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Not really anymore. Synthetic-aperture radar is making the Earth’s surface watchable 24/7 https://www.economist.com/technology-quarterly/2022/01/27/synthetic-a

by mesh 5y ago

Not really anymore. Synthetic-aperture radar is making the Earth’s surface watchable 24/7 https://www.economist.com/technology-quarterly/2022/01/27/synthetic-aperture-radar-is-making-the-earths-surface-watchable-24/7 https://www.economist.com/technology-quarterly/2022/01/27/sy...

Retric 5y ago
I would assume stealth aircraft are rather hard to clearly image with a Synthetic-aperture radar satellite. But the point was more about cutting down on the number of satellites you need to worry about. You can’t exactly hide the fact a satellite is sending out radar for imaging.
- __turbobrew__ 5y ago
  If the surrounding area where the plane is parked is coherent (which pavement and concrete usually is) then you will see an incoherent region in the SAR imagery where the plane resides which would be quite suspicious.
- beerandt 5y ago
  None of that is true. Stealth for jets isn't primarily designed for plan view. (Referring to radar cross section isn't just a generic use of the term for "detectable area of return".) Even if it was stealthy from above, it would be easy to identify and defeat, especially on the ground: just look for the plane-shaped area without a ground return. Or separately, a pair of co-orbital following satellites would entirely defeat all (publicly known) radar stealth (with the transmitter offset from the receiver). The US admittedly has similar pairs of these for "scientific purposes". I assume the military/IC have access or have their own. And synthetic aperture radar can be disguised such that its nearly indistinguishable from background noise. It's one of the features that makes it superior to old school dish radar. That's not even a secret. It's currently deployed throughout the military: ground, sea, and air. Space based platforms probably had it first.
  - raducu 5y ago
    > And synthetic aperture radar can be disguised such that its nearly indistinguishable from background noise So the transmit power is the same as background noise and you can still get useful radar pictures out of it? Amazing. I roughly know you can recover repeating signals that are below the noise floor, but still amazing.
    - ars 5y ago
      See: https://en.m.wikipedia.org/wiki/Spread_spectrum https://en.m.wikipedia.org/wiki/Spread_spectrum along with cryptographically randomized frequency hopping, you would not be able to figure out when there is an actual signal rather than noise.
      - Retric 5y ago
        Picture a point source frequency hopping different collars of visible light on your wall. There are real limits to how many photons it can send before it becomes really obvious. As satellites need to detect returns bounced off the ground hundreds of miles away they have some hard minimums for high resolution images vs aircraft or ground stations. 10x distance needs 100x the signal.
  - deleted 5y ago
    [deleted]
  - Retric 5y ago
    In terms of disguising synthetic aperture radar that’s much harder with a satellite which needs to send out a strong signal to hit stuff at 300+ miles and then bounce back to another detector at 300+ miles. Especially when there is such a limited number of easily tracked satellites to be concerned with. 10x distance requires 100x the signal. When it comes to being stealthy from above, jets bank to turn. Pilots can handle much higher g loads vertically than horizontally.
JumpCrisscross 5y ago
Can one jam an overhead SAR from the ground? For example, by aiming a radar beam at the bird to fuzz a location?
- leoedin 5y ago
  You can jam it (if you know the right frequencies) and you can also passively blow it out with a big corner reflector, which tends to result in a very bright spot and loss of surrounding detail.

by mesh 5y ago

Retric 5y ago

I would assume stealth aircraft are rather hard to clearly image with a Synthetic-aperture radar satellite. But the point was more about cutting down on the number of satellites you need to worry about. You can’t exactly hide the fact a satellite is sending out radar for imaging.

__turbobrew__ 5y ago
If the surrounding area where the plane is parked is coherent (which pavement and concrete usually is) then you will see an incoherent region in the SAR imagery where the plane resides which would be quite suspicious.
beerandt 5y ago
None of that is true. Stealth for jets isn't primarily designed for plan view. (Referring to radar cross section isn't just a generic use of the term for "detectable area of return".) Even if it was stealthy from above, it would be easy to identify and defeat, especially on the ground: just look for the plane-shaped area without a ground return. Or separately, a pair of co-orbital following satellites would entirely defeat all (publicly known) radar stealth (with the transmitter offset from the receiver). The US admittedly has similar pairs of these for "scientific purposes". I assume the military/IC have access or have their own. And synthetic aperture radar can be disguised such that its nearly indistinguishable from background noise. It's one of the features that makes it superior to old school dish radar. That's not even a secret. It's currently deployed throughout the military: ground, sea, and air. Space based platforms probably had it first.
- raducu 5y ago
  > And synthetic aperture radar can be disguised such that its nearly indistinguishable from background noise So the transmit power is the same as background noise and you can still get useful radar pictures out of it? Amazing. I roughly know you can recover repeating signals that are below the noise floor, but still amazing.
  - ars 5y ago
    See: https://en.m.wikipedia.org/wiki/Spread_spectrum https://en.m.wikipedia.org/wiki/Spread_spectrum along with cryptographically randomized frequency hopping, you would not be able to figure out when there is an actual signal rather than noise.
    - Retric 5y ago
      Picture a point source frequency hopping different collars of visible light on your wall. There are real limits to how many photons it can send before it becomes really obvious. As satellites need to detect returns bounced off the ground hundreds of miles away they have some hard minimums for high resolution images vs aircraft or ground stations. 10x distance needs 100x the signal.
- deleted 5y ago
  [deleted]
- Retric 5y ago
  In terms of disguising synthetic aperture radar that’s much harder with a satellite which needs to send out a strong signal to hit stuff at 300+ miles and then bounce back to another detector at 300+ miles. Especially when there is such a limited number of easily tracked satellites to be concerned with. 10x distance requires 100x the signal. When it comes to being stealthy from above, jets bank to turn. Pilots can handle much higher g loads vertically than horizontally.

JumpCrisscross 5y ago

Can one jam an overhead SAR from the ground? For example, by aiming a radar beam at the bird to fuzz a location?

leoedin 5y ago
You can jam it (if you know the right frequencies) and you can also passively blow it out with a big corner reflector, which tends to result in a very bright spot and loss of surrounding detail.