Characterization of atmospheric turbulence using wavefront slope measurements

Silbaugh, Eric E.; Welsh, Byron M.; Roggemann, Michael C.

doi:10.1117/12.254169

Cited by 5 publications

(4 citation statements)

References 16 publications

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“…For the atmospheric turbulence with Kolmogorov law, the structure function of wavefront without overall tilt is r is coherence length of turbulence, D is diameter of telescope. Refer to the analysis results of structure function of gradients on sub-aperture of HS with square shape by E. E. Silbaugh [15] , considering the effect of smoothness on sub-apertures together, we can get the correlation of two gradients with distance of ) , ( y x ∆ ∆ in x direction for the Kolmogorov turbulence without overall tilt:…”

Section: Covariance Matrix Of Gradients In Atmosphere Turbulencementioning

confidence: 99%

Comparing zonal reconstruction algorithms and modal reconstruction algorithms in adaptive optics system

Jiang

2002

SPIE Proceedings

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In this paper, the compensation effects of sub-aperture gradients of Hartmann-Shack wavefront sensor in an adaptive optics (AO) system with four different reconstruction algorithms were analyzed. A kind of optimal-gradient reconstruction algorithm was deduced from least-square (LS) reconstruction algorithm by consider the statistical characteristics of atmospheric turbulence and measurement noise. A kind of sensor-eigen (SE) modal reconstruction algorithm was deduced from LS reconstruction algorithm by orthogonalizing the statistical correlation matrix of drive voltages by means of singular value decomposition (SVD) method. Two kinds of zonal reconstruction algorithms, the LS reconstruction algorithm and the optimal-gradient reconstruction algorithm, along with two modal reconstruction algorithms, the Zernike modal reconstruction algorithm and the SE modal reconstruction algorithm, were compared together on a 61-element AO system working in atmospheric turbulence. Performances of the four reconstruction algorithms were calculated and analyzed in different work conditions. It is showed that zonal reconstruction algorithms can achieve better compensation, but the modal reconstruction algorithms can achieve better stability. Zonal reconstruction algorithms are suitable in general condition, but the modal reconstruction algorithm with ability of partial compensation will be better in lower signal-to-noise ratio (SNR) condition.

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Section: Covariance Matrix Of Gradients In Atmosphere Turbulencementioning

confidence: 99%

Comparing zonal reconstruction algorithms and modal reconstruction algorithms in adaptive optics system

Jiang

2002

SPIE Proceedings

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“…(3) and (4) with Eq. (2), Silbaugh was able to derive an expression for the slope structure function using a Hartmann WFS with square subapertures of size d [12]:…”

Section: H-wfs Slope Structure Functionsmentioning

confidence: 99%

Atmospheric turbulence characterization of a low-altitude long horizontal path

Bernard

Welsh²,

Roggemann³

et al. 1996

SPIE Proceedings

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The limitations placed on optical imaging through the earth's atmosphere are well understood. A large portion of the body of work on this subject deals with vertical optical paths. The transition to the study of horizontal propagation of light is currently being made. Various methods exist that quantify the disturbances introduced on optical signals by turbulent air. Small perturbations of the wave front phase can be measured using a Hartmann Wave Front Sensor (H-WFS). For long optical paths through turbulence spatial and temporal variations in intensity called scintillation arise. Using scintillation statistics and theoretical expressions for structure functions of H-WFS slope values, turbulence strength is studied. Data sets taken from two mountains in Hawaii during an optical communications experiment are studied for comparison with slope structure function and scintillation statistics theory. This experiment was performed at an altitude of 10,000 feet over a horizontal path length of 150 km. Results indicate that very strong scintillation exists under these conditions, and that very little faith can be placed in the H-WFS phase-dependent results. Scintillation may provide a more dependable method for optical characterization of these conditions.

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“…The theoretical analysis of optical turbu lence over land in various coastal zones along with the experimental work to investigate the effects of macro me teorological parameters and the features of refractive index variations in optical atmospheric links was recently con ducted [9] . Atmospheric turbulence over vertical paths has been well characterized, both theoretically and experimen tally [12] , [13] , [14] , [15] , [16] , [17] , [18] , [19] , [20], [40], and less is known about turbulence over long, horizontal paths [22], [23] , [24] , [25] , [26] .…”

Section: Introductionmentioning

confidence: 99%

Bootstrap beacon creation technique for lower altitude and ground based targets

Sergeyev

2014

2014 IEEE Aerospace Conference

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The task of delivering a sufficient amount of laser energy to the ground based targets and the targets located at lower altitudes is of a high interest. The laser beam propagating through atmosphere is significantly degraded by the turbulence. As a result, the laser beam arriving at the target does not have sufficient amount of power. To overcome the degradations induced by atmospheric turbulence the artificial beacon for probing the atmospheric conditions is needed.The current techniques implementing a Rayleigh beacon at the target or at some intermediate distance between the transmitter and the target provide some means of improvement. In this work we extend our work on earlier proposed bootstrap technique in volving creating multiple beacons between the laser transmitter and the target. In the bootstrap technique, the light from each beacon is propagated back to the wavefront sensor located at the receiver. Signal from the wavefront sensor is processed to generate commands for the deformable mirror and the next beacon gets pre-compensated for the further distance.The process continues till the last beacon is created at the target. We have previously reported the results on implementation of the bootstrap techniques on ground based targets demonstrating noticeable improvement in the final laser beam power at the target. In this work we examine the possibility of using the bootstrap technique for cases when laser energy needs to be delivered over nearly horizontal propagation distances and at lower altitudes. The system performance is examined using both Hufnagel-Valley and HufnageVAndrewslPhillips models for structure constant C� characterizing the strength of the index of refraction fluctuation, and compared with the sceneries when the beacon is generated directly on the target or at some intermediate positions between the transmitter and the target.

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Characterization of atmospheric turbulence using wavefront slope measurements

Cited by 5 publications

References 16 publications

Comparing zonal reconstruction algorithms and modal reconstruction algorithms in adaptive optics system

Comparing zonal reconstruction algorithms and modal reconstruction algorithms in adaptive optics system

Atmospheric turbulence characterization of a low-altitude long horizontal path

Bootstrap beacon creation technique for lower altitude and ground based targets

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