像运动法测量视宁度参数中曝光时间的重要性及其测定

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

The Importance of the Exposure-time and its Measurement in the Image Motion Method to Measure the Seeing Parameter

The atmospheric turbulence is a major problem in the optical astronomy as it drastically reduces the angular resolution of telescopes.The degradation of the astronomical image quality is also caused by the atmospheric turbulence.The distortion of the image as well as its motion may vary considerably with time and with the location of the observer.These random displacements are called as the astronomical seeing.The degradation of the astronomical image quality can be characterized by the seeing parameter r 0. The relation between the measured r 0 and the video CCD exposure time in the image motion method measuring the seeing parameter r 0 is given in this paper.It is indicated that the exposure time must be shorter than the atmospheric coherent time.If the exposure time is longer than the coherent time,one will obtaine a bigger r 0 value.For this and the need to check the instrument,an accurate measurement of the video CCD exposure time is necessary.In this paper, an experiment we designed to measure the exposure time is presented.The result of the experiment shows that this method is reliable.