8 ms·

No, SAR Can't See Through Buildings

192 points by Shelnutt2 6y ago

mattlondon 6y ago
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 6y ago
  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/Capella-Space-Spot-Image-Tokyo-Japan.png https://tilde.pt/~fimdomeio/nossa-senhora-do-computismo/img/...
rmrfstar 6y ago
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 https://en.wikipedia.org/wiki/Kyllo_v._United_States
- __turbobrew__ 6y ago
  Maybe this? https://ieeexplore.ieee.org/abstract/document/6894586 https://ieeexplore.ieee.org/abstract/document/6894586
- jcims 6y ago
  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 https://www.sandia.gov/radar/imagery/index.html Example: https://www.sandia.gov/radar/_assets/images/gallery/ka-band.png https://www.sandia.gov/radar/_assets/images/gallery/ka-band....
arcticfox 6y ago
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 6y ago
SAR = Synthetic Aperture Radar
deleted 6y ago
[deleted]
elil17 6y ago
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 https://www.kurzweilai.net/seeing-through-walls-in-real-time
- CamperBob2 6y ago
  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 6y ago
    It helps to think of a monad as just a monoid in the category of endofunctors, with product × replaced by composition of endofunctors and unit set by the identity endofunctor
  - ahakki 6y ago
    That science guy has a good sense of humor.
  - mncharity 6y ago
    > it's probably time to hire some marketing folks Engineering PhD students coached on outreach presentation of their thesis sometimes improve dramatically in just a few hours. Some not so much.
- peter303 6y ago
  Highest frequencies like used in airport scanners
jcims 6y ago
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 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-5.png 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-3.png https://www.sandia.gov/radar/_assets/images/gallery/ka-band-...
- StavrosK 6y ago
  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 https://goo.gl/maps/bsSQjADvWuynPLvq6
  - Firerouge 6y ago
    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 6y ago
      The SAR photo was probably taken before an awning was installed.
      - Firerouge 6y ago
        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.
supernova87a 6y ago
"... 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 6y ago
  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.
- excerionsforte 6y ago
  Lol. Articles like this remind me of Silicon Valley where Pied Piper app is built for engineers rather than "Regular people": https://www.youtube.com/watch?v=QYBcLMiR9b0 https://www.youtube.com/watch?v=QYBcLMiR9b0 and then Richard going in to the focus group trying to explain it science-speak rather than ELI5. It seemed like this article's intended audience is regular people and it missed the mark. First question I had was... what is SAR?
  - Animats 6y ago
    Synthetic Aperture Radar. What you're really seeing here is what happens when you try to put together a 3D image from an angled line scan from a moving scanner. There isn't enough information to do this perfectly, so you get artifacts on tall objects. You can see somewhat similar artifacts in Google Earth when looking down on tall objects for which they don't have full elevation data, like trees. What's impressive is that they're getting 50cm resolution from orbit. Doing this from aircraft is nothing new; that's been going on for decades. But 50cm from a satellite? That's an achievement.
    - 6y ago
JohnJamesRambo 6y ago
They didn't follow the first rule of writing something. I don't know what SAR is. Synthetic-aperture radar (SAR)?
14 6y ago
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 6y ago
  I believe it's called having a phone.
  - 14 6y ago
    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 6y ago
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? EDIT: Ok, after Googling this a little I think I get it. The skyscrapers are upside-down. (I think?) The radar is measuring slant-range distance, and due to the viewing angle, the tops of the skyscrapers are closer to the radar than the bases. So the tops of the buildings are closer to the bottom of the image. Since the skyscrapers are in the “wrong” place in the image, they get blended with ground features that are in the “right” place. Is that right?
- srtjstjsj 6y ago
  That a much better explanation than the OP article. It's like an isometric view of a video game. (But not exactly, since the angles are different) A tall thing and a lower thing nearby it are protected onto the same spot. (Usually in a video game the tall thing blocks the behind thing, instead of blending with it.) Blending the two images makes the front-looking thing look transparent, when in really you are seeing around one object (since the observation angle is not the same as the imaginary viewing angle of the image) and then drawing both objects in the same pixel.
