共查询到20条相似文献，搜索用时 31 毫秒
1.
R. W. Wilson 《Monthly notices of the Royal Astronomical Society》2002,337(1):103-108
This paper discusses the use of Shack–Hartmann wavefront sensors to determine the vertical distribution of atmospheric optical turbulence above large telescopes. It is demonstrated that the turbulence altitude profile can be recovered reliably from time-averaged spatial cross-correlations of the local wavefront slopes for Shack–Hartmann observations of binary stars. The method, which is referred to as SLODAR, is analogous to the well known SCIDAR scintillation profiling technique, and a calibration against contemporaneous SCIDAR observations is shown. Hardware requirements are simplified relative to the scintillation method, and the number of suitable target objects is larger. The implementation of a Shack–Hartmann based turbulence monitor for use at the William Herschel Telescope is described. The system will be used to optimize adaptive optical observations at the telescope and to characterize anisoplanatic variations of the corrected point spread function. 相似文献
2.
Mark Chun Richard Wilson Remy Avila Tim Butterley Jose-Luis Aviles Don Wier Sam Benigni 《Monthly notices of the Royal Astronomical Society》2009,394(3):1121-1130
We present the results of an 18-month study to characterize the optical turbulence in the boundary layer and in the free atmosphere above the summit of Mauna Kea in Hawaii. This survey combined the Slope-Detection and Ranging (SLODAR) and Low-Layer SCIntillation Detection And Ranging (SCIDAR) (LOLAS) instruments into a single manually operated instrument capable of measuring the integrated seeing and the optical turbulence profile within the first kilometre with spatial and temporal resolutions of 40–80 m and 1 min (SLODAR) or 10–20 m and 5 min (LOLAS). The campaign began in the fall of 2006 and observed for roughly 50–60 h per month. The optical turbulence within the boundary layer is found to be confined within an extremely thin layer (≤80 m), and the optical turbulence arising within the region from 80 to 650 m is normally very weak. Exponential fits to the SLODAR profiles give an upper limit on the exponential scaleheight of between 25 and 40 m. The thickness of this layer shows a dependence on the turbulence strength near the ground, and under median conditions the scaleheight is <28 m. The LOLAS profiles show a multiplicity of layers very close to the ground but all within the first 40 m. The free-atmosphere seeing measured by the SLODAR is 0.42 arcsec (median) at 0.5 μm and is, importantly, significantly better than the typical delivered image quality at the larger telescopes on the mountain. This suggests that the current suite of telescopes on Mauna Kea is largely dominated by a very local seeing either from internal seeing, seeing induced by the flow in/around the enclosures, or from an atmospheric layer very close to the ground. The results from our campaign suggest that ground-layer adaptive optics can be very effective in correcting this turbulence and, in principle, can provide very large corrected fields of view on Mauna Kea. 相似文献
3.
R. W. Wilson T. Butterley M. Sarazin 《Monthly notices of the Royal Astronomical Society》2009,399(4):2129-2138
An instrument for monitoring of the vertical profile of atmospheric optical turbulence strength, employing the Slope Detection and Ranging (SLODAR) double star technique applied to a small telescope, has been developed by Durham University and the European South Observatory. The system has been deployed at the Cerro Paranal observatory in Chile for statistical characterization of the site. The instrument is configured to sample the turbulence at altitudes below 1.5 km with a vertical resolution of approximately 170 m. The system also functions as a general-purpose seeing monitor, measuring the integrated optical turbulence strength for the whole atmosphere, and hence the seeing width. We give technical details of the prototype and present data to characterize its performance. Comparisons with contemporaneous measurements from a differential image motion monitor (DIMM) and a multi-aperture scintillation sensor (MASS) are discussed. Statistical results for the optical turbulence profile at the Paranal site are presented. We find that, in the median case, 49 per cent of the total optical turbulence strength is associated with the surface layer (below 100 m), 35 per cent with the 'free atmosphere' (above 1500 m) and 16 per cent with the intermediate altitudes (100–1500 m). 相似文献
4.
