Interesting, surprised they are using optical data for this instead of synthetic aperture radar. SAR (and in particular interferometric SAR, although that requi

Interesting, surprised they are using optical data for this instead of synthetic aperture radar. SAR (and in particular interferometric SAR, although that requires short repeat cycle) shines in this area, and a lot of the data is free. ESA provides worldwide 20m x 5m radar imagery from Sentinel-1 free online. Revisit in the mid-latitudes is generally a few times per week, with an exact repeat cycle every 12 days. Once Sentinel-1C is fully operational, it'll be half that.