Interferential seeing monitor

Abstract

Context. This work is a part of the development of observational instruments for the study of optical turbulence in the atmosphere. These instruments are developed for the optimization of high angular resolution and adaptive optics techniques. Aims. We present a new approach to estimate the astronomical seeing which is a fundamental parameter in high angular resolution, in adaptive optics and site testing. Based on this approach, we developed a simple low-cost seeing monitor, called Interferential Seeing Monitor (hereafter ISM). Methods. The principle of the ISM is based on the study of the diffraction-interference pattern produced by a Young's double-slit in a telescope focus. From the shape of that pattern, we determine the phase difference between the diffracted light rays that meet on the image plane. Then, the phase structure function is calculated which leads to the seeing value. Results. Two seeing measurement campaigns were carried out at Oukaimden observatory and the ENS de Marrakech site using this new seeing monitor and a DIMM monitor. The two results are in good agreement, which makes the ISM a reliable instrument.