Adaptive optics （AO）, which provides diffraction limited imaging over a field-of-view （FOV）, is a powerful technique for solar observation. In the tomographic approach, each wavefront sensor （WFS） is looking at a single reference that acts as a guide star. This allows a 3D reconstruction of the distorted wavefront to be made. The correction is applied by one or more deformable mirrors （DMs）. This technique benefits from information about atmospheric turbulence at different layers, which can be used to reconstruct the wavefront extremely well. With the assistance of the MAOS software package, we consider the tomography errors and WFS aliasing errors, and focus on how the performance of a solar telescope （pointing toward zenith） is related to atmospheric anisoplanatism. We theoretically quantify the performance of the to- mographic solar AO system. The results indicate that the tomographic AO system can improve the average Strehl ratio of a solar telescope in a 10＂ - 80＂ diameter FOV by only employing one DM conjugated to the telescope pupil. Furthermore, we discuss the effects of DM conjugate altitude on the correction achievable by the AO system by selecting two atmospheric models that differ mainly in terms of atmospheric prop- erties at ground level, and present the optimum DM conjugate altitudes for different observation sites. 相似文献
5.
先进多孔径视宁度廓线仪(A-MASP)由两台小望远镜组成,通过望远镜观测太阳表面的米粒结构进行日间湍流廓线测量.两台望远镜之间的相对指向误差可以通过改进的湍流廓线测量公式消除.数值仿真研究表明,使用消除抖动的湍流廓线计算公式后,发现A-MASP对地表附近的湍流不敏感.当两台望远镜距离为0.4 m时,无法测量400 m以下的湍流.在A-MASP中,采样高度的不均匀分布会造成测量结果的失真,可通过等效采样高度的计算方法,对该失真进行修正.通过100层相位屏对大气湍流的仿真,结果表明当望远镜距离不同时,湍流廓线测量的结果各有侧重.当距离较近时(0.4 m),A-MASP对0.4–5 km的湍流廓线测量精度较高.当距离为1.2 m和2.0 m时,对5 km以上的湍流廓线测量较准确. 相似文献
6.
S. V. Drabek V. V. Komarov S. A. Potanin A. D. Savvin A. S. Moskvitin O. I. Spiridonova 《Astrophysical Bulletin》2017,72(2):206-216
The results of studies of the optics of the 1-m Zeiss-1000 telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) by the Shack–Hartmann (SH) method are presented. Using a Shack–Hartmann wavefront sensor (SH WFS) we have adjusted the telescope optical system by means of shifts and tilts of the secondary mirror. The procedure has significantly reduced the aberrations that appeared during the long-term instrument operation. A new method to investigate the surface quality of the mirrors of the Zeiss-1000 being applied, characteristics close to the diffraction limit are achieved. In general, the entire opto-mechanical telescope system provides an image quality of about 0.5″ at 80%energy level. 相似文献
7.
大口径望远镜受大气湍流的影响,光学分辨率远远小于其自身光路所决定的衍射极限。为了相应的自适应光学系统设计,首先有必要对大气波动进行仿真以提供环境数据。通常的大气波前仿真方法需要通过计算结构函数,得到功率谱函数,进而得到仿真波前,但该方法存在计算速度慢,中间变量存储空间大的问题,给大口径望远镜或者长时间仿真带来很大不便。介绍了一种可行的基于迭代分形法的波前仿真方法,复杂度达到O（N）,可以大大提高波前仿真的速度。 相似文献
8.
