"To avoid this problem, the team divided their 100-milliwatt laser into eight beams. Each beam travels along a slightly different path through the turbulent atmosphere and thus receives a different random phase perturbation. Counterintuitively, this incoherent illumination makes the interference effects observable.
When I first started studying optical engineering, my teacher had worked on the first under-the-RADAR guidance system for bombers. He told lots of amusing stories, like how the pilots insisted on a manual override - so they "agreed" to provide a switch, noting to us manual piloting at near-treetop level and 1,000 ft/s is insane.
He taught us about the nominal amount of turbulence in the atmosphere, and that it limited space-based cameras to about half a foot resolution - a limit he said couldn't be broken. Therefore, license plates would never be readable from space...
Before I was out of grad school, they had broken it with laser techniques on nearby targets. Flash the laser at the same time as the image, scan the laser-illuminated spot, calculate the perturbance, and reverse-filter the image. A lot of processing (for that day), but it could be done back on Earth.
As you can see from the test images, the 8 lasers aren't enough to perfectly smooth out the noise. The noise is probably square-root-8 improved, so resolution should improve by a factor of not quite 3. Move those lasers slightly and repeat 12 times; you've improved resolution by 10. This is easy to do quickly; you should be able to read fine print held by a car passenger on the highway.
We are in the middle of a renaissance of image processing across a wide range of fields. Many of the previous limits are being smashed by using new materials and algorithms. See https://en.wikipedia.org/wiki/Fourier_ptychography for an example
Wow, I had no idea. I know nothing about the field, so maybe someone better educated can answer my innocent, probably naive question: my instincts tell me that any technology that makes humans better at manipulating or interpreting light has vast potential to alter our lives. Is that right?
That's how night mode works on Pixel phones, right? I believe it takes a few images in rapid succession and took advantage of the noise being random which meant a high quality image under a noisy sensor with some signal processing.
It also can actually allow you to identify positions within the image at a greater resolution than the pixels, or even light itself, would otherwise allow.
In microscopy, this is called 'super-resolution'. You can take many images over and over, and while the light itself is 100s of nanometers large, you actually can calculate the centroid of whatever is producing that light with greater resolution than the size of the light itself.
Integrating over a longer time to get more accurate light measurements of the a scene has been a principal feature of photography. You need to slow down the shutter and open up the aperture in dark conditions.
Combining multiple exposures is not significantly different from a single longer exposure, except the key innovation of combining motion data and digital image stabilization which allows smartphones to approximate longer exposures without the need of a tripod.
This is how we reduce noise in filmmaking. My de-noise node in DaVinci has two settings: spatial and temporal. Temporal references 3 frames either side of the subject frame.
So what's the summary of how this works? I don't think it was explained well, and I'm fairly up to speed with the physics of photons etc. Is it that the multiple lasers are able to destructively interfere with each other so that they cancel out the noise from each other since the noise will be the same in all of them? That's tricky because if the photons are phase shifted to cancel out the noise that seems like the ENTIRE laser signal would be cancelled out too. Maybe this is what's happening, and the only thing "left over" is the signal from the source (what's being measured)?
>He told lots of amusing stories, like how the pilots insisted on a manual override - so they "agreed" to provide a switch, noting to us manual piloting at near-treetop level and 1,000 ft/s is insane.
You ought to read Tom Wolfe’s “the right stuff” asap if you haven’t already
> To demonstrate the system’s capabilities, the team created a series of 8-mm-wide targets, each made from a reflective material and imprinted with a letter.
> He imagines that the remote-imaging system could have several applications, including monitoring insect populations across agricultural land.
“Insect populations” is a funny way to spell secrets. Jokes aside, it does seem like this could serve a wide range of non-espionage related use cases. Really cool.
there is a now old technology where a laser is shone on a window, and the resulting glow is imaged, the images if anylised are an analog audio signal that is created by voices inside a building vib the newer version under discussion here is a direct fit forthe same use, but at much greater distances and greater fidelity/resolution
there were many,mostly mechanical devices, made to detect aircraft ,deployed durring
WWII, that had two large acoustical horns directed a central binaural detection sensor, the whole aparatus was the mounted on a large stage that turned, and the horns were also aimable, giving a bearing, and speed on aircraft, in dark ,coudy, or other conditions.The inferometer bieng someone in a seat.
That interesting article led me down a research rabbit hole of microwave maser inferometers and whether that could be an explanation for the controversial Havana Syndrome. And, having skimmed descriptions of historical SIGINT projects Buran[1] and Luch[2], and the theoretical advantages of such a system ... my curiosity in Faraday cages is renewed.
