A study of the degradation of daytime astronomical images due to turbulence in the lower atmosphere by measurement of the standard deviation of the angle of arrival

✍ Scribed by J. Borgnino; J. Vernin; C. Aime; G. Ricort

• Publisher: Springer
• Year: 1979
• Tongue: English
• Weight: 644 KB
• Volume: 64
• Category: Article
• ISSN: 0038-0938
• DOI: 10.1007/bf00151449

✦ Synopsis

Fluctuations in the angle-of-arrival of a luminous wavefront are investigated by placing a narrow slit over the image of the solar limb, and observing the entrance pupil through this diaphragm. Measurement of the standard deviation ~rAA of these fluctuations, in a direction perpendicular to the solar limb, provides sufficient information to estimate an absolute parameter characterizing the seeing, i.e. Fried's parameter ro or the equivalent parameter IL C~(h) dh which gives the integral, over an atmosphere thickness L which depends on the spatial and angular filterings performed by the slit, of the 2 .... structure constant CNcharacterlzlng fluctuations in the air's refractive index. Simultaneous estimations of O-~A and ~L C~(h) dh permit a linear relationship to be established between these two quantities. The result is interpreted theoretically by integration of the two-dimensional power spectrum for the angle-ofarrival fluctuations. The influence of filtering effects is discussed. Such a calibration can be performed for a given telescope and slit, enabling the system to be used as a seeing monitor.