RED experiment: an assessment of boundary layer effects in a trade winds regime on microwave and infrared propagation over the sea, The

Includes bibliographical references (pages 1364-1365).The Rough Evaporation Duct experiment aimed to see if the effects of ocean waves account for errors in modeling the ranges at which radar and infrared can detect low-flying targets

Improving bulk Cn2 models for over-ocean applications through new determinations of the dimensionless temperature structure parameter

The performance of imaging and laser systems can be severely degraded by atmospheric turbulence, especially for near-horizon propagation paths. Having the ability to predict turbulence effects from relatively easily obtained measurements can be useful for system design and feasibility studies, and for real-time optimization of optical systems for the current environment. For this reason, so-called ‘bulk’ models have been developed that can estimate turbulence effects through the refractive index structure parameter (Cn2) from mean near-surface meteorological and sea surface temperature measurements. Bulk Cn2 models are directly dependent upon empirically determined dimensionless functions, known as the dimensionless structure parameter functions for temperature and humidity. In this paper we attempt to improve bulk optical turbulence model performance by determining new over-ocean forms for the dimensionless temperature structure parameter (fT). During 2005-2006 atmospheric propagation experiments were conducted in the Zuniga Shoals area near San Diego to examine the impact of environmental conditions on low-altitude electro-optical propagation above the ocean surface. As part of this experiment the Naval Postgraduate School (NPS) deployed its flux research buoy along the propagation path. The measurements obtained on the NPS buoy enabled fT values to be obtained and new functions to be determined. These new functions differ greatly from those presented in the past, in that the new fT values asymptote towards very high values as the stability approaches neutrality. The dependence of the new fT function on the stability parameter in stable conditions was also different from that previously proposed. When these new functions were inserted into the NPS bulk Cn2 model, the resulting values agreed much better with directly measured turbulent Cn2 values in unstable conditions, but in stable conditions the new function actually made the agreement worse

Measurements and modeling of optical turbulence in a maritime environment

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.This work was funded by the Office of Naval Research, Dr. Ron Ferek, program manager

Recent results on modeling the refractive-index structure parameter over the ocean surface using bulk methods

Infrared scintillation measurements were obtained along a 7.2 km path over San Diego Bay, concurrently with mean meteorological and turbulence measurements obtained from a buoy located along the path. Bulk estimates and turbulence measurements of Cn 2 were computed from the buoy data and compared with the optical scintillation-derived Cn 2 values. Similar to the results of previous experiments, the bulk Cn 2 estimates agreed well with both the scintillation and turbulence measurements in unstable conditions, increasingly underestimated Cn 2 as conditions approached neutral, and agreed less well with scintillation and turbulence Cn 2 values in stable conditions. The mean differences between bulk Cn 2 estimates and both the turbulence and scintillation measurements when conditions were not near-neutral exhibited an air-sea temperature difference and wind speed dependence, possibly indicating that the forms of the empirical stability functions used by the bulk model are incorrect. The turbulent Cn 2 measurements from the buoy showed excellent agreement with the scintillation values in unstable conditions, but had surprisingly large differences in weakly stable conditions. This disagreement may be related to the fact that humidity fluctuations begin to increasingly influence refractive index fluctuations when the air-sea temperature difference is small and are not properly taken into account by the sonic temperature measurements. As the absolute air-sea temperature difference approaches zero the bulk Cn 2 estimates decrease much more rapidly and to much smaller values than either the scintillation or turbulence measurements. Fortunately, in such near-neutral conditions scintillation is usually small enough to have little effect on many optical system applications.This work was funded by the Naval Sea Systems Command, PMS405, Dr. Sadegh Siahatgar, program manager

Air-sea interaction processes observed from buoy and propagation measurements during the red experiment

In recent years researchers have spent much effort towards gaining an understanding of the complex physical mechanisms through which the atmosphere and ocean interact with each other. This is due to the fact that knowledge of air-sea exchanges is important for a wide range of applications, such as the diverse topics of global climate modeling and near-horizon electromagnetic (EM) wave propagation assessment and prediction. EM propagation through the atmosphere is highly dependent upon the vertical profiles of air temperature and humidity and the horizontal variations in these profiles. It is well known that under most conditions these near-surface scalar profiles depend upon the turbulent air-sea fluxes. Traditional Monin-Obukhov similarity (MOS) theory has been used to successfully predict near-surface profiles over the ocean for most, but not all, stability conditions. It is also becoming increasingly clear that ocean waves influence near-surface profiles, although an understanding of the exact mechanisms through which this occurs and parameterizations to describe these processes so far have remained elusive (e.g. Hare et al. 1997; Hirstov et al. 1998)

The Red Experiment: an assessment of boundary layer effects in a trade winds regime on microwave and infrared propagation over the sea

The article of record as published may be found at http://dx.doi.org/10.1175/BAMS-85-9-1355The Rough Evaporation Duct experiment aimed to see if the effects of ocean waves account for errors in modeling the ranges at which radar and infrared can detect low-flying targets.Office of Naval Research (Code 322M