Measurements of Optical Turbulence in Complex Terrain

New methods for tracking, pointing, and compensation of laser beams are explored and developed at The Airborne Laser Advanced Concepts Testbed (ABL ACT) which is located on White Sands Missile Range (WSMR), NM. All of these efforts require a knowledge of the optical turbulence along the propagation path. The site utilizes a 52.4 km propagation path over a desert basin between two mountain peaks (North Oscuro Peak (NOP) and Salinas Peak). Characterization of the optical turbulence at ABL ACT is challenging due to the long path length in the atmospheric planetary boundary layer and the complex terrain of the site. A suite of instrumentation is being used to approach the problem; a sodar, fine wire probes, a wave front sensor, a pupil plane imager, a differential image motion monitor, and a scintillometer. In addition, a weather station senses ambient temperature, humidity, pressure, wind speed and direction, and solar radiation- received both horizontally and parallel to the mountain west-facing slope at North Oscuro Peak. Salient features of each instrument as well as the parameters sensed, including path weighting effects, will be presented. Comparisons of results obtained from different sensors will be shown and discussed such as the scintillometer and pupil plane imager. Special emphasis will be on the optical turbulence conditions at the mountain ridge at NOP which were quantified from observations of sensors and a sodar (sonic detection and ranging). Both instruments provide the temperature structure parameter (CT2) from which the refractive index structure parameter (Cn2) is calculated using local measurements of temperature and pressure. The fine wire measurements were used to calibrate the sodar. Of particular emphasis is the relationship of the sodar observations to solar radiation and wind speed and direction. The results are explained in terms of the geometry of the site and the mountain-valley wind regime. Results are shown as contours of Cn2 in a vertical plane oriented normal to the west-facing slope and as estimated profiles of Cn2 along the propagation path. Comparisons of appropriate path-integrated results will be shown.