Inversely Determining Atmospheric Refractivity Structure Using Electromagnetic Wave Propagation Models and Measurements

Physics-based models of electromagnetic wave (EM) propagation through the marine atmospheric boundary layer have been developed and advanced over the last several decades.  When all required parameters of the environment are defined at sufficient resolution, then the models provide a reasonably accurate prediction of the electromagnetic fields in complex atmospheric conditions and over complex sea surfaces; however, limitations of these simulations are driven by an inability to properly characterize the environment.  Numerical weather prediction models lack the needed resolution for EM propagation prediction, high-resolution in-situ measurements are difficult and costly to obtain on a routine basis, and Monin–Obukhov similarity theory is not robust enough to reliably fill-in measurement gaps to enable predictive capability using low resolution (bulk) environmental measurements. 

Over the past three years, we have undertaken research examining the use of inverse problemtechniques to deduce MABL parameters for use in physics-based EM propagation models.   In this effort, we have examined the sensitivity of the Variable Terrain Radio Parabolic Equation (VTRPE) simulation to environmental inputs, evaluated the accuracy of simple parametric refractivity models for use in the inversion problem both with respect to atmospheric measurements as well as in terms of the predicted propagation, integrated the VTRPE model with genetic algorithms to solve the inversion problem, and have demonstrated success in recovering up to three parameters (evaporation duct height, duct curvature, and mixed layer slope) via the inversion process.  This study extends these efforts.  We extend the inversion approach to more parameters in order to inversely determine more complex atmospheric conditions, to examine sensitivity of the inversion approach to the amount, accuracy, and location of EM data, and implement and evaluate the inversion approach using measured data.  This basic research contributes to the development of a semi-empirical approach to determining atmospheric refractivity in an operational environment in order to provide the U.S. Navy fleet with an “EM forecast,” which improves their maritime domain awareness, including their evaluations of susceptibility.