4 ms·

In the 9ghz range, does that mean a sub-1mm wire mesh could mitigate this? Asking for a hypothetical house renovator friend. Thompson's adage of when the going

In the 9ghz range, does that mean a sub-1mm wire mesh could mitigate this? Asking for a hypothetical house renovator friend. Thompson's adage of when the going gets weird, the weird turn pro suggests that the tinfoil hat crowd could be able to corner the emerging domestic Faraday cage market.

leoedin 6y ago
If you want to block SAR, just set up a big corner reflector near you. It'll completely blind the part of the image near you. It would also draw a lot of attention to you... So maybe not the best approach if you're trying to hide.
- craftinator 6y ago
  Well, if enough people do it... Let's make a VPN for satellite surveillance
- jusssi 6y ago
  Big in home decoration fashion next year, upside down pyramids hanging from the ceiling. (edit: my bad, a corner reflector would have 3 corners at the base, not 4 as a pyramid would)
  - AlgorithmicTime 6y ago
    A pyramid is defined as any polygonal base with all vertices connected to an apex, so a triangular pyramid is possible.
- artvark11 6y ago
  How big are we talking? Can I make one out of tinfoil?
- ars 6y ago
  Are you sure a corner reflector will work? The entire premise of the synthetic aperture is that the transmission and reception are distant from each other, but a corner reflector will reflect back to the location of the transmission - i.e. it will entirely miss the receiver.
  - leoedin 6y ago
    Yes, completely sure. Corner reflectors are used to calibrate SARs by providing fixed bright ground points. I've also seen SAR imagery where unintentional corner reflectors (in this case, a building) completely washed out the image at that location. It's true that the SAR antenna has moved a little bit by the time the transmitted signal is received. However, the signal is moving significantly faster than the satellite - with a 600km orbit, velocity is ~8km/s - so the roundtrip time is maybe 0.04s, meaning the satellite has moved 320m. That's about 0.2 degrees from the point of view of the reflector. The synthetic aperture is not just the distance covered in the round trip of a single chirp, but the distance covered during the imaging process. A SAR typically produces chirps constantly (in the tens to hundreds of Hz) and digitises the responses. All of the energy of all those responses can then be combined to form the image. If the corner reflector is in a fixed location, every chirp will have a spike in the response corresponding to that location.
- walrus01 6y ago
  or a whole bunch of small corner cube reflectors (such as you would see attached to a sailboat mast for intentional greater radar visibility) in a grid like array. https://www.westmarine.com/WestAdvisor/Selecting-a-Radar-Reflector https://www.westmarine.com/WestAdvisor/Selecting-a-Radar-Ref...
  - dzhiurgis 6y ago
    Wonder if someone uses this tech for monitoring entire ocean, not just narrow spots. Similarly there's monitoring of AIS by Iridium, but pirates and drug lords turn those off.
throwaway8451 6y ago
The dielectrics that you unavoidably will embed your wire mesh in will slightly change its reflective properties but yes, this should work.
wlll 6y ago
I think this is a balance. Being the only house in the area that can't be seen into might get you more attention someone being able to see you in your underwear at a 50cm x 50cm resolution.
- jolmg 6y ago
  Unless you live underground, then you'll just look like the rest of the ground. EDIT: On a more general case, I wonder how expensive and feasible it would be to cover the roof/ceiling and walls with an array of 9ghz emitting "pixels" with the wire mesh behind that. Then show the satellites whatever image you want. Make it look like funny stuff is going on inside for their own amusement. Wouldn't be able to account for the different angles the satellite might take pictures from, though. Unless you track it.
  - LeifCarrotson 6y ago
    The satellite is looking at the of flight and intensity of the reflected signal, not 'color'. It's basically monochrome. You can make your ceiling either very massive or very conductive to reduce the signal reflected, or install a corner reflector in the attic to overwhelm the sensor with its own high-intensity signals (like taking a photo in a mirror with the flash on).
    - jolmg 6y ago
      I never said anything about color, though. Monochrome displays also have pixels. Color pixels aren't the only type of pixel.
dylan604 6y ago
Mike: "Hey Bob, what's up with this one house in this neighborhood? We aren't able to get a look in side." Bob: "Hmmm, anyone preventing us from getting a look means they are subversive. Get a no-knock warrant to investigate that location. Only illicit activities can be taking place there." In this case, being "invisible" actually makes you more suspicious which only brings their attention upon you that much more intense.

