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检索条件"任意字段=Conference on Optics in Atmospheric Propagation and Adaptive Systems XIX"

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Laser beam propagation through turbulence and adaptive optics for beam delivery improvement 18

Laser beam propagation through turbulence and adaptive optic...

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conference on optics in atmospheric propagation and adaptive systems XVIII

作者： Nicolas, Stephane Norwegian Def Res Estab FFI N-2007 Kjeller Norway

ISBN: (纸本)9781628418514

We report results from numerical simulations of laser beam propagation through atmospheric turbulence. In particular, we study the statistical variations of the fractional beam energy hitting inside an optical aperture placed at several kilometer distance. The simulations are performed for different turbulence conditions and engagement ranges, with and without the use of turbulence mitigation. Turbulence mitigation is simulated with phase conjugation. The energy fluctuations are deduced from time sequence realizations. It is shown that turbulence mitigation leads to an increase of the mean energy inside the aperture and decrease of the fluctuations even in strong turbulence conditions and long-distance engagement. As an example, the results are applied to a high energy laser countermeasure system, where we determine the probability that a single laser pulse, or one of the pulses in a sequence, will provide a lethal energy inside the target aperture. Again, turbulence mitigation contributes to increase the performance of the system at long-distance and for strong turbulence conditions in terms of kill probability. We also discuss a specific case where turbulence contributes to increase the pulse energy within the target aperture. The present analysis can be used to evaluate the performance of a variety of systems, such as directed countermeasures, laser communication, and laser weapons.

关键词： Laser beam propagation Beam delivery turbulence mitigation infrared countermeasures simulations numerical model high-energy laser

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Investigation of dual-wavelength laser beam propagation along the in-door atmospheric path 18

Investigation of dual-wavelength laser beam propagation alon...

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conference on optics in atmospheric propagation and adaptive systems XVIII

作者： Gorelaya, Alina V. Shubenkova, Elena V. Dmitriev, Dmitriy I. Dmitrieva, Anna D. Kudryashov, Alexis V. Lovchiy, Igor L. Shalymov, Egor V. Sheldakova, Yulia V. Tsvetkov, Arkadii D. Venediktov, Dmitriy V. Venediktov, Vladimir Yu. St Petersburg Electrotech Univ LETI Laser Measurement & Nav Syst Dept St Petersburg 197376 Russia NII OEP Sci Res Inst Optoelect Instrument Engn Sosnovyi Bor 188540 Leningrad Regio Russia Act Opt NightN Ltd Moscow 115407 Russia St Petersburg State Univ St Petersburg 199034 Russia

ISBN: (纸本)9781628418514

We present the results of experimental investigation of measuring the wavefront distortions, accumulated during propagation of the bi-chromatic (0.53 and 1.06 mu m) radiation propagation along the in-door atmospheric path by the pair of Shack-Hartmann wavefront sensors. The wavefront distortions for two wavelengths are compared, and the correlation between these distortions is revealed.

关键词： wavefront distortions wavefront sensor atmospheric path

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Influence of aerosols on atmospheric transmission at the Baltic Sea: Comparison of experimental results with model simulations using MODTRAN 18

Influence of aerosols on atmospheric transmission at the Bal...

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conference on optics in atmospheric propagation and adaptive systems XVIII

作者： Vogelbacher, Silke Sprung, Detlev van Eijk, Alexander M. J. Stein, Karin Fraunhofer Inst Optron Syst Technol & Image Explo D-76275 Ettlingen Germany TNO NL-2509 JG The Hague Netherlands

ISBN: (纸本)9781628418514

A recent field trial in the Northern German littoral area of the Baltic Sea yielded a dataset of visibility, meteorological parameters, aerosol size distributions, as well as transmission over a horizontal path of 1344 m. The experimental results are compared to simulations using the MODTRAN (moderate resolution atmospheric transmission) model, that was run with the rural and Navy Aerosol Model, (NAM) in various configurations. Best results were obtained when MODTRAN was tuned with the measured visibility values. When NAM was used without visibility tuning, MODTRAN tended to overestimate the transmission in low-visibility conditions, which was attributed to the presence of a non-maritime aerosol fraction.

