from The Economist rag

[Mark Kohut]

Now Yelnya is emptying out. It is doing so under the cover of cloud, out of
sight of normal optical satellite imagery. But as The Economist explained in
 a recent Technology Quarterly
<https://www.economist.com/technology-quarterly/2022/01/27/synthetic-aperture-radar-is-making-the-earths-surface-watchable-24/7>,
synthetic-aperture radar (sar) satellites help to get around this problem.
The European Space Agency’s Sentinel-1 sar satellites make images of every
spot in Europe every six days. The results are grainy, meaning individual
vehicles or buildings cannot be picked out. But man-made structures reflect
radar waves from SAR satellites particularly well. Here, they have been
coloured purple. That allows us to see the dramatic change at Yelnya
between January 23rd and February 11th.
Sentinel
The 41st Combined Arms Army is moving south, towards the Ukrainian border.
An anonymous open-source analyst, who tweets under the name @danspiun, told The
Economist how he and others discovered this. Russian drivers are
enthusiastic users of cameras fitted to their dashboards, to capture
traffic accidents. In recent weeks, handheld cameras and these have
recorded military equipment being moved by road and rail—images that are
then shared online.