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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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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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天文仪器中图像跟踪定位算法的比较研究 总被引:1,自引:0,他引:1
天文光学观测中采用快速图像跟踪定位可以降低大气视宁度和望远镜跟踪误差的影响,提高观测效率.针对天文仪器观测的需要选择了两类共5种算法,通过数值实验和实验室实测对这两类算法在不同噪声背景下的精度和稳定性进行了比较研究,数值实验和实验室测试的结果表明归一化互相关法和重心法既有较高的精度,又有较好的抗干扰可靠性,将分别被应用于2.16 m望远镜的高色散光谱仪前置系统和SONG(Stellar Observations Network Group)项目的科学仪器. 相似文献
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从天文选址的角度出发 ,介绍了影响望远镜光学成像质量的大气湍流的成因、特性以及它对星光波前的影响 ,进而对衡量大气宁静度的量度值———大气视宁度做了详细的叙述 ,包括其测量方法 ,以及目前国际天文选址界常用的较差像运动测量仪的测量原理 ,介绍了云台三孔较差像运动测量仪的光学和硬件结构组成部分 ,对图像处理 /采集软件中用Waldie法计算大气视宁度值与用Roddier法计算大气视宁度值的不同之处进行了理论的分析 ,编写了Roddier法相应软件 ,并用于实测中测量了大气视宁度的值 ,得到一些有意义的结果。 相似文献
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《天文学报》2016,(5)
光学系统像质评价是光学设计的核心,通过对常用像质评价方法与在30 m望远镜(Thirty Meter Telescope,TMT)的像质评价中提出的归一化点源灵敏度函数(Normalized Point Source Sensitivity,PSSN)的分析比较,对PSSN在TMT宽视场光谱仪(Wide Field Optical Spectrometer,WFOS)中的应用进行了研究.包括对大气视宁度的简化模拟、TMT中M3的移动对系统PSSN的影响、WFOS中准直镜的移动对系统PSSN的影响、在不同大气湍流的条件下PSSN与天顶角的关系以及PSSN与波像差的均方根值(root mean square of wavefront error,RMS WFE)μ之间的关系.结果表明,PSSN对视宁度受限下的TMT的像质评价是有效的. 相似文献
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P. R. Gillingham 《Astrophysics and Space Science》1989,160(1-2):225-230
In seeking to minimize local seeing, some large telescopes are being planned with less wind protection than has been traditional and some sites with very good seeing appear to suffer significantly from ground-transmitted vibration. A great care is needed in designing new telescopes to ensure that vibration does not become a dominant cause of image degradation. A supplementary drive system is proposed which could improve on past tracking performances even in such adverse conditions. The system may also reduce the costs of very large telescopes by easing the demands on the stiffness and accuracy of their mountings and drives.Paper presented at the Symposium on JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988. 相似文献
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《天文和天体物理学研究(英文版)》2020,(6)
In this article,we present a detailed analysis of the statistical properties of seeing for the Muztaghata site which is a candidate site for hosting the future Chinese Large Optical/infrared Telescope(LOT)project.The measurements were obtained with differential image motion monitors(DIMMs) from April2017 to November 2018 at different heights during different periods.The median seeings at 11 m and6 m are very close but significantly different from that on the ground.We mainly analyzed the seeing at11 m monthly and hourly,having found that the best season for observing was from late autumn to early winter and seeing tended to improve during the night only in autumn.The analysis of the dependence on temperature inversion,wind speed and direction also was made and the best meteorological conditions for seeing are given. 相似文献
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《天文和天体物理学研究(英文版)》2016,(8)
In this paper, a cascade acceleration feedback control(AFC) enhanced by a disturbance observation and compensation(DOC) method is proposed to improve the tracking precision of telescope systems.Telescope systems usually suffer some uncertain disturbances, such as wind load, nonlinear friction and other unknown disturbances. To ensure tracking precision, an acceleration feedback loop which can increase the stiffness of such a system is introduced. Moreover, to further improve the tracking precision, we introduce the DOC method which can accurately estimate the disturbance and compensate it. Furthermore,the analysis of tracking accuracy used by this method is proposed. Finally, a few comparative experimental results show that the proposed control method has excellent performance for reducing the tracking error of a telescope system. 相似文献
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Shin Oya Hiroshi Terada Yutaka Hayano Makoto Watanabe Masayuki Hattori Yosuke Minowa 《Experimental Astronomy》2016,42(1):85-98
Stellar images have been obtained under natural seeing at visible and near-infrared wavelengths simultaneously through the Subaru Telescope at Mauna Kea. The image quality is evaluated by the full-width at the half-maximum (FWHM) of the stellar images. The observed ratio of FWHM in the V-band to the K-band is 1.54 ± 0.17 on average. The ratio shows tendency to decrease toward bad seeing as expected from the outer scale influence, though the number of the samples is still limited. The ratio is important for simulations to evaluate the performance of a ground-layer adaptive optics system at near-infrared wavelengths based on optical seeing statistics. The observed optical seeing is also compared with outside seeing to estimate the dome seeing of the Subaru Telescope. 相似文献
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In astronomical observations at optical wavelengths, a fast image tracking system can be adopted to reduce the effects of the atmospheric seeing and telescopic tracking error, and therefore improve the observing efficiency. Aiming at the need of astronomical observations, totally 5 kinds of algorithms in two categories were selected to make a comparative study on their accuracies and stabilities under different noise conditions by both numerical experiment and laboratory test. The results indicate that the normalized cross-correlation method and barycenter method have not only a higher accuracy but also a better reliability against interferences, they will be applied to the high-resolution spectrograph of the Xinglong 2.16 m telescope and the scienti?c instruments of the SONG (Stellar Observations Network Group) project, respectively. 相似文献
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Instrumentation built to record seeing data automatically via image motion measurements of bright stars in small telescopes is described. The centroid of the star image is found 256 times s-1 in one dimension and is analyzed on-line. The device works over a range of FWHM values as would be seen through a large telescope between <0.1 and 3.0 arcsec. The first results for two identical instruments set up at two locations near the duPont Telescope at Las Campanas Observatory are reported. For a total of 61 nights of data (450 h at each site), the median seeing is 0.6 arcsec, with quartiles at 0.4 and 0.8 arcsec. These are FWHM values referred to 5000 Å at the zenith. So far, the two sites are indistinguishable on average. 相似文献
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In this empirical study, we compare high-resolution observations obtained with the 65-cm vacuum reflector at Big Bear Solar
Observatory (BBSO) in 2005 and with the Dunn Solar Telescope (DST) at the National Solar Observatory/Sacramento Peak (NSO/SP)
in 2006. We measure the correction of the high-order adaptive optics (AO) systems across the field of view (FOV) using the
spectral ratio technique, which is commonly employed in speckle masking imaging, and differential image motion measurements.
The AO correction is typically much larger (10′′ to 25′′) than the isoplanatic angle and can be described by a radially symmetric function with a central core and extended wings.
The full-width at half-maximum (FWHM) of the core represents a measure of the AO correction. The average FWHM values for BBSO
and NSO/SP are 23.5′′ and 18.2′′, respectively. The extended wings of the function show that the AO systems still contribute to an improved speckle reconstruction
at the periphery of the 80′′×80′′ FOV. The major differences in the level of AO correction between BBSO and NSO/SP can be explained by different contributions
of ground-layer- and free-atmosphere-dominated seeing, as well as different FOVs of the wavefront sensors. In addition, we
find an anisotropic spectral ratio in sunspot penumbrae caused by the quasi-one-dimensional nature of penumbral filaments,
which introduces a significant error in the estimation of the Fourier amplitudes during the image restoration process. 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