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Boehrer, N. (author), Nieuwenhuizen, R.P.J. (author), Dijk, J. (author)Long-range horizontal path imaging through atmospheric turbulence is hampered by spatiotemporally randomly varying shifting and blurring of scene points in recorded imagery. Although existing software-based mitigation strategies can produce sharp and stable imagery of static scenes, it remains highly challenging to mitigate turbulence in scenes...article 2021
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van Kooten, M.A.M. (author), Doelman, N.J. (author), Kenworthy, M. (author)For high-contrast imaging systems, such as VLT/SPHERE, the performance of the system at small angular separations is contaminated by the wind-driven halo in the science image. This halo is a result of the servo-lag error in the adaptive optics (AO) system due to the finite time between measuring the wavefront phase and applying the phase...article 2020
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Elgammi, M. (author), Schepers, J.G. (author), Osta-Omar, S. (author)Horizontal axis wind turbines (HAWTs) experience three-dimensional rotational and unsteady aerodynamic phenomena at the rotor blades sections. These highly unsteady three-dimensional effects have a dramatic impact on the aerodynamic load distributions on the blades, in particular, when they occur at high angles of attack due to stall delay and...article 2020
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- Boehrer, N. (author), Nieuwenhuizen, R.P.J. (author), Dijk, J. (author) conference paper 2020
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Doelman, N.J. (author)An analytical expression is given for the minimum of the time-delay induced wavefront error (also known as the servo-lag error) in Adaptive Optics systems under temporal prediction filtering. The analysis is based on the von Kármán model for the spectral density of refractive index fluctuations and the hypothesis of frozen flow. An optimal,...article 2020
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Neunaber, I. (author), Holling, M. (author), Stevens, R.J.A.M. (author), Schepers, J.G. (author), Peinke, J. (author)Wind turbines are usually clustered in wind farms which causes the downstream turbines to operate in the turbulent wakes of upstream turbines. As turbulence is directly related to increased fatigue loads, knowledge of the turbulence in the wake and its evolution are important. Therefore, the main objective of this study is a comprehensive...article 2020
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Nieuwenhuizen, R.P.J. (author), Dijk, J. (author), Schutte, K. (author)Long-range imaging with visible or infrared observation systems is typically hampered by atmospheric turbulence. Software-based turbulence mitigation methods aim to stabilize and sharpen such recorded image sequences based on the image data only. Although successful restoration has been achieved on static scenes in the past, a significant...article 2019
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Eisele, C. (author), Seiffer, D. (author), Sucher, E. (author), Ullwer, C. (author), Kociok, T. (author), Sprung, D. (author), van Binsbergen, S. (author), Bijl, P. (author)In the framework of a NATO research group Fraunhofer IOSB and partners conducted a field trial in an arid shrub land environment in southern New Mexico (USA). The group investigates environmental limitations of fielded EO-TDAs (Electro-Optical Tactical Decision Aids). Main objective of the trial was to study the impact of the atmosphere on...conference paper 2019
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Ullwer, C. (author), Sprung, D. (author), Sucher, E. (author), Kociok, T. (author), Grossmann, P. (author), van Eijk, A.M.J. (author), Stein, K. (author)Electro-optical and laser systems are operated world-wide. Their performance in the outside atmosphere is mainly governed by the strength of optical turbulence Cn2. The predictability of Cn2 using weather-forecast models is investigated by performing simulations with the Weather Research and Forecast Model (WRF). The WRF output data were...conference paper 2019
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van Kooten, M. (author), Doelman, N.J. (author), Kenworthy, M. (author)For high-contrast imaging systems, the time delay is one of the major limiting factors for the performance of the extreme adaptive optics (AO) sub-system and, in turn, the final contrast. The time delay is due to the finite time needed to measure the incoming disturbance and then apply the correction. By predicting the behavior of the...article 2019
