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posted by Fnord666 on Thursday June 29 2017, @08:09PM   Printer-friendly
from the picture-this dept.

Until now, LiDAR measurements of surfaces hidden behind foliage have been difficult to acquire. A majority of the original light in these cases gets thrown away, as far as the camera detecting light from the ground is concerned, since the light hitting the leaves never reaches the ground in the first place. Moreover, the light blocked, and therefore reflected, before getting to the ground often overpowers the signal hitting the camera and hides the fainter signal that does make it to the ground and back.

"We have been working with a process called optical phase conjugation for quite some time and it dawned on us that we might be able to use that process to essentially project a laser beam through the openings of the leaves and be able to see through a partial obscuration," Lebow said. "It was something that until maybe the last five years was not viable just because the technology wasn't really there. The stuff we had done about 20 years ago involved using a nonlinear optical material and was a difficult process. Now everything can be done using digital holography and computer generated holograms, which is what we do."

This new system uses a specially designed laser that alone took a year and a half to develop, but was a necessary component according to Lebow and his colleague, Abbie Watnik, who is also at the Naval Research Laboratory and another of the work's authors.

"The real key to making our system work is the interference between two laser beams on the sensor. We send one laser beam out to the target and then it returns, and at the exact same time that return [beam] hits the detector, we interfere it locally with another laser beam," Watnik said. "We need complete coherence between those beams such that they interfere with one another, so we had to have a specially designed laser system to ensure that we would get that coherence when they interfere on the camera."

Using a pulsed laser with pulse widths of several nanoseconds, and gated measurements with similar time resolution, the holographic system selectively blocks the earliest-to-arrive light reflecting off obscurations. The camera then only measures light coming back from the partially hidden surface below.

Seems a much better way than using large quantities of Agent Orange.


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  • (Score: 2) by bob_super on Thursday June 29 2017, @09:05PM (1 child)

    by bob_super (1357) on Thursday June 29 2017, @09:05PM (#533097)

    A couple specialists would like to have a chat with you about their published works on the matter of eyes emitting light beams.
    They'll give you a call under the aliases Scott Summer and Clark Kent.

    Starting Score:    1  point
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    Total Score:   2  
  • (Score: 2) by bob_super on Thursday June 29 2017, @09:12PM

    by bob_super (1357) on Thursday June 29 2017, @09:12PM (#533101)

    *Summers
    (D'oh!)