Electromagnetic Rapid Environment Assessment Using Towed Systems - A Tool for Naval Tactical Support Systems

The purpose of electromagnetic Rapid Environment Assessment (REA) in the underwater domain is to provide the data bases of naval tactical support systems with parameters for electromagnetic wave propagation models. These models are necessary for calculation and prediction of ship vulnerabilities and sensor capabilities with respect to UEP and ELFE signatures. Within the framework of the research and technology project "Underwater sensor systems, establishment in new areas of operation", experimental and theoretical work has been performed towards an operative system for electromagnetic REA. An electrical dipole source has been integrated in the tow cable of an existing towed sensor system and various other improvements have been made. Methods and algorithms for constructing 2D models of the conductivity from measured electric field data have been investigated. For this purpose, a forward and inverse wave propagation code has been developed. In addition, algorithms for parallelization of an existing 3D wavepropagation code have been investigated. Two sea trials have been conducted in the southern Stockholm Archipelago and data exist for a future thorough analysis. The data have been partly analyzed using a sequence of 1D plane-stratified models along the survey tracks. Good results were found for relatively flat sub-bottom structures, whereas this description fails in areas characterized by spatially varying topographies and geological structures. This report summarizes the work performed during the years 2007-2009 on operative electromagnetic REA. It also briefly describes a suggested survey system, methods, analysis tools and wave propagation models. Furthermore, it mentions applications for the REA results, and explains why this is an important resource for tactical support and protection of naval forces.