共查询到18条相似文献,搜索用时 140 毫秒
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大气湍流会导致天文图像的像质衰减,而视宁度r0则是描述这种衰减的特征参数。在本文中,我们给出了像运动法测量中r0和曝光时间之间的关系:曝光时间必须小于大气相干时间,否则测量的r0值将偏大。基于这个原因以及对仪器检测的需要,我们必须对视宁度测量仪的曝光时间进行准确地测量。为此我们设计了一种实验方法来测定视频CCD的曝光时间,实验的结果表明这种方法是可靠的。 相似文献
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讨论了经过大气后天文图象的象质衰减,研究了对这种衰减进行描述的视宁度参数r0及其它几个大气光学参数,介绍了几种测量象质衰减参数的方法,重点介绍了我们将差分像运动法运用于白日视宁度测量的尝试以及新设计的可兼顾昼夜的视宁度测量仪,仪器已用于云台白日的视宁度测量。最后对近场近似假设进行了定量分析,在此基础上给出了新确定的近场近似成立的范围,这一范围比以前所给的要更大些。 相似文献
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讨论了经过大气后天文图象的象质衰减,研究了对这种衰减进行描述的宁度参数r0及其它几个大气光学参数,介绍了几种测量象质衰减参数的方法,重点介绍了我们将差分像运动法运用于白日视宁度测量的尝试以及新设计的可兼顾昼夜的视宁度测量仪,仪器已用于云台白日的视宁度测量。最后对近场近似假设进行了定量分析,在此基础上给出新确定的近场近似成立的范围,这一范围比以前所给的要更大些。 相似文献
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云南天文台丽江高美古和昆明的大气视宁度研究 总被引:5,自引:1,他引:4
研究云南天文台昆明凤凰山和丽江高美古两地点的大气视宁度。利用云南天文台于1994年建立的3孔较差视宁度监视仪(3孔DIMM),对这两个地点的视宁度对比观测。还利用云南天文台的1米望远镜所得到的视宁度与3孔DIMM所测的视宁度进行对比。1米望远镜和3孔DIMM同时观测了7个晚上,各取得308组数据,它们的视宁度平均分别为0.90〃和0.84〃。还讨论了3孔DIMM采用不同曝光时间对视宁度测量值的影响,从实验得出3孔DIMM采用20ms曝光比采用8ms曝光所测视宁度的值要好15%左右。从1995年5月-1996年12月,对丽江高美古和昆明凤凰山二地进行了视宁度的对比观测。在高美古和昆明分别观测了234夜和256夜,观测结果是两个点的视宁度平均;丽江为0.70〃,昆明为0.95〃,同时也统计了两个点的月平均视宁度和最好夜的视宁度,并讨论了两地视宁度随时间的变化规律。 相似文献
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用研制的全自动辐射计在97.8GHz上测量南京市内大气的不透明度以及这种不透明度随时间的变化.辐射计记录大气在不同天顶高度的辐射温度,由此测出天顶方向的大气不透明度。在56小时的测量时间内,取得了1400多组数据,拟合得到了在观测时段内天顶方向的大气不透明度在0.2至0.7之间,典型值为0.4,表明测试地点的大气条件允许进行3mm波段的射电天文观测.由于在工作频段内大气不透明度的主要来源是对流层水汽的吸收,测量的不透明度可用来直接反映大气内水汽的含量,并实时校准大气吸收. 相似文献
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用DIMM测视宁度的几个问题 总被引:3,自引:1,他引:2
DIMM测视宁度是目前世界上通行和好的方法之一,但仪器、观测和处理方法不同会影响观测结果和精度,本文就其中的几个最主要因素进行讨论。包括:望远镜和子瞳,曝光时间,取样时间,星像计算的判据和计算方法问题。 相似文献
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The degradation of astronomic images by optical inhomogeneities in the earth's atmosphere is generally called seeing. It represents the angular diameter of the stellar images as seen through a turbulent medium. Several techniques can be used to determine this parameter. The knowledge of the optical strength of atmospheric turbulence, namely, the integrated structure coefficient of the atmospheric refractive index Cn
2 allows to predict the atmospheric optical quality in terms of seeing. We tried in this study to assess an astronomical seeing using a model forecast using meteorological data collected in three stations in Latin America from 1958 to 1991. The efficiency of the model is tested by comparison with simultaneous seeing measurements, at Chiliean astronomical sites. 相似文献
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在文献」1「4 基础上,根据近年文选址实践中提出的问题,先进一步讨论了大气相干直径和时间的的物理和意义,然后强调了自由大气湍流的天文成像效应及选址中进行研究和测量的重要性。最后对差分像运动方法测量视宁度的定标和系统误差等问题作了分析。 相似文献
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On astronomical seeing: The single Schlieren model 总被引:1,自引:0,他引:1
Ulrich Grossmann-Doerth 《Solar physics》1969,9(1):210-224
A model of astronomical seeing with particular view to solar observations is developed which assumes the atmospheric disturbances to consist of individual turbulence elements called Schlieren. A quantitative account is given of each image motion, image blurring and scintillation as function of Schlieren properties and telescope parameters. The theory permits to explain the observational results under conditions of good seeing; furthermore, it provides a basis for the discussion of the physical phenomena in the atmosphere that cause image deterioration. As an illustration it is shown how the theory could be applied to a problem of interest to solar astronomers searching for a suitable observatory site. 相似文献
