During the Electra-Optical Propagation Assessment in a Coastal Environment

(EOPACE) experiment of August-September 1997, infrared transmission measurements were obtained along a 7 km path over San Diego Bay. Simultaneous meteorological measurements were obtained from a buoy located at the midpoint of the transmission path. In this study transmission-derived values of the refractive index structure parameter, Cn2, are compared with bulk model-derived estimates obtained from the mean buoy data. The bulk CH2 estimates agreed very well with the transmission measurements in unstable conditions. The bulk estimates were very poor in near-neutral conditions because of the great difficulty in accurately measuring the small air-sea temperature differences (AT) encountered, upon which C,, 2 is highly dependent. The bulk C,,2 estimates agreed less well with the transmission measurements in stable conditions than unstable conditions. A theoretical sensitivity and error analysis shows that the bulk C,,2 estimates become extremely sensitive upon the measured value of AT over a narrow Bowen ratio range and under such conditions it is virtually impossible to accurately estimate Cn2 using bulk methods. The sensitivity analysis also indicates whether fluctuations in temperature, humidity or temperature-humidity correlation dominate the determination of Cn2 under various Bowen ratio ranges. 2