关键词： Aerosol distribution horizontal propagation MODTRAN

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Airborne Experiment Results for Spaceborne atmospheric Synchronous Correction System 18

Airborne Experiment Results for Spaceborne Atmospheric Synch...

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conference on optics in atmospheric propagation and adaptive systems XVIII

作者： Cui Wenyu Yi Weining Du Lili Liu Xiao Chinese Acad Sci Anhui Inst Opt & Fine Mech Key Lab Opt Calibrat & Characterizat Hefei 230031 Anhui Peoples R China

ISBN: (纸本)9781628418514

The image quality of optical remote sensing satellite is affected by the atmosphere, thus the image needs to be corrected. Due to the spatial and temporal variability of atmospheric conditions, correction by using synchronous atmospheric parameters can effectively improve the remote sensing image quality. For this reason, a small light spaceborne instrument, the atmospheric synchronous correction device (airborne prototype), is developed by AIOFM of CAS(Anhui Institute of optics and Fine Mechanics of Chinese Academy of Sciences). With this instrument, of which the detection mode is timing synchronization and spatial coverage, the atmospheric parameters consistent with the images to be corrected in time and space can be obtained, and then the correction is achieved by radiative transfer model. To verify the technical process and treatment effect of spaceborne atmospheric correction system, the first airborne experiment is designed and completed. The experiment is implemented by the "satellite-airborne-ground" synchronous measuring method. A high resolution(0.4 m) camera and the atmospheric correction device are equipped on the aircraft, which photograph the ground with the satellite observation over the top simultaneously. And aerosol optical depth (AOD) and columnar water vapor (CWV) in the imagery area are also acquired, which are used for the atmospheric correction for satellite and aerial images. Experimental results show that using the AOD and CWV of imagery area retrieved by the data obtained by the device to correct aviation and satellite images, can improve image definition and contrast by more than 30%, and increase MTF by more than 1 time, which means atmospheric correction for satellite images by using the data of spaceborne atmospheric synchronous correction device is accurate and effective.

关键词： atmospheric correction satellite image synchronous airborne experiment

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An adaptive optics approach for Laser Beam Correction in Turbulence utilizing a Modified Plenoptic Camera 4

An Adaptive Optics approach for Laser Beam Correction in Tur...

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conference on Laser Communication and propagation through the Atmosphere and Oceans IV

作者： Ko, Jonathan Wu, Chensheng Davis, Christopher C. Univ Maryland Dept Elect & Comp Engn College Pk MD 20742 USA

ISBN: (纸本)9781628417807

adaptive optics has been widely used in the field of astronomy to correct for atmospheric turbulence while viewing images of celestial bodies. The slightly distorted incoming wavefronts are typically sensed with a Shack-Hartmann sensor and then corrected with a deformable mirror. Although this approach has proven to be effective for astronomical purposes, a new approach must be developed when correcting for the deep turbulence experienced in ground to ground based optical systems. We propose the use of a modified plenoptic camera as a wavefront sensor capable of accurately representing an incoming wavefront that has been significantly distorted by strong turbulence conditions (C-n(2)>10(-13) m(2/3)). An intelligent correction algorithm can then be developed to reconstruct the perturbed wavefront and use this information to drive a deformable mirror capable of correcting the major distortions. After the large distortions have been corrected, a secondary mode utilizing more traditional adaptive optics algorithms can take over to fine tune the wavefront correction. This two-stage algorithm can find use in free space optical communication systems, in directed energy applications, as well as for image correction purposes.

