共查询到19条相似文献，搜索用时 250 毫秒
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差分像运动视宁度测量实验 总被引：1，自引：0，他引：1
本文首先阐明了Ｆｒｉｅｄ参数（大气相干长度）ｒ０的物理含义及为什么选取ｒ０作为表征大气视宁度的参数；然后介绍了一种优良的测量ｒ０的方法－差分像运动法，总结了该方法的六个特点，最后给出了在云南天文台用该方法的六个特点，最后给出了在云南天文台用该方法两次实测大气视宁度的实验结果及实验参数，并对结果进行了分析。 相似文献
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大气视宁度是衡量台址大气光学品质的重要指标。差分像运动视宁度监测仪(Differential Image Motion Monitor,DIMM)被广泛应用于国内外天文选址的视宁度测量作业。介绍了一种优良的视宁度测量方法——差分像运动视宁度优化监测(Improved to Differential Image Motion Monitor,I-DIMM)法。首先对I-DIMM的结构设计和视宁度计算方法进行了详细描述;随后通过设置0. 36 m和0. 12 m两种口径望远镜进行视宁度的模拟测量,将I-DIMM测量结果与传统的DIMM测量的结果进行对比,均证明I-DIMM视宁度计算方法比DIMM更为精确;最后对模拟结果进行了分析,证明了I-DIMM相比于DIMM的优势。 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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E. J. Seykora 《Solar physics》1993,145(2):389-397
A non-telescopic method of determining the quality of atmospheric seeing is discussed for large angular diameter objects, such as the Sun. In this method the concept of thermodynamic fluctuations is used to relate the observed intensity fluctuations to the r.m.s. angular diameter of the atmospheric seeing cells and telescopic angle of arrival fluctuations. Comparison between the measured r.m.s. cell size and telescopic angle of arrival fluctuations are presented for various degrees of seeing. Cross-correlation coefficients of 0.95 have been measured during such comparisons.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA), under cooperative agreement with the National Science Foundation. Partial support for NSO is provided by USAF under a Memorandum of Understanding with the NSF. 相似文献
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Starting November 1999 we are carrying out simultaneous seeing observations with the Solar Differential Image Motion Monitor (S-DIMM) at the Fuxian Lake station of the Yunnan Observatory and a solar scintillometer of the type used in the recent site survey by one of us (Beckers et al., 1997). The purpose was to compare the two methods of assessing the daytime atmospheric seeing for a lake site. We report here the first results of this comparison. We find that the relation between the seeing as measured by the S-DIMM (the Fried parameter r
0) and the scintillation in the solar irradiance (I) differs greatly from the relation found by Seykora (1993) for NSO/Sac Peak. We conclude that the I measurements give a good indication for the amount of near-Earth seeing but that they are a poor proxy for the total atmospheric seeing. We interpret the simultaneous (r
0, I) observations in terms of an atmospheric seeing model and find good quantitative agreement with a model in which a fraction () of the seeing originated near the Earth (ground or water) and the rest (1–) originates at higher layers. For lake sites is small all day and the seeing is determined primarily by the refractive index variations at higher atmospheric layers. For land sites is small in the early morning but rapidly increases as the day progresses, near-Earth seeing dominating there most of the time. 相似文献
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A. Bounhir Z. Benkhaldoun E. Carrasco M. Sarazin 《Monthly notices of the Royal Astronomical Society》2009,398(2):862-872
This paper aims at studying the wind at 200 mbar over the Moroccan observatory Oukaimeden, as high-altitude winds have been adopted as a useful parameter for site characterization in terms of the suitability of a site for the development of some adaptive optics techniques. The data used come from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data base, which is widely acknowledged as being reliable. Statistical analyses of 200-mbar wind speed since 1983 are performed. Comparison with some of the main observatory sites worldwide qualifies Oukaimeden as one of the best observatory sites in terms of 200-mbar wind statistics. Our analysis of a record of seeing measurements during the years 2003 and 2004 concludes that while 200-mbar wind speed can be used as a parameter for ranking astronomical sites in term of their suitability for adaptive optics, it cannot be used for the whole atmospheric seeing prediction. A comparison of monthly values of the seeing parameter at Oukaimeden, La Silla and Paranal demonstrates the high seeing quality of Oukaimeden, as the seeing values measured were lower than those of La Silla and Paranal for most of the time during the comparison period. Furthermore, a statistical analysis of atmospheric stratified seeing, wavefront coherence time and isoplanatic angle measured with a Multi-Aperture Scintillation Sensor instrument over Paranal from 2004 to 2007 have been performed. We found good correlations between 200-mbar wind velocity and levels 4, 5 and 6 seeing, wavefront coherence time and isoplanatic angle, with corresponding correlation coefficients of 0.74, 0.79, 0.70, 0.97 and 0.78. 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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Observations of the solar photosphere from the ground encounter significant problems caused by Earth’s turbulent atmosphere. Before image reconstruction techniques can be applied, the frames obtained in the most favorable atmospheric conditions (the so-called lucky frames) have to be carefully selected. However, estimating the quality of images containing complex photospheric structures is not a trivial task, and the standard routines applied in nighttime lucky imaging observations are not applicable. In this paper we evaluate 36 methods dedicated to the assessment of image quality, which were presented in the literature over the past 40 years. We compare their effectiveness on simulated solar observations of both active regions and granulation patches, using reference data obtained by the Solar Optical Telescope on the Hinode satellite. To create images that are affected by a known degree of atmospheric degradation, we employed the random wave vector method, which faithfully models all the seeing characteristics. The results provide useful information about the method performances, depending on the average seeing conditions expressed by the ratio of the telescope’s aperture to the Fried parameter, \(D/r_{0}\). The comparison identifies three methods for consideration by observers: Helmli and Scherer’s mean, the median filter gradient similarity, and the discrete cosine transform energy ratio. While the first method requires less computational effort and can be used effectively in virtually any atmospheric conditions, the second method shows its superiority at good seeing (\(D/r_{0}<4\)). The third method should mainly be considered for the post-processing of strongly blurred images. 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