Characteristics of long-range scintillation data over maritime coastal areas

The knowledge on scintillation, caused by atmospheric turbulence, is of vital importance for the performance prediction of threat detection systems and for the development of associated detection algorithms. Additionally, scintillation data may support the knowledge on turbulence characteristics. Along these ideas, data have been analysed, collected during the FATMOSE trials, carried out over the False Bay (South Africa) over a range of 15.7 km from November 2009 until October 2010. The collected data include long-range scintillation measurements, taken with the MSRT radiometer and a modulated source and with a high resolution imager and static sources. In addition a standard scintillometer was used over a short range, 1.8 km parallel path and a mid-path sonic anemometer for direct measurement of windspeed and air temperature fluctuations. Indirectly, information on turbulence parameters is predicted from the weather data, collected at the mid-path station, by using our TARMOS code for the marine boundary layer. Details on the set-up and the method of analysis are given, including some relevant examples. Scintillation spectra between 0.1 and 100 Hz are shown for investigation of the validity of Kolmogorov's theory of turbulence. In addition, signal (irradiance) statistics are shown for testing the log-normality of their characteristics. In relation to this, attention is spent on the subject of saturation of scintillation, which may occur in conditions of strong turbulence, combined with small apertures and long ranges. Output from the various sensors is compared with TARMOS predictions and related to the simultaneously collected blur and beam wander data. Related to this, data on the signal correlations from the various MSRT apertures provide information on the transverse atmospheric coherence length n0, which parameter is directly linked to the blur. Examples are shown of the wavelength dependence of scintillation, predicted from the theory of weak turbulence, in comparison with the 3-band scintillation data from the MSRT sensor. In the comparison of the local and path-averaged scintillation, the effect of path inhomogeneities of the atmospheric conditions along the path is taken into account. Conditions with low scintillation are getting special attention, as they do not always correspond to conditions with small blur. © 2012 SPIE.