Estimating the Refractive Index Structure Parameter () over the Ocean Using Bulk Methods

Abstract

Infrared scintillation measurements were obtained along a 7-km path over San Diego Bay concurrently with meteorological measurements obtained from a buoy at the midpoint of the path. Bulk estimates of the refractive index structure parameter were computed from the buoy data and compared with scintillation-derived values. The bulk estimates agreed well with the scintillation measurements in unstable conditions. In stable conditions the bulk estimates became increasingly higher than the scintillation values as the air–sea temperature difference increased. This disagreement may be due to enhanced wave-induced mixing of the lower atmosphere that decreases the vertical temperature and humidity gradients in stable conditions from the assumed Monin–Obukhov similarity (MOS) theory forms, resulting in bulk values that are too high. The bulk estimates decrease rapidly when the absolute air–sea temperature difference approaches small positive values. These predicted decreases in were not observed in either the path-averaged scintillation measurements or in single-point turbulence measurements, indicating that bulk models for estimating scalar structure parameters based on mean air–sea scalar differences are not valid when the mean air–sea difference approaches zero. The authors believe that the most promising means toward improving the bulk model is to obtain a better understanding of the MOS functions over the ocean for a wide stability range, and particularly of the role of ocean waves in modifying near-surface vertical gradients and turbulence characteristics.

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

“…The cause of this 'bump' is not known, but indications of a similar feature have been observed in previous scintillation measurements made across San Diego Bay (see Fig. 12 of Frederickson et al [2000] 3 ). From Fig.…”

“…(11-12) by an iterative process. Full details on the Naval Postgraduate School's bulk C n 2 model are provided by Frederickson et al (2000) 3 .…”

Climate Change: Anticipated Effects on High-Energy Laser Weapon Systems in Maritime Environments

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“…[7][8][9] In those works, the wavelengths of the optical measurements were in the mid-infrared (3 to 5 m), and all showed that humidity along the measurement volume plays a significant role in the temporal behavior of C n 2 .…”