From the grating scale monitor to the generalized seeing monitor

An instrument named the grating scale monitor for measuring the outer scale L-0 from the angle-of-arrival (AA) fluctuations of a perturbed wave front was developed a few years ago at Nice University. The AA is detected with a 5-ms time resolution by modulation of the stellar image in a small telesco pe with a grating. One uses the normalized covariance of AA fluctuations to estimate L-0. A new version of this instrument, the generalized seeing mon itor (GSM) is described. It consists of four identical modules for measurin g the AA at four locations on the wave front. A spatiotemporal analysis of these data leads to the determination of seeing epsilon(0), outer scale L-0 , and the wave-front speed. In addition, isoplanatic angle theta(0) is dete rmined from scintillation, making the characterization of turbulence with t he GSM almost complete. We describe the instrument and make a detailed anal ysis of its performance and accuracy. Several site-testing campaigns have b een conducted with the GSM: at La Silla (Chile), Oukaimeden (Morocco), Maid anak (Uzbekistan), and Cerro Pachon and Cerro Paranal (Chile). The main res ults of these campaigns are presented and discussed. (C) 2000 Optical Socie ty of America OCIS codes: 010.1290, 010.1330, 010.1300, 010.1350, 010.1080.