Mei Rong Hu Zhong-wen Xu Teng Sun Chang-sheng 《Chinese Astronomy and Astrophysics》2018,42(3):475-486
In stellar interferometers, the fast-steering mirror (FSM) is widely utilized to correct the wavefront tilt caused by the atmospheric turbulence and internal instrumental vibration, because of its high resolution and fast response frequency. In this study, the non-coplanar error between the FSM and the actuator deflection axis introduced by the manufacturing, assembly, and adjustment is analyzed systematically. Via a numerical method, the additional optical path difference (OPD) caused by the above factors is studied, and its effect on the fringe tracking accuracy of a stellar interferometer is also discussed. On the other hand, the starlight parallelism between the beams of two arms is one of the main factors for the loss of fringe visibility. By analyzing the influence of wavefront tilt caused by the atmospheric turbulence on fringe visibility, a simple and efficient real-time correction scheme of starlight parallelism is proposed based on a single array detector. The feasibility of this scheme is demonstrated by a laboratory experiment. The results show that after the correction of fast-steering mirror, the starlight parallelism meets preliminarily the requirement of a stellar interferometer on the wavefront tilt. 相似文献
9.
The altitude distribution of optical turbulence is derived from the MASS instrument data by solving an inverse problem. In
this paper, some modifications of the profile restoration are described. The principal change is the introduction of the Non
Negative Least Squares algorithm which has good regularizing properties. An averaging of scintillation indices was replaced
with averaging of obtained solutions what leads to clearer physical results. It is shown that restoration with a number of
turbulent layers as large as 14–15 can be successfully performed. 相似文献
10.
N. A. Bharmal † D. F. Buscher C. A. Haniff 《Monthly notices of the Royal Astronomical Society》2005,360(4):1325-1332
A new method of wavefront sensing that uses a pair of equally defocused images to derive the wavefront aberrations is presented. Unlike in conventional curvature-sensing systems, the sensor works in a near-focus regime where the transport of intensity equation is not valid, and, unlike in phase-diversity methods, a non-iterative algorithm is used to infer the wavefront aberrations. The sensor designs outlined only require a small number of detector pixels: two designs with five and nine pixels per plane are analysed, and the nine-element sensor (NES) is shown to have a competitive measurement sensitivity compared with existing low-order astronomical wavefront sensors. The NES is thus well suited to applications such as adaptive optics for the individual telescopes in an optical interferometer array. 相似文献
11.
The daytime atmospheric turbulence profile is crucial for the design of both optical systems and the control algorithm of a solar Multi-Conjugate Adaptive Optics(MCAO) system. The Multi-Aperture Seeing Profiler(MASP) is a portable instrument which can measure the daytime turbulence profile up to~30 km. It consists of two portable small telescopes that can deliver performance similar to a SolarDifferential Image Motion Monitor +(S-DIMM+) on a 1.0 m solar telescope. In the original design of MASP, only two guide stars are used to retrieve the turbulence profile. In this paper, we studied the usage of multiple guide stars in MASP using numerical simulation, and found that there are three main advantages.Firstly, the precision of the turbulence profile can be increased, especially at a height of about 15 km, which is important for characterizing turbulence at the tropopause. Secondly, the equivalent diameter of MASP can be increased up to 30%, which will reduce the cost and weight of the instruments. Thirdly, the vertical resolution of the turbulence profile near the ground increases with the help of multiple guide stars. 相似文献
12.
大气湍流极大限制了地基大口径望远镜观测天文目标图像的空间分辨率.根据最大似然估计原理,提出了用实际光学带宽约束的可有效减小天文观测图像中大气湍流影响的盲反卷积方法,通过共轭梯度优化算法使卷积误差函数趋向最小.建立了望远镜光学系统参数和图像频域带宽的关系,采用变量正性约束、点扩散函数带宽有限约束,提高算法的收敛性.为避免图像处理中有效傅立叶变换频率超出截止频率,要求采集望远镜焦面图像时单个成像单元(如CCD像素单元)应小于四分之一衍射斑直径.算法中未用目标支持域约束,所提出的方法适用于全视场天文图像恢复.用计算机模拟和对实际天文目标双鱼座图像数据的恢复结果验证了所提出方法的有效性. 相似文献
13.
14.