关键词： atmospheric turbulence adaptive optics wavefront correction modified plenoptic camera deformable mirror stochastic parallel gradient descent (SPGD)

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Entropy Studies on Beam Distortion by atmospheric Turbulence 4

Entropy Studies on Beam Distortion by Atmospheric Turbulence

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conference on Laser Communication and propagation through the Atmosphere and Oceans IV

作者： Wu, Chensheng Ko, Jonathan Davis, Christopher C. Univ Maryland Dept Elect & Comp Engn College Pk MD 20742 USA

ISBN: (纸本)9781628417807

When a beam propagates through atmospheric turbulence over a known distance, the target beam profile deviates from the projected profile of the beam on the receiver. Intuitively, the unwanted distortion provides information about the atmospheric turbulence. This information is crucial for guiding adaptive optic systems and improving beam propagation results. In this paper, we propose an entropy study based on the image from a plenoptic sensor to provide a measure of information content of atmospheric turbulence. In general, lower levels of atmospheric turbulence will have a smaller information size while higher levels of atmospheric turbulence will cause significant expansion of the information size, which may exceed the maximum capacity of a sensing system and jeopardize the reliability of an AO system. Therefore, the entropy function can be used to analyze the turbulence distortion and evaluate performance of AO systems. In fact, it serves as a metric that can tell the improvement of beam correction in each iteration step. In addition, it points out the limitation of an AO system at optimized correction as well as the minimum information needed for wavefront sensing to achieve certain levels of correction. In this paper, we will demonstrate the definition of the entropy function and how it is related to evaluating information ( randomness) carried by atmospheric turbulence.

关键词： adaptive optics atmospheric turbulence entropy plenoptic sensor turbulence evaluation

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The meter-class carbon fiber reinforced polymer mirror and segmented mirror telescope at the Naval Postgraduate School 27

The meter-class carbon fiber reinforced polymer mirror and s...

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conference on Free-Space Laser Communication and atmospheric propagation XXVII

作者： Wilcox, Christopher Fernandez, Bautista Bagnasco, John Martinez, Ty Romeo, Robert Agrawal, Brij US Naval Res Lab Washington DC 20375 USA US Naval Postgrad Sch Monterey CA USA Composite Mirror Applicat Inc Tucson AZ USA

ISBN: (纸本)9781628414448

The adaptive optics Center of Excellence for National Security at the Naval Postgraduate School has implemented a technology testing platform and array of facilities for next-generation space-based telescopes and imaging system development. The Segmented Mirror Telescope is a 3-meter, 6 segment telescope with actuators on its mirrors for system optical correction. Currently, investigation is being conducted in the use of lightweight carbon fiber reinforced polymer structures for large monolithic optics. Advantages of this material include lower manufacturing costs, very low weight, and high durability and survivability compared to its glass counterparts. Design and testing has begun on a 1-meter, optical quality CFRP parabolic mirror for the purpose of injecting collimated laser light through the SMT primary and secondary mirrors as well as the following aft optics that include wavefront sensors and deformable mirrors. This paper will present the design, testing, and usage of this CFRP parabolic mirror and the current path moving forward with this ever-evolving technology.

关键词： Mirrors Telescopes Space telescopes Collimation adaptive optics Imaging systems optics manufacturing Carbon Segmented mirrors Fiber reinforced polymers

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New Optical Receiving System Design for Portable Camera Lidar 18

New Optical Receiving System Design for Portable Camera Lida...

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conference on optics in atmospheric propagation and adaptive systems XVIII

作者： Qin Laian He Feng Jing Xu Tan Fengfu Chinese Acad Sci Key Lab Atmospher Composit & Opt Radiat Hefei 230031 Peoples R China Chinese Acad Sci Anhui Inst Opt & Fine Mech Hefei 230031 Peoples R China

ISBN: (纸本)9781628418514

For its better spectral response characterization, higher quantum efficiency and signal-to-noise ratio, camera is more and more used in atmospheric parameters measurement lidar. Camera lidars retrieval atmospheric parameters by analyzing the light column images acquired by the cameras and objectives through gathering the backscatter light of the laser beam. Lidars of this kind usually have higher spatial resolution and better real time performance. However, because of its limited depth of field (DOF), the measurement accuracy of the area out of the DOF is influenced by optical defocus in different degree. In the meantime, it is also not suitable for portable equipments for using small relative aperture receiving objective. Based on improving the design of the receiving objective, a new design scheme is proposed in this paper about improving the optical receiving system of the camera lidar. This scheme can improve the measurement accuracy of the area out of the DOF in traditional structure by using large DOF, large relative aperture off-axis objective and the special using mode of the camera. The optical receiving system designed according to this scheme is more compact and is especially suitable for portable instrument. Furthermore, the relation among the focus length, the distance between laser and objective and the installation angle is also analyzed in this paper. The formula is given at the same time. This scheme is carried out in camera lidar system in laboratory and the results are satisfactory.