- galangalalgol 6y ago
  Yes, and you said it much better than the article.
- gaudat 6y ago
  There is a proper-looking scan of high-rise buildings in the linked SAR 101 article: https://capellaspace.wpengine.com/wp-content/uploads/2020/02/SpaceNet6-Blog_urban-SAR-imagery.png https://capellaspace.wpengine.com/wp-content/uploads/2020/02... See how only the 2 near sides of the buildings got imaged. The skyscrapers in that Tokyo image only have the 2 far sides imaged. So I guess the image was acquired upside-down on the satellite. The team fliped the 2D image and called it a day. Now if Capella can release raw range information of their scans and let us play with it...
- Jach 6y ago
  You can build your own SAR system pretty easily, but of course the really cool stuff results from being able to fly a plane or in this case have some satellites. The PDF for Experiment 3 here https://ocw.mit.edu/resources/res-ll-003-build-a-small-radar-system-capable-of-sensing-range-doppler-and-synthetic-aperture-radar-imaging-january-iap-2011/projects/ https://ocw.mit.edu/resources/res-ll-003-build-a-small-radar... shows an example of using a weak 2.4 GHz system on the ground taking snapshots every two inches for 10 feet or so, facing down a road towards a warehouse. A visualization algorithm is overlayed on top of a satellite image to show that the system can at least detect front surfaces. The professor has also built other hobbyist high-frequency systems before, including demonstrating through-wall capabilities for some of them. This PDF (others on his site) has some good examples of what the environment looks like with a camera, and what you get when you process some SAR data with matlab into a 2D image: http://glcharvat.com/website%20pdfs/Charvat_MIT_Haystack_DIY_SAR.pdf http://glcharvat.com/website%20pdfs/Charvat_MIT_Haystack_DIY...
Itsdijital 6y ago
Can someone explain what the advantage of this is over a typical optical visible range satellite.
- _adamb 6y ago
  It can see through clouds and take pictures at night!
  - reasonabl_human 6y ago
    Yep, and depending on power and focusing, can ascertain better resolution and more clearly see object definition as opposed to blended colors
- pratyushc 6y ago
  I don't all the pros and cons, but SAR can see through cloud cover.
- shash 6y ago
  It can see through buildings, it can do some pretty precise depth estimates,... It’s not a replacement for visual range (or infrared for that matter) but an additional sensor. It’s usually used to create things like elevation maps. So all those altitude measurements that you see on Google Earth might be at least partially SAR.
  - K0balt 6y ago
    "it can see through buildings" Perhaps you missed the point of the article? While it is true that some implementations of SAR can image through walls at short distances (tens of meters), SAR is a very broad term and those systems are very different from the imaging systems in the article.
    - shash 6y ago
      OK, never comment from a mobile phone! Of course I meant it can't see through buildings!
zyxzevn 6y ago
But SAR can see changes after earth-quakes https://maps.disasters.nasa.gov/arcgis/apps/MapSeries/index.html?appid=a6e721ce85704bdfb3ef3f9e0b780a9b https://maps.disasters.nasa.gov/arcgis/apps/MapSeries/index.... So it can track your mum
the__alchemist 6y ago
Anecdote you may or may not find relevant: SAR maps are used regularly by fighter aircraft (And have been for decades) to generate high-precision coordinates (Absolute or relative) that can be used to target weapons. They do this from relatively far away. Most 4th gen+ fighter radars are capable of doing this in hardware and software. The layover effect at the center of this article is due to the map being of skyscrapers.
deleted 6y ago
[deleted]
fnord77 6y ago
no where on the page or the site do they explain what "SAR" stands for. https://en.wikipedia.org/wiki/Synthetic-aperture_radar https://en.wikipedia.org/wiki/Synthetic-aperture_radar
molticrystal 6y ago
If you do want something that can look inside a building and determine the positions of people and objects, look up wifi slam [0] which was acquired by apple. It can use the wifi signals to map out the inside of a building and determine the location of objects inside. About a decade later, thanks to neural networks and other techniques, they can use wifi to determine pose information, they can create a rough skeletal model of a person that moves as you move. [1] The 2020 enhancements are a decent upgrade. [2] [0] https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=wifi+slam https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=wifi... [1] http://rfpose.csail.mit.edu/ http://rfpose.csail.mit.edu/ [2] https://cse.buffalo.edu/~lusu/papers/MobiCom2020.pdf https://cse.buffalo.edu/~lusu/papers/MobiCom2020.pdf