R. Avila J. L. Avilés R. W. Wilson M. Chun T. Butterley E. Carrasco 《Monthly notices of the Royal Astronomical Society》2008,387(4):1511-1516
We report the development and first results of an instrument called Low Layer SCIDAR (Scintillation Detection and Ranging) (LOLAS) which is aimed at the measurement of optical-turbulence profiles in the atmospheric boundary layer with high altitude resolution. The method is based on the Generalized SCIDAR (GS) concept, but unlike the GS instruments which need a 1-m or larger telescope, LOLAS is implemented on a dedicated 40-cm telescope, making it an independent instrument. The system is designed for widely separated double-star targets, which enables the high altitude resolution. Using a 200-arcsec-separation double star, we have obtained turbulence profiles with unprecedented 12-m resolution. The system incorporates necessary novel algorithms for autoguiding, autofocus and image stabilization. The results presented here were obtained at Mauna Kea Observatory. They show LOLAS capabilities but cannot be considered as representative of the site. A forthcoming paper will be devoted to the site characterization. The instrument was built as part of the Ground Layer Turbulence Monitoring Campaign on Mauna Kea for Gemini Observatory. 相似文献
15.
Olivier Lardière Rodolphe Conan Colin Bradley Kate Jackson Peter Hampton 《Monthly notices of the Royal Astronomical Society》2009,398(3):1461-1467
Sodium laser guide stars (LGSs) are elongated sources due to the thickness and the finite distance of the sodium layer. The fluctuations of the sodium layer altitude and atom density profile induce errors on centroid measurements of elongated spots, and generate spurious optical aberrations in closed-loop adaptive optics (AO) systems. According to an analytical model and experimental results obtained with the University of Victoria LGS bench demonstrator, one of the main origins of these aberrations, referred to as LGS aberrations, is not the centre-of-gravity (CoG) algorithm itself, but the thresholding applied on the pixels of the image prior to computing the spot centroids. A new thresholding method, termed 'radial thresholding', is presented here, cancelling out most of the LGS aberrations without altering the centroid measurement accuracy. 相似文献
16.
《Chinese Astronomy and Astrophysics》2023,47(2):257-284
Atmospheric turbulence has been confirmed as the primary source affecting the quality of ground-based telescope image. To reduce the effect of atmosphere, a good site should be selected, and adaptive optics (AO) should be installed for the telescope. In general, the daytime atmospheric turbulence is more intense than that at night under the effect of solar radiation. Numerous solar telescopes have built AO systems worldwide. Conventional AO is only capable of improving the image quality in a small field of view, whereas it cannot satisfy the needs of a large field of view. The novel wide field adaptive optical system is capable of achieving a large field of view and high-resolution images, whereas the atmospheric turbulence profile should be accurately detected, which is the prerequisite and key parameter of the novel AO system. Moreover, the astronomical high-resolution technology in accordance with the turbulence imaging theory requires more detailed detection of turbulence. Accordingly, a brief review about the latest detection technology of the daytime optical turbulence profile is valuable for astronomical observations. Besides, the parameters of atmospheric turbulence are briefly introduced. Subsequently, SNODAR, SHABAR, MOSP, DIMM+, A-MASP, and other detection technologies of the stratified atmospheric turbulence for daytime are primarily presented, and the advantages and disadvantages of the different technologies are summarized. 相似文献
17.
Modelling the optical turbulence boiling and its effect on finite-exposure differential image motion
It is usually accepted that whenever dealing with astronomical observation through the atmosphere, the optical turbulence temporal evolution can be sufficiently described with the so-called frozen turbulence hypothesis. In this model, turbulence is supposed to be equivalent to a series of solid phase screens that slide horizontally in front of the observation field of view. Experimental evidence shows, however, that an additional physical process must be taken into account when describing the temporal behaviour of the optical turbulence. In fact, while translating above the observer, turbulence undergoes a proper temporal evolution and affects differently the astronomical and, more specifically, the astrometric observations. The proper temporal evolution of the turbulence-induced optical turbulence observable quantities is here called the optical turbulence boiling. We are proposing through this paper a theoretical approach to the modelling of the optical turbulence temporal evolution when the turbulent layer horizontal translation and the optical turbulence boiling are both involved. The model we propose, as a working hypothesis though, has a direct relevance to differential astrometry because of its explicit dependence upon the optical turbulence temporal evolution. It can also be generalized to other techniques of high angular resolution astronomical observation through the atmospheric turbulence. 相似文献
18.
