While most satellite imagery is optical, meaning it captures sunlight reflected by the earth’s surface, Synthetic Aperture Radar (SAR) satellites such as Sentinel-1 work by emitting pulses of radio waves and measuring how much of the signal is reflected back:
Coincidentally, the radars on some missile defence batteries and other military radars operate using frequencies in the NATO G-band (4,000 to 6,000 Gigahertz) which overlaps with the civilian C-band (4,000, to 8,000 Gigahertz), commonly used by open source SAR satellites.
In the simplest terms, this means that when the radar on the likes of a Patriot battery is turned on, Sentinel-1 picks up both the echo from its own pulse of radio waves, as well as a powerful blast of radio waves from the ground-based radar. This shows up as a stripe of interference perpendicular to the orbital path of the satellite.
Patriot missiles are not the only system that create this type of interference. Other military radars that operate on the same C-band frequency include naval radars such as the Japanese FCS-3, the Chinese Type-381 and the Russian S-400 surface-to-air missile system. All should be detectable when switched on and in view of Sentinel-1.
Dan confirmed the site of the radars he discovered during his initial research by using other open sources such as imagery on Google Maps and even data from the Strava running app.
He also highlighted other interesting missile battery locations, such as the Swedish STRIL array which acts as the country’s early warning system against Russian aircraft and missiles.
The use of radar and radio detection is kinda like having a gun fight in a pitch dark house. You can turn your flashlight on to see, then you’re also the first thing everyone else sees, too.