Aircraft to Ground Profiling: Turbulence Measurements and Optical System Performance Modeling

Diskin, Yakov; Whiteley, Matthew R.; Grose, Mitchell; Jackovitz, Kevin; Drye, Richard; Hampshire, Brandon; Owens, Monte; Smith, Eric; Magee, Eric P.; Kalensky, Matthew; Jumper, Eric J.; Gordeyev, Stanislav; Archibald, Aaron

doi:10.2514/1.j060580

Cited by 9 publications

(6 citation statements)

References 33 publications

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“…Proper choice of the superposition coefficients dictates the distribution (along z) of the on-axis intensity pattern of the beam, which also corresponds to different beam widths along z. To simplify the analysis and simulation, the turbulence distribution along z is divided into M equal-length regions, each having constant, region-dependent turbulence strength 6 , 13 , 14 (i.e., for the turbulence region j). At the Tx, M longitudinally structured beams are sequentially transmitted, in which beam i has its narrow width in region i .…”

Section: Resultsmentioning

confidence: 99%

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Atmospheric turbulence strength distribution along a propagation path probed by longitudinally structured optical beams

Zhou,

Su,

Duan

et al. 2023

Nat Commun

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Atmospheric turbulence can cause critical problems in many applications. To effectively avoid or mitigate turbulence, knowledge of turbulence strength at various distances could be of immense value. Due to light-matter interaction, optical beams can probe longitudinal turbulence changes. Unfortunately, previous approaches tended to be limited to relatively short distances or large transceivers. Here, we explore turbulence probing utilizing multiple sequentially transmitted longitudinally structured beams. Each beam is composed of Bessel-Gaussian ($${{{{{{\rm{BG}}}}}}}_{{{{{{\mathcal{l}}}}}}{{=}}0,{k}_{z}}$$ BG l = 0 , k z ) modes with different $${k}_{z}$$ k z values such that a distance-varying beam width is produced, which results in a distance- and turbulence-dependent modal coupling to $${{{{{\mathcal{l}}}}}}{{{{{\mathscr{\ne }}}}}}0$$ l {{\relax \special {t4ht̂3)}\o:mathrel: {\unhbox \voidb@x \special {t4ht@+{38}{35}x2260;}x}}} 0 orders. Our simulation shows that this approach has relatively uniform and low errors (<0.3 dB) over a 10-km path with up to 30-dB turbulence-structure-constant variation. We experimentally demonstrate this approach for two emulated turbulence regions (~15-dB variation) with <0.8-dB errors. Compared to previous techniques, our approach can potentially probe longer distances or require smaller transceivers.

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Section: Resultsmentioning

confidence: 99%

“…Consequently, such a short distance may not provide sufficient warning to avoid turbulence. Another technique that can operate over many kilometers is based on transmitting two beams that intersect each other along the path 6 , 11 – 14 . Changing the angle between these beams results in their overlap at different z locations.…”

Section: Introductionmentioning

confidence: 99%

Atmospheric turbulence strength distribution along a propagation path probed by longitudinally structured optical beams

Zhou,

Su,

Duan

et al. 2023

Nat Commun

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“…In order to better understand the underlying physics associated with these aero-optical aberrations, extensive lab-based 2 – 5 , 7 , 8 , 14 – 21 and aircraft-based 6 , 22 – 30 testing has been conducted in recent years. Although many foundational aero-optical experiments and analyses have been conducted, there is still much to learn about the coupling of fluidic properties and optical aberrations.…”

Section: Introductionmentioning

confidence: 99%

Experimental and computational investigation of Shack–Hartmann wavefront sensor measurements through a free shear layer

Wells,

Kalensky,

Rennie

et al. 2024

Opt. Eng.

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Experimental Shack-Hartmann wavefront sensor (SHWFS) measurements were collected for a laser beam that propagated through a weakly compressible shear layer. Complementary computational fluid dynamics (CFD) was also conducted to match the experiment. The path-integrated CFD results were then applied to a SHWFS model such that the experimental and CFD results could be compared. Using both the experimental and CFD wavefront results, it was found that, although the CFD results slightly overestimated the resultant wavefront error, the CFD and experimental results revealed extremely similar wavefront topology. In order to further examine the aberrations imposed onto the laser beam in both datasets, the SHWFS image-plane irradiance patterns and circulation of phase gradients were studied. Similar to the overall wavefront topology, these data reduction approaches revealed similar phenomena in both the experimental and CFD-modeled results. Specifically, appreciable circulation and beam spread of the SHWFS image-plane irradiance patterns were exhibited throughout the shear layer's braid region. Both of these findings suggest that sharp phase gradients exist in the weakly compressible shear layer and both (1) the SHWFS resolution and (2) the continuous nature of the phase estimate obtained using SHWFS data in a least-squares reconstruction algorithm make these phase gradients challenging to resolve. The findings presented here inform efforts looking to experimentally or computationally study aero-optical environments.

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“…As such, it is desirable to quantify the atmospheric-optical-turbulence environments in which these systems operate in order to 1) predict system performance and 2) make system design decisions which appropriately account for the degradation to performance imposed by the atmosphere. [1][2][3] However, turbulence strength is variable and depends on location, weather, and diurnal changes, to name a few. Therefore, it is desirable to develop approaches which can easily and robustly characterize optical-turbulence strength.…”

Section: Introductionmentioning

confidence: 99%

Optical-turbulence characterization of a littoral test environment using a Shack-Hartmann wavefront sensor

Bukowski,

O'Sullivan,

Kalensky

et al. 2023

Unconventional Imaging, Sensing, and Adaptive Optics 2023

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Beam propagation systems are often used in a wide range of atmospheric environments. Therefore, it is important to be able to characterize those environments in order to appropriately assess performance and inform design decisions. In this paper, a variety of methods for measuring atmospheric coherence length, r0, were analyzed including a Shack–Hartmann-based differential image motion monitor (DIMM), gradient-tilt variance, slope discrepancy variance, and phase variance methods, as well as using the modulation transfer function (MTF). These methods were tested on varying turbulence strength environments with known atmospheric coherence lengths, first using a single modified von Kármán phase screen, then using full wave-optics simulations with 20 phase screens. The Shack–Hartmann based approaches were shown to greatly increase in error for d/r0> 1 due to discrepancies between gradient tilt and the centroid tilt measured from the SHWFS’ image-plane irradiance patterns. An atmospheric data collection system was built and experimental results were taken for a beam propagating 2.4 km through a littoral environment over a 24 hour period.

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Aircraft to Ground Profiling: Turbulence Measurements and Optical System Performance Modeling

Cited by 9 publications

References 33 publications

Atmospheric turbulence strength distribution along a propagation path probed by longitudinally structured optical beams

Atmospheric turbulence strength distribution along a propagation path probed by longitudinally structured optical beams

Experimental and computational investigation of Shack–Hartmann wavefront sensor measurements through a free shear layer

Optical-turbulence characterization of a littoral test environment using a Shack-Hartmann wavefront sensor

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