Ideal signals and processing for continuous active sonar

Abstract

The ideal signal for continuous active sonar would be linear in both time and Doppler and have no time or Doppler leakage. Here two signals/signal processing methods are presented that have half the requisite condition - zero time leakage. But we show a way to use the time property to eliminate Doppler interference (clutter) from zero Doppler reverberation (bottomed) sources and from direct arrivals. Here we develop an m-sequence processed with a matched filter approach and a special class of inverted binary sequences processed with a matched -inverse filter. In both cases, there is a perfect pulse correlation property; that is, a large signal when they line up in time and hard zero when they don't. This property is used to develop a Complete Ortho-Normal (CON) data sets in both waveform and pulse response space. The CON pulse response allows elimination of the easily identified zero Doppler reverberation arrivals. Then, reprocessing for Doppler, the zero Doppler signals are cleanly removed as is all of their Doppler leakage. In effect one has the ideal clutter free signal with leakage from direct arrivals and bottom reverberation removed and a target signal displayed in a time-Doppler plane against a noise only background.