Coherence Time Monitoring

Introduction to the Coherence Monitor

Balloon borne sensors have been used at the VLT observatory to monitor the temporal coherence of the atmosphere. From such data coupled with statistics on wind velocity vertical profiles, we may estimate (or even forecast) the wavefront temporal characteristics (ps file). However, the need for a real-time monitoring device is clear, in particular with the development of observations coupled to adaptive optics system. This is a project in development in the frame of the VLT Astronomical Site Monitor (ASM). It aims at measuring the average and the rms of the transverse velocity of the wavefront perturbations following the technique described in the paper by Lopez [92] below.

Publications regarding the Coherence Monitor

91: B. Lopez, M. Sarazin; Optimum exposure times for interferometry; Proc. ESO-Conf. on High Resolution Imaging by Interferometry II; Garching, Oct 14-18, 1991.
92: B. Lopez; How to Monitor Exposure Times for High Resolution Imaging; Astron. Astrophys. 253, 635-640 (1992) Full Refereed Scanned Article (PDF)
93: B. Lopez and M. Sarazin; The ESO Atmospheric Temporal Coherence Monitordedicated to High Resolution Imaging; Astron. Astrophys. 276, 320-326 (1993) Full Refereed Scanned Article (PDF)