Limits of the small-angle approximation to the radiative transport equation

Swanson, Nancy L.; Gehman, V. M.; Billard, Barton D.; Gennaro, Theresa L.

doi:10.1364/josaa.18.000385

Cited by 12 publications

(8 citation statements)

References 12 publications

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“…For the twin beams with beam width of 1mm and τ=1, 2, 3, 4, 5, 6, respectively, the resolution limits are 2.1 mm, 4.1 mm, 9.1 mm, 21.4 mm, 52.1mm and 129 mm. Given that the resolution degrades significantly after τ>6 (assumed that the SAA is still valid in this regime [22]), another methods must be explored to detect objects in turbid underwater environments.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

Object detection and geometric profiling through dirty water media using asymmetry properties of backscattered signals

Lee

Davis

2018

Ocean Sensing and Monitoring X

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The scattering of light observed through the turbid underwater channel is often regarded as the leading challenge when designing underwater electro-optical imaging systems. There have been many approaches to address the effects of scattering such as using pulsed laser sources to reject scattered light temporally, or using intensity modulated waveforms and matched filters to remove the scattered light spectrally. In this paper, a new method is proposed which primarily uses the backscattering asymmetry property for object detection and geometric profiling. In our approach, two parallel and identical continuous wave (CW) laser beams with narrow beam widths (~2mm) are used as active illumination sources. The two beams also have controllable spacing and aiming angle, as well as initial phase difference for convenience of scanning and profiling a target. Through theory and experimental results, it will be shown that when an object leans or tilts towards one of the beam's central trajectory, the asymmetry in the backscattered signals can be used to indicate the location or slope of the target's surface, respectively. By varying the spacing or aiming angle of the two beams, a number of surface samples can be collected to reconstruct the object's shape geometrically. The resolution and range limit of our approach are also measured and reported in this work. In application, our proposed method provides an economic solution to perform imaging through turbid underwater environments. Additionally, the idea can be combined with the pulsed or modulated laser signals for enhanced imaging results. Compared with the normal visibility limit achieved by using bright light from a LED or lamp for active illumination in the dirty water medium, the twin beam method can extend the range of object recognition by a factor between 3~5.

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Section: Conclusion and Discussionmentioning

confidence: 99%

Object detection and geometric profiling through dirty water media using asymmetry properties of backscattered signals

Lee

Davis

2018

Ocean Sensing and Monitoring X

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“…Both sphere and cylinder have radius R = 0.1 mm and are normally irradiated with plane waves at a frequency ω = 2π × 2.4 THz (kR ≈ 6.74). The forward-peaked single scattering for this set of parameters allow us to use the small-angle approximation of the radiative transfer equation for small optical thicknesses [39].…”

Section: A Optical Memory Effect For Dielectric Spheres and Cylindersmentioning

confidence: 99%

Controlling optical memory effects in disordered media with coated metamaterials

2018

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Most applications of memory effects in disordered optical media, such as the tilt-tilt and shiftshift spatial correlations, have focused on imaging through and inside biological tissues. Here we put forward a metamaterial platform not only to enhance but also to tune memory effects in random media. Specifically, we investigate the shift-shift and tilt-tilt spatial correlations in metamaterials composed of coated spheres and cylinders by means of the radiative transfer equation. Based on the single-scattering phase function, we calculate the translation correlations in anisotropically scattering media with spherical or cylindrical geometries and find a simple relation between them. We show that the Fokker-Planck model can be used with the small-angle approximation to obtain the shift-tilt memory effect with ballistic light contribution. By considering a two-dimensional scattering system, composed of thick dielectric cylinders coated with subwavelength layers of thermally tunable magneto-optical semiconductors, we suggest the possibility of tailoring and controlling the shift-shift and tilt-tilt memory effects in light scattering. In particular, we show that the generalized memory effect can be enhanced by increasing the temperature of the system, and it can be decreased by applying an external magnetic field. Altogether our findings unveil the potential applications that metamaterial systems may have to control externally memory effects in disordered media.

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“…Because of the angular singularities of the radiance field, the numerical summation of the series is not stable. In practice, necessary precision of the calculations often is determined by the limit of the instrumental angular resolution of the experimental device used for the measurements [32][33][34]. For these reasons, the numerical solution can be apodized, i.e., convolved with some profile MðΩÞ, effectively regularizing the numerical simulation and limiting its angular resolution at the definite level.…”

Section: Numerical Simulationsmentioning

confidence: 99%

Narrow beams in scattering media: the advanced small-angle approximation

Ilyushin

Budak

2011

J. Opt. Soc. Am. A

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The problem of the propagation of narrow radiation beams in a scattering medium is considered. The previously formulated small-angle approximation solution accounting for the path length spread is further developed. The numerical scheme for practical calculations is implemented, and the simulation results are presented and discussed. Applicability of the new solution to certain problems of optical communications and data transfer techniques is shown.

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Limits of the small-angle approximation to the radiative transport equation

Cited by 12 publications

References 12 publications

Object detection and geometric profiling through dirty water media using asymmetry properties of backscattered signals

Object detection and geometric profiling through dirty water media using asymmetry properties of backscattered signals

Controlling optical memory effects in disordered media with coated metamaterials

Narrow beams in scattering media: the advanced small-angle approximation

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