November 10, 2016
I'm definitely showing my age when I recall the 1961 recording, "Does Your Chewing Gum Lose Its Flavour (On the Bedpost Overnight?)" by Lonnie Donegan. Donnegan and his music were a British staple before The Beatles and the "British Invasion." The Chewing Gum record reached fifth position on the Billboard Hot 100.
I mention the Chewing Gum record for its inclusion of the simple riddle, "If tin whistles are made of tin, what do they make foghorns out of?" While this illustrates the imprecision of the English language, it also serves as a roundabout introduction to our topic of seeing things through a fog.
I've driven through dense fogs on several occasions, and it was not a pleasant experience. several fog idioms come to mind: Not seeing your hand in front of your face, fog so thick you could cut it with a knife, and fog as thick as pea soup. As we all know, fog is a mass of water droplets suspended in air at ground level; in other words, a cloud at the Earth's surface. Fog forms when the air temperature is very close to the dew point.
It's fairly obvious that the optical properties of fog arise from light bouncing off the water droplets. This scattering is called Mie scattering, named after German physicist, Gustav Mie. Mie solved Maxwell's electromagnetic equations for a medium containing refractive transparent spheres, which is a good approximation to the water droplets in fog.
Source code for Mie scattering calculations is available online for nearly every computer language. One C language implementation that compiled for me can be found in ref. 2. Using this program, I calculated the optical scattering from a water fog in air with the following properties:
Water refractive index = 1.33
The calculated scattering coefficient at optical wavelengths for such a fog was calculated to be about 85%.
My experience in driving through fog demonstrated to me the utility of a system for viewing things through fog, although it was not apparent how such a system could be made. Now, engineers at the California Institute of Technology (Pasadena, California) have devised a camera system that can image objects behind fog or other murky media by canceling out the glare.[3-4] Their method, called "coherence gated negation," uses destructive optical interference to accomplish this task.[3-4]
The Caltech team was lead by Changhuei Yang, a professor of electrical engineering, bioengineering, and medical engineering. Yang shared lead authorship of the paper describing the system with graduate student, Edward Zhou. Their coauthors included postdocs, Atsushi Shibukawa and Haowen Ruan, and graduate student, Joshua Brake.
The Caltech system departs from the method of conventional anti-glare imaging systems in which the target optical signal is acquired in a short time window that rejects most of the glare when the target is illuminated by a pulse of light. The Caltech coherence gated negation method selectively cancels the scattered light instead.[3-4] This is done by destructive interference that combines one beam of light over another beam to cancel the unwanted signal.
The illuminating laser beam is split into twin parallel beams, with one used to illuminate the target and the other to cancel the glare. The combination of these beams cancels most of the glare at a camera sensor. To do this, the system must try a range of amplitude and phase values of a reference beam to get the best cancellation of glare. They found that they are able to suppress glare by an order of magnitude, even for a non-uniform optical wavefront.
As a test, the research team placed text behind a millimeter thick block of glass beads suspended in a gel. This gel filter rendered the text completely illegible. Using their coherence gated negation method, they could increase the contrast of the text by a factor of about thirty (see figure). This produced a legible image.
While imaging through terrestrial fog is one potential application, there are others. This might be a noninvasive way to optically examine tissue under the skin, as in mammography, since the optical scattering of skin is similar to a dense fog. While the image acquisition rate of the system needs to be improved, says Yang,
Fog droplet diameter = 10 μm
Fog/air concentration = 0.00005 g/g
"A very nice aspect of this method is that there is a fairly straightforward approach for increasing its speed by several orders of magnitude. Wouldn't it be nicer and safer if you can see the whole San Francisco bridge as you drive across it on a foggy day?"
This research was funded by the National Institutes of Health, and the National Institute of Biomedical Imaging and Bioengineering, among others.
- Stephen Wolfram, "Computational Law, Symbolic Discourse, and the AI Constitution," Backchannel, October 12, 2016.
- Lihong Wang, and Steven L. Jacques, "Sphere Mie Scattering Program," (a C Language re-coding of a Fortran program by Tony Durkin and Craig Gardner created from information in Craig F. Bohren and Donald R. Huffman, "Absorption and Scattering of Light by Small Particles," John Wiley & Sons, 1983), 1993.
- Edward Haojiang Zhou, Atsushi Shibukawa, Joshua Brake, Haowen Ruan, and Changhuei Yang, "Glare suppression by coherence gated negation," Optica, vol. 3, no. 10 (October 5, 2016), pp. 1107-1113, https://doi.org/10.1364/OPTICA.3.001107. This is an open access publication with a PDF file available at the same URL.
- Robert Perkins, "Noise-Canceling Optics," Caltech Press Release, October 10, 2016.
