Coherent integration of sub-pulse matched filtering for long LFM pulse in active sonar

To address the issue of processing gain degradation in matched filtering which caused by spectral distortion of linear frequency modulation (LFM) long-pulse acoustic waveforms propagating through time-varying underwater acoustic channels, this paper proposes a sub-pulse coherent integration method with matched filtering. The long-pulse waveform is partitioned into M sub-pulses for segmented matched filtering. After aligning the matched filter peaks of these sub-pulses, the inter-pulse phase differences are accurately estimated and compensated. The phase-compensated and aligned peaks are then coherently integrated to restore the processing gain. Simulation and experimental results demonstrate that the proposed method effectively overcomes channel coherence limitations through sub-pulse partitioning, significantly mitigating processing gain degradation in long-pulse matched filtering caused by spectral distortion. By preserving the advantageous large time-bandwidth product of long-pulse waveforms, this approach provides a novel framework for addressing active detection challenges of LFM long-pulse signals in time-varying underwater acoustic channels.