Correlation Signal Processing for Depth Sounding

Abstract

Abstract : Replica correlation acoustic depth sounders have several significant advantages over conventional system. Although development has been primarily oriented toward bathymetric survey missions, replica correlation systems can provide significant improvements for both deep submersibles and support ships. Greatly improved resistance to depth measurement errors, resulting from impulsive noise sources commonly encountered with submersibles and support ships, is provided by hard clipping of the signal and integration over the pulse length. Better resolution and sub-bottom penetration can be obtained, due to the increased signal-to-noise ratio resulting from the signal processing gain. The requirement for manual gain or threshold adjustments during operations is eliminated by the normalized output noise characteristics of hard clipping correlators, and the reliability of digital depth data is improved. A computer simulation of the performance of a replica correlation echo sounder has verified theoretical results in the areas of signal duration and bandwidth limitations, improved signal waveform design, and the effects of quantization and sampling. Further at-sea testing of a complete system is planned, and hardware has been developed for this purpose.