Sensitivity of tri-linear refractivity models to perturbations in refractivity

Previous work has shown that when a well defined stratified layer exists over several tens of kilometres, so that the troposphere possesses a high degree of horizontal homogeneity, the refractivity is well approximated by a tri-linear profile and that using this approximation leads to good agreement between measured attenuations and those obtained by solution of the parabolic wave equation. The most common method of obtaining refractivity data is through the measurement of the meteorological parameters, pressure. temperature and humidity. However, the turbulent nature of the troposphere, combined with the resolution of the measurement sensors, places an upper limit on the accuracy to which the refractivity profile can be determined. Therefore it is important to quantify the effect of these inaccuracies on the solutions of the parabolic wave equation. and hence, the work presented in the paper, investigates the sensitivity of the predicted signal level to small perturbations in the refractivity profile