leoedin 6y ago

If you want to block SAR, just set up a big corner reflector near you. It'll completely blind the part of the image near you. It would also draw a lot of attention to you... So maybe not the best approach if you're trying to hide.

craftinator 6y ago
Well, if enough people do it... Let's make a VPN for satellite surveillance
jusssi 6y ago
Big in home decoration fashion next year, upside down pyramids hanging from the ceiling. (edit: my bad, a corner reflector would have 3 corners at the base, not 4 as a pyramid would)
- AlgorithmicTime 6y ago
  A pyramid is defined as any polygonal base with all vertices connected to an apex, so a triangular pyramid is possible.
artvark11 6y ago
How big are we talking? Can I make one out of tinfoil?
ars 6y ago
Are you sure a corner reflector will work? The entire premise of the synthetic aperture is that the transmission and reception are distant from each other, but a corner reflector will reflect back to the location of the transmission - i.e. it will entirely miss the receiver.
- leoedin 6y ago
  Yes, completely sure. Corner reflectors are used to calibrate SARs by providing fixed bright ground points. I've also seen SAR imagery where unintentional corner reflectors (in this case, a building) completely washed out the image at that location. It's true that the SAR antenna has moved a little bit by the time the transmitted signal is received. However, the signal is moving significantly faster than the satellite - with a 600km orbit, velocity is ~8km/s - so the roundtrip time is maybe 0.04s, meaning the satellite has moved 320m. That's about 0.2 degrees from the point of view of the reflector. The synthetic aperture is not just the distance covered in the round trip of a single chirp, but the distance covered during the imaging process. A SAR typically produces chirps constantly (in the tens to hundreds of Hz) and digitises the responses. All of the energy of all those responses can then be combined to form the image. If the corner reflector is in a fixed location, every chirp will have a spike in the response corresponding to that location.
walrus01 6y ago
or a whole bunch of small corner cube reflectors (such as you would see attached to a sailboat mast for intentional greater radar visibility) in a grid like array. https://www.westmarine.com/WestAdvisor/Selecting-a-Radar-Reflector https://www.westmarine.com/WestAdvisor/Selecting-a-Radar-Ref...
- dzhiurgis 6y ago
  Wonder if someone uses this tech for monitoring entire ocean, not just narrow spots. Similarly there's monitoring of AIS by Iridium, but pirates and drug lords turn those off.

throwaway8451 6y ago

The dielectrics that you unavoidably will embed your wire mesh in will slightly change its reflective properties but yes, this should work.

wlll 6y ago

I think this is a balance. Being the only house in the area that can't be seen into might get you more attention someone being able to see you in your underwear at a 50cm x 50cm resolution.

jolmg 6y ago
Unless you live underground, then you'll just look like the rest of the ground. EDIT: On a more general case, I wonder how expensive and feasible it would be to cover the roof/ceiling and walls with an array of 9ghz emitting "pixels" with the wire mesh behind that. Then show the satellites whatever image you want. Make it look like funny stuff is going on inside for their own amusement. Wouldn't be able to account for the different angles the satellite might take pictures from, though. Unless you track it.
- LeifCarrotson 6y ago
  The satellite is looking at the of flight and intensity of the reflected signal, not 'color'. It's basically monochrome. You can make your ceiling either very massive or very conductive to reduce the signal reflected, or install a corner reflector in the attic to overwhelm the sensor with its own high-intensity signals (like taking a photo in a mirror with the flash on).
  - jolmg 6y ago
    I never said anything about color, though. Monochrome displays also have pixels. Color pixels aren't the only type of pixel.

dylan604 6y ago

Mike: "Hey Bob, what's up with this one house in this neighborhood? We aren't able to get a look in side." Bob: "Hmmm, anyone preventing us from getting a look means they are subversive. Get a no-knock warrant to investigate that location. Only illicit activities can be taking place there." In this case, being "invisible" actually makes you more suspicious which only brings their attention upon you that much more intense.