关键词： camera lidar aerosol sCMOS camera atmospheric parameter measurement large relative aperture off-axis objective

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Shortwave Infrared for Night Vision Applications - Illumination levels and sensor performance 18

Shortwave Infrared for Night Vision Applications - Illuminat...

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conference on optics in atmospheric propagation and adaptive systems XVIII

作者： Adomeit, Uwe Krieg, Juregen Fraunhofer IOSB D-76725 Ettlingen Germany

ISBN: (纸本)9781628418514

Radiation created by stimulation and recombination/deactivation of atoms and molecules in the higher earth atmosphere is called nightglow. This nightglow can be found in the spectral range from the ultraviolet up to the thermal infrared, with a maximum in the shortwave infrared (SWIR). During moonless nights the illumination in the SWIR is by an order of magnitude higher than the visual one. Within the last years the SWIR sensor technology improved to a level of using the nightglow for night vision applications. This necessitates understanding of the highly variable illumination levels created by the nightglow and the performance assessment of the SWIR detectors in comparison to the image intensifiers respectively Si focal plane array detectors. Whereas the night illumination levels for the visual are standardized, corresponding ones for the SWIR are missing. IOSB started measuring and comparing night illumination levels and camera performance in both spectral ranges based on continuous illumination measurements as well as recording imagery of reflectance reference targets with cameras and analyzing the resulting signal-to-noise ratios. To date the number of illumination measurements are not yet statistically sufficient to standardize the levels, but at least allowed a first comparison of the two technologies for moonless night, clear sky conditions. With comparable F-number, integration time and frame rate, the SWIR sensors available in Europe were found to be inferior to the visual technology. An improvement of at least one magnitude would be necessary to ensure similarity between SWIR and visual technologies for all environmental conditions.

关键词： Airglow Nightglow Night Vision SWIR InGaAs Focal Plane Arrays Illumination Levels atmospheric Conditions

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Object Recognition through Turbulence with a Modified Plenoptic Camera 27

Object Recognition through Turbulence with a Modified Plenop...

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conference on Free-Space Laser Communication and atmospheric propagation XXVII

作者： Wu, Chensheng Ko, Jonathan Davis, Christopher Univ Maryland Dept Elect & Comp Engn College Pk MD 20742 USA

ISBN: (纸本)9781628414448

atmospheric turbulence adds accumulated distortion to images obtained by cameras and surveillance systems. When the turbulence grows stronger or when the object is further away from the observer, increasing the recording device resolution helps little to improve the quality of the image. Many sophisticated methods to correct the distorted images have been invented, such as using a known feature on or near the target object to perform a deconvolution process, or use of adaptive optics. However, most of the methods depend heavily on the object's location, and optical ray propagation through the turbulence is not directly considered. Alternatively, selecting a lucky image over many frames provides a feasible solution, but at the cost of time. In our work, we propose an innovative approach to improving image quality through turbulence by making use of a modified plenoptic camera. This type of camera adds a micro-lens array to a traditional high-resolution camera to form a semi-camera array that records duplicate copies of the object as well as "superimposed" turbulence at slightly different angles. By performing several steps of image reconstruction, turbulence effects will be suppressed to reveal more details of the object independently (without finding references near the object). Meanwhile, the redundant information obtained by the plenoptic camera raises the possibility of performing lucky image algorithmic analysis with fewer frames, which is more efficient. In our work, the details of our modified plenoptic cameras and image processing algorithms will be introduced. The proposed method can be applied to coherently illuminated object as well as incoherently illuminated objects. Our result shows that the turbulence effect can be effectively suppressed by the plenoptic camera in the hardware layer and a reconstructed "lucky image" can help the viewer identify the object even when a "lucky image" by ordinary cameras is not achievable.

关键词： atmospheric turbulence plenoptic camera imaging through turbulence object recognition reconstruction

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