Christopher J. Earls

Duct heights inferred from radar sea clutter using proper orthogonal bases

Maritime electromagnetic (EM) based communication and detection systems are strongly influenced by meteorological conditions, as they can cause anomalous electromagnetic propagation within the surface layer. To predict the performance of such systems, detailed knowledge of the refractivity profile is required. In recent years, refractivity from clutter (RFC) methods have been developed to estimate this refractivity profile by measuring radar clutter return from the rough ocean surface. The current work proposes an RFC framework that utilizes a novel surrogate model for EM propagation. The surrogate model is based on an offline created library of sparsely sampled field data of clutter returns, compressed into proper orthogonal bases, and indexed on specific surface layer refractive parameters. By exploiting the Riemannian manifold structure of the space that proper orthogonal bases occur in, we are able to interpolate among them. This, then, enables us to use the surrogate model in an inverse problem setting, whose goal is to uncover in situ maritime EM propagation conditions efficiently. We demonstrate the feasibility of our proposed surrogate model-based RFC approach for evaporation duct by testing it with field data obtained from an experimental campaign.

Inverting for Maritime Environments Using Proper Orthogonal Bases From Sparsely Sampled Electromagnetic Propagation Data

Predicting in situ maritime electromagnetic (EM) propagation conditions is of great importance to radar operations within the marine atmospheric boundary layer. To characterize the EM propagation conditions, at a specific location in time and space, the current research constructs (offline) a library of sparsely sampled EM coverage data, expressed as proper orthogonal modes, so as to enable the solution of an inverse problem for the current EM propagation conditions (online). The online inversion is effected within a context that exploits an implied differential geometric structure associated with the manifold containing the proper orthogonal mode library entries.

Inverting for maritime propagation environments using proper orthogonal modes from radar imagery data

Radar wave front arrival times and spatial energy deposition, associated with propagation through a given marine atmospheric boundary layer, may be described using proper orthogonal modes, and subsequently represented as points on a compact Stiefel manifold. By exploiting the Riemannian structure of Stiefel, interpolation within the cloud of manifold points is possible when solving inverse problems aimed at uncovering in situ maritime conditions affecting radar propagation on a given day.