alt Hacker NewsThe photons arriving at the satellite from a ground target aren’t getting weaker due to distance in any way that defeats you, because the sun is illuminating the target and the NRO just needs to collect enough of the reflected photons.
SQUID sensors (the most sensitive magnetometers that exist) require magnetically shielded rooms to record cardiac signals at centimeter range.
They require a shielded room to increase the SNR. SQUID sensors are sensitive enough to record cardiac signals at distance. The issue is SNR.
What they are saying is that they produced a low noise sensor array and managed to increase the SNR through computation. They also stated that it was an ideal environment with no other electrical/magnetic interference.