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In order to deduce significant astrophysical results from solar diameter measurements it is necessary to take an accurate account of instrumental and atmospheric effects. This paper presents a comparison between visual and CCD camera measurements performed by means of the Calern Observatory solar astrolabe during the last 4 years; this allows us to evaluate visual measurements done previously (from 1975 to 1989). Then, a study of atmospheric effects is developed. From CCD measurements, the image quality, expressed by Fried's seeing parameter,r
0, is estimated and related to the errors occurring in solar diameter measurements. A statistical analysis gives about 0.26 arc sec (or 0.13 arc sec for the semi-diameter) as the lowest value that this error may reach at Calern Observatory. One conclusion of this work is that it is important in the future to have image quality observations, obtained using a dedicated monitor, in order to evaluate and classify the measurements. A survey of the seeing might so lead to improve the precision of the results by weighting each diameter estimation and eventually to schedule the observations. 相似文献
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《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
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B. García-Lorenzo A. Eff-Darwich J. J. Fuensalida J. Castro-Almazán 《Monthly notices of the Royal Astronomical Society》2009,397(3):1633-1646
Current projects for large telescopes demand a proper knowledge of atmospheric turbulence to design efficient adaptive optics systems in order to reach large Strehl ratios. However, the proper characterization of the turbulence above a particular site requires long-term monitoring. Because of the lack of long-term information on turbulence, high-altitude winds (in particular winds at the 200 mbar pressure level) were proposed as a parameter for estimating the total turbulence at a particular site, with the advantage of records of winds going back several decades. We present the first complete study of atmospheric adaptive optics parameters above the Teide Observatory (Canary Islands, Spain) in relation to wind speed. On-site measurements of C 2 N ( h ) profiles (more than 20 200 turbulence profiles) from G-SCIDAR (Generalized Scintillation Detection and Ranging) observations and wind vertical profiles from balloons have been used to calculate the seeing, the isoplanatic angle and the coherence time. The connection of these parameters to wind speeds at ground and at 200 mbar pressure level are shown and discussed. Our results confirm the well-known high quality of the Canary Islands astronomical observatories. 相似文献
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Matwey V. Kornilov 《Experimental Astronomy》2016,41(1-2):223-242
Atmospheric turbulence is the one of the major limiting factors for ground-based astronomical observations. In this paper, the problem of short-term forecasting seeing is discussed. The real data that were obtained by atmospheric optical turbulence (OT) measurements above Mount Shatdzhatmaz in 2007–2013 have been analysed. Linear auto-regressive integrated moving average (ARIMA) models are used for the forecasting. A new procedure for forecasting the image characteristics of direct astronomical observations (central image intensity, full width at half maximum, radius encircling 80 % of the energy) has been proposed. Probability density functions of the forecast of these quantities are 1.5–2 times thinner than the respective unconditional probability density functions. Overall, this study found that the described technique could adequately describe temporal stochastic variations of the OT power. 相似文献