Turbulence Profiles with Generalized Scidar at San Pedro Mártir Observatory and Isoplanatism Studies

Abstract

ABSTRACTThe results obtained from 3398 vertical profiles of atmospheric turbulence measured during 11 nights at the Observatorio Astronómico Nacional in San Pedro Mártir (Baja California, México) are presented. The observations were carried out with the generalized scidar (GS) installed at the 1.5 m and the 2.1 m telescopes of that site, in 1997 March and April. The open‐air seeing was measured with a differential image motion monitor (DIMM). The GS can detect turbulence profiles along the whole optical path, unlike the classical scidar, which is insensitive to low‐altitude turbulence. For the first time, to our knowledge, profiles including turbulence near the ground are monitored and statistically analyzed. Isoplanatic angles for speckle interferometry and adaptive optics (AO) in either full or partial compensation are deduced, as well as the focus anisoplanatism parameter for sodium laser guide stars. The advantage of minimizing the distance between the turbulent layers and the conjugated plane of the deformable mirror of an AO system is studied. The comparison of GS profiles obtained at both telescopes, together with DIMM measurements, show that the turbulence near the ground is more strongly dominant at the 1.5 m telescope than at the 2.1 m telescope, where the median values of the seeing near the ground, in the free atmosphere and in the whole optical path are 0.″56, 0.″44 and 0.″77, respectively. These values are comparable to or better than those of the major astronomical observatories, although a larger data sample is needed for a definitive comparison.