- pottertheotter 6y ago
  I find this both fascinating and terrifying.
- mstade 6y ago
  Setting obvious privacy implications aside, I'm surprised how good the animations look. I wonder if this could be developed further to enable cheap motion capture solutions for film/game studios. If it works in real-time then coupled with a game engine it could give you a direct in-camera look on what a cgi heavy scene might look like, without requiring (too) fancy hardware and also not adding distracting jump suits and reflective tennis balls and dot makeup all over the place. The Mandalorian production comes to mind, they've been pushing this kind of direction hard. Very cool stuff, thanks for sharing!
- noizejoy 6y ago
  Never mind toilet paper shortages - I’ll be stocking up on tinfoil - for real this time! :-)
bitminer 6y ago
There is a lot marketing bullshit in the Capella articles. For example, the Singapore image of buildings and other detections by the SAR is clearly overlaid on an optical image with trees and bushes and respective shadows. Trees and bushes are invisible to X-band (10GHz) SAR. It has to be an optical image underlaying the radar data. Look at it. The detections by SAR are bright white. Most of the image is grey-scale showing background items. It is not advertised as such. As an interpretable image, perhaps this is an improvement over notoriously hard-to-understand monochrome SAR imagery. BUT! It is not described as such. Hence my subjective evaluation as "bullshit". [0] https://ichef.bbci.co.uk/news/976/cpsprodpb/C172/production/_116122594_capella-space-spot-image_exxonmobil_petrochemical_complex_jurong_island_singapore-nc.png https://ichef.bbci.co.uk/news/976/cpsprodpb/C172/production/... [1] https://www.bbc.com/news/science-environment-55326441 https://www.bbc.com/news/science-environment-55326441
- edgineer 6y ago
  Speaking as someone with experience working with SAR imagery, the example you link to does not appear overlaid on optical imagery.
- derstander 6y ago
  > Trees and bushes are invisible to X-band (10GHz) SAR. It has to be an optical image underlaying the radar data Trees and bushes are very much visible to X-band radar systems. See e.g. http://web.eecs.umich.edu/~saraband/KSIEEE/J54IEEETGRSJan00StilesSarabandi.pdf http://web.eecs.umich.edu/~saraband/KSIEEE/J54IEEETGRSJan00S... Foliage Penetration (FOPEN) radars, in my experience, do not use X-band.
andi999 6y ago
Do I believe that. Not really. Frequency is around 9,7GHz which is the upper limit of ground and wall penetrating radar systems. Of course you cannot look through metal or conductive structures, but why not thin plastic tents or thin walls? For this we need to know the sensors sensitivity. Of course imaging gets a bit messier, since the imageing algorithm is based on the assumption that you only get an entry reflex (so basically it is 2D or lets call it 2,5D imaging). For full 3D you also need to scan/move orthogonal to the first satelite direction.
deleted 6y ago
[deleted]
ganstyles 6y ago
I've heard of c band sar, and x band sar. Is x band higher resolution? I understand it has properties where x sees through fewer things, but is x fundamentally better resolution or something? If not wouldn't higher wavelength be better for seeing through and resolving objects?
fithisux 6y ago
Given this opportunity, anyone has any good tutorial on the mathematics of SAR image formation from electromagnetic scattering ?? Thanks
IshKebab 6y ago
Wow that was a terrible explanation. As far as I can figure out, it is only 1D SAR - that is the X axis is spatial, but the Y axis is actually time. If you fire radio waves at the ground at an angle, and the ground is flat, then you can easily map time to position. But buildings and hills mess up that mapping. I always assumed SAR used 2D arrays. Again, really terrible explanation. It feels like they really didn't want to explain it at all.
fourthark 6y ago
The blow-up picture doesn’t make sense either - hardly any difference in zoom and the little circle contains only a small part of the image in the big circle. Do they understand how these diagrams are supposed to work?
mikewarot 6y ago
I know better than to worry about seeing through buildings. What I want to do is to explore the data, and see how the land rises and falls with the tides, the rain levels, temperature, etc. There have to be all sorts of new and beautiful images and movies to be made from this data. I look forward to getting my hands on it eventually.

