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 Cool! Sounds like a great dataset to use in a hobby project!
@pkok yeah, there's obviously a huge amount of national and commercial stuff that you can't access (or have to pay for: the best publicly available commercial imagery nowadays is almost certainly better than what the US had access to for most of the Cold War). That said, the free offerings are really cool. Landsat is low-res optical imagery that's been running forever (you could independently go measure the last 30 years of land clearing in the Amazon), and the Sentinel program covers a huge range of data: optical, radar, IR bands for temperature measurement, spectroscopy for atmospheric gas quantification… the data are all available online from the ESA for anyone interested to go wild with