods/insar/
for more on the Three Sisters "bulge": http://volcanoes.usgs.gov/volcanoes/three_sisters/three_sisters_geo_hist_129.html]