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Boehrer, N. (author), Nieuwenhuizen, R.P.J. (author), Dijk, J. (author)Long range horizontal path imaging through atmospheric turbulence is hampered by spatiotemporally randomly varying shifting and blurring of scene points in recorded imagery. Typical mitigation strategies employ software algorithms that combine optical flow to estimate and reduce tip/tilt aberrations with lucky patch identification and data...conference paper 2019
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Mehta, D. (author), Zhang, Y. (author), van Zuijlen, A. (author), Bijl, H. (author)Despite advances in turbulence modelling, the Smagorinsky model remains a popular choice for large eddy simulation (LES) due to its simplicity and ease of use. The dissipation in turbulence energy that the model introduces, is proportional to the Smagorinsky constant, of which many different values have been proposed. These values have been...article 2019
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- Sprung, D. (author), Sucher, E. (author), Grossmann, P. (author), Kociok, T. (author), van Eijk, A.M.J. (author), Stein, K. (author) conference paper 2019
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Sucher, E. (author), Sprung, D. (author), Kremer, M. (author), Kociok, T. (author), Van Eijk, A.M.J. (author), Stein, K. (author)Wave propagation of electro-optical systems, lasers or imaging depends on the state of the atmosphere their beams are passing through. Fluctuations in the refractive index of air are responsible for signal attenuation and image degradation. This atmospheric effect is called optical turbulence and its strength is quantified by the structure...conference paper 2018
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Sprung, D. (author), Sucher, E. (author), van Eijk, A.M.J. (author), Eisele, C. (author), Seiffer, D. (author), Stein, K. (author)A field trial was performed in the arid scrub area of White Sands, NM /USA in October 2017 investigating the atmospheric influence on imaging and sensor performance. In this paper we focus on the strength of optical turbulence. Optical turbulence is described by the structure function parameter of the refractive index Cn 2. It is responsible for...conference paper 2018
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van Kooten, M.A.M. (author), Doelman, N.J. (author), Kenworthy, M. (author)In an adaptive optics (AO) system, finite time delays contribute a relatively large amount to the overall wavefront error. The temporal error, due to the time delays, adds to the speckle halo which is visible in the science plane of a high contrast imaging (HCI) instrument. The halo limits the inner working angle, preventing HCI from probing...conference paper 2018
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Ullwer, C. (author), Sprung, D. (author), van Eijk, A.M.J. (author), Gunter, W. (author), Stein, K. (author)Atmospheric turbulence impacts on the propagation of electro-optical radiation. Typical manifestations of optical turbulence are scintillation (intensity fluctuations), beam wander and (for laser systems) reduction of beam quality. For longer propagation channels, it is important to characterize the vertical and horizontal distribution ...conference paper 2018
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Sprung, D. (author), Van Eijk, A.M.J. (author), Ullwer, C. (author), Gunter, W. (author), Eisele, C. (author), Seiffer, D. (author), Sucher, E. (author), Stein, K. (author)The atmospheric influence on wave propagation was investigated during the First European South African Transmission ExpeRiment from June 2015 to February 2016. The focus in this article was set on optical turbulence, the main atmospheric factor affecting the position and strength of Laser beams, the performance of electro-optical systems and...conference paper 2018
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Sprung, D. (author), van Eijk, A.M.J. (author), Günter, W. (author), Griffith, D. (author), Eisele, C. (author), Sucher, E. (author), Seiffer, D. (author), Stein, K. (author)Atmospheric turbulence impacts on the propagation of electro-optical radiation. Typical manifestations of optical turbulence are scintillation (intensity fluctuations), beam wander and (for laser systems) reduction of beam quality. For longer propagation channels, it is important to characterize the vertical and horizontal distribution ...conference paper 2017
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Sprung, D. (author), Sucher, E. (author), Eisele, C. (author), Seiffer, D. (author), van Eijk, A.M.J. (author), Stein, K. (author)Electro-optical and laser systems are presently deployed in naval operations around the world. The performance of these systems is negatively affected by optical turbulence in the atmosphere, quantified by the parameter Cn 2. The strength of the integrated optical turbulence Cn 2 was investigated for several coastal locations in different...conference paper 2017