192 points by Shelnutt2 6y ago

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 6y ago
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/Capella-Space-Spot-Image-Tokyo-Japan.png https://tilde.pt/~fimdomeio/nossa-senhora-do-computismo/img/...

rmrfstar 6y ago

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 https://en.wikipedia.org/wiki/Kyllo_v._United_States

__turbobrew__ 6y ago
Maybe this? https://ieeexplore.ieee.org/abstract/document/6894586 https://ieeexplore.ieee.org/abstract/document/6894586
jcims 6y ago
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 https://www.sandia.gov/radar/imagery/index.html Example: https://www.sandia.gov/radar/_assets/images/gallery/ka-band.png https://www.sandia.gov/radar/_assets/images/gallery/ka-band....

arcticfox 6y ago

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 6y ago

SAR = Synthetic Aperture Radar

deleted 6y ago

[deleted]

elil17 6y ago

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 https://www.kurzweilai.net/seeing-through-walls-in-real-time

CamperBob2 6y ago
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 6y ago
  It helps to think of a monad as just a monoid in the category of endofunctors, with product × replaced by composition of endofunctors and unit set by the identity endofunctor
- ahakki 6y ago
  That science guy has a good sense of humor.
- mncharity 6y ago
  > it's probably time to hire some marketing folks Engineering PhD students coached on outreach presentation of their thesis sometimes improve dramatically in just a few hours. Some not so much.
peter303 6y ago
Highest frequencies like used in airport scanners

jcims 6y ago

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 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-5.png 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-3.png https://www.sandia.gov/radar/_assets/images/gallery/ka-band-...

StavrosK 6y ago
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 https://goo.gl/maps/bsSQjADvWuynPLvq6
- Firerouge 6y ago
  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 6y ago
    The SAR photo was probably taken before an awning was installed.
    - Firerouge 6y ago
      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.

supernova87a 6y ago

"... 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 6y ago
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.
excerionsforte 6y ago
Lol. Articles like this remind me of Silicon Valley where Pied Piper app is built for engineers rather than "Regular people": https://www.youtube.com/watch?v=QYBcLMiR9b0 https://www.youtube.com/watch?v=QYBcLMiR9b0 and then Richard going in to the focus group trying to explain it science-speak rather than ELI5. It seemed like this article's intended audience is regular people and it missed the mark. First question I had was... what is SAR?
- Animats 6y ago
  Synthetic Aperture Radar. What you're really seeing here is what happens when you try to put together a 3D image from an angled line scan from a moving scanner. There isn't enough information to do this perfectly, so you get artifacts on tall objects. You can see somewhat similar artifacts in Google Earth when looking down on tall objects for which they don't have full elevation data, like trees. What's impressive is that they're getting 50cm resolution from orbit. Doing this from aircraft is nothing new; that's been going on for decades. But 50cm from a satellite? That's an achievement.
  - 6y ago

JohnJamesRambo 6y ago

They didn't follow the first rule of writing something. I don't know what SAR is. Synthetic-aperture radar (SAR)?

14 6y ago

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 6y ago
I believe it's called having a phone.
- 14 6y ago
  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 6y ago

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? EDIT: Ok, after Googling this a little I think I get it. The skyscrapers are upside-down. (I think?) The radar is measuring slant-range distance, and due to the viewing angle, the tops of the skyscrapers are closer to the radar than the bases. So the tops of the buildings are closer to the bottom of the image. Since the skyscrapers are in the “wrong” place in the image, they get blended with ground features that are in the “right” place. Is that right?

