COHERENT PROCESSING FOR LOFARGRAMS

Because narrowband submarines emissions are constantly being reduced, one is forced to use broadband information to detect and track, still relying upon narrowband tonal energy for classification. In addition, broadband energy frominterfering sources such as biologics or profilers can clutter LOFARGRAM displays. As a result existing LOFARGRAM methods are of limited utility for quiet threats operating in high clutter environments (e.g., shallow water). We propose to demonstrate new signal processing methods that will allow existing LOFARGRAM techniques and displays to be used for 1) the detection of submarinetransients, and 2) to the discrimination of quiet submarine signatures from strong ocean clutter. Our approach is based on using directional, coherent beamforming techniques to increase the signal-to-noise ratios pf possible targets, thereby exposing the narrowband signals and tonals that would otherwise be masked by the ocean noise. Beam steering information will be derived from the initial detection of transient energy which will also be accomplished via the LOFARGRAM through the use of advanced image enhancement pre-processing techniques. The follow-on Phase II program will produce a prototype preprocessor to be used in conjunction with an existing LOFARGRAM system, as a vehicle for Navy operational personnel to evaluate the effectiveness of this technology.