You can extract signals lower than background routinely. See GPS.
Did you bother to read the 2nd article?
2 SSBNs collided with each other. Even afterwards, they both
still didn't realise they actually hit another submarine
Your reference to GPS signal discrimination makes no sense, given what actually happened.
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Also remember that GPS radio signals are deliberately designed to be detected as regular signals.
In comparison, submarine emissions are designed to be random as much as possible. Plus sound waves represent physical movement, which contains far less data to work with.
Have you heard of clouds?
This is what I mean.
Take that SCMP article to its logical conclusion.
300 satellites gives you a 10 minute revisit time.
Say you have another 300 SAR satellites working together.
That's only 600 satellites and will provide near-real time tracking.
And at 41 satellites per launch, that's less that 15 launch rockets.
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In the coming years, we're going to be looking at 50K+ satellites in low earth orbit.
Real-time satellite reconnaissance constellations are going to be common.
I imagine every medium sized country will have one.
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And again, if ICBMs on TELs were a better option, then why didn't China build many, many more DF-41?
For a long while, I was puzzled at the slow adoption rate of the DF-41.
But it makes sense if they decided that missile silos are a better option that more TELs.
And they've really gone with large numbers of silos.