ELF Nonsinusoidal Airborne ASW Radar

We propose an ELF airborne radar operating below 50 Hz that will detect acoustically quiet threat sumersibles at moderate depths in coastal/harbor waters. Bisatic as well as backscatter geometries are to be considered. The investigation will optimize nonsinusoidal signal waveforms for this problem. We have already developed and discuss in the proposal: (i) the latest theoretical tools for numerically predicting low-frequency radiation and propagation above and through sea water; (ii) the abiilty to digitally synthesize and process non-sinusoidal signals of any desired shape. By considering a typical example, we identify the two major limitations to the feasibility of such a system: external noise and clutter. "Clutter" refers to unwanted versions of the transit signal including direct feedthrough, surface reflections, and bottom reflections. Non-sinusoidal signal design can mitigate clutter problems. Signal-to-noise ration is improved by increasing the received echo enery; this is possible at the transmit end by more input power or more efficient antennas, while at the receive end it is accomplished by longer coherent integration via digital signal processing. Tradeoffs utilizing the numerical tools we have developed will arrive at the optimum system configuration along with performance bounds. Critical hardware and system elements are identified, and their implementation for this application will optimize their performance while minimizing size, weight, radiated power, complexity, and cost. This will lead to an overall assessment of system feasiblity.