[HN Gopher] No, SAR Can't See Through Buildings
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No, SAR Can't See Through Buildings
Author : Shelnutt2
Score : 64 points
Date : 2020-12-19 20:21 UTC (2 hours ago)
(HTM) web link (www.capellaspace.com)
(TXT) w3m dump (www.capellaspace.com)
| supernova87a wrote:
| _"... It helps to think of it just as your brain's interpretation
| of a two dimensional representation of the coherent sum of
| backscatter responses from electromagnetic waves... "_
|
| Well that clears it right up, thanks! Lol.
|
| I'm pleased that they think any general public person or even
| journalist is capable of seeing the difference between the left
| and right figure in the article.
| mekkkkkk wrote:
| I was about to write this same thing. It is amazing to me how
| scientists/experts sometimes seem utterly incapable to level
| with an audience. I get that it's tough if there is a lot of
| ground to cover, but the quote you pulled is so telling. Those
| who are now convinced that the NSA are looking at them from
| space when they shower will probably gain absolutely nothing
| from this release.
| mattlondon wrote:
| Does anyone have any links to full-resoluton examples from
| Capella?
|
| All of the ones I have seen so far appear to be resized for use
| in their blog/press releases ... or are those images as high-res
| and as sharp as they get?
| fimdomeio wrote:
| this is a copy of the highest res I could find after messing
| with futurism blog image urls:
| https://tilde.pt/~fimdomeio/nossa-senhora-do-computismo/img/...
| JohnJamesRambo wrote:
| They didn't follow the first rule of writing something. I don't
| know what SAR is.
|
| Synthetic-aperture radar (SAR)?
| 14 wrote:
| It will be scary the day they can track every human movement at
| all times. But I think it is coming. One side and I think well we
| would know what happened to Michael Dunahee, a child that went
| missing when I was a kid, being able to reverse the video of what
| happened. But also it wasn't that long ago that Canada punished a
| man for being gay so this is a very dangerous technology if it
| can track humans. Privacy is critical to a free society.
| fimdomeio wrote:
| I believe it's called having a phone.
| 14 wrote:
| Sure a phone can do a lot of that but someone who plans on
| burying a body may consider tracking and leave it at home.
| But if a satellite was tracking everyone even in heavy
| weather conditions at all times and all they had to do was
| reverse the camera then there won't be a lot of crimes we
| can't solve. At first probably just used to catch high
| profile killers because they won't want the knowledge out
| that they can track anyone. So it will be used to track down
| high profile targets who won't have much of a trial anyways.
| Then other countries will utilize the same technology and
| track down any dissidents. After some time and many other
| countries are using it and tracking becomes the normal and it
| is more accepted that you will be tracked then every day
| crimes can be persecuted. No more slow stopping at stop signs
| you better come to a full stop or an automated ticket can be
| sent to you. Pettie crimes like vandalism will be tracked
| down and people arrested. Of course then there will be
| private entities that launch their own satellites and begin
| tracking people. Want to know where your spouse goes, no
| problem for a monthly fee. Track your teen sure. Safety
| monitoring of old grandma would be a nice one now she won't
| wander. What neighborhood is a person driving in from a nice
| neighborhood well I will push the penthouse suit and extra
| amenities since they can afford it. Those are just a few of
| the ideas I thought of.
| danaliv wrote:
| I don't understand this at all. Is there a side-by-side
| comparison of radar and visible wavelength somewhere? Or maybe a
| version of the geometric diagrams with example objects and the
| imagery they'd produce?
| rmrfstar wrote:
| Does anyone have a white paper about corner reflectors and X-band
| SAR?
|
| For what it's worth, the state very likely needs a warrant to use
| technologies capable of looking inside structures [1]. Not that
| the law applies to them, but hypothetically.
|
| [1] https://en.wikipedia.org/wiki/Kyllo_v._United_States
| jcims wrote:
| Dunno, but if you look at some of the image gallery photos
| here, there's a very bright specular reflection from a number
| of vehicles. Police radar is right in this frequency range, so
| it would make sense of they have a retroreflective effect built
| into the paint on the plate.
|
| https://www.sandia.gov/radar/imagery/index.html
|
| Example:
| https://www.sandia.gov/radar/_assets/images/gallery/ka-band....
| __turbobrew__ wrote:
| Maybe this?
| https://ieeexplore.ieee.org/abstract/document/6894586
| arcticfox wrote:
| Can someone edit in a comma to the HN title?
|
| "No, SAR Can't See Through Buildings" is the real title, which is
| completely different than the current (awkward) "No SAR Can't See
| Through Buildings"
| chrisbolt wrote:
| SAR = Synthetic Aperture Radar
| [deleted]
| elil17 wrote:
| Actually, some specially designed SAR can see through buildings,
| but not the kind of SAR that's in publicly available remote
| sensing data.
|
| One example (of many): https://www.kurzweilai.net/seeing-through-
| walls-in-real-time
| CamperBob2 wrote:
| Exactly. "SAR" is a very broad term encompassing various ways
| to make an antenna seem larger than it is. That's about all you
| can say about it, generically speaking.
