Least mean square (LMS) normalizer for active sonar

In an active sonar including a matched filter processor for processing received waveform echoes, an improved normalizer responsive to a sequence of matched filter output data to provide a normalizer output, comprising:

• means responsive to said matched filter output data for providing the logarithm of said output data;
• a normalizer means responsive to said logarithm of said matched filter output data to provide a normalizer output, said normalizer means comprising tapped delay line means having a plurality of tap outputs, wherein said first group of said tap outputs comprise a signal window, and second and third groups of said tap outputs on either side of said signal window taps comprise first and second noise windows, adaptive filter means responsive to said normalizer output for adapting respective tap weights applied to said tap outputs, means for respectively combining said signal window tap outputs, said first noise window tap outputs and said second noise window tap outputs to provide respective combined signal, first noise and second noise components, means for combining said first and second noise components to provide a composite noise component, and means for subtracting said composite noise component from said signal component to provide said normalizer output,
• wherein said normalizer adapts to locally non-stationary noise and time-spreading of said signal component.

An active sonar, comprising:

• a transmitter for generating a transmit waveform signal;
• a transmit transducer array for transmitting said transmit signal;
• a receiver transducer array;
• a beamformer responsive to outputs of said receiver array for producing a beamformer output;
• matched filter processing means responsive to a replica of said transmit waveform signal and to said beamformer output for producing a sequence of matched filter output signals;
• a normalizer for processing said matched filter output signals;
• threshold test means responsive to normalizer outputs for comparing said normalizer outputs to a threshold and declaring a detection when said threshold is exceeded;
• and
• wherein said normalizer comprises:
• means responsive to said matched filter output signals for providing the logarithm of said matched filter output signals;
• tapped delay line means having a plurality
• of tap outputs, wherein said first group of said tap outputs comprise a signal window, and second and third groups of said tap outputs on either side of said signal window taps comprise first and second noise windows, adaptive filter means responsive to said normalizer output for adapting respective tap weights applied to said tap outputs, means for respectively combining said signal window tap outputs, said first noise window tap outputs and said second noise window tap outputs to provide respective combined signal, first noise and second noise components, means for combining said first and second noise components to provide a composite noise component, and means for subtracting said composite noise component from said signal component to provide said normalizer output,
• wherein said normalizer adapts to locally non-stationary noise and time-spreading of said signal component.