Theoretical performance limits on tropospheric refractivity estimation using point-to-point microwave measurements

Ducted propagation above the ocean surface can seriously impact shipboard r adar and communications. Point-to-point microwave measurements have been pr oposed as a means of estimating tropospheric refractivity for the purposes of characterizing surface-based ducts. This paper addresses the theoretical performance of refractivity estimates that can be made by combining held m easurements at different frequencies with prior statistics of refractivity variation. Parameterizing the refractivity profile using:empirical orthogon al functions derived from a historical database, both Cramer-Rao performanc e bounds and the maximum a posteriori (MAP) estimate are discussed using co herent or incoherent signals. Results obtained using a realistic model of r efractivity conditions off Southern California suggest that multifrequency propagation measurements can significantly improve the estimation of refrac tivity and propagation loss profiles.