I've got a hobby-interest in remote sensing (satellite imagery). Over the past couple of days, I've been playing around with data from the ESA's Sentinel-1 mission. The ESA (being cool and European Union-y) makes most of the data from Sentinel series of satellites freely accessible to the public, and provides some decent software for processing and analysing the data.
Sentinel-1 is a synthetic aperture radar (SAR) satellite. I don't fully understand the physics behind SAR, but it's basically an active radar measurement of the ground track the satellite passes over. Different surfaces give different sorts of radar returns (measured as a change in polarisation), and so SAR can be used to classify different terrains (crops, forests, grasslands, rock, etc), like in the false-colour image of Flevoland I've attached. Resolution is moderate: for Sentinel-1, each pixel ends up being about 4x4 m on the ground.
@spinflip My gut suspicion is TR module tech changes. I found a IEEE article[1] that provides a little support but I don't know enough about the specific platforms to verify that. I'm not a radar engineer but I'm friends with several. I'll ask around if you want specific answers.
@drewfer I'd guess so, but which advances in particular? I'd guess it's most likely to be linked to onboard data storage and processing, but have no real evidence to support that