Thread by @coastal8049

Here's how to understand the RADAR data I'm sharing.

The Russian MERIDIAN satellites are in High Earth Orbit and have their apogees fixed above the Northern hemisphere over Russia and North America. This allows the spacecraft to see both places at once.

THREAD
1.

Being in a highly elliptical orbit the MERIDIAN satellite is actually visible to observers on the opposite side of the world at a very low elevation in their sky. Here's an example plot of simulation of MERIDIAN 8 at the North American apogee visible from Ukraine.
2.

Examining geometry you can easily see that the satellite is visible to both stations in North America and Europe/Asia. The geometry below is when MERIDIAN 8 is setting over Ukraine. Satellite footprint is the yellow circle on the Earth. Anything within that can see satellite.
3.

On the MERIDIAN satellite there is a 'bent pipe' transponder downlink on ~995MHz. Uplink ~825MHz. Bent Pipe meaning that whatever it hears on the uplink it just turns around and retransmits without modification on the downlink. Just like a bent plumbing pipe...
4.

RADARs spin and output a lot of power in a very brief period of time. The pulse is modulated to assist in detecting signals. As this powerful beam sweeps over the MERIDIAN satellite the transponder retransmits the signal.
5.

Horizontal axis is frequency. The 'waterfall' is falling in time. Latest moments at the top oldest at the bottom. The plot below shows 2 radars. One usually active red and the other orange that just lights up very infrequently. Note period of 10s, period of radar sweep.
6.

So there you go, welcome to the world of open source SIGINT. If you're curious about how other satellites have been used for SIGINT in the past consider the Moon... Read this story...
7.
skyriddles.wordpress.com/2018/04/01/the…

And here:
That time the US collected Soviet radar technology via the moon.
8.
wearethemighty.com/mighty-history…