Measurements and modeling of optical turbulence in a maritime environment

Abstract

Turbulence can be a dominant factor in image and laser beam degradation for optical systems operating in the near-surface maritime environment. A long-term propagation field experiment was conducted at Zuniga Shoal (near San Diego) to study the impact of environmental conditions on low-altitude laser propagation above the ocean surface. Test periods of one month duration were conducted at various points of the year, during which scintillometer measurements were obtained along a 7.2 km over-water path and a 'flux' research buoy deployed along the propagation path collected concurrent mean meteorological, atmospheric turbulence, and wave data. We use the refractive index structure parameter (C n 2 ) as the critical parameter for quantifying the effects of atmospheric turbulence on laser system performance, including received power fluctuations, beam spread and beam wander. Bulk estimates of C n 2 were derived from the buoy mean meteorological measurements using the Navy Surface Layer Optical Turbulence (NSLOT) model. C n 2 was also determined from atmospheric turbulence measurements obtained from a sonic anemometer on the buoy. These independent C n 2 values derived from the buoy data are compared with C n 2 values computed from the infrared propagation measurements to determine how the NSLOT model performs under different environmental conditions. In addition, the optical measurements and bulk estimates of C n 2 are used to study the effects of the atmospheric turbulence on operational optical systems.