Comparison of Horizontal Scintillation Measurements and Models

Measurements of the variance of log amplitude, 02, were performed over a 183 m optical path using a NOAA horizontal scintillometer. The otical index of refraction structure constant, Cr21, was measured at several locations along the path using AFGL thermosondes. The theoretical model decribing the relationship between the scintillometer 02 and CA along the path is tested. The comparison is made by numerically integrating CA along the path. This comparison is made for conditions of strong and weak turbulence as well as strong and weak winds. For averages of 10 minutes, the agreement is very good. At shorter time scales of the order of seconds, there is agreement in trend. However, the scintillometer and thermosondederived 02 differ in terms of the magnitude of their fluctuations. The importance of volume ava'aging is discussed when comparing measurements, models and data. The data is then used to consider the stationarity of the ensemble model implicitly used in averaging data. The short term fluctuations in the 02 data are analyzed statistically. These fluctuations in 02 are modeled in terms of a Ylog-normal distribution. The analysis of the spectrum and 4orrelation function of log(02) suggest that quasistationarity may be restricted to time intervals of the order of 10 seconds.