Using radar sea echo to estimate surface layer refractivity profiles

Abstract

A method for inferring the atmospheric boundary layer evaporation duct height from sea clutter is described. The method is based on the observation that the radar signal from the evaporation duct manifests itself in the slope of the clutter power, while the horizontal variability of the sea clutter RCS (radar cross section) is a contaminant in the problem. The inversion method has been tested using data from the Wallops '98 measurement campaign. A good level of performance was obtained without the benefit of the 360/spl deg/ of observations that are usually available to a ship. This is encouraging as the geography of the experiment-looking out onto an ocean from a continent-is arguably a very inhomogeneous environment and stressful to the inversion. Clearly, the grazing angle dependence question must be addresed further. At least some of the questions in the area of low grazing angle backscatter (LGAB) arise from measurements and analysis having been performed prior to the time where evaporation ducting was understood in a quantitative manner. Other questions arise from how quantities such as grazing angles are defined and computed. So one need is further research into establishing how the results presented in this paper fit in the existing body of work in this area. Beyond that, the techniques used in this paper may be a valuable tool for use in analyzing LGAB experimental data and design of the experiments themselves.