srtjstjsj 6y ago
That a much better explanation than the OP article. It's like an isometric view of a video game. (But not exactly, since the angles are different) A tall thing and a lower thing nearby it are protected onto the same spot. (Usually in a video game the tall thing blocks the behind thing, instead of blending with it.) Blending the two images makes the front-looking thing look transparent, when in really you are seeing around one object (since the observation angle is not the same as the imaginary viewing angle of the image) and then drawing both objects in the same pixel.
galangalalgol 6y ago
Yes, and you said it much better than the article.
gaudat 6y ago
There is a proper-looking scan of high-rise buildings in the linked SAR 101 article: https://capellaspace.wpengine.com/wp-content/uploads/2020/02/SpaceNet6-Blog_urban-SAR-imagery.png https://capellaspace.wpengine.com/wp-content/uploads/2020/02... See how only the 2 near sides of the buildings got imaged. The skyscrapers in that Tokyo image only have the 2 far sides imaged. So I guess the image was acquired upside-down on the satellite. The team fliped the 2D image and called it a day. Now if Capella can release raw range information of their scans and let us play with it...
Jach 6y ago
You can build your own SAR system pretty easily, but of course the really cool stuff results from being able to fly a plane or in this case have some satellites. The PDF for Experiment 3 here https://ocw.mit.edu/resources/res-ll-003-build-a-small-radar-system-capable-of-sensing-range-doppler-and-synthetic-aperture-radar-imaging-january-iap-2011/projects/ https://ocw.mit.edu/resources/res-ll-003-build-a-small-radar... shows an example of using a weak 2.4 GHz system on the ground taking snapshots every two inches for 10 feet or so, facing down a road towards a warehouse. A visualization algorithm is overlayed on top of a satellite image to show that the system can at least detect front surfaces. The professor has also built other hobbyist high-frequency systems before, including demonstrating through-wall capabilities for some of them. This PDF (others on his site) has some good examples of what the environment looks like with a camera, and what you get when you process some SAR data with matlab into a 2D image: http://glcharvat.com/website%20pdfs/Charvat_MIT_Haystack_DIY_SAR.pdf http://glcharvat.com/website%20pdfs/Charvat_MIT_Haystack_DIY...

Itsdijital 6y ago

Can someone explain what the advantage of this is over a typical optical visible range satellite.

_adamb 6y ago
It can see through clouds and take pictures at night!
- reasonabl_human 6y ago
  Yep, and depending on power and focusing, can ascertain better resolution and more clearly see object definition as opposed to blended colors
pratyushc 6y ago
I don't all the pros and cons, but SAR can see through cloud cover.
shash 6y ago
It can see through buildings, it can do some pretty precise depth estimates,... It’s not a replacement for visual range (or infrared for that matter) but an additional sensor. It’s usually used to create things like elevation maps. So all those altitude measurements that you see on Google Earth might be at least partially SAR.
- K0balt 6y ago
  "it can see through buildings" Perhaps you missed the point of the article? While it is true that some implementations of SAR can image through walls at short distances (tens of meters), SAR is a very broad term and those systems are very different from the imaging systems in the article.
  - shash 6y ago
    OK, never comment from a mobile phone! Of course I meant it can't see through buildings!

zyxzevn 6y ago

But SAR can see changes after earth-quakes https://maps.disasters.nasa.gov/arcgis/apps/MapSeries/index.html?appid=a6e721ce85704bdfb3ef3f9e0b780a9b https://maps.disasters.nasa.gov/arcgis/apps/MapSeries/index.... So it can track your mum

the__alchemist 6y ago

Anecdote you may or may not find relevant: SAR maps are used regularly by fighter aircraft (And have been for decades) to generate high-precision coordinates (Absolute or relative) that can be used to target weapons. They do this from relatively far away. Most 4th gen+ fighter radars are capable of doing this in hardware and software. The layover effect at the center of this article is due to the map being of skyscrapers.

deleted 6y ago

[deleted]

fnord77 6y ago

no where on the page or the site do they explain what "SAR" stands for. https://en.wikipedia.org/wiki/Synthetic-aperture_radar https://en.wikipedia.org/wiki/Synthetic-aperture_radar

molticrystal 6y ago

If you do want something that can look inside a building and determine the positions of people and objects, look up wifi slam [0] which was acquired by apple. It can use the wifi signals to map out the inside of a building and determine the location of objects inside. About a decade later, thanks to neural networks and other techniques, they can use wifi to determine pose information, they can create a rough skeletal model of a person that moves as you move. [1] The 2020 enhancements are a decent upgrade. [2] [0] https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=wifi+slam https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=wifi... [1] http://rfpose.csail.mit.edu/ http://rfpose.csail.mit.edu/ [2] https://cse.buffalo.edu/~lusu/papers/MobiCom2020.pdf https://cse.buffalo.edu/~lusu/papers/MobiCom2020.pdf