Giacomo Colombatti Alessio Aboudan Francesca Ferri Francesco Angrilli 《Planetary and Space Science》2008,56(5):601-612
During the first phase of Huygens arrival into Titan's atmosphere the probe is subjected to gravitational and aerodynamic forces in aerodynamic hypersonic regime. Atmospheric drag exerts a strong deceleration on the capsule measured by Huygens atmospheric structure instrument (HASI) servo accelerometer. A 6 DOF (Degree of Freedom) model of the Huygens probe entry dynamics has been developed and used for data analysis. The accelerometer data are analysed and the model allows the retrieval of dynamics information of Huygens probe from 1545 km altitude down to end of the entry phase. Probe's initial conditions (velocity and position) were refined to match the measured deceleration profile resulting in a different altitude at interface epoch with respect to those of the Cassini Navigation Team. Velocity and position of probe at interface epoch are compatible with those used by Descent Trajectory Working Group (DTWG).Measurements acquired before atmosphere detection are used to estimate probe's angular rate, bound attitude and characterise the angle of attack profile which results to be lower than 4° during the whole entry. Probe's spin calculated (6.98 RPM) is slightly different with respect to DTWG of 7.28 RPM but considering a 2% error in the Inertia matrix these results are inside the 1-σ error band. 相似文献
19.
The capability to measure nearly simultaneously the entire spectrum of atmospheric emission from the extreme ultraviolet to the near infrared, with relatively high spectral resolution and high sensitivity, while also obtaining global and altitude coverage, would provide a database from which significant advances could be made in our current understanding of the atmosphere and its processes. The large payload capacity of the shuttle orbiter offers the first opportunity to put such instrumentation into space. The Imaging Spectrometric Observatory (ISO) comprises an array of five spectrometers designed to make full use of the shuttle as an observing platform for remote sensing of the atmosphere. ISO covers the wavelength range 300–12000 Å at 2–7 Å resolution. Use of area array detectors (intensified-CCD's) permits simultaneous measurements of ～1000 Å at a time. The instrument is capable of scanning the entire wavelength range in less than 20 s, or dwelling on weaker features for longer periods of time. The detectors are two dimensional and permit spectral imaging in one direction and spatial imaging in the other. The spatial imaging and spatial scanning features permit measurement of altitude profiles, or mapping of strongly spatially varying features such as aurorae. The instrument is designed to allow versatility. The various functions are programmable and software controlled. The key subsystems are modular for convenient replacement or upgrading. It is anticipated that the instrument will have applications not only in the area of atmospheric science, but also in studies of the ionosphere and magnetosphere, and in support of active experiments to be performed in space. 相似文献
20.
Atmospheric optics is the study of optical effects induced by the atmosphere on light propagating from distant sources. Of particular concern to astronomers is atmospheric turbulence, which limits the performance of ground-based telescopes. The past two decades have seen remarkable growth in the capabilities and performance of adaptive optics (AO) systems. These opto-mechanical systems actively compensate for the blurring effect of the Earth’s turbulent atmosphere. By sensing, and correcting, wavefront distortion introduced by atmospheric index-of-refraction variations, AO systems can produce images with resolution approaching the diffraction limit of the telescope at near-infrared wavelengths. This review highlights the physical processes and fundamental relations of atmospheric optics that are most relevant to astronomy, and discusses the techniques used to characterize atmospheric turbulence. The fundamentals of AO are then introduced and the many types of advanced AO systems that have been developed are described. The principles of each are outlined, and the performance and limitations are examined. Aspects of photometric and astrometric measurements of AO-corrected images are considered. The paper concludes with a discussion of some of the challenges related to current and future AO systems, particularly those that will equip the next generation of large, ground-based optical and infrared telescopes. 相似文献