Modulating a laser beam for communications is not new but this distance effort by amateurs doing a two-way voice transmission over 167km in New Zeland is pretty cool. This article also mentions a number of other laser communication long distance efforts.
My (mis?)understanding was that two receivers acting as an interferometer can only resolve things that are on a line parallel with the line between the receivers--so if the receivers are on a horizontal, then they can resolve left and right in their targets, but not up and down. But the images shown in the paper have more or less full 360 degrees resolution. Is that because they rotated the target? The paper says they did, but it's not clear how many increments of partial rotation they did--every 10 degrees, 20,...
If the target cannot be rotated, can the two (or more) receivers revolve around a central axis? If so, presumably one of the receivers could revolve around the other (fixed) receiver to the same effect.
If it’s truly just like the methods astrophysicists use for transit imaging, you might even be able to do some funky stuff like monitor invisible gasses. Could potentially be revolutionary for things like fume safety and viral spread tracking, among other uses. Might even be able to analyze liquids in a container without having to touch the liquid (the name for this type of testing evades me at the moment)
I believe it'd be pretty wonky coloring, or at least it could be, since it'd be capturing snapshots of individual frequency responses. If something is visibly green, reflecting across most of the greenish areas of spectrum, but happens to absorb the exact frequency of the laser, it'd appear black when imaged this way. Or at least not green.
I think that’s the case for regular cameras too though, the filter for the pixels doesn’t exactly replicate the response of the cones in the eyes either, right? So you have things where the camera sees a different color than a human eye.
Readit News
"To avoid this problem, the team divided their 100-milliwatt laser into eight beams. Each beam travels along a slightly different path through the turbulent atmosphere and thus receives a different random phase perturbation. Counterintuitively, this incoherent illumination makes the interference effects observable.
When I first started studying optical engineering, my teacher had worked on the first under-the-RADAR guidance system for bombers. He told lots of amusing stories, like how the pilots insisted on a manual override - so they "agreed" to provide a switch, noting to us manual piloting at near-treetop level and 1,000 ft/s is insane.
He taught us about the nominal amount of turbulence in the atmosphere, and that it limited space-based cameras to about half a foot resolution - a limit he said couldn't be broken. Therefore, license plates would never be readable from space...
Before I was out of grad school, they had broken it with laser techniques on nearby targets. Flash the laser at the same time as the image, scan the laser-illuminated spot, calculate the perturbance, and reverse-filter the image. A lot of processing (for that day), but it could be done back on Earth.
As you can see from the test images, the 8 lasers aren't enough to perfectly smooth out the noise. The noise is probably square-root-8 improved, so resolution should improve by a factor of not quite 3. Move those lasers slightly and repeat 12 times; you've improved resolution by 10. This is easy to do quickly; you should be able to read fine print held by a car passenger on the highway.
Dramatically improve microscope resolution with an LED array and Fourier Ptychography
https://www.youtube.com/watch?v=9KJLWwbs_cQ
In microscopy, this is called 'super-resolution'. You can take many images over and over, and while the light itself is 100s of nanometers large, you actually can calculate the centroid of whatever is producing that light with greater resolution than the size of the light itself.
https://en.wikipedia.org/wiki/Super-resolution_imaging
Combining multiple exposures is not significantly different from a single longer exposure, except the key innovation of combining motion data and digital image stabilization which allows smartphones to approximate longer exposures without the need of a tripod.
That's also how some adaptive optics work in astronomy,
https://en.wikipedia.org/wiki/Laser_guide_star
You ought to read Tom Wolfe’s “the right stuff” asap if you haven’t already
https://youtu.be/tUJDbj9Vp5w?si=YFeau8vskUvpDUNV
Deleted Comment
> To demonstrate the system’s capabilities, the team created a series of 8-mm-wide targets, each made from a reflective material and imprinted with a letter.
imaging technologies you mistook for imagination technologies and their gpu inside of a sega dreamcast or iphone, ipad,...
1.36 km = 0.85 miles
“Insect populations” is a funny way to spell secrets. Jokes aside, it does seem like this could serve a wide range of non-espionage related use cases. Really cool.
[1]https://en.wikipedia.org/wiki/Laser_microphone
[2]https://en.wikipedia.org/wiki/Olymp-K
And we are about to be saturated in them as soon as LiDAR full self driving goes mainstream
https://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment...
Not quite there yet at the amateur level, private industry soon, but then there is the question of safety to air traffic.
Can you imagine the first moon data link? JWST has 8mbps
https://www.modulatedlight.org/Modulated_Light_DX/MODULATED_...
If the target cannot be rotated, can the two (or more) receivers revolve around a central axis? If so, presumably one of the receivers could revolve around the other (fixed) receiver to the same effect.