&lt;title&gt;Differential-tilt technique for saturation-resistant profiling of atmospheric turbulence&lt;/title&gt;

Whiteley, Matthew R.; Washburn, Donald C.; Wright, Lawrence A.

doi:10.1117/12.454795

Cited by 21 publications

(13 citation statements)

References 14 publications

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“…Whiteley et al 11,12 describe the analysis that develops a normalized path-weighting function w(ξ) for a given geometry and separation of a pair of apertures. The analysis can be extended to an array of receiver apertures, generating M DDTV measurements.…”

Section: Difference Of Differential-tilt Variancementioning

confidence: 99%

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Investigation of scintillometer designs for dynamic path measurement

2014

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The characterization of atmospheric effects on a propagated laser beam is important to applications ranging from free-space optical communications to high-energy laser systems for ship defense. These applications are frequently developed for a dynamic propagation environment in which either one or both ends of the optical link are moving. The instruments are often constrained by size, weight, and power limitations due to the platforms on which they will be installed. The dynamic nature of the optical link induces several difficulties in link-path instrumentation: turbulence statistics on a continuously changing path are hard to interpret, and the optical instruments must be designed to maintain a high-quality link between beacon and receiver. We will review some of the scintillometer designs and we examine the associated data produced by these different instruments.

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Section: Difference Of Differential-tilt Variancementioning

confidence: 99%

“…11,12 A basic configuration to introduce the measurement process uses two apertures (1 and 2) and two differential-tilt measurements (primary and secondary). The DDTV quantity σ 2 δ is defined…”

Section: Difference Of Differential-tilt Variancementioning

confidence: 99%

Investigation of scintillometer designs for dynamic path measurement

2014

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“…These techniques include scintillometry, Scintillation, Detection and Ranging (SCIDAR) [1,2], Differential Image Motion Monitoring (DIMM) [3], and Difference in Differential Tilt Variance (DDTV) [4]. Recently reported techniques include using weather radar [5,6] and satellite data [7].…”

Section: Introductionmentioning

confidence: 99%

Estimation of atmospheric parameters from time-lapse imagery

McCrae¹,

Basu²,

Fiorino³

2016

SPIE Proceedings

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A time-lapse imaging experiment was conducted to estimate various atmospheric parameters for the imaging path. Atmospheric turbulence caused frame-to-frame shifts of the entire image as well as parts of the image. The statistics of these shifts encode information about the turbulence strength (as characterized by C n 2 , the refractive index structure function constant) along the optical path. The shift variance observed is simply proportional to the variance of the tilt of the optical field averaged over the area being tracked. By presuming this turbulence follows the Kolmogorov spectrum, weighting functions can be derived which relate the turbulence strength along the path to the shifts measured. These weighting functions peak at the camera and fall to zero at the object. The larger the area observed, the more quickly the weighting function decays. One parameter we would like to estimate is r 0 (the Fried parameter, or atmospheric coherence diameter.) The weighting functions derived for pixel sized or larger parts of the image all fall faster than the weighting function appropriate for estimating the spherical wave r 0 . If we presume C n 2 is constant along the path, then an estimate for r 0 can be obtained for each area tracked, but since the weighting function for r 0 differs substantially from that for every realizable tracked area, it can be expected this approach would yield a poor estimator. Instead, the weighting functions for a number of different patch sizes can be combined through the Moore-Penrose pseudo-inverse to create a new weighting function which yields the least-squares optimal linear combination of measurements for estimation of r 0 . This approach is carried out, and it is observed that this approach is somewhat noisy because the pseudo-inverse assigns weights much greater than one to many of the observations.

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“…al. [7]. The technique required two receiver apertures and an accompanying focal plane camera at one end of the path and three point source beacons at the other end.…”

Section: Introductionmentioning

confidence: 99%

Comparison of the path-weighted Cn2 derived from time-lapse imagery and weather radar

Basu

Burchett

Fiorino

et al. 2016

2016 IEEE Aerospace Conference

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Irradiance based techniques are not suitable for profiling over long, nearly horizontal paths through atmospheric turbulence since they suffer from saturation effects. Alternate techniques that can provide reliable turbulence information over strong turbulence paths are currently being investigated. Two such approaches are introduced here. The first approach is a phase-based technique that uses the turbulence induced random motion in time-lapse images of a distant scene to estimate the path-weighted C n 2. An imaging experiment was conducted at the Air Force Institute of Technology to demonstrate this approach. A tripodmounted digital camera captured images of a distant building every minute. Two different components of motion were apparent in the imagery: the random, faster motion due to atmospheric turbulence and the slower, vertical motion due to changes in the average refractive index gradient along the path. A correlation algorithm was used to measure the image shifts. The technique uses a derived set of path weighting functions that depend on the size of the imaging aperture and the patch size in the image whose motion is being tracked. The second method estimates C n 2 values at different locations along a path using a combination of weather (NEXRAD) radar and numerical weather prediction (NWP) data. Two techniques have been used to derive the estimates. The first uses radar doppler information to determine the eddy thermal dissipation rate and combining this with NWP gradients to form a C n 2 estimate. The second technique attempts to correct C n 2 derived from radar clear-air reflectivity for noise and clutter and wavelength. The weights derived in the time-lapse imaging method have been applied to the noise and wavelength corrected NWP-radar derived C n 2 profile to obtain the pathweighted value. The path-weighted estimates obtained using the optically-based, time-lapse imaging and weather radarbased methods have been compared. Both approaches show great potential in estimating turbulence strengths over strong turbulence paths.

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<title>Differential-tilt technique for saturation-resistant profiling of atmospheric turbulence</title>

Cited by 21 publications

References 14 publications

Investigation of scintillometer designs for dynamic path measurement

Investigation of scintillometer designs for dynamic path measurement

Estimation of atmospheric parameters from time-lapse imagery

Comparison of the path-weighted Cn2 derived from time-lapse imagery and weather radar

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