Summary of optical turbulence measurements taken at the Starfire Optical Range

Since 1987, we have measured the transverse coherence length (Fried's r o parameter) and the isoplanatic angle, (theta) o , using optical instruments at the Starfire Optical Range (SOR). Through the end of December 1994, we have accumulated 160, 653 r o measurements and 185,488 (theta) o measurements. The transverse coherence length, r o , was determined by measuring the short exposure modulation transfer function of the atmosphere using a 35.5 cm Celestron transfer observing bright stars. The isoplanatic angle was obtained using a stellar scintillation technique on bright stars with a 10 cm Meade telescope. Prior to 1992, a 20 cm Celestron telescope with an apodized aperture was used. Means and frequency distributions of r o and (theta) o have been determined for the period 1987 through December 1994, for each individual year and for each month using measurement from all years. In addition, for the period November 1993 to December 1994, we used Albuquerque National Weather Service rawinsonde wind data and a model of the C n 2 profile to estimate the Greenwood frequency f G . These estimates generally compare well with measured Greenwood frequency data obtained from the high speed wavefront sensor in the 1.5 m adaptive optics system. The summaries presented are a first attempt to characterize the optical turbulence at the SOR and may be used to plan experiments during months of statistically low atmospheric turbulence and Greenwood frequency.