Seeing objects through clouds and fog

Date:
September 9, 2020
Source:
Stanford University
Summary:
Using a new algorithm, researchers have reconstructed the movements
of individual particles of light to see through clouds, fog and
other obstructions.



FULL STORY ==========================================================================
Like a comic book come to life, researchers at Stanford University have developed a kind of X-ray vision -- only without the X-rays. Working
with hardware similar to what enables autonomous cars to "see" the
world around them, the researchers enhanced their system with a highly efficient algorithm that can reconstruct three-dimensional hidden scenes
based on the movement of individual particles of light, or photons. In
tests, detailed in a paper published Sept. 9 in Nature Communications,
their system successfully reconstructed shapes obscured by 1-inch-thick
foam. To the human eye, it's like seeing through walls.


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"A lot of imaging techniques make images look a little bit better,
a little bit less noisy, but this is really something where we make
the invisible visible," said Gordon Wetzstein, assistant professor of electrical engineering at Stanford and senior author of the paper. "This
is really pushing the frontier of what may be possible with any kind of
sensing system. It's like superhuman vision." This technique complements
other vision systems that can see through barriers on the microscopic
scale -- for applications in medicine -- because it's more focused on large-scale situations, such as navigating self-driving cars in fog
or heavy rain and satellite imaging of the surface of Earth and other
planets through hazy atmosphere.

Supersight from scattered light In order to see through environments
that scatter light every-which-way, the system pairs a laser with a super-sensitive photon detector that records every bit of laser light
that hits it. As the laser scans an obstruction like a wall of foam, an occasional photon will manage to pass through the foam, hit the objects
hidden behind it and pass back through the foam to reach the detector.

The algorithm-supported software then uses those few photons -- and
information about where and when they hit the detector -- to reconstruct
the hidden objects in 3D.

This is not the first system with the ability to reveal hidden objects
through scattering environments, but it circumvents limitations associated
with other techniques. For example, some require knowledge about how far
away the object of interest is. It is also common that these systems
only use information from ballistic photons, which are photons that
travel to and from the hidden object through the scattering field but
without actually scattering along the way.



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"We were interested in being able to image through scattering media
without these assumptions and to collect all the photons that have been scattered to reconstruct the image," said David Lindell, a graduate
student in electrical engineering and lead author of the paper. "This
makes our system especially useful for large-scale applications, where
there would be very few ballistic photons." In order to make their
algorithm amenable to the complexities of scattering, the researchers
had to closely co-design their hardware and software, although the
hardware components they used are only slightly more advanced than
what is currently found in autonomous cars. Depending on the brightness
of the hidden objects, scanning in their tests took anywhere from one
minute to one hour, but the algorithm reconstructed the obscured scene
in real-time and could be run on a laptop.

"You couldn't see through the foam with your own eyes, and even just
looking at the photon measurements from the detector, you really don't
see anything," said Lindell. "But, with just a handful of photons, the reconstruction algorithm can expose these objects -- and you can see not
only what they look like, but where they are in 3D space." Space and
fog Someday, a descendant of this system could be sent through space to
other planets and moons to help see through icy clouds to deeper layers
and surfaces.

In the nearer term, the researchers would like to experiment with
different scattering environments to simulate other circumstances where
this technology could be useful.

"We're excited to push this further with other types of scattering
geometries," said Lindell. "So, not just objects hidden behind a thick
slab of material but objects that are embedded in densely scattering
material, which would be like seeing an object that's surrounded by fog." Lindell and Wetzstein are also enthusiastic about how this work represents
a deeply interdisciplinary intersection of science and engineering.

"These sensing systems are devices with lasers, detectors and advanced algorithms, which puts them in an interdisciplinary research area between hardware and physics and applied math," said Wetzstein. "All of those are critical, core fields in this work and that's what's the most exciting
for me."

========================================================================== Story Source: Materials provided by Stanford_University. Original written
by Taylor Kubota.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Lindell, D.B., Wetzstein, G. Three-dimensional imaging through
scattering
media based on confocal diffuse tomography. Nat Commun, 2020 DOI:
10.1038/s41467-020-18346-3 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200909132102.htm

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