In order to improve the performance of multi-frame blind deconvolution algorithm, the analysis was conducted on the image restoration quality and convergence rate of the multi-frame blind deconvolution algorithm using Conjugate Gradient + Brent, Conjugate Gradient + Dbrent, Conjugate Gradient + Macopt, and L-BFGS + Wolfe combination optimization algorithms. The mathematical principles of above optimization algorithms were elaborated in detail, and they were introduced into the multi-frame blind deconvolution algorithm to achieve high quality restored images. Theoretical and experimental results indicate that the L-BFGS + Wolfe combination algorithm has the fastest convergence rate, but the restoration quality is lower compared to the other combination algorithms; Compared with the other combination algorithms, the Conjugate Gradient + Brent/Dbrent combination algorithm can obtain higher quality restored images, but its convergence rate is slower; The convergence rate and restoring quality of the Conjugate Gradient +Macopt combination algorithm are between L-BFGS + Wolfe and Conjugate Gradient + Brent/Dbrent.
Adaptive optics plays an important role to compensate the atmosphere turbulence therefore concentrate the laser energy for satellite-ground laser communication. However, as the satellite especially LEO (Low-Earth orbit) moves, the communication laser from downlink (satellite to ground) and uplink (ground to satellite) will experience a different turbulence path, called the point ahead angle (PAA). PAA can be much larger than the atmosphere isoplanatic angle for strong turbulence or fast moving satellites, causing the AO system not working. For now there is no simple and effective way to solve this problem. In this paper, a new wavefront sensing technique called Projected Pupil Plane Pattern (PPPP) is used, where the Rayleigh backscattered light of the uplink laser is used to sense the uplink path of the turbulence. Specifically, PPPP uses at least two scattered images from two different heights to reconstruct the integrated turbulence phase due to the TIE (transport-of-intensity). As PPPP uses the uplink laser itself, the PAA problem is solved automatically. We demonstrate that PPPP method can be effectively used as a simple wavefront sensor in the adaptive optics system for satellite-ground laser communication by numerical simulation for 1m class ground telescope and AO system. Several important PPPP coefficients such as the propagation heights, number of Zernike Modes for reconstruction are studied, and their optimum choices are given.
Multi-frame blind deconvolution (MFBD) is a well-known numerical restoration technique for obtaining highresolution images of astronomical targets through the Earth’s turbulent atmosphere. The performance of MFBD algorithms depend on initial estimates for the object and the PSFs. Even though the observed image might be close to the object and could be used for the initial estimate for the object, as is often the case with the PSFs, we lack prior knowledge on the PSFs for each image. In order to provide high-quality initial estimates and improve the performance of the MFBD algorithm, one of the most effective methods is to introducing an imaging Shack-Hartmann Wave-front sensor which is similar to the traditional Shack-Hartmann Wave-front sensor but with a smaller number of lenslets across the aperture, and to process the data using a multi-channel joint restoration algorithm. In this paper, we proposed a multi-channel joint restoration algorithm which involves the usage of an imaging Shack Hartmann channel data alongside with the science camera data to improve the overall performance of the MFBD restoration algorithm. The numerical results are given in order to illustrate the performance of the joint restoration process.
Optimal transmission of pulsed laser energy to a target is essential for the maximization of reflected signal power in Debris Laser Ranging (DLR) systems. We describe the use of the PPPP measurement technique to allow compensation for both wavefront aberration, tip/tilt and errors arising from misalignment of the transmit and receive optical axes. This paper provides an update on the bistatic Wavefronts Obtained by Measuring Beam-profiles through Atmospheric Turbulence (WOMBAT) trial1 conducted with the EOS Space Systems 1.8m DLR system2 on Mt Stromlo, Australia, using an adjacent telescope to observe the 170 Hz PPPP intensity profiles.
Adaptive optics (AO) is widely used in optical/near-infrared telescopes to remove the effects of atmospheric distortion, and laser guide stars (LGSs) are commonly used to ease the requirement for a bright, natural reference source close to the scientific target in an AO system. However, focus anisoplanatism renders single LGS AO useless for the next generation of extremely large telescopes. Here, we describe proof-of-concept experimental demonstrations of a LGS alternative configuration, which is free of focus anisoplanatism, with the corresponding wavefront sensing and reconstruction method, termed projected pupil plane pattern (PPPP). This laboratory experiment is a critical milestone between the simulation and on-sky experiment, for demonstrating the feasibility of PPPP technique and understanding technical details, such as extracting the signal and calibrating the system. Three major processes of PPPP are included in this laboratory experiment: the upward propagation, return path, and reconstruction process. From the experimental results, it has been confirmed that the PPPP signal is generated during the upward propagation and the return path is a reimaging process whose effect can be neglected (if the images of the backscattered patterns are binned to a certain size). Two calibration methods are used: the theoretical calibration is used for the wavefront measurement, and the measured calibration is used for closed-loop control. From both the wavefront measurement and closed-loop results, we show that PPPP achieves equivalent performance to a Shack–Hartmann wavefront sensor.
PPPP, Pupil Plane Projected Pattern, is a LGS alternative (described more fully in the paper by Yang, this meeting #10703-26) which is inherently free of focal anisoplanatism. It has other practical and scientific advantages, but it is the disadvantages that this paper concentrates on since they are foremost when considering a real implementation. An on-sky test of the technique is funded and here we describe progress in solving the fundamental questions for any new technique: how to actually do it at a real telescope? Our targeted platform is a Nasmyth platform of the 4.2m WHT on La Palma. We discuss the difficulties of projecting an afocal beam from the primary mirror without causing excessive back-reflections/-scatter, which drowns the beam-profile, and instead suggest two alternative experiments. By splitting the validation of PPPP on-sky into two parts, each experiment can address a separate aspect of the validation without the disadvantage of trying to “do it all” within one experiment.
For the next generation of extremely large telescopes with the primary mirrors over 30 m in diameter, focal anisoplanatism renders single laser guide star AO useless. The laser tomography AO (LTAO) technique demonstrates an effective approach to reduce focal anisoplanatism, although it requires multiple LGSs & WFSs, and complex tomographic reconstruction. Here we propose a novel LGS alternative configuration with the corresponding wavefront sensing and reconstruction method, termed Projected Pupil Plane Pattern (PPPP). A key advantage of this method is that a single collimated beam is launched from the telescope primary mirror, and the wavefront sensed on the uplink path, which will not suffer from the effects of focal anisoplanatism. In addition, the power density of the laser beam is significantly reduced compared to a focused LGS, which decreases aircraft and satellite safety hazards. A laboratory experiment for PPPP has been setup to anchor the PPPP concept and compare against a Shack-Hartmann WFS.
Speckle imaging techniques are effective post-processing methods to eliminate atmospheric perturbations on the imaging
of space objects, in which speckle interferometry and bispectrum methods are usually used to estimate the magnitude and
phase spectrum of the objects separately. The spectral ratio technique used in this paper is convenient and efficient to
evaluate r0, which is crucial for calibrating the speckle transfer function in the magnitude estimation. It is shown that
power spectrum, the second moment of the magnitude spectrum, needs bias removal whereas bispectrum processing does
not. Reconstructed images from the observed data of binary stars and Jupiter are presented.
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