pottertheotter 6y ago
I find this both fascinating and terrifying.
mstade 6y ago
Setting obvious privacy implications aside, I'm surprised how good the animations look. I wonder if this could be developed further to enable cheap motion capture solutions for film/game studios. If it works in real-time then coupled with a game engine it could give you a direct in-camera look on what a cgi heavy scene might look like, without requiring (too) fancy hardware and also not adding distracting jump suits and reflective tennis balls and dot makeup all over the place. The Mandalorian production comes to mind, they've been pushing this kind of direction hard. Very cool stuff, thanks for sharing!
noizejoy 6y ago
Never mind toilet paper shortages - I’ll be stocking up on tinfoil - for real this time! :-)

bitminer 6y ago

There is a lot marketing bullshit in the Capella articles. For example, the Singapore image of buildings and other detections by the SAR is clearly overlaid on an optical image with trees and bushes and respective shadows. Trees and bushes are invisible to X-band (10GHz) SAR. It has to be an optical image underlaying the radar data. Look at it. The detections by SAR are bright white. Most of the image is grey-scale showing background items. It is not advertised as such. As an interpretable image, perhaps this is an improvement over notoriously hard-to-understand monochrome SAR imagery. BUT! It is not described as such. Hence my subjective evaluation as "bullshit". [0] https://ichef.bbci.co.uk/news/976/cpsprodpb/C172/production/_116122594_capella-space-spot-image_exxonmobil_petrochemical_complex_jurong_island_singapore-nc.png https://ichef.bbci.co.uk/news/976/cpsprodpb/C172/production/... [1] https://www.bbc.com/news/science-environment-55326441 https://www.bbc.com/news/science-environment-55326441

edgineer 6y ago
Speaking as someone with experience working with SAR imagery, the example you link to does not appear overlaid on optical imagery.
derstander 6y ago
> Trees and bushes are invisible to X-band (10GHz) SAR. It has to be an optical image underlaying the radar data Trees and bushes are very much visible to X-band radar systems. See e.g. http://web.eecs.umich.edu/~saraband/KSIEEE/J54IEEETGRSJan00StilesSarabandi.pdf http://web.eecs.umich.edu/~saraband/KSIEEE/J54IEEETGRSJan00S... Foliage Penetration (FOPEN) radars, in my experience, do not use X-band.

andi999 6y ago

Do I believe that. Not really. Frequency is around 9,7GHz which is the upper limit of ground and wall penetrating radar systems. Of course you cannot look through metal or conductive structures, but why not thin plastic tents or thin walls? For this we need to know the sensors sensitivity. Of course imaging gets a bit messier, since the imageing algorithm is based on the assumption that you only get an entry reflex (so basically it is 2D or lets call it 2,5D imaging). For full 3D you also need to scan/move orthogonal to the first satelite direction.

deleted 6y ago

[deleted]

ganstyles 6y ago

I've heard of c band sar, and x band sar. Is x band higher resolution? I understand it has properties where x sees through fewer things, but is x fundamentally better resolution or something? If not wouldn't higher wavelength be better for seeing through and resolving objects?

fithisux 6y ago

Given this opportunity, anyone has any good tutorial on the mathematics of SAR image formation from electromagnetic scattering ?? Thanks

IshKebab 6y ago

Wow that was a terrible explanation. As far as I can figure out, it is only 1D SAR - that is the X axis is spatial, but the Y axis is actually time. If you fire radio waves at the ground at an angle, and the ground is flat, then you can easily map time to position. But buildings and hills mess up that mapping. I always assumed SAR used 2D arrays. Again, really terrible explanation. It feels like they really didn't want to explain it at all.

fourthark 6y ago

The blow-up picture doesn’t make sense either - hardly any difference in zoom and the little circle contains only a small part of the image in the big circle. Do they understand how these diagrams are supposed to work?

mikewarot 6y ago

I know better than to worry about seeing through buildings. What I want to do is to explore the data, and see how the land rises and falls with the tides, the rain levels, temperature, etc. There have to be all sorts of new and beautiful images and movies to be made from this data. I look forward to getting my hands on it eventually.