|
| Impulse radar with range gating substitutes time resolution for
| spatial resolution, and has been used to 'look' through walls
| with varying degrees of success. I think you can even buy a
| studfinder that uses similar principles.
|
| Also, when you catch yourself writing things like this:
| One of our radar scientists accurately described the
| phenomenon (to reporters, presumably): It helps to
| think of it just as your brain's interpretation of
| a two dimensional representation of the coherent sum of
| backscatter responses from electromagnetic waves.
|
| .... it's probably time to hire some marketing folks.
| williamdclt wrote:
| It helps to think of a monad as just a monoid in the category
| of endofunctors, with product x replaced by composition of
| endofunctors and unit set by the identity endofunctor
| jcims wrote:
| Why does it seem that press releases and public statements like
| this tend to overstate things, to the point of fallacy, in order
| to make a definitive point?
|
| If you took a SAR image of my home you would _absolutely_ see how
| many vehicles are in my garage.
|
| Some examples from Sandia labs SAR image gallery -
| https://www.sandia.gov/radar/imagery/index.html
|
| (I believe these are aerial vs. orbital but the technology is the
| same)
|
| Ku band SAR
|
| Airport Historical Site - Can see parked vehicles right through
| the roof of the building on the left -
| https://www.sandia.gov/radar/_assets/images/gallery/ku-band-...
|
| Ka band SAR
|
| Golf Course - Can see right through the roof of the clubhouse and
| golfers (eg. human bodies) on the greens -
| https://www.sandia.gov/radar/_assets/images/gallery/ka-band-...
| Technically wrote:
| You can make the same claim about your own post: "seeing" is a
| very misleading description of the phenomenon you're
| describing.
| StavrosK wrote:
| I don't understand what you think is shown "through" the roof
| of the clubhouse (or cars, for that matter). That's just the
| roof:
|
| https://goo.gl/maps/bsSQjADvWuynPLvq6
| Firerouge wrote:
| Interestingly it does seem to see right through the awning
| that's to the right of the roof.
|
| There appears to be a couple tables that are hiden from
| Google's satellite view but clearly visible to the bottom
| right of the building in the ka band SAR image.
| StavrosK wrote:
| The SAR photo was probably taken before an awning was
| installed.
| Firerouge wrote:
| I thought that might of been the case as well, but based
| on Google Earth Pro's historic satellite data, it's been
| there since 2009.
| technick wrote:
| How long has this witchcraft been around?
| StavrosK wrote:
| That's odd, but you can see in the SAR photo that there
| isn't even an outline of the awning, nor the golf carts
| under it, nor the columns that hold the awning up, but
| there are trees which aren't there in the photos from the
| ground.
| Firerouge wrote:
| It certainly looks like you're right.
|
| While I can't find the image online earlier than 2010,
| there's an ieee research paper titled TanDEM-X for High-
| Resolution SAR Interferometry from 2007, so it certainly
| could predate the awning.
| enriquto wrote:
| I don't think that you are interpreting these images correctly
| (but the screenshots do not indicate the viewing direction, so
| it's not your fault). The objects that you see "through the
| roof" may be _in front_ of the building, not inside. Radar
| imaging is based on the return time of a chirp to the antenna.
| If two objects appear on the same pixel in the image it means
| that they are at the same distance to the antenna. For example,
| if the sensor is at a (common) elevation of 45 degrees, a 10m
| vertical wall will seem to cover the 10m of ground next to it,
| and any object there will be superimposed with the roof of the
| building.
|
| EDIT: I have some professional experience with the
| interpretation of satellite SAR imagery.
| jcrawfordor wrote:
| I have the local knowledge to tell you that there aren't parked
| vehicles in or near that part of the building. You can even see
| in aerials that it's that it's a lawn with walking paths and a
| prefab outbuilding. I think this SAR image may be from before
| the outbuilding was there, and historical imagery shows that it
| used to just be an extension of the lawn. I think the bright
| objects are a distorted reflection from elements of the
| building facade, perhaps. I don't know, I'm squinting at the
| SAR image having a hard time deciding if it depicts the
| outbuilding or not, and it perhaps says something about the
| _limitations_ of SAR images that it 's not clear to the
| untrained eye whether or not an entire building is there. I
| think it's possible the building is there and is just made of
| materials with very low reflectivity, there are sort of "ghost
| lines" that seem in the right place for its edges.
| studius wrote:
| > Why does it seem that press releases and public statements
| like this tend to overstate things, to the point of fallacy, in
| order to make a definitive point?
|
| While in my mind, things were better with Fairness Doctrine and
| Equal-time Rule restrictions, I think we could solve this in
| the US by greater tax-funded federal, state, and local
| government-funded media, where the government has no control
| over that media aside from that of regulation to promote fair
| and equal representation within that media.
|
| Basically, put PBS, state, and local programming into a
| streamed source similar to Netflix/Hulu/Prime, produce content
| with quality surpassing other streaming services, and give the
| public air time both via meritocratic decision by randomly
| selected electorate as well as via lottery and availability.
| The BBC might be a good model to emulate also.
|
| At that point, there would at least be an alternative to B.S.
| journalism and bad media behavior reinforced by viewership and
| advertising dollars.
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