Permanent Link to this article
Linked Keywords: Recording; Does Your Chewing Gum Lose Its Flavour (On the Bedpost Overnight?); Lonnie Donegan; Great Britain; British; The Beatles; British Invasion; Billboard Hot 100; riddle; tin whistle; tin; foghorn; English language; fog; idiom; hand; face; knife; pea soup fog; air mass; water; droplet; suspension; suspended; air; lithosphere; ground level; cloud; Earth's surface; temperature; dew point; morning; landscape; west; Tikalon; Morris County, New Jersey; Northern New Jersey; Scheibbs, Austria; Uoaei1; Wikimedia Commons; optics; optical; light; light scattering; Mie scattering; Germany; German; physicist; Gustav Mie; Maxwell's electromagnetic equations; refraction; refractive; transparent; sphere; approximation; source code; calculation; programming language; computer language; C language; compiler; compile; refractive index; diameter; micrometer; μm; concentration; gram; wavelength; Gustav Mie (1868-1957); Mie scattering; particle; wavelength; light; Rayleigh scattering; driving; engineer; California Institute of Technology (Pasadena, California); digital camera; destructive optical interference; Changhuei Yang; professor; electrical engineering; bioengineering; biomedical engineering; medical engineering; authorship; academic publishing; paper; postgraduate education; graduate student; Edward Zhou; postdoctoral research; postdoc; Atsushi Shibukawa; Haowen Ruan; Joshua Brake; pulse; laser beam; parallel; amplitude; phase; reference; order of magnitude; wavefront; research; text; millimeter; glass; bead; suspension; suspended; gel; filter; contrast; word; terrestrial; noninvasive; tissue; skin; mammography; bit rate; San Francisco-Oakland Bay Bridge; National Institutes of Health; National Institute of Biomedical Imaging and Bioengineering.
Latest Books by Dev Gualtieri
Thanks to Cory Doctorow of BoingBoing for his favorable review of Secret Codes!
Blog Article Directory on a Single Page
- J. Robert Oppenheimer and Black Holes - April 24, 2017
- Modeling Leaf Mass - April 20, 2017
- Easter, Chicks and Eggs - April 13, 2017
- You, Robot - April 10, 2017
- Collisions - April 6, 2017
- Eugene Garfield (1925-2017) - April 3, 2017
- Old Fossils - March 30, 2017
- Levitation - March 27, 2017
- Soybean Graphene - March 23, 2017
- Income Inequality and Geometrical Frustration - March 20, 2017
- Wireless Power - March 16, 2017
- Trilobite Sex - March 13, 2017
- Freezing, Outside-In - March 9, 2017
- Ammonia Synthesis - March 6, 2017
- High Altitude Radiation - March 2, 2017
- C.N. Yang - February 27, 2017
- VOC Detection with Nanocrystals - February 23, 2017
- Molecular Fountains - February 20, 2017
- Jet Lag - February 16, 2017
- Highly Flexible Conductors - February 13, 2017
- Graphene Friction - February 9, 2017
- Dynamic Range - February 6, 2017
- Robert Boyle's To-Do List for Science - February 2, 2017
- Nanowire Ink - January 30, 2017
- Random Triangles - January 26, 2017
- Torricelli's law - January 23, 2017
- Magnetic Memory - January 19, 2017
- Graphene Putty - January 16, 2017
- Seahorse Genome - January 12, 2017
- Infinite c - January 9, 2017
- 150 Years of Transatlantic Telegraphy - January 5, 2017
- Cold Work on the Nanoscale - January 2, 2017
- Holidays 2016 - December 22, 2016
- Ballistics - December 19, 2016
- Salted Frogs - December 15, 2016
- Negative Thermal Expansion - December 12, 2016
- Verbal Cues and Stereotypes - December 8, 2016
- Capacitance Sensing - December 5, 2016
- Gallium Nitride Tribology - December 1, 2016
- Lunar Origin - November 27, 2016
- Pumpkin Propagation - November 24, 2016
- Math Anxiety - November 21, 2016
- Borophene - November 17, 2016
- Forced Innovation - November 14, 2016
- Combating Glare - November 10, 2016
- Solar Tilt and Planet Nine - November 7, 2016
- The Proton Size Problem - November 3, 2016
- Coffee Acoustics and Espresso Foam - October 31, 2016
- SnIP - An Inorganic Double Helix - October 27, 2016
- Seymour Papert (1928-2016) - October 24, 2016
- Mapping the Milky Way - October 20, 2016
- Electromagnetic Shielding - October 17, 2016
- The Lunacy of the Cows - October 13, 2016
- Random Coprimes and Pi - October 10, 2016
- James Cronin (1931-2016) - October 6, 2016
- The Ubiquitous Helix - October 3, 2016
- The Five-Second Rule - September 29, 2016
- Resistor Networks - September 26, 2016
- Brown Dwarfs - September 22, 2016
- Intrusion Rheology - September 19, 2016
- Falsifiability - September 15, 2016
- Fifth Force - September 12, 2016
- Renal Crystal Growth - September 8, 2016
- The Normality of Pi - September 5, 2016
- Metering Electrical Power - September 1, 2016
Deep Archive 2006-2008