Yesterday a well known OM told me about Graves radar located near Dijon in Framce. It's waves are transmitted on 143.050 MHz.
If you tune your rx on this frequency and watch the FFT with HDSDR for e.g. you can see reflections of these waves on objects that are flying in the air above.
There objects could be planes, asteroids, meteroids, ISS and other things in heaven above.
Have a look at this video, please. You can see a few of these reflections. Some a small, some are bigger. The duration of the recording is about 34 minutes.
The distance between my ocation and the Graves radar is about 680km.