摘要
本文对测量视宁度的几种主要方法:包括测量衍射像好坏的目视衍射环方法,测量星像运动的北极星拖影、光电刀口宁静度监视、双光束视宁度拖影和双光束视宁度监视方法,直接测量大气温度结构参数(用微热传感器或声雷达)或相干直径(用干涉仪)的方法进行了综述和评价。
The site testing is one of the most important work for a new powerful ground-based telescope. Seeing, or the quality of a star image, is vital to make finally decision of a site. Techniques of its measurement are more complicate than those of other parameters, such as sky transparency and night sky brightness.Methods of seeing measurements are reviewed, (i) The Danjon's method. What is to be determined is, by means of a high-power eyepiece, the appearance of a stellar diffraction image at the focus of a small telescope. Since the diffraction ring is not seriously hampered by the image motion, the value of seeing obtained with this way is much smaller than that got with other methods, (ii) The polar star trail method.The stellar trails of Polaris are photographed with a small telescope, which is situated about 2 to 3 meters above the ground. This way is mainly used to measure the image motion. There are several instruments which are of similar principle. One is called the photoelectric knife-edge seeing monitor, a knife-edge in the focal plane being movable in right ascension to mask a half of the stellar image. Movements of the edge are recorded and used to calculate the RMS value a of its variations. For eliminating the effects of wind and/or tracking errors, a simulating double-beam telescope has been built by using a mask. Differential motions of the images formed by the two beams are measured. The typical one is the seeing monitor used for the NNTT 15-meter telescope site testing. (iii) Since the seeing quality depends on the atmospheric character, we can determine the atmospheric parameters instead of seeing measurement. The microthermal sensors and an acoustic sounder are used to obtain the refractive index structure parameter Cn2. A folded-shearing interferometer is used to measure the atmospheric coherance diameter, r0.According to the physics of seeing described by C. E. Coulman (1987) and B. L. Ulich(1987), the angular diameter φ of a long exposure image can be shown as follows: or, the full-width-at half-maximum of the intensity profile of a long-exposure image is given byφ0=0.996(λ/r0) where A is the wavelength.
出处
《天文学进展》
CSCD
北大核心
1992年第1期48-55,共8页
Progress In Astronomy
